July 2015

NASA/TM2015-218781/Volume I

NESC-RP-12-00783

 

Empirical Model Development for Predicting 

Shock Response on Composite Materials 

Subjected to Pyroshock Loading

Steven J. Gentz/NESC

Langley Research Center, Hampton, Virginia

David O. Ordway, David S. Parsons, Craig M. Garrison, C. Steven Rodgers, and Brian W. Collins

Marshall Space Flight Center, Huntsville, Alabama
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July 2015

NASA/TM2015-218781/Volume I

NESC-RP-12-00783

 

Empirical Model Development for Predicting 

Shock Response on Composite Materials 

Subjected to Pyroshock Loading

Steven J. Gentz/NESC

Langley Research Center, Hampton, Virginia

David O. Ordway, David S. Parsons, Craig M. Garrison, C. Steven Rodgers, and Brian W. Collins

Marshall Space Flight Center, Huntsville, Alabama
Available from:

NASA STI Program / Mail Stop 148

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Hampton, VA 23681-2199

Fax: 757-864-6500

Acknowledgments

The team would like to acknowledge the following for providing their expertise:

Dr. Curt Larsen/Johnson Space Center (JSC), of the NESC, for championing the 

Pyroshock Characterization of Composites task.

Mr. Ken Johnson/MSFC for his tireless support statistically analyzing the postprocessed acceleration data.

Mr. Lee Allen/MSFC for supporting Ken Johnson in statistically analyzing the 

post-processed data

Ms. Barbara Breithaupt/MSFC for post-processing the pseudo-velocity data.

Mr. Justin Jackson/MSFC for providing his expertise in composite test panel 

fabrication.

The use of trademarks or names of manufacturers in the report is for accurate reporting and does not 

constitute an official endorsement, either expressed or implied, of such products or manufacturers by the 

National Aeronautics and Space Administration.
NASA Engineering and Safety Center 

Technical Assessment Report 

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Composite Materials Subjected to Pyroshock Loading

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Empirical Model Development for Predicting Shock Response on Composite 

Materials Subjected to Pyroshock Loading

April 16, 2015
NASA Engineering and Safety Center 

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Report Approval and Revision History

NOTE: This document was approved at the April 16, 2015, NRB. This document was 

submitted to the NESC Director on May 4, 2015, for configuration control.

Approved: Original Signature on File 5/5/15

NESC Director Date

Version Description of Revision Office of Primary 

Responsibility Effective Date

1.0 Initial Release Mr. Steve J. Gentz, NESC 

Chief Engineer’s Office, 

MSFC

4/16/15
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Table of Contents

Technical Assessment Report

1.0 Notification and Authorization.....................................................................................................8

2.0 Signature Page................................................................................................................................9

3.0 Team List......................................................................................................................................10

3.1 Acknowledgements...........................................................................................................10

4.0 Executive Summary.....................................................................................................................11

5.0 Assessment Plan ...........................................................................................................................14

6.0 Problem Description....................................................................................................................14

7.0 Composite Panel Fabrication, Pyroshock Test Conduct, and Data Analysis.........................15

7.1 Composite Panel Fabrication and NDE ............................................................................15

7.2 Pyroshock Test Conduct ...................................................................................................18

7.2.1 Test Planning ....................................................................................................................18

7.2.2 Test Articles......................................................................................................................25

7.2.3 Test Setup .........................................................................................................................28

7.2.4 Instrumentation and Data Acquisition ..............................................................................31

7.2.5 Procedures.........................................................................................................................37

7.2.6 Post-Test Operations.........................................................................................................39

7.2.7 Data Requirements............................................................................................................39

7.2.8 Evaluation Criteria............................................................................................................39

7.3 Post-Test Data Processing and Data Evaluation...............................................................40

7.3.1 Post-Test Data Processing.................................................................................................40

7.3.2 Post-Test Data Evaluation.................................................................................................45

7.3.3 Algorithm Response Spectra Development ......................................................................49

7.3.4 PV Spectra ........................................................................................................................59

7.3.5 Energy Spectral Density ...................................................................................................59

7.3.6 SRS Evaluation.................................................................................................................59

7.3.7 PV Evaluation...................................................................................................................88

7.3.8 ESD Evaluation.................................................................................................................97

7.3.9 Time History, Velocity, and Displacement.....................................................................102

7.3.10 Temporal Moments.........................................................................................................106

7.3.11 MEFE Prediction Example .............................................................................................107

7.3.12 MAF Qualitative Pyroshock Assessment .......................................................................114

8.0 Findings, Observations, and NESC Recommendations..........................................................118

8.1 Findings ..........................................................................................................................118

8.2 Observations...................................................................................................................120

8.3 NESC Recommendations ...............................................................................................120
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9.0 Alternate Viewpoint...................................................................................................................120

10.0 Other Deliverables.....................................................................................................................121

11.0 Lessons Learned.........................................................................................................................121

12.0 Recommendations for NASA Standards and Specifications..................................................121

13.0 Definition of Terms....................................................................................................................121

14.0 Acronyms List ............................................................................................................................122

15.0 References...................................................................................................................................123

List of Figures

Figure 4.0-1. Pyroshock of Composites Task Flow Diagram..........................................................13

Figure 7.1-1. IR Thermography Indications not present using PAUT.............................................16

Figure 7.1-2. CT Scan of ROHACELL® Foam with known Flaw...................................................17

Figure 7.2.2-1. LSC Severance Plate to Test Panel Mounting............................................................25

Figure 7.2.2-2. Solid Composite Test Panel .......................................................................................26

Figure 7.2.2-3. Al Pathfinder Panel ....................................................................................................26

Figure 7.2.2-4. LSC Mounted to Shims on LSC Plate........................................................................26

Figure 7.2.2-5. Composite Solid Panel Test Setup .............................................................................27

Figure 7.2.2-6. Composite Sandwich Panel Test Setup ......................................................................27

Figure 7.2.2-7. Composite Sandwich Panel Test Setup, LSC Plate Mounting ...................................28

Figure 7.2.2-8. Composite Sandwich Panel with MAF ......................................................................28

Figure 7.2.3-1. Panel Attachment to Test Facility ..............................................................................29

Figure 7.2.3-2. Calculated Severance Al Sheath LSC with Al Target................................................30

Figure 7.2.3-3. Optimum Standoff Al Sheath LSC.............................................................................30

Figure 7.2.4.1-1. PCB 350C02 and PCB 350D02 Accelerometer Comparisons...................................31

Figure 7.2.4.1-2. Location of Accelerometers, PCB 350C02 versus PCB 350D02...............................32

Figure 7.2.4.1-3. Monolithic Composite Panel Pyroshock Test Setup (Typical) ..................................33

Figure 7.2.4.1-4. Composite Sandwich Panel Pyroshock Test Setup (Typical) ....................................34

Figure 7.2.4.1-5. Composite Sandwich Panel Pyroshock Test Setup with Composite LSC Panel 

(Typical).....................................................................................................................35

Figure 7.2.4.1-6. Composite Panel with Melamine Foam Pyroshock Test Setup (Typical)..................36

Figure 7.2.5.2-1. Estimated Source Shock, 10-gpf LSC........................................................................38

Figure 7.2.5.2-2. Estimated Source Shock, 22-gpf LSC........................................................................38

Figure 7.3.1.2-1. Comparison of Raw Time History Signal (Top) to Post-Processed Signal 

(Bottom) .....................................................................................................................41

Figure 7.3.1.2-2. Acceleration Time History Signal Post-Processing Procedure ..................................42

Figure 7.3.1.2-3. MATLAB® Code for Retrieving the First 20 msec of a Shock Pulse from a Time 

History Signal.............................................................................................................43

Figure 7.3.1.2-4. MATLAB® Code for Shifting a Time Signal to Begin at 0 sec .................................44

Figure 7.3.1.2-5. Reference MATLAB® Code for Mean Removal .......................................................44

Figure 7.3.2-1. Data Output from SRS Enveloping Algorithm ..........................................................47

Figure 7.3.2-2. Data Output from SRS Enveloping Algorithm – Double Plateau..............................48
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Figure 7.3.2-3. PVRS (4CP) ...............................................................................................................49

Figure 7.3.3.1-1. SRS Enveloping Procedure ........................................................................................50

Figure 7.3.3.1-2. MATLAB® Code for Performing SRS Enveloping Procedure ..................................51

Figure 7.3.3.1-3. (a) Enveloping SRS Algorithm ..................................................................................52

Figure 7.3.3.1-3. (b) Enveloping SRS Algorithm..................................................................................53

Figure 7.3.3.1-3. (c) Enveloping SRS Algorithm ..................................................................................54

Figure 7.3.3.1-3. (d) Enveloping SRS Algorithm..................................................................................55

Figure 7.3.3.1-3. (e) Enveloping SRS Algorithm ..................................................................................56

Figure 7.3.3.1-3. (f) Enveloping SRS Algorithm...................................................................................57

Figure 7.3.3.1-4. Sample of the SRS Enveloping Algorithm.................................................................58

Figure 7.3.4-1. Reference Code for Calculating Max PV and Frequency ..........................................59

Figure 7.3.6.1-1. SRS Predicted Slope from Statistical Analysis (untransformed) ...............................62

Figure 7.3.6.1-2. SRS Predicted Slope from Statistical Analysis (log-transformed).............................63

Figure 7.3.6.1-3. SRS Predicted Slope from Statistical Analysis (Percentile).......................................64

Figure 7.3.6.1-4. Monolithic Composite Average SRS Slope ...............................................................65

Figure 7.3.6.1-5. Composite Sandwich Panel Slope Change versus Distance.......................................66

Figure 7.3.6.2-1. Predicted Frequency Breakpoint versus Distance by Panel Type ..............................68

Figure 7.3.6.2-2. SRS Frequency Breakpoint – Ply Type Evaluation ...................................................69

Figure 7.3.6.2-3. SRS Frequency Breakpoint Composite Sandwich Fill Evaluation (all data) .............70

Figure 7.3.6.2-4. SRS Frequency Breakpoint Composite Sandwich Fill Evaluation (less 69-inch 

data and composite LSC plate data)...........................................................................70

Figure 7.3.6.3-1. Predicted SRS Peak Acceleration versus Distance by Panel Type ............................74

Figure 7.3.6.3-2. Monolithic Composite Panel Peak Acceleration with Distance Comparison ............77

Figure 7.3.6.3-3. Peak Acceleration versus Distance, Group I Re-Test 2 .............................................78

Figure 7.3.6.3-4. Monolithic Composite Group I, Re-Test 2, Percent Median Peak Acceleration 

versus Distance...........................................................................................................79

Figure 7.3.6.3-5. Peak Acceleration – Tape versus Fabric Ply ..............................................................80

Figure 7.3.6.3-6. Comparison of Ply Layup Direction –Peak Acceleration and PV..............................81

Figure 7.3.6.3-7. Comparison of Monolithic Composite Panel Thickness – Peak Acceleration and 

PV...............................................................................................................................82

Figure 7.3.6.3-8. Comparison of Monolithic Composite Panel and Sandwich Composite Panel –

Peak Acceleration versus Distance.............................................................................83

Figure 7.3.6.3-9. Percentile of Shock Remaining – All Panel Types ....................................................84

Figure 7.3.6.3-10. Percentile of Shock Remaining - Monolithic Composite Panel.................................85

Figure 7.3.6.3-11. Percentile of Shock Remaining – Al Honeycomb Composite Sandwich Panel.........86

Figure 7.3.6.3-12. Percentile of Shock Remaining – ROHACELL® Foam Composite Sandwich 

Panel...........................................................................................................................87

Figure 7.3.6.3-13. Percentile of Shock Remaining- Comparison of Martin Marietta Data with Al 

Honeycomb Sandwich Panel Data .............................................................................88

Figure 7.3.7-1. Mean PV versus Distance, 0.2-inch-thick Monolithic Composite Panel ...................89

Figure 7.3.7-2. Percentile of PV Remaining versus Distance, 0.2-inch-thick Monolithic 

Composite Panel.........................................................................................................90
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Figure 7.3.7-3. Mean PV versus Distance, 0.3-inch-thick Monolithic Composite Panel ...................91

Figure 7.3.7-4. Percentile of PV Remaining versus Distance, 0.3-inch-thick Monolithic 

Composite Panel.........................................................................................................92

Figure 7.3.7-5. Mean PV versus Distance, Al Honeycomb Composite Sandwich Panel ...................93

Figure 7.3.7-6. Percentile of PV Remaining versus Distance, Al Honeycomb Composite 

Sandwich Panel ..........................................................................................................94

Figure 7.3.7-7. Mean PV versus Distance, ROHACELL® Foam Composite Sandwich Panel ..........95

Figure 7.3.7-8. Percentile of PV Remaining versus Distance, ROHACELL® Foam Composite 

Sandwich Panel ..........................................................................................................96

Figure 7.3.8-1. ESD Plot – 0.2-inch Monolithic Panel, 10-gpf LSC ..................................................98

Figure 7.3.8-2. ESD Plot – Al Honeycomb Composite Sandwich Panel, 10-gpf LSC.......................99

Figure 7.3.8-3. ESD Plot – ROHACELL® Foam Composite Sandwich Panel, 10-gpf LSC............100

Figure 7.3.8-4. Maximum Predicted ESD – LSC Plate Type and LSC Explosive Core Load .........102

Figure 7.3.9-1. Time Histories for Group I, Test 2, Monolithic Composite Panel –

Accelerometers 2 and 8 ............................................................................................103

Figure 7.3.9-2. Time Histories for Group II, Test 11, Al Honeycomb Sandwich Composite Panel 

– Accelerometers 2 and 8 .........................................................................................104

Figure 7.3.9-3. Time Histories for Group II, Test 13, ROHACELL® Foam Sandwich Composite 

Panel – Accelerometers 2 and 8 ...............................................................................105

Figure 7.3.10-1. Monolithic Composite Temporal Energy Sensitivities ............................................107

Figure 7.3.11-1. Predictive MEFE, Monolithic Composite ................................................................108

Figure 7.3.11-2. Predicted MEFE Example at 48 inches, Monolithic Composite ..............................110

Figure 7.3.11-3. Predicted MEFE, Al Honeycomb.............................................................................111

Figure 7.3.11-4. Predicted MEFE at 48-inch Distance, Al Honeycomb.............................................112

Figure 7.3.11-5. Predicted MEFE, ROHACELL® Foam....................................................................113

Figure 7.3.11-6. Predicted MEFE at a Distance of 48-inches, ROHACELL® Foam .........................114

Figure 7.3.12-1. MAF Evaluation, SRS Slope....................................................................................115

Figure 7.3.12-2. MAF Evaluation, SRS Frequency Breakpoint .........................................................116

Figure 7.3.12-3. MAF Evaluation, SRS Peak Acceleration................................................................117
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List of Tables

Table 7.2.1-1. Pyroshock Composite Material Characterization Test Matrix (Pathfinder Tests)......18

Table 7.2.1-2. Modified Pyroshock Composite Material Characterization Test Matrix ...................20

Table 7.2.1-3. Modified Pyroshock Composite Material Characterization Test Matrix ...................21

Table 7.2.1-4. Modified Pyroshock Composite Material Characterization Test Matrix ...................22

Table 7.2.1-5. Pyroshock Composite LSC Plate Ply Layup..............................................................23

Table 7.2.1-6. Pyroshock Composite Group II Re-Tests...................................................................24

Table 7.2.1-7. Melamine Foam Damped Test Series ........................................................................24

Table 7.3.6.1-1. Predictive Slope versus Distance (regardless of panel type)......................................61

Table 7.3.6.2-1. Predicted Frequency Breakpoint with Distance (by panel type)................................67

Table 7.3.6.3-1. Predicted Peak Acceleration Values by Panel Material Type ....................................75

Table 7.3.8-1. Predicted Maximum ESD.........................................................................................101

Table 7.3.11-1. Predictive 8,000 g Shock, Monolithic Composite....................................................109

Table 7.3.11-2. Predictive 8,000-g Shock Attenuated for 48-inch Distance, Monolithic 

Composite.................................................................................................................110
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Technical Assessment Report

1.0 Notification and Authorization

The NASA Engineering and Safety Center (NESC) received a request to develop an analysis 

model based on both frequency response and wave propagation analyses for predicting shock 

response spectrum (SRS) on composite materials subjected to pyroshock loading. The model 

would account for near-field environment (~9 inches from the source) dominated by direct wave 

propagation, mid-field environment (~2 feet from the source) characterized by wave propagation 

and structural resonances, and far-field environment dominated by lower frequency bending 

waves in the structure.

Mr. Steve Gentz, NESC Chief Engineer at Marshall Space Flight Center (MSFC), was selected 

to lead this assessment. Mr. David Ordway (MSFC) was selected as the Technical Lead. 

