Kelly S. Carney and Charles Lawrence

Glenn Research Center, Cleveland, Ohio

Determination of Acreage Thermal Protection 

Foam Loss From Ice and Foam Impacts

NASA/TM—2015-218938

December 2015
NASA STI Program . . . in Profile

Since its founding, NASA has been dedicated 

to the advancement of aeronautics and space science. 

The NASA Scientific and Technical Information (STI) 

Program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Officer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI Program provides access 

to the NASA Technical Report Server—Registered 

(NTRS Reg) and NASA Technical Report Server—

Public (NTRS) thus providing one of the largest 

collections of aeronautical and space science STI in 

the world. Results are published in both non-NASA 

channels and by NASA in the NASA STI Report 

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major significant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of significant 

scientific and technical data and information 

deemed to be of continuing reference value. 

NASA counter-part of peer-reviewed formal 

professional papers, but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary or of 

specialized interest, e.g., “quick-release” reports, 

working papers, and bibliographies that contain 

minimal annotation. Does not contain extensive 

analysis.

• CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientific and technical 

conferences, symposia, seminars, or other 

meetings sponsored or co-sponsored by NASA.

• SPECIAL PUBLICATION. Scientific, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific and 

technical material pertinent to NASA’s mission.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question to help@sti.nasa.gov

• Fax your question to the NASA STI 

Information Desk at 757-864-6500

• Telephone the NASA STI Information Desk at

757-864-9658

• Write to:

NASA STI Program

Mail Stop 148

NASA Langley Research Center

Hampton, VA 23681-2199
Kelly S. Carney and Charles Lawrence

Glenn Research Center, Cleveland, Ohio

Determination of Acreage Thermal Protection 

Foam Loss From Ice and Foam Impacts

NASA/TM—2015-218938

December 2015

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
Available from

Trade names and trademarks are used in this report for identification 

only. Their usage does not constitute an official endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 

NASA STI Program

Mail Stop 148

NASA Langley Research Center

Hampton, VA 23681-2199

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22161

703-605-6000

This report is available in electronic form at http://www.sti.nasa.gov/ and http://ntrs.nasa.gov/
NASA/TM—2015-218938 iii

Contents

Abstract.........................................................................................................................................................1

1.0 Introduction...........................................................................................................................................1

2.0 Material Models and Certification........................................................................................................2

3.0 Impact Model Verification....................................................................................................................5

3.1 Ice Verification Results.................................................................................................................7

3.2 PDL-1034 Foam Verification Results.........................................................................................14

4.0 Impact Assessment Results.................................................................................................................19

4.1 Ice Impact Results.......................................................................................................................20

4.2 PDL Foam Impact Results..........................................................................................................31

4.3 Impact Results Summary ............................................................................................................40

5.0 Summary.............................................................................................................................................41

References...................................................................................................................................................41

NASA/TM—2015-218938 1

Determination of Acreage Thermal Protection 

Foam Loss From Ice and Foam Impacts

Kelly S. Carney and Charles Lawrence

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Abstract

A parametric study was conducted to establish Thermal Protection System (TPS) loss from foam and 

ice impact conditions similar to what might occur on the Space Launch System. This study was based 

upon the large amount of testing and analysis that was conducted with both ice and foam debris impacts 

on TPS acreage foam for the Space Shuttle Project External Tank. Test verified material models and 

modeling techniques that resulted from Space Shuttle related testing were utilized for this parametric 

study. Parameters varied include projectile mass, impact velocity and impact angle (5° and 10° impacts). 

The amount of TPS acreage foam loss as a result of the various impact conditions is presented.

1.0 Introduction

Several elements of the Space Launch System (SLS) launch vehicle were derived from similar 

systems that were a part of the Space Shuttle Program (SSP). These include an aluminum (Al) Core 

Vehicle covered with thermal insulating foam; a configuration similar to the foam covered External Tank 

of the Space Shuttle. During the Return to Flight effort after the Columbia accident, the External Tank 

was assessed for the SSP specific debris environment, using a combination of testing and analysis. As a 

result, the tools necessary for a full assessment of potential impacts to a similar configuration, such as 

SLS, were available. Using these models from the Space Shuttle program, damage to thermal insulating 

foam resulting from a range of impact masses and velocities can be predicted. These predictions can give 

insight and relevant technical data to the SLS program debris assessment.

During the Return-to-Flight effort all of the materials which were identified as either potential debris 

sources were tested to determine their mechanical properties. These materials included several varieties of 

low-density thermally insulating foam, ablators, and ice. The tests were conducted at a variety of 

locations including NASA’s Marshall Spaceflight Center, Langley Research Center, and Glenn Research 

Center. Material models of the most threatening debris sources were created using the mechanical 

properties obtained from these tests and were certified by the SSP (Refs. 1 and 2). Because of their 

potential for causing significant damage, ice and the densest of the foams, PDL-1034 (Product 

Development Laboratory) were selected for assessment as projectiles in this study. A material model had

also been created for the foam which covers the general surface of the tank or the SLS core vehicle, 

referred to as acreage foam. The acreage foam was a sprayed-on-foam, NCFI 24-124 (North Carolina 

Foam Industries). This acreage foam was used as the target in the current study.