The key stakeholders for this assessment include:

Space Launch System (SLS) Program

 Todd May (SLS Program Manager)

 Gary Lyles (SLS Chief Engineer)

 Mindy Nettles (SLS Advanced Development Program Manager)

 Chris Crumbly (SLS Spacecraft and Payload Integration Manager)

Technical Discipline

 Dynamic Environment Analysts

Other NASA Programs

 Atlas V

 Delta IV

 SpaceX

Other Government Agencies

 Department of Defense
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2.0 Signature Page

Submitted by:

Team Signature Page on File – 5/27/15

Mr. Steven J. Gentz Date

Significant Contributors: 

Mr. David O. Ordway Date Mr. David Parsons Date

Mr. Craig Garrison Date Mr. Steven Rodgers Date

Mr. Justin Jackson Date

(for Mr. Brian Collins)

Signatories declare the findings, observations, and NESC recommendations compiled in the 

report are factually based from data extracted from program/project documents, contractor 

reports, and open literature, and/or generated from independently conducted tests, analyses, and 

inspections.
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3.0 Team List

Name Discipline Organization

Core Team

Steve Gentz NESC Lead MSFC

David Ordway Technical Lead MSFC

Brian Collins Structural Materials, Composite MSFC

Craig Garrison Pyroshock Test, Structural Dynamics MSFC

Steve Rodgers Pyroshock, Structural Dynamics MSFC

Karen Oliver Pyroshock Analysis MSFC

Patricia Pahlavani MTSO Program Analyst LaRC

David Parsons Pyroshock Analysis MSFC

Ken Johnson NESC Systems Engineering Office/ 

Statistics and Trending MSFC

Lee Allen Nonmetallic Materials MSFC

Stephen Richardson Flight Systems MSFC

Stanley Smeltzer Composite Materials LaRC

Jackie Thomas CAD Support MSFC

Administrative Support

Linda Burgess Project Coordinator LaRC/AMA

Tina Dunn-Pittman Planning and Control Analyst LaRC/AMA

Erin Moran Technical Writer LaRC/AMA

3.1 Acknowledgements

The team would like to acknowledge the following for providing their expertise:

 Dr. Curt Larsen/Johnson Space Center (JSC), of the NESC, for championing the Pyroshock 

Characterization of Composites task.

 Mr. Ken Johnson/MSFC for his tireless support statistically analyzing the post-processed 

acceleration data.

 Mr. Lee Allen/MSFC for supporting Ken Johnson in statistically analyzing the postprocessed data

 Ms. Barbara Breithaupt/MSFC for post-processing the pseudo-velocity data.

 Mr. Justin Jackson/MSFC for providing his expertise in composite test panel fabrication.
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4.0 Executive Summary

Historically, the aerospace industry has used the shock response spectrum for defining a 

maximum expected flight environment (MEFE) at any one location, or zone, for a spacecraft or 

launch vehicle. The data used for defining the MEFE is usually based on the collective data 

compiled by Martin Marietta in NASA CR-114606, Pyrotechnic Shock Design Guidelines 

Manual, which was compiled about 45 years ago. The compilation of data in NASA CR-114606 

is primarily for metallic structures. The pyroshock data and the data evaluation process 

documented within this report are to expand upon the data compilation contained in NASA 

CR-114606 for composite structures.

The objective of this assessment was to develop an analytical tool to be used for accurate 

prediction of the MEFE for pyroshock induced into a composite material. Pyroshock tests were 

conducted to capture the acceleration time history of the shock wave as it transverses across the 

composite panel at various locations (commonly referred to as near field, mid-field, and far field) 

on the panel. These data provided the necessary information for the generation of attenuation 

curves for each of the types of composite materials resulting in an empirical analytical model for 

prediction of the shock MEFE. The composite material variables that were evaluated in this 

assessment included the thickness of the composite (monolithic) material, direction of the ply 

orientation (unidirectional versus quasi-isotropic plies), tape versus fabric plies, monolithic 

versus filled composite, and the type of fill used in the composite sandwich. The explosive load 

of the pyroshock source induced into the composite panel was also evaluated. 

Composite materials offer a number of advantages with respect to isotropic materials due to their 

low density and the possibility of optimizing their strength and stiffness by properly determining 

the fiber or tape orientation of every layer in the laminate. As a result, the analysis of their static 

and dynamic behavior is important, especially in the aerospace engineering field where the 

minimization of the structural mass is one of the first objectives of the design. 

A composite test panel configuration of 3 feet in height and 6 feet in length was selected for the 

pyroshock testing. The test panel thickness was one of the variables for evaluation, which is 

governed by the type and number of plies used for panel fabrication. The test panel fabrication 

processes and nondestructive evaluation (NDE) of the composite material is summarized in 

Appendix A. 

Transient shock, which is induced by explosives, occurs in all three orthogonal axes. It was 

decided to measure the acceleration in only the out-of-plane axis since these data would be the 

most useful for comparison of the variables being evaluated. The number of tests performed 

exceeded the baseline test matrix originally proposed for the Pyroshock Characterization of 

Composites task. The additional tests include performing five pathfinder tests validating the test 

setup, repeating four Group I monolithic composite panel tests, and performing pyroshock tests 

with acoustic dampening melamine foam bonded to the composite panels (or Al panel) for a total 

of 47 tests. The test results for each of the pyroshock tests performed are documented in 

Appendix B.
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The acceleration data acquired from the pyroshock test were evaluated for suitability (or quality) 

prior to post-test processing. Post-test data processing was performed by input of the data into 

MATLAB® algorithms for generation of data sets that could efficiently evaluate each of the 

variables independent of the other variable effects. Any changes made to the test matrices were 

analyzed using STATGRAPHICS® and Design-Expert® software for test design efficiency 

evaluation prior to incorporation into the test planning and procedural documentation.

Once the acceleration data were acquired, they were post-processed and MATLAB® algorithms 

were developed to provide a data set of factors to be further analyzed statistically to determine 

whether the factor was significant to the shock response. An outline of the steps involved for 

post-processing the data, the MATLAB® algorithms, and a summary of the statistical software 

utilized in these analyses is documented in Section 7.3.

A summary of the tasks for conducting the pyroshock tests and data processing is shown in 

Figure 4.0-1.

The single value inputs (SVI) used for evaluation of the shock response were centric for shock 

response spectrum (SRS) since it is the shock data processing methodology of choice for the 

aerospace industry (including NASA). Evaluation of the SVIs for the SRS included the SRS 

slope, frequency breakpoint, and the peak acceleration. 

The composite sandwich panels attenuated the shock (with distance) much better than the 

monolithic composite panels with the ROHACELL® foam sandwich-filled panels having the 

greatest shock attenuation characteristics. The SRS slope showed little change from 20 inches 

up to 60 inches from the shock source whereas the SRS frequency breakpoint decreased with 

distance from the shock source. 

Other composite materials factors evaluated, such as ply orientation and type of ply, were not 

significant factors for the shock response. The thickness of the monolithic composite panels did 

show different levels of shock attenuation (a lower level for the 0.2-inch-thick versus the 

0.3-inch-thick) but the rate at which the shock was attenuated was equivalent.

Evaluation of the pseudo-velocity response spectrum (PVRS) was also performed to supplement 

the SRS since the PVRS provides an indication on the severity of the shock, which cannot be 

directly discerned from the SRS. The shock induced into the composite panels is classified as a 

moderate to severe shock and post-test NDE (phased array ultrasound) showed no indications of 

damage to the composites after being subjected to pyroshock loading. The attenuation of the 

mean (rather than maximum) pseudo-velocity (PV) with distance from the shock source was in 

alignment SRS peak acceleration attenuation. The determination of the mean PV was performed 

manually since a MATLAB® algorithm for determining the mean PV was not developed.
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Figure 4.0-1. Pyroshock of Composites Task Flow Diagram

The addition of melamine foam for acoustic dampening did not affect the SRS peak acceleration, 

SRS slope, or the attenuation of the shock with distance (peak acceleration). The acoustic 

melamine foam did decrease the SRS frequency breakpoint approximately 30 to 40 percent as 

compared to the composite material without the acoustic foam.

To make most efficient use of NASA or other provider resources, the project should consider 

using the results from this testing in planning future testing, including test article design, test 

article quality assurance, sensor placement, expected magnitude of effect and variability around 

the effect, and analysis method.

The pyroshock characterization of composites project was successful in establishing a 

methodology for evaluating the quality of the acceleration time history data, developing 

algorithms for post-processing the data, and for establishing a database, which may be used for 

future higher-fidelity pyroshock testing of composites (e.g., large cylindrical structures). It is 

recommended further tests be performed to increase the composite shock database for the Space 

Launch System (SLS) Composite Exploration Upper Stage (EUS) technology and development 

project to more accurately predict pyroshock loading for the EUS.
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5.0 Assessment Plan

A series of pyroshock tests were conducted on various types of composite panels and the shock 

response obtained from the tests were used to develop an analytical tool to predict a MEFE shock 

environment based on the explosive loading of the separation system and the type of composite 

material into which the shock was induced. Initially, 28 pyroshock tests were planned for this 

assessment to evaluate each of the variables described above. 

This assessment required the test specimens (i.e., the different types of composite panels) to be 

fabricated and detail design drawings developed. MSFC pyrotechnic test facility personnel 

conducted testing and quick-look data reduction. There was sufficient linear-shaped charge 

(LSC) of various core loads available at MSFC for conducting these tests without the need to 

procure new LSC. Loads and dynamics personnel developed the analytical model based on the 

reduced data from the test results. 

The activities required to complete this assessment included:

 Test planning and composite panel fabrication 

– Test plan development

– Composite panel computer aided design drawings

– Composite panel fabrication and Insert Installation

– Pyroshock test setup

 Pyroshock testing and data reduction

– Perform pyroshock tests

– Reduce data and generate SRS plots

 Analytical model and accompanying handbook development and final report

– Assist in test planning and development

– Research development of distance attenuation curves and shock propagation 

prediction methods

– Research pyroshock analytical modeling methods

– Correlate pyroshock test data with analytical model

– Develop analytical model to predict shock MEFE

– Develop handbook for analytical model usage

– Generate final report

6.0 Problem Description

The primary purpose of this test series was to capture the acceleration time history of the shock 

wave as it transverses across various types of composite panels at various locations (commonly 

referred to as near field, mid-field, and far field) on the panel. These tests were performed to 

provide the necessary information for the generation of attenuation curves for each of the types 

of composite materials resulting in an empirical analytical model for prediction of the shock 

MEFE.
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This test series did not determine the cumulative effects of vibro-acoustic exposure of the 

composite material prior to being subjected to the induced pyroshock event. The test series was 

limited to flat panel testing only, which did not allow evaluation of the composite material 

response to pyroshock with regard to ring frequency. Ring frequency corresponds to the mode in 

which all points move radially outward together and then radially inward together. This is the 

first extension mode of a cylindrical structure and is analogous to a longitudinal mode in a rod. 

Evaluation of the ring frequency of a composite material cylindrical structure would greatly 

enhance analytical prediction of the shock MEFE for flight structures.

7.0 Composite Panel Fabrication, Pyroshock Test Conduct, and Data 

Analysis

7.1 Composite Panel Fabrication and NDE

All of the composite panels used for the pyroshock tests were fabricated at MSFC by the 

Nonmetallic Materials and Manufacturing Branch (EM42) personnel. The panels were 

fabricated per steps listed in MSFC work orders approved by EM42 Engineering and the task 

assessment technical lead. The baseline task assessment composite panels were fabricated from 

IM7/TC350 composite material manufactured by TenCate Advanced Composites. This material 

is a 350°F toughened epoxy resin system used for structural advanced composite applications, 

which include space structures. The composite material in both tape and fabric prepreg formats 

was used for this assessment. The composite material was chosen in place of IM7/977-3 

composite material, which is more commonly used for aviation and aerospace applications, 

primarily due to the long lead-time for procurement (29 weeks) of the IM7/977-3 material. 

Additionally, the material properties for the IM7/TC350 and the IM7/977-3 are comparable. 

A second composite material was also used for the pyroshock characterization, which was 

IM7-R913. This material was originally procured by Redstone Arsenal for fabrication of 

helicopter blades and later given to MSFC since its age life had expired. Prior to usage, some of 

the material was removed from the freezer, thawed, and evaluated to determine if it was suitable 

for usage. The material was determined to be acceptable and three 38-ply tape panels were 

fabricated for usage in the five test pathfinder test series.

In addition to the composite prepreg material, two other primary materials were required for the 

composite sandwich panel configurations, which was the filler materials. The two-filler 

materials chosen were Al honeycomb and ROHACELL® foam, both of which are used for 

aerospace applications. The Al honeycomb fill material used was procured from Texas Almet 

part number 3.1 1/8 .0007P 5052 (3.1 pounds per cubic feet (pcf), 1/8-inch hexagonal cell size, 

0.0007-inch foil gauge, P = perforated, and 5052 was the Al alloy). The ROHACELL® foam 

used was ROHACELL® 200 WF, which is a closed-cell rigid polymethacrylimade foam and was 

procured from Evonik Industries. The thickness of the filler materials was 1 inch; whether Al 

honeycomb or ROHACELL® foam, and 8-ply face sheets of IM7/TC350 (tape or fabric plies) 

were used to make up the composite sandwich panel. 
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The type of ply material, ply orientation, number of plies used, fill material type (as applicable), 

along with dimensional requirements were documented on drawings generated by EV32 

Engineering (reference Appendix A for drawing details).

Following fabrication of the composite test panels, the panels were subjected to NDE for flaws 

(voids, delamination, etc.) and the location of the flaws, if they existed, for correlation to 

accelerometer location time history data to aid in understanding whether the flaw influenced the 

shock response. Initially, two NDE methods were used, infrared (IR) thermography and phased 

array ultrasonic testing (PAUT). It was determined from the initial NDE of the composite panels 

the IR thermography method produced false indications for the monolithic composite panels, 

which were 0.2 inches or 0.3 inches in thickness. The conclusion was IR thermography was not 

the NDE methodology of choice for composites materials of the thicknesses used in this testing 

and only PAUT was used thereafter. Figure 7.1.1 illustrates an indication from IR thermography 

inspection, which was not present using PAUT and as considered to be a surface condition.

Figure 7.1-1. IR Thermography Indications not present using PAUT

Fabrication of the composite sandwich panels generated new challenges of NDE methodology 

for evaluation of the filler material. PAUT generated acceptable results for evaluation of the face 

sheets and the bond line between the face sheets and the filler, but was unable to detect flaws in 

the filler material. It was concluded PAUT is not a suitable NDE method for evaluating flaws in 

the foam filler core material. A study was undertaken to evaluate an acceptable NDE 
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methodology for resolving a flaw (crack) in the ROHACELL® foam. Two methods were 

evaluated; digital radiography (DR) and computed tomography (CT). The results of the study 

are documented in Appendix A, reference Figure A35, which show only the CT method was able 

to detect flaws in the foam filler material. Figure 7.1-2 illustrates the CT results for detecting a 

known flaw (crack) in the ROHACELL® foam.

Figure 7.1-2. CT Scan of ROHACELL

® Foam with known Flaw
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7.2 Pyroshock Test Conduct

7.2.1 Test Planning

A Pyroshock Characterization of Composites Test Plan was generated by the assessment 

technical lead to document the specifics for the test panel configurations, test order, test setup, 

and instrumentation for data acquisition. The approved baseline test plan was dated July 2, 2012, 

and during the course of this estimate, the test plan was revised four times, ultimately ending in 

revision D, to accommodate changes to the test matrices and scope of the testing performed.

Initially, 28 tests (initial baseline task assessment plan) were planned for this test series utilizing 

the composite panel configurations. 

Prior to conducting the tests, using composite panels fabricated from IM7/TC350 material, it was 

decided to conduct a series of five pathfinder tests to evaluate the test setup and data acquisition 

system (DAS). The configuration for the pathfinder panel tests are tabulated in Table 7.2.1-1. 

The IM7/913 composite panels were inspected using pulse echo ultrasound prior to subjection to 

the pyroshock test. The baseline panels used for this testing, fabricated from IM7/TC350, were 

initially inspected using both flash thermography and pulse echo ultrasound (PAUT), but only 

pulse echo ultrasound was ultimately used, prior to test for the reasons documented in 

Section 7.1.

Table 7.2.1-1. Pyroshock Composite Material Characterization Test Matrix (Pathfinder Tests)

Test 

Number

Material Panel 

Thickness

Ply Orientation Type LSC Core 

Load

1 Al (Al), 5052 

alloy

0.187 N/A N/A Homogenous 10 gpf

2 Al, 5052 

alloy

0.187 N/A N/A Homogenous 22 gpf

3 Composite, 

IM7/R913

0.200 Tape

38 plies

((+45°/-45° (2X), 

0° (2x),

+45°/-45° (2X),

90° (2x)) (X 3.2)

Solid 10 gpf

4 Composite, 

IM7/R913

0.200 Tape

38 plies

All plies 0° Solid 10 gpf

5 Composite, 

IM7/R913

0.200 Tape

38 plies

All plies 90° Solid 10 gpf

Following completion of the pathfinder tests and determination the test setup and instrumentation 

was satisfactory for progressing with the baseline composite panel tests. Initially, the tests were 

divided into three groups: Group I representing the monolithic composite panels, Group II being 

the first eight sandwich panels, and Group III was the last ten sandwich panels. Of note, a 

change in the scope of the testing included repeating four of the Group I monolithic composite 

panels to help better understand within panel variability and also to evaluate the panel for 

damage utilizing PAUT as the NDE method after subjection to pyroshock. (Note: Since new 
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indications were not noted, it was concluded the damage tolerance of the composite material was 

above the shock levels induced into the composite). The increased scope of the task also 

included the addition of the tests with and without melamine acoustic foam (MAF), identified as 

Group IV, utilizing panels previously subjected to shock in either the pathfinder test series (Al 

panel), Group I (monolithic composite panel), or Group II (composite sandwich panel). 

Randomness in testing of the panels, whether they were from Groups I, II, III, or IV, was 

introduced for determination of which parameters have the greatest sensitivity to shock response. 

Each test matrix was planned so the effects of each input factor (i.e., core load, monolithic panel 

thickness, presence of foam dampening, etc.) could be efficiently calculated and separated from 

the effects of the other input factors per the goals of this task. Standard efficient test matrix 

design methods (design of experiments (DOE)) were used. The test matrices were planned and 

the efficiency of changes recommended by subject matter experts (SME) were analyzed using 

STATGRAPHICS® and Design-Expert® software before implementation of the changes into the 

test plan.

The initial tests, identified in the test planning as Group I, are tabulated in Table 7.2.1-2. These 

tests evaluated the following parameters:

 Composite thickness

 Type of ply and ply orientation

 Source shock induced into the panel

Following completion of the Group I tests, the results from these tests were evaluated and, based 

on the evaluation, the test matrix in Table 7.2.1-3 was adjusted to focus the follow-on tests (tests 

10-18) for focus on evaluating the data processing SVI in comparison with the Group I test 

results, which have the greatest sensitivity to the induced shock. The SVIs evaluated were:

 Acceleration time history

 Velocity time history

 Displacement time history

 SRS peak g’s, frequency breakpoint, and slope
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Table 7.2.1-2. Modified Pyroshock Composite Material Characterization Test Matrix

Group I – Solid Composite Panels

Test 

Number Material Panel 

Thickness Ply Orientation Type

LSC 

Core 

Load

1 Composite, 

IM7/TC350 0.200 Fabric 0-Deg, 18 ply Solid 10

2 Composite, 

IM7/TC350 0.200 Fabric

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 18 ply

Solid 10

3 Composite, 

IM7/TC350 0.300 Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 54 ply

Solid 10

4 Composite, 

IM7/TC350 0.300 Fabric

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 27 ply

Solid 22

5 Composite, 

IM7/TC350 0.200 Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 38 ply

Solid 22

Analyzed results from Tests 1-5 to incorporate any re-planning for tests 6 through 10 was deemed necessary. 

(Note: No re-planning was required.)

6 Composite, 

IM7/TC350 0.200 Fabric 0-Deg, 18 ply Solid 22

7 Composite, 

IM7/TC350 0.200 Fabric

+45°/-45°, 0° (2x),

+45°/-45°,

90°, 18 ply

Solid 22

8 Composite, 

IM7/TC350 0.300 Fabric

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 27 ply

Solid 10

9 Composite, 

IM7/TC350 0.300 Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 54 ply

Solid 22

10 Composite, 

IM7/TC350 0.200 Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2x), 38 ply

Solid 10
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Table 7.2.1-3. Modified Pyroshock Composite Material Characterization Test Matrix

Group II – Sandwich Composite Panels

Test 

Number Material Panel 

Thickness Fill/Ply Orientation Type

LSC 

Core 

Load

11 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill Al Honeycomb

& Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 10

12 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill Al Honeycomb

& Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 22

13 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill ROHACELL®

Foam &Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 10

14 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill ROHACELL®

Foam &Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 22

15 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill Al Honeycomb

& Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 10

16 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill Al Honeycomb

& Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 22

17 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill ROHACELL®

Foam &Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 10

18 Composite, 

IM7/TC350

8 Ply/ 1-inchthick fill ROHACELL® 

Foam &Tape

+45°/-45°, 0° (2x),

+45°/-45°,

90° (2X), 8 ply both faces

Sandwich 22

Upon completion of the tests tabulated in Table 7.2.1-3, the test series continued with the tests 

shown in Table 7.2.1-4 for the Group III tests (test numbers 19 through 28). One new variable 

was introduced in the Group III tests, which was using a monolithic composite LSC plate in lieu 

of the Al panel used in all of the previous testing. The new variable was introduced since in 

some applications (e.g., a LSC-based stage separation system required to separate at a composite 

filament wound motor case interface, would have the shock introduced into the composite 

material from severance of the composite interface). The ply type, number of plies, and their 

layup for the composite LSC plates are tabulated in Table 7.2.1-5.
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Table 7.2.1-4. Modified Pyroshock Composite Material Characterization Test Matrix

Group III – Sandwich Composite Panels

Panel and Test 

Number Material Panel Thickness Fill/Ply Test Panel Ply Orientation Type LSC (gpf) LSC Plate*

19 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 10 Fabric Composite, 

IM7/TC350

20 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill ROHACELL® Foam & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 22 Fabric Composite, 

IM7/TC350

21 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Tape Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 22 Al

22 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill ROHACELL® Foam & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 10 Al

23 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 10 Al

24 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 22 Al

25 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 22 Fabric Composite, 

IM7/TC350

26 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill ROHACELL® Foam & Tape Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 22 Tape Composite, 

IM7/TC350

27 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill ROHACELL® Foam & Fabric Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 10 Fabric Composite, 

IM7/TC350

28 Composite, 

IM7/TC350 8 Ply/1-inch-thick fill Al Honeycomb & Tape Face Sheets

90°/+45°/-45°/0°/0°/

-45°/+45°/90°,

8 ply both faces

Sandwich 10 Tape Composite, 

IM7/TC350

*See Table 7.2.1-5 for LSC plate ply layup.
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Table 7.2.1-5. Pyroshock Composite LSC Plate Ply Layup

Ply Number Orientation 

Fabric Ply

Orientation Tape 

Ply

1 45° 45°

2 -45° -45°

3 0° 0°

4 0° 0°

5 45° 45°

6 -45° -45°

7 90° 90°

8 90° 90°

9 -45° 45°

10 45° -45°

11 90° 0°

12 90° 0°

13 -45° 45°

14 45° -45°

15 0° 0°

16 0° 90°

17 -45° 90°

18 45° 0°

19 -45°

20 45°

21 0°

22 0°

23 -45°

24 45°

25 90°

26 90°

27 -45°

28 45°

29 0°

30 0°

31 -45°

32 45°

Following evaluation of the Group I tests 1 through 10 test data, it was determined to perform retests of selected Group II tests, which were performed as tabulated in Table 7.2.1-6. NDE (pulse 

echo ultrasound) was performed and an evaluation comparing the initial NDE results and the 

post-test results for any differences in the panel’s integrity was performed prior to conducting the 

re-tests. As previously stated, no new indications were found in the four composite monolithic 

panels.
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Table 7.2.1-6. Pyroshock Composite Group II Re-Tests

Test 

No.

Group I 

Previous 

Test #

LSC 

Core 

Load

Panel Thickness 

(in)

Composite 

Ply

Rep 1 10 10 0.2 Tape

Rep 2 4 22 0.3 Fabric

Rep 3 2 22 0.2 Fabric

Rep 4 9 22 0.3 Tape

Based on input from the SLS Program, a test series incorporating the use of foam acoustic 

damping material, which is designed to mitigate acoustics transmitted to components mounted 

inside a payload fairing to selected test panels, was performed. The objective of this test series 

was to characterize the damping ability of the material when mounted to either metallic (Al), 

monolithic composite, or sandwich composite panels with regards to pyroshock. The data from 

these tests allowed data analysis from dampened panels to be directly compared with the data 

collected with the panels without the dampening material.

These tests provided a qualitative comparison of pyroshock energy attenuation of Al, monolithic 

composite with a quasi-isotropic ply layup, and composite sandwich panels (Al honeycomb or 

ROHACELL® foam fill and quasi-isotropic ply face sheets) with and without the acoustic 

dampening material. Test panels that were previously subjected to the pyroshock test were 

modified with the addition of the foam acoustic material adhesively bonded to the backside of 

the panels for this testing. See Table 7.2.1-7 for the test panels used for this testing.

Table 7.2.1-7. Melamine Foam Damped Test Series

Test 

Order Panel No Type Core Load Dampening

1 17 ROHACELL® 22 0

2 12 Monolithic 22 Damped

3 8 Al 22 0

4 18 ROHACELL® 22 Damped

5 11 Al Honeycomb 22 0

6 Pathfinder Al 22 0

7 Pathfinder Al 22 Damped

8 17 ROHACELL® 22 Damped

9 11 Al Honeycomb 22 Damped

10 8 Monolithic 22 Damped

The replicate tests performed in the Group IV testing used a number of different panels since the 

panel-to-panel variability was considered more important than the “within-panel” variability 

(i.e., for a flight application the composite material would only be subjected to pyroshock once 

within its anticipated lifetime). Note: For tests 27 and 28, severance of the LSC composite plate 
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was not achieved; however, the shock data were acquired and used in the analysis of the shock 

data, but not in the statistical analysis of the post-processed data.

7.2.2 Test Articles

Figure 7.2.2-1 illustrates the concept for mounting the LSC to an Al severance plate and the 

mounting of the severance plate to either the Al or composite panel. The LSC was mounted to 

the Al plate on shims to obtain the optimum standoff for each of the LSCs used. 

Figure 7.2.2-2 illustrates the solid composite panel configuration. 

Figure 7.2.2-3 illustrates the Al pathfinder panel and Figure 7.2.2-4 illustrates the shimmed LSC 

mounted onto the LSC plate. 

The LSCs were secured to Al standoff shims (mounted to the sacrificial severance LSC plate) 

with tape. However, for some of the Group IV tests there was insufficient 4-ft lengths of 22-gpf 

LSC remaining and two 2-ft lengths spliced together were used. For mounting, the two short 

lengths of LSC splice plates were introduced for securing the LSC to the LSC shims along with 

tape. (Reference Appendix A, Section A1, Figure A13 for details on the splice plate drawing).

Figures 7.2.2-5 and 7.2.2-6 illustrate the solid and sandwich composite panel configurations, 

respectively. Figure 7.2.2-7 illustrates the mounting of the LSC to the sandwich panel 

configuration. 

Figure 7.2.2-8 illustrates the melamine foam bonded to the backside of the composite sandwich 

panel. 

Figure 7.2.2-1. LSC Severance Plate to Test Panel Mounting Figure 1: LSC Severance Plate to Test Panel Mounting

0.125-inch thick 

aluminum or 0.176-inch 

thick (ref) composite 

plate

Support plate 

0.187-inch thick

Test Panel

LSC 

installed on 

shims
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Figure 7.2.2-2. Solid Composite Test Panel

Figure 7.2.2-3. Al Pathfinder Panel

Figure 7.2.2-4. LSC Mounted to Shims on LSC Plate

36”

72”
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Figure 7.2.2-5. Composite Solid Panel Test Setup

Figure 7.2.2-6. Composite Sandwich Panel Test Setup

Figure 6: Composite Sandwich Panel Test Setup

Blind Insert for accelerometer 

mounting (12 plcs) 12-inches apart 

with each pair 3.0 inches from the 

panel centerline Centerline

Through sleeve (14 plcs) 

for mounting LSC plate 

and hanging panel

9”
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Figure 7.2.2-7. Composite Sandwich Panel Test Setup, LSC Plate Mounting

Figure 7.2.2-8. Composite Sandwich Panel with MAF

7.2.3 Test Setup

To achieve the objectives outlined for this task, acquiring “quality” shock time history data is 

imperative. Acquiring “quality” data begins with careful test planning. IEST-RP-DTE012.1, 

Handbook for Dynamic Data Acquisition and Analysis, provides some recommended guidelines 

for pyroshock measurement locations listed below.

 For homogeneous structures between the pyrotechnic source and measurement location, 

never select a measurement location within 6 inches of the source.

 Always select measurement locations that are as far from the pyrotechnic source as feasible 

to continue to acquire meaningful engineering information.

 When applicable, select measurement locations that are separated from the source by a 

structural path with discontinuities (e.g., riveted or bolted joints or isolation elements).

The test setup for the pyroshock characterization of composites was purposely designed to 

acquire the shock data via the accelerometers separated by a bolted joint from the source shock. 

Another recommendation from IEST-RP-DTE012.1 to check for possible electromagnetic 

radiation (EMR) by freely suspending an additional accelerometer adjacent to, but not touching, 

the structure, and to acquire data from the accelerometer using an identical signal conditioner 

Figure 8: Composite Sandwich Panel with Melamine Acoustic Foam

Melamine Acoustic Foam 

with Dura-Sonic 5666 mass 

barrier

Composite Sandwich 

Panel
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with the same gain setting. Any significant output from the signal conditioner on the freely 

suspended accelerometer due to the pyroshock event is an indication of an EMR noise 

interference problem. Per the test reports contained in Appendix B of this report, accelerometer 

channel 13 used in each test was a freely suspended accelerometer. The data from this 

accelerometer were analyzed and output from accelerometer channel 13 for any of the pyroshock 

tests conducted for this task assessment was insignificant.

The tests were conducted at MSFC Building 4619 by Structural Dynamics Test Branch (ET40) 

personnel. The tests were conducted in accordance with an ET40 test checkout procedure (TCP), 

which included all explosive safety handling requirements. The panels were suspended at two 

corners from the facility ceiling using braided steel cables and secured to the facility floor at the 

opposite corners of the panel with braided steel cable. An LSC was fired, and acceleration data 

were collected at multiple locations on the panel. Figure 7.2.3-1 illustrates this configuration.

Figure 7.2.3-1. Panel Attachment to Test Facility

ET40 provided D-rings and cables for attaching the panels to the facility ceiling and rope for 

securing the bottom edge of the panel to the facility floor. 

Both 10-gpf and 22-gpf LSC were used to generate the source shock. To determine the Al LSC 

shim heights for the respective LSC used for this testing and to determine a thickness of the Al 

LSC severance plate the theoretical severance of the LSC was calculated and is shown in 

Figure 7.2.3-2. The LSC severance calculations were based upon positioning the LSC at its 

optimum standoff, which is shown in Figure 7.2.3-3.
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Figure 7.2.3-2. Calculated Severance Al Sheath LSC with Al Target

Figure 7.2.3-3. Optimum Standoff Al Sheath LSC

Figure 12: Optimum Standoff Aluminum Sheath LSC
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7.2.4 Instrumentation and Data Acquisition

7.2.4.1 Instrumentation

Response data of interest for this testing was in the frequency range from 100 Hz to 10,000 Hz. 

Stud-mount PCB 350C02 and PCB 350D02 accelerometers were used to collect both high and 

low frequency shock data. The pathfinder tests and the initial Group I test (tests 1 through 5) 

were all instrumented with the PCB 350C02 accelerometers mounted to the panel for data 

collection. Starting with Group I, Tests 7 through 10, continuing with the same pattern through 

the Group II tests, 11 through 18, and the Group III tests, 19 through 28, and Group IV tests, the 

PCBD02 accelerometers were introduced in a random pattern to evaluate whether a difference 

exists in the data acquired by the two versions of accelerometers. This evaluation resulted in the 

conclusion the difference data output between the two versions of accelerometers was 

undiscernible.

Figure 7.2.4.1-1 shows the attributes of both the PCB 350C02 and PCB 350D02 accelerometers. 

Figure 7.2.4.1-2 illustrates the pattern for locating for the PCB 350C02 and PCB 350D02 for 

Group I tests 7 through 10 and the balance of the remaining tests performed (i.e., alternating the 

PCB 350C02 and PCB 350 D02 from top to bottom on alternating tests).

Figure 7.2.4.1-1. PCB 350C02 and PCB 350D02 Accelerometer Comparisons

Accelerometers were mounted every 12 inches along the length of the plate, beginning at 

9 inches from the location of the LSC and 3 inches from either side of the panel centerline. 

(Reference Figures 7.2.2-5 and 7.2.2-6).

Figure 13: PCB 350C02 and PCB 350 D02 Accelerometer Comparisons

PCB 350C02 PCB 350D02
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Figure 7.2.4.1-2. Location of Accelerometers, PCB 350C02 versus PCB 350D02

Inserts were installed in each of the panels for accelerometer mounting. The type of insert used 

for the monolithic composite was a stainless steel threaded insert (7/16-14 outside diameter 

thread and 1/4-28 internal diameter thread). Prior to installation of the threaded inserts, the 

monolithic composite panels were tapped with a 7/16-14 tap for insert installation and bonded in 

place (flush with the composite panel surface) with Hysol® EA 9394 adhesive. For the 

composite sandwich panels, a different type of insert was needed to mount the accelerometers. 

For the sandwich panels, a clipnut blind insert was used, which had a 1/4-28 internal thread. The 

blind inserts were installed to a specified depth, such that the top surface of the insert would be 

flush with the top surface of the composite face sheet, and bonded in place. The location of the 

inserts are as depicted on the composite panel drawings for mounting the accelerometers 

(reference Appendix A, Section A1). Appendix A, Section A2.3, provides details on each of the 

inserts used and mounting of the inserts into the composite test panels.

Typical pyroshock test setups for the monolithic composite panels, sandwich composite panels, 

and the tests with the MAF added to the composite panel is shown in Figures 7.2.4.1-3 through 

7.2.4.1-6.
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Figure 7.2.4.1-3. Monolithic Composite Panel Pyroshock Test Setup (Typical)
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Figure 7.2.4.1-4. Composite Sandwich Panel Pyroshock Test Setup (Typical)
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Figure 7.2.4.1-5. Composite Sandwich Panel Pyroshock Test Setup with Composite LSC Panel 

(Typical)
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Figure 7.2.4.1-6. Composite Panel with Melamine Foam Pyroshock Test Setup (Typical)
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7.2.4.2 Data Acquisition

The instrumentation DAS was set up for data to be acquired from the response accelerometers at 

a rate consistent with best lab practice to obtain meaningful data in the frequency range specified 

which was a sample rate of 1 M samples per second. One of the absolute necessities for 

acquiring pyroshock acceleration data is to use anti-aliasing filters to prevent the high-frequency 

shock from “rolling-off” into the low-frequency data content thus artificially elevating the shock 

response in the low frequencies. Anti-aliasing filters were used for each of the response 

accelerometers and filtered output response from the accelerometers recorded. The filters used 

were Bessel infinite-impulse-response (IIR) (Fc@-3 dB) set at 33 kHz for each channel, as 

shown in the data acquisition setup tables at the end of each test report (reference Appendix B). 

Nicolet 614CB 4-channel cards were the specific cards chosen to acquire the accelerometer data.

7.2.5 Procedures

7.2.5.1 Roles/Responsibilities

ET40 provided the LSC plate, the backer plate, shims for mounting the LSC, the LSC, and 

electric blasting caps for initiation of the LSC.

ET40 test engineers installed all accelerometers, cables, and data acquisition equipment and 

verified the equipment was in proper working order. ET40 test engineers took digital 

photographs to document the pre-test setup, including locations and orientations of all 

accelerometers for each test, and the post-test results. ET40 test engineers secured the test panel 

to the facility ceiling/flooring. EV32 engineer (task assessment technical lead) assisted in 

installation of the LSC as required.

7.2.5.2 Test Levels

Two core loads of LSC were used for this testing for generation of the source shock. A 10-gpf 

LSC was used for the source shock and to evaluate the effect the core load had on the shock 

propagation through the composite material, 22-gpf LSC was used to generate the source shock 

for comparison with the 10-gpf LSC. To ensure proper data acquisition from the accelerometers, 

the peak acceleration needs to be estimated to ensure the proper model of accelerometer is used 

and the DAS is properly ranged. Figures 7.2.5.2-1 and 7.2.5.2-2 illustrate the estimated source 

shock produced by each of these LSCs. The source shock estimates are based on Martin 

Marietta Aerospace Systems Pyrotechnic Shock Design Guidelines Manual (NASA-CR-116406, 

Contract NAS5-15208, March 1970).
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Figure 7.2.5.2-1. Estimated Source Shock, 10-gpf LSC

Figure 7.2.5.2-2. Estimated Source Shock, 22-gpf LSC

Estimated Source Shock, 22 gpf LSC 

1

10

100

1000

10000

100000

10 100 1000 10000

Frequency [Hz]

SRS [G]
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7.2.6 Post-Test Operations

Following completion of each LSC firing, the test panel was visually inspected for indications of 

damage, loosening of accelerometers, and any other off-nominal condition. Post-test digital 

photographs were taken of each test documenting the test result. Off-nominal conditions, for 

example failure of the LSC to sever the LSC plate, were photographed and documented. 

Typical pre-test and post-test photos are documented in the test reports for each test group in 

Appendix B.

7.2.7 Data Requirements

The ET40 TCP used to perform the testing included data sheets to record the following 

information:

 Panel material and configuration

 Panel serial number (S/N)

 LSC core load and explosive material

 LSC L/N

 Accelerometer S/N by location

 Al LSC panel severance (yes/no)

The response data from all accelerometers was provided to EV32 and the Mechanical, Thermal 

and Life Support Analysis Branch (ES22) in electronic format as the acceleration time history 

(raw data and Fourier transform) and “quick-look” (prior to post-test data processing) shock 

response spectra. The test reports within Appendix B contain all of the time history and shock 

response spectra generated by ET40 for each of the accelerometers for each test categorized by 

test group.

Digital photographs of each test article, along with the corresponding data listed above, were 

provided to EV32. Photographs were labeled such that panel S/N, LSC core load, and 

instrumentation locations and orientations were easily discernible.

All test data from this test series will be retained for a minimum of 10 years following 

completion of the testing.

7.2.8 Evaluation Criteria

There were no pass/fail criteria for this test series; tests were performed for data acquisition only. 

The test was considered successful if a shock was introduced into the test panel as defined herein 

and the acceleration response data from the test was considered valid.
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7.3 Post-Test Data Processing and Data Evaluation

7.3.1 Post-Test Data Processing

7.3.1.1 Pyroshock Time History Data Processing Overview

The purpose of this section is to describe the procedures, methodologies, and tools used and 

developed to post-process the measured pyroshock time history data and characterize the 

pyroshock environment for developing empirical models describing the behavior of the shock 

environment as it propagates across a composite panel. The procedures, methodologies, and 

algorithms are presented are to provide clarity to the processes involved in preparing the data for 

empirical model development using statistical analysis methods. The purpose is twofold:

 To provide guidance for processing any future data that may be collected to expand upon 

the empirical models developed in this study.

 To provide the tools developed for use in processing shock data and for possible 

additional uses (e.g., "spin off" tools).

7.3.1.2 Data Analysis Procedure

Although “best practices” were incorporated into the pyroshock test setup, the acquired data 

must be evaluated to ensure it is “suitable” for analysis. The first step identified for analyzing 

the pyroshock accelerometer data is to develop a set of criteria used to define “suitable,” or 

“quality” time history data. The following criteria were used to define “suitable” time history 

data:

 An adequate length of time was recorded to produce results in the frequency range of 

interest.

 The acceleration time history and the integral and double integral is illustrated in 

Figure 7.3.1.2-1 (i.e., velocity and displacement time histories, begin and end at or near 

zero and have similar characteristics), 

 The methods developed from the processed time history signal used to characterize the 

pyroshock environment show no signs of typical time history errors such as a 0-g shift 

(typically a flattening of the SRS curve in the lower frequencies).
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Figure 7.3.1.2-1. Comparison of Raw Time History Signal (Top) to Post-Processed Signal (Bottom)

A primary goal of this assessment was to obtain data that could be used to compare responses 

across the different test configurations as cleanly and easily as possible given the variations 

generally seen in this type of data. In addition to the constraints listed above, two additional 

constraints were applied to the criteria to mitigate the potential for unnecessary variation and 

uncertainty due to human error and to mitigate human bias:

 All calculations for each test were performed in the same manner.

 Subjective decisions were removed or mitigated. For example, when windowing the time 

history, simply “eyeballing” a start point for the beginning of the shock pulse would not 
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meet the criteria of suitable since this is a subjective decision; therefore, an algorithm was 

developed for identifying the beginning of the shock pulse. This way, the same criteria for 

identifying the start of the shock pulse was applied to each data set.

Using the above criteria, the following procedure, reference Figure 7.3.1.2-2, was established for 

this test program as a process that produces suitable time history data for the characterizing the 

pyroshock environment.

Figure 7.3.1.2-2. Acceleration Time History Signal Post-Processing Procedure

The first step of the procedure, identify first 20 msec of the time history pulse, can be subjective 

and therefore an algorithm was developed to perform this task to meet the suitability criteria. 

For reference, Figure 7.3.1.2-3 shows the MATLAB® code developed to retrieve the first 

20 msec of a shock pulse from the time history data.

Isolate first 20msec of 

the Time History Signal

Shift time history 

signal to begin at 0sec

Remove mean from 

the time history signal

Apply a 70Hz high pass 

filter to the time signal
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Figure 7.3.1.2-3. MATLAB

® Code for Retrieving the First 20 msec of a Shock Pulse from a Time 

History Signal

Note: This algorithm is dependent upon consistent procedures followed by the test 

laboratory personnel conducting the pyroshock test and should not be considered robust. 

Engineering judgment must be used when applying this algorithm to other data sets (e.g., the 

algorithm will not work for a variable sample rate). Therefore, the algorithm may require 

modifications in order to be suitable for other data sets.
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The second step of the signal processing procedure (shift time to begin at zero) is intended to 

remove any negative time values as certain SRS or PVRS codes may have issues dealing with 

negative values of time. The following MATLAB® code for shifting the time signal to begin at 

0-sec is provided in Figure 7.3.1.2-4, for reference.

Figure 7.3.1.2-4. MATLAB

® Code for Shifting a Time Signal to Begin at 0 sec

The third step in the data processing procedure (remove the mean from the signal) is intended to 

remove any 0-g offsets in the acceleration time history. While there are multiple ways to 

perform this action, the following MATLAB® code, which uses MATLAB®’s “de-trend” 

function, is provided in Figure 7.3.1.2-5, for reference.

Figure 7.3.1.2-5. Reference MATLAB

® Code for Mean Removal

The fourth step in the data processing procedure (apply a high pass filter to the time signal) is a 

step that in combination with the mean removal produces a cleaner time history signal. For this 

test program, a 70-Hz high pass sixth-order Butterworth filter was used. The program used to 

apply this filter was from Tom Irvine’s “vibrationdata” signal analysis package, which can be 

accessed from the link listed below:

https://vibrationdata.wordpress.com/2013/05/29/vibrationdata-matlab-signal-analysis-package/
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Note: The above procedure was established to produce a “suitable” signal for data 

processing specifically for this task assessment test program. Utilization of other procedures 

for cleaning up the time history signal may be more suitable for other data sets to 

accomplish producing a time history signal the meets the “suitable” signal criteria as 

previously discussed. Engineering judgment should always be used when processing a time 

history signal for a pyroshock environment.

7.3.2 Post-Test Data Evaluation

The overall goal of post-processing the measured acceleration time history data was to put the 

data in a form that could be developed into an empirical model that captures the behavior of the 

shock environment as it propagates across the composite structure. There were two challenges 

that needed to be overcome:

1. Characterizing the pyroshock environment in a manner that would be suitable to multiple 

regression and other statistics-based engineering analysis methods. For this test program, 

that required characterizing the environment using single-value-inputs (SVI), a single 

number that characterizes some aspect of the environment.

2. Developing a procedure to calculate these SVIs that eliminates or mitigates data noise 

and the often-subjective decisions made when characterizing a shock environment.

Due to the complex nature of pyroshock acceleration time histories and the difficulties in test 

labs to recreate these time histories, the acceleration time history has limited practical value in 

characterizing a pyroshock environment. Therefore, response spectrums are the most common 

way to capture the nature and severity of a pyroshock environment. The two most common 

response spectrums for representing a pyroshock environment in the aerospace industry are the 

SRS and the PVRS. These response spectrums provide the environment as the peak response of 

a single-degree-of-freedom system to the pyroshock environment across a range of natural 

frequencies of the single-degree-of-freedom system. Therefore, response spectrums require two 

values, peak response and frequency, to characterize an environment and therefore are not SVIs. 

However, these response spectrums are often represented as a simple envelope of the actual 

spectrums. Therefore, the approach chosen for this test program was to break the spectrums 

down into SVI inputs that when evaluated together describe the spectrum. One complication is 

the actual enveloping is often left up to the analyst with little in the way of an industryestablished procedure, which introduces an additional source of “human input” to the SVIs used 

to characterize the shock environment.

To address the first challenge the following methods and the subsequent SVIs used to represent 

them, for characterizing shock data were calculated for this test series for the purposes of 

statistical analysis:

 SRS

– Slope

– Frequency Break Point
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– Peak SRS Value

 PVRS

– Mean of the Constant Velocity Line

 Acceleration, Velocity, and Displacement Time History

– Maximum and minimum value of the acceleration time history

 Energy Spectral Density (ESD)

– Frequency and amplitude of the peak ESD value

 Temporal Energy (area of the time history squared), which is already an SVI

This report assumes the user has the capabilities to calculate the above shock characterizing 

methods; however, there are also well-established software codes available online. Several of 

these codes can be found at https://vibrationdata.wordpress.com/. Maxi-max (the maximum 

value of the combined positive and negative curves), SRS, and PVRS curves were used for this 

test program. 

While each of these methods listed above can provide insight into the nature of a pyroshock 

environment, based upon the evaluation of the data at the conclusion of this study, the following 

characteristics were chosen as the most effective for detecting and calculating shock attenuation 

trends:

 SRS

 Mean PV Value

To address the second challenge, procedures needed to be established for calculating the SVIs of 

the SRS and PVRS that mitigated noise and subjective decision making that could introduce 

human error and bias. The maximum PV can be calculated directly from the PV curve and did 

not need further algorithm processing. To assess the SRS, and divide them into SVIs that may 

be quantified, an algorithm was required to envelope the SRS and provide the envelope as a set 

of SVIs that characterize the shock. The SRS was divided into the slope, the maximum peak 

acceleration plateau, and the intersection of those two lines defined as the frequency break point. 

The test article parameters were then evaluated in terms on the effect to changes on specific 

parameters with regard to the slope value (within the sloped portion of the SRS), the break point 

(defined the beginning of plateau region of the SRS), and the maximum value of the plateau 

region of the SRS (or peak acceleration). As an example, Figure 7.3.2-1 illustrates the 

enveloping SRS algorithm calculated slope, plateau, and frequency break point for Group I, 

Test 2, accelerometer channels 3 and 4 at location 21 inches from the shock source.
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Figure 7.3.2-1. Data Output from SRS Enveloping Algorithm

As the data from the enveloping SRS was being generated it became apparent that certain 

composite materials produced a double plateau SRS across all locations of the test article. 

Therefore, the SVI for SRS curves needed to account for this double plateau possibility. The 

SRS algorithm was modified to account for this result as illustrated in Figure 7.3.2-2 for 

Group III, Test 25, accelerometer channels 3 and 4 at location 21 inches from the shock source.

Plateau Frequency 

Break Point

Slope
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Figure 7.3.2-2. Data Output from SRS Enveloping Algorithm – Double Plateau

The PVRS of a simple shock plotted on four-coordinate paper (4CP) looks like a flattened hill, as 

shown in Figure 7.3.2-3, for Group I, Test 1, accelerometer channels 5 and 6 at location 

33 inches from the shock source. The plateau, or top of the hill, shows the severe frequency 

range of the shock. The hill slopes down and to the right with an asymptote equal to the 

maximum acceleration. Maximum acceleration usually defines the high-frequency extent of the 

plateau. The hill slopes down and to the left with an asymptote equal to the maximum 

displacement, and maximum displacement defines the low-frequency plateau limit. The height 

of the plateau of the PVRS on 4CP and its frequency range is the severity of the shock.

Plateau

Plateau

Slope

Slope
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Figure 7.3.2-3. PVRS (4CP)

7.3.3 Algorithm Response Spectra Development

7.3.3.1 Shock Response Spectra

Enveloping an SRS curve can be subjective. Therefore, an algorithm was developed to perform 

this task to meet the suitability criteria listed in Section 7.3.1. Figure 7.3.3.1-1 illustrates the 

procedure developed to envelope the SRS curves. 

Displacement

Pseudo-velocity

Acceleration
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Figure 7.3.3.1-1. SRS Enveloping Procedure

For the tests results acquired for this task assessment, MATLAB® was used to perform the 

procedure, illustrated in Figure 7.3.3.1-1. Figure 7.3.3.1-2 provides the code for enveloping the 

SRS, for reference. Note: The SRS developed is a combination of the SRS curves produced by 

the two-paired accelerometers at any one location on the test panel (reference Figure C10, line 

124).
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Figure 7.3.3.1-2. MATLAB

® Code for Performing SRS Enveloping Procedure

Within the MATLAB® code for performing the SRS enveloping procedure is the SRS 

enveloping algorithm. Provided for reference in Figures 7.3.3.1-3 (a) through 7.3.3.1-3 (f) is the 

MATLAB® code developed for an enveloping curve of an SRS.
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Figure 7.3.3.1-3. (a) Enveloping SRS Algorithm
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Figure 7.3.3.1-3. (b) Enveloping SRS Algorithm
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Figure 7.3.3.1-3. (c) Enveloping SRS Algorithm
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Figure 7.3.3.1-3. (d) Enveloping SRS Algorithm
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Figure 7.3.3.1-3. (e) Enveloping SRS Algorithm
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Figure 7.3.3.1-3. (f) Enveloping SRS Algorithm

Using a single plateau SRS as an example, the primary features of the SRS enveloping algorithm 

are:

1. The properties of the sloped region of the SRS are calculated from the Linear Least 

Squares fit of the base 10-log transpose of the SRS sloped region selected by the user as 

an input to the algorithm. This operation (LinearModel.fit function in MATLAB®) 

calculates the coefficients b and N of the equation, SRSslope = b ∗ f

N (Figure 

7.3.3.1-3 (a), lines 18-25).

2. The Linear Least Squares line is then adjusted to envelope the peak value of the sloped 

region of the SRS. This is performed by adjusting the coefficient b using the equation: 

bmax =

SRS(fi)

fi

N , where fi is the natural frequency value at the maximum value of SRSSRSslope (Figure 7.3.3.1-3 (a), lines 29-31).

3. The equation of the max envelope of the sloped portion of the SRS curve is then 

SRSslope_envelope = bmax ∗ f

N.

4. The maximum value of the SRS curve is used as the value of the plateau region, 

i.e., SRSplateau_envelope = SRSmax (Figure 7.3.3.1-3 (a), line 34).

5. Therefore, the max envelope of the SRS curve is the combination of the two curves 

SRSslope_envelope and SRSplateau_envelope (Figure 7.3.3.1-3 (a) and 7.3.3.1-3 (b), 

lines 38-72). The SVIs are then the slope (in dB/oct), N, of the SRSslope_envelope curve 

(Figure 7.3.3.1-3 (b), line 60), the peak SRS value from the SRSplateau_envelope curve 

(Figure 7.3.3.1-3 (a), line 34), and the frequency break point is the natural frequency 

value, fb, at the intersection of the two curves (Figure 7.3.3.1-3 (a), line 36).

For example,

 Figure 7.3.3.1-4 shows the initial Linear Least Squares fit of the slope portion of the SRS 

curve as the line SRSslope (red dashed line) defined by equation SRSslope = b ∗ f

N, where 

b = 5.1439 g and N = 5.8131 dB/Oct (or 0.9655 g/Hz) as calculated by the Linear Least 

Squares curve fit.

 To adjust the line SRSslope such that it envelopes the curve, find the frequency where 

SRS-SRSslope is greatest, for Figure 7.3.3.1-4 this occurs at fi = 518.8 Hz where 

2704 g - 2151 g= 553 g, then modify the value b using the equation bmax =

SRS(fi)

fi

N . 
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Therefore, bmax =

2704

518.8

0.9655 = 6.4664 and the enveloping equation of the sloped portion 

of the SRS curve becomes SRSslope_envelope = bmax ∗ f

N = 6.4664 ∗ f0.9655 (solid red 

line).

 Next, the plateau region of the SRS envelope curve is simply the max value of the SRS 

curve (i.e., SRSplateau_envelope = max(SRS) = 12,754g).

 The full SRS envelope curve is then developed by combining the SRSslope_envelope and 

SRSplateau_envelope curves with the intersection frequency (i.e., the frequency break 

point, calculated with the equation fb = (

SRSplateau_envelope

bmax

)

1

N = (

12,754

6.4664

)

1

0.9655 = 2,587Hz.)

Figure 7.3.3.1-4. Sample of the SRS Enveloping Algorithm

The same procedure is followed for enveloping double plateau SRS curves with the primary 

difference being that an additional initial value input is needed from the user to separate the 

regions of the SRS curve, reference Figures 7.3.3.1-3 (c) through 7.3.3.1-3 (f).

The algorithm for enveloping SRS curves does require input from the user for determination of 

the initial evaluation points. Since the user input can be categorized as a subjective decision, the 
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algorithm does not truly meet the criteria for suitability listed in Section 7.3.1. Prior to the 

development of the SRS enveloping algorithm published in this report, there were two other 

pattern recognition algorithms developed that did not require input from the user; a MSFC 

developed algorithm and an algorithm that utilized a k-means cluster analysis algorithm. 

The advantage of these initial algorithms was user input was eliminated, thus mitigating user 

bias. However, there were multiple issues, which ultimately led to these algorithms not being 

used. 

 Neither algorithm could effectively envelope SRS curves with multiple plateau regions.

 The least-squares method used for calculating slope was too sensitive to the sudden roll-off 

of the slope commonly seen below 200 Hz, therefore, two input values were needed to 

calculate the slope: the starting and ending frequency of the sloped region, reference Figure 

C9.

 The k-means cluster analysis method appeared to have a random component as it could 

provide different results with different runs.

7.3.4 PV Spectra

The maximum PV value and corresponding frequency were calculated from the PVRS using the 

built-in MATLAB® function, max. Figure 7.3.4-1 provides the code for reference. Note: The 

PVRS developed is a combination of the PVRS curves produced by the two-paired 

accelerometers at any one location on the test panel (reference Figure 7.3.4-1, line 47).

Figure 7.3.4-1. Reference Code for Calculating Max PV and Frequency

7.3.5 Energy Spectral Density

The maximum ESD value and corresponding frequency were calculated from the ESD using the 

built-in MATLAB® function, “max.”

7.3.6 SRS Evaluation

A multiple linear regression analysis was performed for each of the SVIs listed in Section 7.3.3. 

For example, SRS slope, SRS frequency break point, and SRS plateau (peak acceleration) for 

panel type (monolithic versus sandwich panel), thickness of monolithic panels, fill type for 
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sandwich panels, composite ply type (tape versus fabric), source shock induced (10-gpf LSC 

versus 22-gpf LSC), and ply orientation (unidirectional versus quasi-isotropic).

Analysis was performed using STATGRAPHICS® CenturionTM XVI Version 16.1.8, StatPoint 

Technologies, Inc., Warrenton, VA, © 1982 – 2012, and JMP® Version 11.1.1 , SAS Institute, 

Inc., Cary, NC, © 1989 - 2013. Appropriate analysis files are available on request.

The test matrix was designed to be analyzed as a split-plot experiment (seminal source: Fisher, 

R. A., (1925). Statistical Methods for Research Workers. Edinburgh: Oliver and Boyd). For 

instance, some panels were tested more than once. There is no panel-to-panel variation 

associated with tests using a single panel. Therefore, even though there were 48 individual tests 

performed, only 32 panels were used. It would be incorrect to assume there were 48 independent 

estimates of the effect of panel thickness when panel thickness only changed it 32 times. The 

engineering effect is a better handle on which effects significantly affected each response, less 

bias in the model parameter estimates, and presumably better estimates of variance components 

(see below).

In nearly all cases, the response was transformed before analysis. The logarithm of each 

response was characterized. This let the analyst use the important assumption of constant 

variance in regression analysis. The engineering importance is that the prediction’s bias is 

reduced and the tests for significant effects are more trustworthy (Box, G. E. P. and Cox, D. R. 

(1964). An analysis of transformations, Journal of the Royal Statistical Society, Series B, 26, 

211-252). Note that SRS plots are already scaled logarithmically, so there is an existing 

justification for using this transformation. 

Transformation slightly increases complexity of the prediction model. It greatly increases 

interpretation of the estimates of variability: the standard deviations calculated only make sense 

for the log of the response. Thus the uncertainty bounds around a predicted response value will 

be wider in the “+” direction than on the low side.

The bulk of the final analyses were performed in JMP® using standard least squares regression. 

The restricted maximum likelihood (REML) estimation method was used because of its 

capability to estimate variance components and other strengths. Variance components, for a 

design engineer, would give estimates of standard deviation of the variability in response for any 

single firing event (within-test variation), the variability added through manufacturing (panel-topanel variation), and the variability due to differences between firings that isn’t due to 

manufacturing differences (test-to-test variation).

This was partially successful, but panel-to-panel and test-to-test variability were inadvertently

confounded during analysis. The result is that the values reported here as panel-to-panel and 

test-to-test variability are not individually inaccurate. Panel-to-panel variability should usually 

be higher, and test-to-test lower (within-test variability is believed accurate.) If these values are 

important to a user, it is believed that a workaround has been identified. It was not exercised for 
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this report, but a statistics-savvy analyst may be able to obtain better variance component 

estimates for most or maybe all responses.

Only a single Al panel was tested. This means that panel-to-panel variation for Al panels is not 

available for either analysis or conclusions. This created some complexity for analysis, though 

the effects are estimated to be negligible for engineering use. Nevertheless, had at least three 

different Al panels been used, some analysis complexities could have been reduced, including 

issues with variance components estimation mentioned above.

7.3.6.1 SRS Slope

The data used in the statistical analysis of the slope were generated from the SRS algorithm 

discussed in Section 7.3.3. If the SRS had a single slope, only initial slope was used in the 

analysis. If the enveloping SRS generated two slopes (predominate with the sandwich panel 

tests), only the second slope was used in the statistical analysis. It was found the first slope, in a 

multiple-slope case, appeared to be due to a different phenomenon than the slope in a singleslope case, whereas the second slope acted like a single slope. No model was found, which 

adequately characterized the first slope in a multiple-slope case.

The results from the statistical analysis indicated the significant factors to be:

 Distance

 Distance2

 Distance3

 Severance of the LSC panel times distance. 

Note: Although the shock data from the tests where the LSC failed to sever the LSC plate 

(sever = 0 as shown in the plots) were used in the analysis of the shock data, they are not a 

parameter used for predictive MEFE. Failure of a LSC to sever the target material in flight 

would likely be a catastrophic occurrence, and therefore is not used in the slope predictive 

equation.

Slope predictive equation:

=Exp (2.39316377208557 + -0.185201911061676 * ((Distance from LSC - 39) / 30) + 

(0.133271932004697) + ((Distance from LSC - 39) / 30) * (0.106188564068464) + ((Distance 

from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * (0.195326659484799) + ((Distance 

from LSC - 39) / 30) * (((Distance from LSC -39) / 30) * (((Distance from LSC - 39) / 30) * 

0.352644069684689))

The empirical model prediction for the SRS slope by distance is tabulated in Table 7.3.6.1-1.

Table 7.3.6.1-1. Predictive Slope versus Distance (regardless of panel type)

Factor Predicted Slope by Distance from LSC

Distance 9 21 33 45 57 69

Slope 8.9 10.0 9.8 9.5 10.6 15.3
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A couple of conclusions may be drawn from the slope empirical model prediction:

 The variance in the slope is fairly flat from 9 inches to 57 inches

 The predicted slope at the 69-inch location is elevated likely due to the reflective shock 

wave from the boundary condition the end of the panel represents.

Figure 7.3.6.1-1 illustrates graphs of the SRS slope data (top graph) and the predicted slope using 

the untransformed response (linear). For reference, the green dashed line represents a slope of 

10 dB/oct.

Figure 7.3.6.1-1. SRS Predicted Slope from Statistical Analysis (untransformed)

Flatness of 

predictive slope 

No sever data (not 

used for MEFE)
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Figure 7.3.6.1-2 illustrates graphs of the SRS slope data (top graph) and the predicted slope using 

a log-transformed response. Again, for reference, the green dashed line represents a slope of 

10 dB/oct.

Figure 7.3.6.1-2. SRS Predicted Slope from Statistical Analysis (log-transformed)

No sever data (not 

used for MEFE)

Flatness of 

predictive slope 
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Figure 7.3.6.1-3 illustrates the statistical analysis using the prediction equation with the data 

normalized at 10 inches and plotted as a percentile. As shown from these data, there is little 

change to the slope out to approximately 60 inches and may be held as a constant value for 

MEFE estimation purposes. 

Figure 7.3.6.1-3. SRS Predicted Slope from Statistical Analysis (Percentile)

Using the guidelines outlined in NASA-HDBK-7005, Dynamic Environmental Criteria, Figure 

5.7 (Shock Response Spectrum versus Distance from the Pyroshock Source), the spectrum peak 

and spectrum ramp both decay, at different rates, with distance from the shock source. The 

greater the distance the less the percentage of source shock value remains. However, based on 

the prediction equation for the SRS predicted slope derived from the flat panel test data, as 

shown in Figures 7.3.6.1-2 and 7.3.6.1-3, the slope can be held constant for the calculation of the 

MEFE, out to a distance of 20 to 60 inches from the source shock, without introducing a large 

error (i.e., the slope of an SRS curve stays constant with distance. This is consistent with current 

practices).

Characterization of the composite monolithic panel SRS slope is shown in Figure 7.3.6.1-4. 

Although mean slope range varies from 10.6 dB/oct to 6.2 dB/oct, the average SRS ramp-up, or 

slope, was consistent whether the 10-gpf LSC was used or the 22-gpf LSC was used (8.6 dB/oct 

and 8.4 dB/oct, respectively).
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Figure 7.3.6.1-4. Monolithic Composite Average SRS Slope

The sandwich panels were evaluated separately from the monolithic panels due to the 

predominance of the dual plateau enveloping SRS as computed by the SRS algorithm. Each of 

the slopes (low frequency first slope 100 Hz to ~350 Hz and mid-frequency slope ~950 Hz to 

~2500 Hz) were evaluated. The evaluation showed the first slope of the SRS to be relatively 

high (average slope of 15 dB/oct) and the second slope to be also relatively high (13 dB/oct), 

which is not atypical of a far-field pyroshock maxi-max SRS (reference NASA-STD-7003, 

Figure 1). The average first slope (low-frequency slope) and the second (or mid-frequency 

slope) plotted versus distance from the shock source is graphically shown in Figure 7.3.6.1-5. 

Similarly, as shown in Figure 7.3.6.1-4, the delta change for the second slope over distance is 

minimal. The reasoning for statistically evaluating only the second slope is it can be directly 

compared to the Al and monolithic composite panels, with a single plateau and typically have a 

frequency break point between 2000 and 3000 Hz.

6

7

8

9

10

11

12

0 2 4 6 8 10 12 14

Slope (dB/octave)

Test Number

Monolithic Composite Panel SRS Slope

Average Slope 8.5 

db/octave
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Figure 7.3.6.1-5. Composite Sandwich Panel Slope Change versus Distance

7.3.6.2 SRS Frequency Breakpoint Evaluation

The frequency breakpoint on a SRS is the intersection between the plateau frequency range (peak 

acceleration) and the slope of the acceleration. Typically, the frequency breakpoint is a resultant 

point on the SRS based upon how the SRS is enveloped with regard to both the plateau and the 

slope. For this task, the SRS frequency breakpoint was determined by the enveloping SRS 

MATLAB® algorithm (reference Section 7.3.3). 

The results from the algorithm were statistically evaluated for sensitivities. There are two 

significant factors associated with determination of the frequency breakpoint. 

 Distance from the shock source

 The presence of acoustic damping

Factors that were determined to be less significant include type of panel (sandwich versus 

monolithic versus Al) with distance and composite ply (tape versus fabric). 

From the statistical analysis the predictive equation for SRS frequency breakpoint was developed 

for each type of material type (i.e., Al and composite (monolithic and sandwich)). The 

predictive equation is listed below and the predictive results for each material type are tabulated 

in Table 7.3.6.2-1.

y = 0.1204x + 10.278

y = 0.0185x + 12.07

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

22.0

0 10 20 30 40 50 60 70 80

Slope (dB/oct)

Distance (inch)

Group II-III Sandwich Panel Slope vs Distance

First Slope Second Slope Linear (First Slope) Linear (Second Slope)
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Frequency breakpoint predictive equation:

= Exp (7.47667461668358 + 0.256726082283925 * ((Distance from LSC - 39) / 30) 

+ (Type – Thick:

If "Monolithic - 0.2", -0.071171881273597,

If "Monolithic - 0.3", -0.132292944311272,

If "Al Honey - 1", 0.0876199515198583,

If "Rohacell - 1", -0.0130949295614228,

If "Aluminum - 0.187", 0.128939803626434) 

+ (Acoustic Damped:

If "0", 0.208717894264659,

If "1", -0.208717894264659) 

+ ((Distance from LSC - 39) / 30) * (Acoustic Damped:

If "0", -0.102207869493011,

If "1", 0.102207869493011) 

+ ((((Distance from LSC - 39) / 30) * (Distance from LSC - 39)) / 30) * 0.0279313603300628 

+ ((Distance from LSC - 39) / 30) * (Type – Thick:

If "Monolithic - 0.2", 0.0761703094306936,

If "Monolithic - 0.3", 0.0659903940637854,

If "Al Honey - 1", -0.0510118941049901,

If "Rohacell - 1", -0.105802245822947,

If "Aluminum - 0.187", 0.0146534364334584) 

+ ((((((Distance from LSC - 39) / 30) * (Distance from LSC - 39)) / 30) * (Distance from LSC -

39)) / 30) * -0.284608051208915

Table 7.3.6.2-1. Predicted Frequency Breakpoint with Distance (by panel type)

Factors Predicted Frequency Breakpoint by Distance 

from LSC, inches

Type Panel 

Thicknes

s (inch)

Acoustic 

Damped 

(Yes/No)

9 21 33 45 57 69

Al Honey 1 No 2927.9 2398.1 2334.9 2422.5 2401.1 2038.2

Al Honey 1 Yes 1572.1 1397.4 1476.4 1662.4 1788.1 1647.2

Homogeneous 0.187 No 2857.5 2402.7 2401.6 2558.1 2603.0 2268.4

Homogeneous 0.187 Yes 1534.3 1400.1 1518.6 1755.4 1938.4 1833.2

Monolithic 0.2 No 2199.7 1895.7 1942.0 2120.1 2211.0 1974.8

Monolithic 0.3 No 2090.4 1794.2 1830.6 1990.3 2067.3 1838.9

Monolithic 0.3 Yes 1122.5 1045.5 1157.6 1365.8 1539.5 1486.1

ROHACELL® 1 No 2796.5 2240.8 2134.4 2166.5 2100.9 1744.7

ROHACELL® 1 Yes 1501.6 1305.7 1349.7 1486.7 1564.5 1410.0
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The results from the statistical analysis are graphically presented in Figure 7.3.6.2-1 for the type 

of panel (and whether it was acoustically damped) versus distance from the source shock. Of 

note, regardless of the panel type, the change in frequency breakpoint is relatively flat at midpanel distances (2 ft to 5 ft).

Figure 7.3.6.2-1. Predicted Frequency Breakpoint versus Distance by Panel Type

Small Δ change for SRS 

frequency breakpoint
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The SRS frequency breakpoint was further evaluated to discern a difference in the SRS 

frequency breakpoint with regard to the type of ply used for the monolithic composite panels. 

As illustrated in Figure 7.3.6.2-2, the ply type showed little effect in the average SRS frequency 

breakpoint.

Figure 7.3.6.2-2. SRS Frequency Breakpoint – Ply Type Evaluation

The SRS frequency breakpoint was further analyzed by fill type for the composite sandwich 

panel types (i.e., Al honeycomb versus ROHACELL® foam). Figures 7.3.6.2-3 and 7.3.6.2-4 

illustrate the change in the frequency breakpoint for the Al honeycomb sandwich composite 

panels, which was small (similar to the monolithic composite panels), and the ROHACELL®

foam sandwich panels showed a slight decrease (~800 Hz over a distance of 60 inches) in 

frequency breakpoint with distance from the shock source. The frequency breakpoint data were 

evaluated both with and without the composite LSC plate data (from Group III) and the data at 

the 69-inch location. The composite LSC data and the data at the 69-inch location artificially 

elevated the frequency breakpoint, which on average was 2500 Hz (regardless of sandwich fill 

type) as compared to 2100 Hz for the monolithic composite panels.

y = 1.6571x + 2107.7

y = 2.9679x + 2098.2

0

500

1000

1500

2000

2500

3000

0 10 20 30 40 50 60 70 80

FREQUENCY (HZ)

DISTANCE (INCH)

Monolithic Composite Frequency Breakpoint 

versus Distance - Fabric versus Tape Ply

Monolithic Fabric Ply Monolithic Tape Ply

Linear (Monolithic Fabric Ply) Linear (Monolithic Tape Ply)
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Figure 7.3.6.2-3. SRS Frequency Breakpoint Composite Sandwich Fill Evaluation (all data)

Figure 7.3.6.2-4. SRS Frequency Breakpoint Composite Sandwich Fill Evaluation (less 69-inch 

data and composite LSC plate data)

y = -8.1442x + 2873

y = -20.763x + 3182.5

0

500

1000

1500

2000

2500

3000

3500

0 10 20 30 40 50 60 70 80

Frequency (Hz)

Distance (inch)

Composite Sandwich Panel Average Frequency Breakpoint 

versus Distance 

(All Data)

Aluminum Honeycomb Rohacell Foam

Linear (Aluminum Honeycomb) Linear (Rohacell Foam)

y = -3.1845x + 2560.8

y = -13.185x + 2563

0

500

1000

1500

2000

2500

3000

3500

0 10 20 30 40 50 60

Frequency (Hz)

Distance (inch)

Composite Sandwich Panel Frequency Breakpoint versus 

Distance

(Less Composite LSC Plate and 69-inch Data)

Aluminum Honeycomb Rohacell Foam

Linear (Aluminum Honeycomb) Linear (Rohacell Foam)
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7.3.6.3 SRS Peak Acceleration

The SRS peak acceleration is the plateau region of the SRS beyond the frequency breakpoint 

within the SRS frequency domain. The peak acceleration from the SRS is also commonly 

referred to as the maximum acceleration and the two terms are used interchangeably herein. The 

statistical analysis from the data output of the SRS algorithm indicated the significant factors to 

be distance from the shock source, the explosive core load of the LSC used to induce the shock, 

and the thickness of the monolithic composite panel. The predictive equations from the SRS 

algorithm data output statistical analysis by panel type and core load are listed below.

For Monolithic 0.2” Thick panels at Core Load = 10 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ 0.239841649170964 

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0946234438399386 

+ -((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Monolithic 0.2” Thick panels at Core Load = 22 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ 0.239841649170964 

+ 0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0946234438399386 

+ ((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Monolithic 0.3” Thick panels at Core Load = 10 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.0259617976444534

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0857940847197687

+ -((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))
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For Monolithic 0.3” Thick panels at Core Load = 22 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.0259617976444534 

+ 0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0857940847197687

+ ((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Al Honeycomb panels at Core Load = 10 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.114859502597656

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * -0.0900791110938465

+ -((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Al Honeycomb panels at Core Load = 22 gpf:

Maximum SRS Acceleration 

= Exp(

9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.114859502597656

+ 0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * -0.0900791110938465

+ ((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))
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For ROHACELL® panels at Core Load = 10 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.158934902223547

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * -0.155745103509068

+ -((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For ROHACELL® panels at Core Load = 22 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ -0.158934902223547

+ 0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * -0.155745103509068

+ ((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Al panel at Core Load = 10 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ 0.059914553294692

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0654066860432069

+ -((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))

For Al panel at Core Load = 22 gpf:

Maximum SRS Acceleration 

= Exp (9.12264279357447 

+ -0.175906636393387 * ((Distance from LSC - 39) / 30) 

+ 0.059914553294692

+ -0.0684974241978297 

+ ((Distance from LSC - 39) / 30) * 0.0654066860432069

+ ((Distance from LSC - 39) / 30) * 0.0323247729199656

+ ((Distance from LSC - 39) / 30) * (((Distance from LSC - 39) / 30) * 0.186658985688534))
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The results from the statistical analysis predictive equations are graphically presented in 

Figure 7.3.6.3-1 and tabulated in Table 7.3.6.3-1.

Figure 7.3.6.3-1. Predicted SRS Peak Acceleration versus Distance by Panel Type
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Table 7.3.6.3-1. Predicted Peak Acceleration Values by Panel Material Type

Factor Predicted Peak Acceleration by Distance from LSC

Type - Thick

LSC 

Core 

Load

9 21 33 45 57 69

Al Honey - 1 10 12385.2 9754.4 8155.2 7237.9 6819.2 6820.1

Al Honey - 1 22 13314.4 10760.9 9232.4 8408.6 8129.7 8343.8

Al - 0.187 10 12626.4 10582.4 9415.3 8892.5 8915.6 9489.1

Al - 0.187 22 13573.7 11674.4 10659.0 10330.8 10629.1 11609.0

Monolithic - 0.2 10 14680.2 12448.4 11205.7 10707.8 10861.9 11696.4

Monolithic - 0.2 22 15781.6 13733.0 12685.8 12439.8 12949.4 14309.6

Monolithic - 0.3 10 11353.5 9593.5 8605.3 8194.0 8282.7 8887.5

Monolithic - 0.3 22 12205.3 10583.5 9742.0 9519.4 9874.4 10873.1

ROHACELL®- 1 10 12655.5 9708.9 7906.8 6835.5 6273.1 6111.3

ROHACELL®- 1 22 13605.0 10710.7 8951.1 7941.1 7478.6 7476.6

It is notable the tabulated peak acceleration, for any given panel type, does not correspond well 

with the peak accelerations that were predicted for the 10 grains per foot (gpf) and 22 gpf LSC as 

shown in Figures 7.2.5.2-1 and 7.2.5.2-2, respectively. The most likely reason is the 0.125-inch 

Al thick LSC plate used in the test setup is close to the maximum thickness for Al the 10-gpf 

LSC is capable of severing. Post-test visual examination of the LSC plate using the 10-gpf LSC 

typically showed approximately 50% of the plate cut by the LSC jet and the remaining 50% 

fracture from the explosive detonation. (Note: Evidence of fracture of up to 50% of the LSC 

target thickness is expected when near the upper thickness limitation of the LSC is reached). 

The 22-gpf LSC fully cut the LSC plate with no visual evidence of fracture meaning the excess 

energy of the 22-gpf LSC is lost into the atmosphere and not transmitted into the LSC panel as 

shock. Excerpted below from NASA-HDBK-7005 is the guideline specified for source shock 

energy scaling, which includes as a caveat with regard to excess explosive energy.

5.3.4.1 Source Energy Scaling. Letting Er and En denote the total explosive energy released by 

the pyrotechnic device on the reference and new spacecraft, respectively, the shock response 

spectrum at all frequencies is scaled from the reference to the new vehicle by 

SRSn ( D 1 ) = SRSr ( D 1 ) √En/Er (5.77)

where SRSr and SRSn are the shock response spectra for the reference and new 

spacecraft, respectively, at the same distance D1 from the pyrotechnic source. 

Caution should be exercised in the utilization of Equation (5.77) since, in many 

cases, an excess of source energy beyond that required to cause structural 

separation will not increase the shock transmission, but instead will generate an 

increased shock or blast wave that will be transmitted into the atmosphere or 

vacuum adjacent to the structure. This excess energy may not be as effective in 
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generating structural response. Thus, when En > Er, the application of Equation 

(5.77) may cause an over-prediction of the pyroshock environment. Similarly, an 

under-prediction may result when En < Er.

The peak acceleration versus distance for the four main types of composite panels evaluated for 

this task, (two thicknesses of monolithic composite panels and the two sandwich panels with 

different core materials) were evaluated. Figure 7.3.6.3-2 shows the evaluation of the monolithic 

composite panels with regard to both the LSC explosive core load and the thickness of the 

composite material. The peak acceleration decreases with distance from the source shock 

ranging from 24 g to 100 g per inch with the exception of the 0.3-inch-thick composite panel and 

the 22-gpf LSC, which showed little attenuation of the shock with distance. Further evaluation 

of the 0.3-inch-thick composite panel with the 22-gpf LSC was performed on a randomly 

selected test and the results from this evaluation indicated the enveloping SRS algorithm, which 

captures highest peak acceleration within the plateau region of the SRS, for this particular test 

case, resulted in little or no attenuation of the shock with distance. Figure 7.3.6.3-3 and 

Figure 7.3.6.3-4 show the peak acceleration versus distance and the median peak acceleration 

percentile remaining with distance for the Group I, re-test of test 2 results, respectively.
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Figure 7.3.6.3-2. Monolithic Composite Panel Peak Acceleration with Distance Comparison

y = -76.067x + 15428

y = -99.629x + 13937

y = -65.948x + 16715

y = -13.879x + 11418

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 10 20 30 40 50 60

Acceleration (g's)

Distance (Inches)

Monolithic Composite Thickness and Coreload, Peak 

Acceleration vs Distance Comparison (less 69-inch data)

0.2-inch thick, 10 gpf LSC 0.3-inch thick, 10 gpf LSC

0.2-inch thick, 22 gpf LSC 0.3-inch thick, 22 gpf LSC

Linear (0.2-inch thick, 10 gpf LSC) Linear (0.3-inch thick, 10 gpf LSC)

Linear (0.2-inch thick, 22 gpf LSC) Linear (0.3-inch thick, 22 gpf LSC)
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Figure 7.3.6.3-3. Peak Acceleration versus Distance, Group I Re-Test 2

10000

11000

12000

13000

14000

15000

16000

0 10 20 30 40 50 60 70 80

Peak Acceleration (g)

Distance (inch)

Group I, Re-Test 2, Max Peak Acceleration vs Distance
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Figure 7.3.6.3-4. Monolithic Composite Group I, Re-Test 2, Percent Median Peak Acceleration 

versus Distance

Further evaluations performed for the SRS peak acceleration included fabric versus tape ply, 

orientation of ply layup (unidirectional versus quasi-isotropic), and monolithic versus sandwich 

composite configurations. Figure 7.3.6.3-5 provides the peak acceleration evaluation results for 

comparison of the two types of ply used and Figure 7.3.6.3-6 illustrates the evaluation of the 

peak acceleration with regard to the direction of the ply layup. Figure 7.3.6.3-7 shows the peak 

acceleration evaluation of the monolithic composite panel with regard to thickness of the 

composite panel (i.e., number of plies) and Figure 7.3.6.3-8 provides the peak acceleration test 

results of the monolithic composite panels versus the sandwich composite panel test results.

y = -0.2515x + 104.9

50

60

70

80

90

100

110

0 10 20 30 40 50 60 70 80

Percentile Acceleration Remaining

Distance (inch)

Group I, Re-Test 2, Percentile Median Peak Acceleration vs 

Distance
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Figure 7.3.6.3-5. Peak Acceleration – Tape versus Fabric Ply

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 10 20 30 40 50 60

Acceleration (g)

Distance (inches)

Group I (Monolithic) Tape versus Fabric Ply (no 69-inch 

data)

Fabric, 10 gpf LSC Tape, 10 gpf LSC Fabric, 22 gpf LSC

Tape, 22 gpf LSC Linear (Fabric, 10 gpf LSC) Linear (Tape, 10 gpf LSC)

Linear (Fabric, 22 gpf LSC) Linear (Tape, 22 gpf LSC)
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Figure 7.3.6.3-6. Comparison of Ply Layup Direction –Peak Acceleration and PV

307

300

13914

13682

11500

12000

12500

13000

13500

14000

14500

15000

15500

16000

16500

240

260

280

300

320

340

360

380

PSEUDO

PEAK ACCELERATION (G)

-VELOCITY (IPS)

PLY ORIENTATION, 

UNIDIRECTIONAL VS QUASI-ISOTROPIC

Unidirectional

Quasi-isotropic

Δ = -0.15 dB
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Figure 7.3.6.3-7. Comparison of Monolithic Composite Panel Thickness –

Peak Acceleration and PV

7000

8000

9000

10000

11000

12000

13000

14000

15000

150

170

190

210

230

250

270

290

310

330

0 . 1 6 0 . 1 8 0 . 2 0 . 2 2 0 . 2 4 0 . 2 6 0 . 2 8 0 . 3 0 . 3 2

PSEUDO

PEAK ACCELERATION (G)

-VELOCITY (IPS)

PANEL THICKNESS (INCH)

PV & PEAK ACCELERTION VS MONOLITHIC 

PANEL THICKNESS

Δ = -.2.1 dB
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Figure 7.3.6.3-8. Comparison of Monolithic Composite Panel and Sandwich Composite Panel –

Peak Acceleration versus Distance

Some general conclusions that may be drawn from Figures 7.3.6.3-5 through 7.3.6.3-8 include:

 The type of ply (tape of fabric) is not a significant factor with regard to peak acceleration.

 There is little difference in the peak acceleration due to the direction of the ply layup.

 The change in amount of peak acceleration attenuation with distance is not significantly 

different based upon the thickness of the monolithic composite.

 The change in the peak acceleration attenuation between the monolithic composite and the 

sandwich filled composite is significantly different with a given similar source shock.

Given the limitation of performing the characterization of the composite material for pyroshock 

using flat panels, the percentile of the remaining shock with distance was evaluated since it is an 

invaluable tool for predicting the MEFE at a given distance from the shock source. The data 

provided herein are limited to approximately 48 inches from the shock source due to the limited 

size of the test panels.

The predicted peak acceleration generated from the statistical analysis from the SRS algorithm 

output (reference Table 7.3.6.3-1) was used to generate graphical representations of the 

percentile of the shock remaining at a given distance. Figures 7.3.6.3-9 through 7.3.6.3-12 

illustrate the results from this evaluation for the compilation of each panel type, the monolithic 

composite panels, the Al honeycomb sandwich composite panels, and the ROHACELL® foam 

0

2000

4000

6000

8000

10000

12000

14000

16000

0 10 20 30 40 50 60

Acceleration (g)

Distance (inch)

Monolithic vs Sandwich Panels (no 69-inch data)

Mono, 10 gpf LSC Sandwich, 10 gpf LSC Mono, 22 gpf LSC

Sandwich, 22 gpf LSC Linear (Mono, 10 gpf LSC) Linear (Sandwich, 10 gpf LSC)

Linear (Mono, 22 gpf LSC) Linear (Sandwich, 22 gpf LSC)
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sandwich composite panels, respectively. All of the data for this evaluation was normalized for 

the 9-inch data to be set at 100% and the data at distances further from the shock source shown 

as a percentile of the 9-inch data.

Figure 7.3.6.3-9. Percentile of Shock Remaining – All Panel Types

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Percent Peak Acceleration Remaining

Distance (inch)

Percentile of Peak Acceleration Remaining versus Distance -

All Panel Types & Core Load

Aluminum - 10 gpf LSC Aluminum - 22 gpf LSC

Monolithic - 10 gpf LSC Monolithic - 22 gpf LSC

Aluminum Honeycomb - 10 gpf LSC Aluminum Honeycomb - 22 gpf LSC

Rohacell Foam 10 gpf LSC Rohacell Foam 22 gpf LSC

Log. (Aluminum - 10 gpf LSC) Log. (Aluminum - 22 gpf LSC)

Log. (Monolithic - 10 gpf LSC) Log. (Monolithic - 22 gpf LSC)

Log. (Aluminum Honeycomb - 22 gpf LSC) Log. (Rohacell Foam 10 gpf LSC)

Log. (Rohacell Foam 22 gpf LSC)
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Figure 7.3.6.3-10. Percentile of Shock Remaining - Monolithic Composite Panel 

y = -15.17ln(x) + 131.92

y = -11.55ln(x) + 123.52

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Percent Pelak Acceleration Remaining

Distance (inch)

Monolithic Composite Panel 

Percent Peak Acceleration Remaining versus Distance

10 gpf LSC 22 gpf LSC
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Figure 7.3.6.3-11. Percentile of Shock Remaining – Al Honeycomb Composite Sandwich Panel

y = -25.03ln(x) + 154.65

y = -21.87ln(x) + 147.42

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Percent Peak Acceleration Remaining

Distance (inch)

Aluminum Honeycomb Composite Sandwich Panel

Percent Acceleration Remaining versus Distance

10 gpf LSC 22 gpf LSC
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Figure 7.3.6.3-12. Percentile of Shock Remaining – ROHACELL

® Foam Composite Sandwich 

Panel

NASA-CR-116406, Pyrotechnic Shock Design Guidelines Manual, prepared by Martin Marietta, 

does include a graph for honeycomb percentile of shock remaining. 

For reference, Figure 7.3.6.3-13 illustrates the Martin Marietta data in comparison with the data 

collected, reduced, and analyzed for this task. The figure shows the reduction of the shock over 

distance documented in NASA-CR-116406 and the Al honeycomb test panel data to be slightly 

greater based upon the testing performed for this task assessment, but the attenuation slopes (log) 

to be comparable.

y = -27.94ln(x) + 161.24

y = -25.07ln(x) + 154.76

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Percent Peak Acceleration Remaining

Distancd (inch)

Rohacell Foam Composite Sandwich Paanel

Percent Peak Acceleration Remaining versus Distance 

10 gpf LSC 22 gpf LSC
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Figure 7.3.6.3-13. Percentile of Shock Remaining- Comparison of Martin Marietta Data with Al 

Honeycomb Sandwich Panel Data

7.3.7 PV Evaluation

The PVRS may be regarded as the second most common method for characterizing the shock 

environment in the aerospace industry. ANSI/ASA S2.62-20098, Shock Test Requirements for 

Equipment in a Rugged Shock Environment, specifies shock severity levels according to the 

plateau level on the PVRS plotted on 4CP or displayed as a four coordinate plot. The maximum 

PV may be calculated directly from the PV curve without further algorithm processing. The data 

output from the maximum PV was not empirically modeled since no factors were determined, 

which correlated meaningfully from the statistical analysis. To evaluate the mean PV the data 

from the algorithm was imported to Excel® and a graph of each test data set was generated. 

From the graph the frequency band was chosen for the PV plateau, the values averaged and new 

plots generated for the mean PV at each of the accelerometer distances from the shock source. 

Then the data were normalized from the 9-inch data set to produce plots of the percentile PV 

remaining with distance in a similar manner to the evaluation of the SRS peak acceleration data. 

y = -22.66ln(x) + 146.33

y = -19.88ln(x) + 139.16

y = -18.65ln(x) + 140.23

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

0 10 20 30 40 50 60 70 80

Percent of original shock level remaining

Distance (inches)

Aluminum Honeycomb Sandwich Panel Percent Attenuation 

vs Distance

Al HC, 10 gpf LSC Al HC, 22 gpf LSC

Al HC, Martin Marietta Data Log. (Al HC, 10 gpf LSC)

Log. (Al HC, 22 gpf LSC) Log. (Al HC, Martin Marietta Data)
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The results from this evaluation for the monolithic composite panels are shown in 

Figures 7.3.7-1 and 7.3.7-2 for the 0.2-inch-thick monolithic composite panels and 

Figures 7.3.7-3 and 7.3.7-4 for the 0.3-inch-thick monolithic composite panels, respectively.

Figure 7.3.7-1. Mean PV versus Distance, 0.2-inch-thick Monolithic Composite Panel

100

120

140

160

180

200

220

240

260

280

300

3000

4000

5000

6000

7000

8000

9000

10000

0 10 20 30 40 50 60 70 80

Pseudo-Velocity (ips)

Acceleration (g)

Distance (inch)

Monolithic Composite Panel, 0.2-inch, PV versus Distance

0.2-inch, 10 gpf Acceleration 0.2-inch, 22 gpf Acceleration

0.2-inch, 10 gpf PV 0.2-inch, 22 gpf PV
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Figure 7.3.7-2. Percentile of PV Remaining versus Distance, 0.2-inch-thick Monolithic Composite 

Panel

y = -12.41ln(x) + 130.05

y = -10.41ln(x) + 125.21

50

55

60

65

70

75

80

85

90

95

100

0 10 20 30 40 50 60 70 80

Percentile Pseudo-Velocity Remaining

Distance (inch)

Monolithic Composite Panel Percentile of Pseudo-Velocity 

Remaining (0.2-inch Thick)

0.2-inch, 10 gpf LSC 0.2-inch, 22 gpf LSC

Log. (0.2-inch, 10 gpf LSC) Log. (0.2-inch, 22 gpf LSC)
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Figure 7.3.7-3. Mean PV versus Distance, 0.3-inch-thick Monolithic Composite Panel

100

120

140

160

180

200

220

240

260

280

300

3000

4000

5000

6000

7000

8000

9000

10000

0 10 20 30 40 50 60 70 80

Pseudo-Velocity (ips)

Acceleration (g)

Distance (inch)

Monolithic Composite Panel (0.3-inch Thick) Pseudo-Velocity 

versus Distance

Acceleration, 10 gpf LSC Acceleration, 22 gpf LSC PV, 10 gpf LSC PV, 22 gpf LSC
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Figure 7.3.7-4. Percentile of PV Remaining versus Distance, 0.3-inch-thick Monolithic Composite 

Panel

The results from the mean PV for the composite sandwich panels are presented similarly in 

Figures 7.3.7-5 through 7.3.7-8 for the Al honeycomb sandwich panels and the ROHACELL®

foam sandwich panels.

y = -9.113ln(x) + 122.09

y = -12.17ln(x) + 129.47

50

55

60

65

70

75

80

85

90

95

100

0 10 20 30 40 50 60 70 80

Percentile Pseudo-Velocity Remaining

Distance (inch)

Monolithic Composite Panel Percentile of Pseudo-Velocity 

Remaining (0.3-inch Thick)

0.3, 10 gpf LSC 0.3, 22 gpf LSC Log. (0.3, 10 gpf LSC) Log. (0.3, 22 gpf LSC)
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Figure 7.3.7-5. Mean PV versus Distance, Al Honeycomb Composite Sandwich Panel

120

140

160

180

200

220

240

260

280

300

5000.0

6000.0

7000.0

8000.0

9000.0

10000.0

11000.0

12000.0

0 10 20 30 40 50 60 70 80

Pseudo-velocity (ips)

Acceleration (g)

Distance (inch)

Aluminum Honeycomb Composite Sandwich Panel 

Pseudo-Velocity versus Distance

Acceleration, 10 gpf LSC Acceleration, 22 gpf LSC PV, 10 gpf LSC PV, 22 gpf LSC
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Figure 7.3.7-6. Percentile of PV Remaining versus Distance, Al Honeycomb Composite Sandwich 

Panel

y = -8.696ln(x) + 121.08

y = -19.56ln(x) + 147.39

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80

Percentile Pseudo-velocity Remaining

Distance (inch)

Percentile Pseudo-velocity Remaining 

Aluminum Honeycomb Composite Sandwich

10 gpf LSC 22 gpf LSC Log. (10 gpf LSC) Log. (22 gpf LSC)
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Figure 7.3.7-7. Mean PV versus Distance, ROHACELL

® Foam Composite Sandwich Panel

55

105

155

205

255

3000

4000

5000

6000

7000

8000

9000

10000

11000

0 10 20 30 40 50 60 70 80

Pseudo-Velocity (ips)

Accleration (g)

Distance (inch)

Rohacell Foam Composite Sandwich Panel 

Pseudo-Velocity versus Distance

Acceleration, 10 gpf LSC Accleration, 22 gpf LSC PV, 10 gpf LSC PV, 22 gpf LSC
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Figure 7.3.7-8. Percentile of PV Remaining versus Distance, ROHACELL

® Foam Composite 

Sandwich Panel

The acceleration values shown in the PV figures (Figures 7.3.7-1, 7.3.7-3, 7.3.7-5, and 7.3.7-7) 

are for reference only since acceleration and PV are frequency interdependent. (Note that 

velocity = acceleration/2πf, where f is the natural frequency). The PV was not statistically 

analyzed with the exception for calculating an overall mean of the PV induced into the 

composite materials, which was 264 inches per second (ips). The acceleration was calculated 

from the corresponding PV and a constant frequency (2100 Hz for the monolithic composite 

panels and 2560 Hz for the sandwich composite panels) was used in the calculations. Overall, 

the attenuation of the PV corresponds well with the distance peak acceleration attenuation except 

for the Al honeycomb sandwich panel with the 10-gpf LSC (reference Figure 7.3.7-6). The 

attenuation of the Al honeycomb with 10-gpf LSC was similar to the percentile attenuation of the 

monolithic composite panels. One notable difference between the peak acceleration percentile 

attenuation and the PV percentile attenuation is the sandwich composite panels and the 

0.3-inch-thick monolithic composite panels had less attenuation with the 10-gpf LSC as 

compared to the 22-gpf LSC, which is the opposite for the percentile peak acceleration 

attenuation. 

y = -20.39ln(x) + 149.4

y = -24.39ln(x) + 159.09

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80

Percentile Pseudo-Velocity Remaining

Distance (inch)

Percentile Pseudo-velocity Remaining 

Rohacell Foam Composite Sandwich

10 gpf LSC 22 gpf LSC Log. (10 gpf LSC) Log. (22 gpf LSC)
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7.3.8 ESD Evaluation

Section 2.2.9 of NASA-HDBK-7005 provides a definition of energy spectra as follows:

2.2.9 Energy Spectra. A transient random environment represented by the signal x(t) is 

sometimes described in the frequency domain by an energy spectral density function (usually 

called an energy spectrum where the term “energy” evolves from an electrical analogy), which 

is given by

(2.12)

where X(f,T) is defined in Equation (2.1), E[ ] denotes expected value of [ ], and the factor of 2 is 

needed to obtain a one-sided spectrum with values at positive frequencies only.

(2.1)

Although the energy spectrum is computed only at the discrete frequencies, the exact energy 

spectrum can be interpolated from these discrete values. The units for the energy spectral 

density are similar to acceleration spectral density commonly used for characterizing random 

vibration spectra, g2-sec/Hz. ESD is not particularly useful for determination of a shock MEFE, 

but can be a useful tool for evaluation of the shock energy with respect to frequency, especially 

for component failure analysis. The maximum energy, calculated from the shocks induced into 

the composite material, occurred at a wide range of frequencies (from less than 400 Hz to greater 

than 5000 Hz) depending upon the composite material type, the LSC explosive core load, and the 

location of the accelerometer. Some examples of ESD plots are shown in Figures 7.3.8-1 

through 7.3.8-3 for each of the types of composite panels and with a core load of 10-gpf LSC.
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Figure 7.3.8-1. ESD Plot – 0.2-inch Monolithic Panel, 10-gpf LSC
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Figure 7.3.8-2. ESD Plot – Al Honeycomb Composite Sandwich Panel, 10-gpf LSC
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Figure 7.3.8-3. ESD Plot – ROHACELL

® Foam Composite Sandwich Panel, 10-gpf LSC

The maximum ESD was statistically analyzed and the following significant factors were 

determined:

 If an Al or composite LSC, plate was used.

 The location of the accelerometers (top row versus bottom row).

The Al was more efficient in coupling the shock energy through the bolted joint to the composite 

panel than a composite-to-composite interface. The top row of accelerometers rather 

consistently showed higher maximum energies, at a given location down the test panel, than the 

lower row of accelerometers, which was likely an artifact of the test setup. The LSC was always 

initiated from below the test panel; therefore, the detonation wave was traveling from the bottom 

of the test panel to the top of the test panel. The shock wave likely vectored across the panel, 

hence the higher maximum energies calculated from the top row of accelerometers. The 

predictive equation for maximum ESD based upon the explosive core load, whether a LSC plate 

was Al or composite, and the distance from the shock source is listed below.
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Maximum ESD 

=Exp(1.88508105265126 

+ -0.00428823884622233 * Distance from LSC 

+ (LSC Core Load, 

If 10, -0.181783869892254, 

If 22, 0.181783869892254) 

+ (Distance from LSC - 39.0223048327138) * (LSC Core Load,

If 10, 0.00174623217523917,

If 22, -0.00174623217523917) 

+ (Distance from LSC - 39.0223048327138) * ((Distance from LSC - 39.0223048327138) * -

0.000177622933837467) 

+ (Aluminum LSC Plate, 

If 0, -0.550041910060047, 

If 1, 0.550041910060047 ))

The predictive results for the maximum ESD with regard to the type of LSC plate used and LSC 

core load versus distance is tabulated in Table 7.3.8-1.

Table 7.3.8-1. Predicted Maximum ESD

Factors Prediction at Distance from LSC

LSC Core 

Load

Al LSC 

Plate LSC Plate 9 21 33 45 57 69

10 0

Fabric 

Composite 2.465 2.649 2.704 2.623 2.418 2.117

10 1 Al 7.405 7.958 8.124 7.881 7.264 6.361

22 0

Fabric 

Composite 3.938 4.057 3.972 3.695 3.266 2.743

22 0

Tape 

Composite 3.938 4.057 3.972 3.695 3.266 2.743

22 1 Al 11.830 12.190 11.935 11.10

2

9.813 8.240

A graphical representation of the statistically predicted maximum ESD for type of LSC plate and 

LSC explosive core load is shown in Figure 7.3.8-4.
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Figure 7.3.8-4. Maximum Predicted ESD – LSC Plate Type and LSC Explosive Core Load

7.3.9 Time History, Velocity, and Displacement

The acceleration, velocity, and displacement for each of the accelerometers for each test was 

generated from the post-processed data. Generation of the time histories allows the data to be 

scrutinized to verify data “quality” (i.e., free of zero-shifts and offsets). The velocity and 

displacement time histories are examined to ensure they are consistent with the acceleration time 

history. The time histories are qualitatively scrutinized and therefore post-processing statistical 

analysis is required. Examples of acceleration, velocity, and displacement time histories for the 

monolithic and composite sandwich test panels are shown in Figures 7.3.9-1 through 7.3.9-3, 

respectively. The results from evaluation of the time histories for each of the accelerometers, for 

each test, verified the accelerometer data was indeed quality data.
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Figure 7.3.9-1. Time Histories for Group I, Test 2, Monolithic Composite Panel –

Accelerometers 2 and 8
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Figure 7.3.9-2. Time Histories for Group II, Test 11, Al Honeycomb Sandwich Composite Panel –

Accelerometers 2 and 8
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Figure 7.3.9-3. Time Histories for Group II, Test 13, ROHACELL

® Foam Sandwich Composite 

Panel – Accelerometers 2 and 8
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7.3.10 Temporal Moments

David O. Smallwood, Sandia National Laboratories, developed a method to characterize shocks 

in terms of Fourier energy spectrum and temporal moments of the shock (reference Shock and 

Vibration, Vol 1, No 6, pp 507-527 (1994) © 1994 John Wiley and Son, Characterization and 

Simulation of Transient Vibrations Using Band Limited Temporal Moments). Temporal 

moments are analogous to the moments of probability density functions. For pyroshock 

applications the square of the time history is used, which allows relating between the temporal 

moments and moments with the frequency domain. The ith temporal moment, mi(a), of a time 

history, (x)t, about a time location, a, is defined as:

The moments are useful to describe simple time history shapes and to describe envelopes of 

more complicated shock time histories. The energy moment, referred to as the time history 

energy, is the integral of the magnitude squared of the time history. The square root of the 

energy normalized by the root mean square (RMS) duration is referred to as the root energy 

amplitude and is a convenient way to describe the energy of the shock transient. For this task, 

the temporal energy (TE) was calculated and statistically evaluated for the monolithic composite 

panel test results. The results from the evaluation indicated the following significant factors: 

 The panel thickness 

 The distance from the shock source.

Factors determined not to be significant

 The explosive core load used for inducing the shock

 The type and orientation of the ply used in fabrication of the monolithic composite panel.

General conclusions that may be drawn are:

 Thin panels had higher TE

 TE decreased with increasing distance from the shock source

Figure 7.3.10-1 graphically presents the results of the TE statistical analysis.

Statistical analyses of the TE was not performed for sandwich composite panel test results since 

in practicality TE has seen little use for satisfying shock test requirements. Although, 

Smallwood proposed its usage in conjunction with the SRS to improve the agreement between 

the shock test requirement and the laboratory test results as reported in his paper entitled, A 

Methodology for Defining Shock Tests Based on Shock Response Spectra and Temporal 

Moments, Jerome S. Cap and David O. Smallwood, Sandia National Laboratories, Mechanical 

and Thermal Environments Department. The process proposed by Smallwood was to develop a 

procedure to implement shock testing defined by both the SRS and the temporal moments. The 

proposed procedure was to be performed in two phases with the first phase assessing the shock 

requirement via the SRS and temporal moments, applying the margins to the SRS, temporal 
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energy and root energy amplitude, and develop the SRS test requirements (straight-line 

envelope). The second phase is to compute the SRS and temporal moments of the field test data 

and compare the values with the test requirements. Iteration of the field-testing would be 

required to be performed until the upper and lower limit specified shock tolerances for both the 

SRS and temporal moments are met.

As previously stated, the procedural process incorporating temporal moments into specified 

shock tests requirements has not been adopted within the aerospace community, which 

extensively uses SRS, nor the structural community or Navy, both of which use PVRS 4CP.

Figure 7.3.10-1. Monolithic Composite Temporal Energy Sensitivities

7.3.11 MEFE Prediction Example

For prediction of the MEFE, using the guidelines developed from the data evaluation within this 

report, a hypothetical shock that is characterized as having a peak shock of 8,000 g at 10,000 Hz 

(similar to a source shock from a 10-gpf linear explosive induced into a 0.19-inch metallic 

structure) is used as an example for the prediction of the MEFE at a distance of 48 inches from 
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the shock source. (Note: The hypothetical source shock is assumed to have been predicted 

through a bolted interface). The first example will be for the monolithic composite material 

followed by the Al honeycomb sandwich composite material and then the ROHACELL® foam 

sandwich composite material.

The first step for the prediction is to generate an SRS for source shock. The peak acceleration is 

given so the two attributes that need to be included are the slope (in dB/oct) and the frequency 

breakpoint (in Hz). For this exercise Table 7.3.6.1-1 is used for the slope at the 9-inch location, 

which is 8.9 dB/oct (for all panel types). The second step is to determine the frequency 

breakpoint. Table 7.3.6.2-1 provides the predicted frequency breakpoint for both the 

0.2-inch-thick monolithic composite and the 0.3-inch monolithic composite materials. The 

median frequency breakpoint for these materials is 2100 Hz. Usage of this value is further 

substantiated by Figure 7.3.6.2-2. Figure 7.3.11-1 provides the predicted SRS for a monolithic 

composite material for a given 8,000 g shock.

Figure 7.3.11-1. Predictive MEFE, Monolithic Composite

234 ips constant 

velocity
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The predictive MEFE would be defined in tabular format as shown in Table 7.3.11-1.

Table 7.3.11-1. Predictive 8,000 g Shock, Monolithic Composite

Frequency 

(Hz)

Acceleration 

(g)

100 122

2100 8000

5000 8000

10000 8000

Of note, the velocity for this predicted shock is 234 ips, which is within the upper half of the 

moderate range in relative severity.

To predict the shock for a component mounted 48 inches away from the 9-inch location given for 

the shock source, Figure 7.3.6.3-10 for the 10-gpf LSC is used. At a distance of 48 inches (from 

the 9-inch location), the percent peak acceleration remaining is approximately 70%. Therefore, 

the peak acceleration at 48 inches away would be 5,600 g. Given in Section 7.3.6.1 for the 

evaluation of the SRS slope the slope is held constant for prediction of the attenuated shock 

spectrum. Referencing back to Table 7.3.6.2-1 for the frequency breakpoint the median value for 

the monolithic composite at 57 inches is 2067 Hz. The velocity for this shock is 166 ips, which 

is still considered to be a moderate shock, but on the lower half of the moderate range. The 

prediction of the MEFE at a distance of 48 inches from the shock source is illustrated in 

Figure 7.3.11-2.
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Figure 7.3.11-2. Predicted MEFE Example at 48 inches, Monolithic Composite

The predictive MEFE would be defined in tabular format as shown in Table 7.3.11-2.

Table 7.3.11-2. Predictive 8,000-g Shock Attenuated for 48-inch Distance, Monolithic Composite

Frequency 

(Hz)

Acceleration 

(g)

100 65

2067 5600

5000 5600

10000 5600

For reference, the same process is repeated for the Al honeycomb sandwich composite material 

and the ROHACELL® foam sandwich composite material illustrated in Figures 7.3.11-3, 

7.3.11-4, 7.3.11-5, and 7.3.11-6, respectively. 

For the Al honeycomb sandwich composite, the same slope is used (8.9 dB/oct) and the unattenuated frequency breakpoint is 2900 H121z per Table 7.3.6.2-1. The 48-inch distance 

attenuated frequency breakpoint is 2400 Hz per Table 7.3.6.2-1. For the ROHACELL® foam 

sandwich composite the un-attenuated frequency breakpoint is 2800 Hz and the 48-inch distance 

attenuated frequency breakpoint is 2100 Hz.

1

10

100

1000

10000

100 1000 10000

ACCELERATION (G)

FREQUENCY (HZ)

MEFE Monolithic Composite MEFE Prediction, at 

a Distance of 48-inches 

166 ips constant 

velocity
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Using Figure 7.3.6.3-11 and the 10-gpf LSC, attenuation line shows 46% attenuation at a 

distance of 48 inches from the 9-inch location. Using Figure 7.3.6.3-12 and the 10-gpf LSC line, 

the attenuation is 52% at a distance of 48 inches from the 9-inch location.

Figure 7.3.11 Figure 7.3.11--3. Predicted MEFE, Al Honeycomb 3. Predicted MEFE, Al Honeycomb

170-inch constant 

velocity
NASA Engineering and Safety Center 

Technical Assessment Report 

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Version:

1.0

Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.11-4. Predicted MEFE at 48-inch Distance, Al Honeycomb

1

10

100

1000

10000

100 1000 10000

ACCELERATION (G)

FREQUNCY (HZ)

MEFE Auminum Honeycomb Sandwich Composite MEFE 

Prediction, at a Distance of 48-inches 

111 ips constant 

velocity
NASA Engineering and Safety Center 

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Version:

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Title:

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Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.11-5. Predicted MEFE, ROHACELL

® Foam

1

10

100

1000

10000

100 1000 10000

ACCELERATION (G)

FREQUENCY (HZ)

MEFE Rohacell Foam Sandwich Composite

176 ips constant 

velocity
NASA Engineering and Safety Center 

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Version:

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Title:

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Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.11-6. Predicted MEFE at a Distance of 48-inches, ROHACELL

® Foam

7.3.12 MAF Qualitative Pyroshock Assessment

MAF has been evaluated to dampen acoustic levels for usage as replacement of fiberglass 

blankets within a payload fairing, reference NESC TI-12-00811, NESC Enhanced Melamine 

Foam Acoustic Tests. This report evaluated a number of configurations of melamine foam 

acoustic attenuation properties and one of the more promising configurations (i.e., two layers of 

2-inch-thick melamine foam was included as the Group IV test series to evaluate whether the 

MAF provided additional pyroshock attenuation). 

The data from the Group IV tests were qualitatively evaluated for four material types: Al, 

monolithic composite, Al honeycomb sandwich composite, and ROHACELL® foam sandwich 

composite, both with and without the melamine foam bonded to the backside (opposite sided of

the accelerometer locations) of the test panel. The qualitative evaluation included the three 

primary attributes of the SRS: slope, frequency breakpoint, and peak acceleration. The results 

for the evaluation are shown in Figures 7.3.12-1, 7.3.12-2, and 7.3.12-3, for the slope, frequency 

breakpoint, and peak acceleration, respectively.

1

10

100

1000

10000

100 1000 10000

ACCLERATION (G)

FREQUENCY (HZ)

MEFE Rohacell Foam Sandwich Composite MEFE 

Prediction, at a Distance of 48-inches 

113 ips constant 

velocity
NASA Engineering and Safety Center 

Technical Assessment Report 

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Version:

1.0

Title:

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Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.12-1. MAF Evaluation, SRS Slope

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

1 2 3 4

Slope (dB/oct)

Panel Type

Test Group IV Average Slope, with and without Melamine Acoustic 

Foam

Without Melamine Acoustic Foam With Melamine Acoustic Foam

Aluminum Monolithic

Aluminum 

Honeycomb

Rohacell 

Foam
NASA Engineering and Safety Center 

Technical Assessment Report 

Document #:

NESC-RP12-00783

Version:

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Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.12-2. MAF Evaluation, SRS Frequency Breakpoint

0

500

1000

1500

2000

2500

3000

1 2 3 4

Frequency (Hz)

Panel Type

Test Group IV Frequency Breakpoint (9-inch location), with and 

without Melamine Acoustic Foam

Predicted Frequency Breakpoint without MAF Predicted Frequency Breakpoint with MAF

Aluminum 

Honeycomb

Aluminum Monolithic 

Composite

Rohacell 

Foam
NASA Engineering and Safety Center 

Technical Assessment Report 

Document #:

NESC-RP12-00783

Version:

1.0

Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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Figure 7.3.12-3. MAF Evaluation, SRS Peak Acceleration

Of the three SRS attributes, only the frequency breakpoint indicated a significant difference for 

the pyroshock response with melamine foam and without melamine foam. Figure 7.3.12-2 

illustrates approximately a 30 to 40% decrease in the frequency breakpoint with the melamine 

foam adhered to the test panels in comparison to the test panels without the melamine foam. The 

reduction in the frequency breakpoint may be considered a reflection of lowering the natural 

frequency of the test panel with the addition of the melamine foam.

0

2000

4000

6000

8000

10000

12000

14000

1 2 3 4

Peak Acceleration (g)

Panel Type

Test Group IV Peak Acceleration, with and without Melamine 

Acoustic Foam

Without Melamine Acoustic Foam With Melamine Acoustic Foam

Aluminum Monolithic

Aluminum 

Honeycomb

Rohacell 

Foam
NASA Engineering and Safety Center 

Technical Assessment Report 

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Version:

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Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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8.0 Findings, Observations, and NESC Recommendations

8.1 Findings

The following findings were identified:

Composite Panel Fabrication and NDE

F-1. Phased array, or pulse echo, ultrasound was determined to be an acceptable NDE 

method for monolithic composite panels up to 0.3 inches thick and the composite 

skin and bond line for composite sandwich panels.

F-2. For the monolithic composite panels used in this study, infrared thermography NDE 

gave false indications for panels 0.2 inches thick and greater.

F-3. Computed radiography was the only nondestructive test method capable of detecting 

flaws in the composite sandwich fill material.

Pyroshock Test Articles

F-4. Subscale flat panels of at least 5 feet in length appear to be sufficient for at least 

preliminary pyroshock testing on composite panels. 

Pyroshock Test Conduct

F-5. The response between the PCB350-C02 and PCB350-D02 accelerometers was not 

discernable.

Pyroshock Acceleration Time History Post-Test Data Processing

F-6. The “suitability” or quality of the acquired acceleration data was evaluated and 

determined to be acceptable.

F-7. Initial MATLAB® algorithms eliminating human subjectivity used to process the 

post-test acceleration data did not yield acceptable results. These algorithms 

required modification to include a level of human subjectivity for determination of 

the acceptability of the post-test processed data. (Algorithm data output 

unsubstantiated, without human oversight for acceptability, was evaluated and 

determined undesirable).

SRS Post-Test Processed Data Evaluation

F-8. There was little change in SRS slope from 20 inches to 60 inches from the shock 

source on the 72-inch panels except for a relatively small-reflected shock end-effect 

region.

F-9. After an initial increase the SRS frequency breakpoint decreases with distance from 

the shock source.
NASA Engineering and Safety Center 

Technical Assessment Report 

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Version:

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Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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F-10. The peak acceleration generated from the 10-gpf LSC and the 22-gpf LSC was 

similar.

F-11. Ply orientation (unidirectional versus quasi-isotropic) was not a significant factor for 

monolithic composite pyroshock response.

F-12. The type of ply (fabric versus tape) was not a significant factor for monolithic 

composite shock response.

F-13. The rate at which the shock attenuated with distance for the 0.2-inch-thick and the 

0.3-inch-thick monolithic composite panel was equivalent.

F-14. The shock attenuation of the sandwich composite panels, either Al honeycomb or 

ROHACELL® foam, was greater than the monolithic composite panel.

F-15. The shock attenuation of the ROHACELL® fill sandwich panel was greater than the 

Al honeycomb fill composite sandwich panel.

PVRS Post-Test Processed Data Evaluation

F-16. The shock induced into the test panels was moderate-to-severe; reference H. 

Gaberson, Shock Severity Estimation, Sound & Vibration, January 2012, with the 

overall velocity quantified to be 264 ips.

F-17. The skin-stiffened composite layup, which have both monolithic and sandwich-filled 

characteristics, may respond differently from either the singular monolithic or 

sandwich composite layups used herein.

F-18. Based on the accelerometer(s) response at the 66-inch location, there appeared to be 

a reflected shock wave from the end of the panel artificially elevating the peak 

acceleration.

Statistical Analysis of Post-Test Processed Data

F-19. The following responses were found to have statistically significant differences 

depending on panel design: peak acceleration and frequency breakpoint.

F-20. In evaluating SRS traces exhibiting multiple frequency break points, it appears that 

the maximum frequency break, maximum plateau, and maximum slopes have similar 

quality to response values reduced from single-frequency-break traces. 

Pyroshock Response Evaluation of Composites with Melamine Foam

F-21. Acoustic damping reduced maximum frequency break point value by 30 to 40% over 

the un-damped value, with the percent of decrease decreasing with increasing 

distance from shock source.
NASA Engineering and Safety Center 

Technical Assessment Report 

Document #:

NESC-RP12-00783

Version:

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Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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8.2 Observations

Pyroshock Test Conduct

O-1. Since the United States Army Redstone Arsenal stores explosives for MSFC, logistical 

pre-coordination was required to ensure the LSC was available at the test facility for test.

SRS Post-Test Processed Data Evaluation

8.3 NESC Recommendations

The following NESC recommendations were identified and directed towards the SLS Stages 

Project, specifically the Composites for EUS Technology Development Project:

R-1. Conduct additional testing to include a skin-stiffened composite layup as a variable to 

evaluate its dynamic response. (F-5, F-6, F-10, F-11, F-12, F-14, O-6)

R-2. Since composite panel design and construction, influences shock response, evaluate and 

correlate acoustic modal response with pyroshock response for each composites type. 

(F-2, F-5, F-6, F-10, F-11, F-12, F-14, O-7)

R-3. Conduct higher-fidelity (more flight-like) pyroshock testing on composite ring structures, 

of sufficient size to minimize edge effects, to corroborate post-test data processing and 

MEFE predictive evaluation. (F-2, F-3, F-5, F-6, F-10, F-11, F-12, F-14, O-7)

R-4. Request accelerometer time history data used for qualification or acceptance of flight 

hardware to evaluate the data quality. (F-3)

R-5. Process pyroshock acceleration time history data for both SRS and PVRS to correlate 

severity of the induced shock. (F-5, F-6, F-7, F-8, F-9, F-10, F-11, F-12, F-13)

R-6. For system designs, utilizing composite materials, where shock response is important to 

vehicle reliability and risks, uncharacterized designs should be characterized through test. 

(F-2, F-14, F-15)

R-7. If attenuation of shock is important to system performance and reliability than weight, 

consider using ROHACELL®-filled construction in lieu of Al honeycomb. (F-12)

R-8. For NDE to find panel flaws, consider phased array ultrasound for monolithic composite 

panels and skins on sandwich panels. For sandwich panels, consider computed 

radiography. Do not use IR thermography for composite materials greater than 3/16-inch 

in thickness. (F-1, O-1, O-2)

9.0 Alternate Viewpoint

There were no alternate viewpoints identified during the course of this assessment by the NESC 

team or the NRB quorum.
NASA Engineering and Safety Center 

Technical Assessment Report 

Document #:

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Version:

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Title:

Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

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10.0 Other Deliverables

Deliverables include all data collected during the pyroshock testing, the final report documenting 

the outcome of the testing and development of the analytical tool, and the empirical analytical 

tool for prediction of the pyroshock MEFE.

No unique hardware, software, or data packages, outside those contained in this report, were 

disseminated to other parties outside this assessment.

11.0 Lessons Learned

No applicable lessons learned were identified for entry into the NASA Lessons Learned 

Information System (LLIS) as a result of this assessment.

12.0 Recommendations for NASA Standards and Specifications

No recommendations for NASA standards and specifications were identified as a result of this 

assessment.

13.0 Definition of Terms

Corrective Actions Changes to design processes, work instructions, workmanship practices, 

training, inspections, tests, procedures, specifications, drawings, tools, 

equipment, facilities, resources, or material that result in preventing, 

minimizing, or limiting the potential for recurrence of a problem. 

Finding A relevant factual conclusion and/or issue that is within the assessment 

scope and that the team has rigorously based on data from their 

independent analyses, tests, inspections, and/or reviews of technical 

documentation.

Lessons Learned Knowledge, understanding, or conclusive insight gained by experience 

that may benefit other current or future NASA programs and projects. The 

experience may be positive, as in a successful test or mission, or negative, 

as in a mishap or failure.

Observation A noteworthy fact, issue, and/or risk, which may not be directly within the 

assessment scope, but could generate a separate issue or concern if not 

addressed. Alternatively, an observation can be a positive 

acknowledgement of a Center/Program/Project/Organization’s operational 

structure, tools, and/or support provided.

Problem The subject of the independent technical assessment.

Proximate Cause The event(s) that occurred, including any condition(s) that existed 

immediately before the undesired outcome, directly resulted in its 
NASA Engineering and Safety Center 

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Composite Materials Subjected to Pyroshock Loading

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occurrence and, if eliminated or modified, would have prevented the 

undesired outcome.

Recommendation A proposed measurable stakeholder action directly supported by specific 

Finding(s) and/or Observation(s) that will correct or mitigate an identified 

issue or risk.

Root Cause One of multiple factors (events, conditions, or organizational factors) that 

contributed to or created the proximate cause and subsequent undesired 

outcome and, if eliminated or modified, would have prevented the 

undesired outcome. Typically, multiple root causes contribute to an 

undesired outcome.

Supporting Narrative A paragraph, or section, in an NESC final report that provides the detailed 

explanation of a succinctly worded finding or observation. For example, 

the logical deduction that led to a finding or observation; descriptions of 

assumptions, exceptions, clarifications, and boundary conditions. Avoid 

squeezing all of this information into a finding or observation

14.0 Acronyms List

4CP Four-Coordinate Paper

Al Aluminum

AMA Analytical Mechanics Associates

CAD Computer Aided Design

CEUS Composites for Exploration Upper Stage 

CT Computed Tomography 

DAS Data Acquisition System

DOE Design of Experiments

DR Digital Radiography 

EM42 Nonmetallic Materials and Manufacturing Branch

EMR Electromagnetic Radiation

ES22 Mechanical, Thermal and Life Support Analysis Branch 

ESD Energy Spectral Density

ET40 Structural Dynamics Test Branch 

EUS Exploration Upper Stage

gpf Grains Per Foot

IIR Infinite-Impulse-Response

ips Inches per Second

IR Infrared

JSC Johnson Space Center

LaRC Langley Research Center

LSC Linear-Shaped Charge
NASA Engineering and Safety Center 

Technical Assessment Report 

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Composite Materials Subjected to Pyroshock Loading

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MAF Melamine Acoustic Foam

MEFE Maximum Expected Flight Environment

MSFC Marshall Space Flight Center

MTSO Management and Technical Support Office

NDE Nondestructive Evaluation

NESC NASA Engineering and Safety Center

PAUT Phased Array Ultrasonic Testing 

pcf Pounds Per Cubic Feet 

PV Pseudo-Velocity

PVRS Pseudo-Velocity Response Spectrum

RELM Restricted Maximum Likelihood

RMS Root Mean Square

SLS Space Launch System

SME Subject Matter Experts

SRS Shock Response Spectrum 

SVI Single Value Inputs

TCP Test Checkout Procedure

TE Temporal Energy

15.0 References

1. NASA CR-114606, Pyrotechnic Shock Design Guidelines Manual

2. IEST-RP-DTE012.1, Handbook for Dynamic Data Acquisition and Analysis

3. Fisher, R. A., (1925). Statistical Methods for Research Workers. Edinburgh: Oliver and 

Boyd

4. Box, G. E. P. and Cox, D. R. (1964). An analysis of transformations, Journal of the Royal 

Statistical Society, Series B, 26, 211-252

5. NASA-HDBK-7005, Dynamic Environmental Criteria, Figure 5.7 (Shock Response 

Spectrum versus Distance from the Pyroshock Source

6. NASA-STD-7003, Figure 1

7. ANSI/ASA S2.62-20098, Shock Test Requirements for Equipment in a Rugged Shock 

Environment

8. Shock and Vibration, Vol 1, No 6, pp 507-527 (1994) © 1994 John Wiley and Son, 

Characterization and Simulation of Transient Vibrations Using Band Limited Temporal 

Moments

9. Smallwood: A Methodology for Defining Shock Tests Based on Shock Response Spectra and 

Temporal Moments, Jerome S. Cap and David O. Smallwood, Sandia National Laboratories, 

Mechanical and Thermal Environments Department

10. NESC TI-12-00811, NESC Enhanced Melamine Foam Acoustic Tests
REPORT DOCUMENTATION PAGE Form Approved

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Empirical Model Development for Predicting Shock Response on 

Composite Materials Subjected to Pyroshock Loading

5a. CONTRACT NUMBER

 6. AUTHOR(S)

Gentz, Steven J.; Ordway, David O.; Parsons, David S.; Garrison, Craig 

M.; 

Rodgers, C. Steven; Collins, Brian W.

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NASA Langley Research Center

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Subject Category 24 Composite Materials

Availability: NASA STI Program (757) 864-9658

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14. ABSTRACT

The NASA Engineering and Safety Center (NESC) received a request to develop an analysis model based on both frequency 

response and wave propagation analyses for predicting shock response spectrum (SRS) on composite materials subjected to 

pyroshock loading. The model would account for near-field environment (~9 inches from the source) dominated by direct 

wave propagation, mid-field environment (~2 feet from the source) characterized by wave propagation and structural 

resonances, and far-field environment dominated by lower frequency bending waves in the structure. This report documents 

the outcome of the assessment.

15. SUBJECT TERMS

NASA Engineering and Safety Center; Shock response spectrum; Pyroshock loading; Model development

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