Multiple series of impact tests were conducted by the Glenn Research Center Impact Dynamics 

Group in conjunction with Lockheed Martin Space Systems Company, Michoud Assembly Facility

(MAF) (Refs. 3 and 4) in support of SSP. These tests included multiple debris materials, with varying 

angle impacts, onto acreage foam covered tank panels and foam covered protuberances. They were 

conducted to both assess the damage tolerance and to verify analytical models. For this study, selected 

tests from both the series of ice impacts onto acreage NCFI foam panels, and the series of PDL foam 
NASA/TM—2015-218938 2

impacts onto acreage NCFI foam panels, were used as model verification tests. These selected tests were 

re-analyzed using current software and material model versions, and current finite element meshes, 

demonstrating prediction capability.

As a part of the effort to demonstrate damage tolerance of the Space Shuttle External Tank, Lockheed 

Martin MAF performed a series of analyses assessing the rise in thermal stresses due to the loss of

insulating foam (Ref. 3). A general set of impact cases was not assessed, but only specific debris transport 

cases were evaluated. The only resulting parameters from the impact analysis, which are inputs to the 

damage assessment, are descriptions of the foam loss. As a result, any impact condition which results in a 

similar foam loss can be compared to the baseline thermal stress assessment. For this study, the margin 

assessment of the LH2 barrel panel due to damage in the insulating acreage foam was used as a baseline. 

The margin of safety in the LH2 barrel panel was reduced to +0.01 because of the worst case foam loss. 

Therefore, the damage assessment in this study was conducted by comparing the resulting foam loss from 

a general set of input cases to the worst case foam assessed by Lockheed Martin MAF.

Components of the External Tank other than the LH2 barrel panel will have a margin greater than 

+0.01 for the same area of foam loss. In addition, if the Core Vehicle is designed with larger margins for 

nominal flight conditions than the External Tank, then greater foam loss can be tolerated. As a result, the 

results from these analyses are presented both in terms of LH2 barrel panel margin and area of foam loss. 

Using the results presented in terms of LH2 barrel panel margin can give a quick margin assessment, and 

for a more complete assessment the provided area of foam loss charts can be used.

2.0 Material Models and Certification

Previous to Return-to-Flight, numerical analyses involving ice were rarely performed for many 

reasons, including the absence of sufficient computer power, software that could handle both the extreme 

deformations of the ice and accurately model the structural response of the vehicle, and most important; 

the availability of an accurate model for ice. The Columbia Space Shuttle tragedy motivated a large scale 

safety review of the Space Shuttle, and included in that review was a requirement for certifying the ability 

of the leading edge of the wing to safely sustain impacts of various types of debris including ice. Ice, 

however, is not a commercial structural material, and aside from high velocity impact situations of 

interest to the aerospace industry, is rarely subjected to high strain rate impact conditions. Although ice 

had been studied extensively, only a very few efforts had been made to model it numerically at the high 

strain rates expected for shuttle, and for the present SLS vehicle. To overcome the lack of an appropriate 

ice model for Return-to-Flight, a new ice model was developed and is described in detail in Reference 2. 

This ice model is used for the present SLS ice impact study. 

Then, as now, the primary analytical tool was LS-DYNA, which is commercial finite element 

software (Ref. 5). The constitutive relationships of the ice model were implemented into LS-DYNA as 

MAT PLASTICITY COMPRESSION TENSION EOS. The material model inputs used in this study are 

given in Table 1. This model also allows the inclusion of ice’s strain rate sensitivity, which is given in 

Table 2. An Equation of State is also used with this constitutive model, in this case to prevent high 

frequency stress oscillations from triggering unrealistic, premature ice failure. This Equation of State was 

determined heuristically and is shown in Table 3.

The density of the ice used in this assessment, and reflected in Table 1, is that of clear, solid ice. 

Where bare metal is exposed to air, and is in contact with cryogenic temperature fluids, ice will form. 

This ice is sometimes lower-density frost, but depending on conditions, clear, solid ice also forms. This 

higher density, clear, solid ice creates more damage as an impactor than frost. However, the differences in 

damage that occurs due to the smaller variations in clear, solid ice density and strength are not significant, 
NASA/TM—2015-218938 3

especially when impacting a soft, weak material such as thermal insulating foam. The ice density and 

strength values shown in Table 1 are the same as those used for all SSP certification analysis, and reflect

the highest density ice. This value is appropriately conservative because ice that forms in remelting, such 

as in an icicle, is often single crystal ice, and this is the type of ice formation that occurred on the External 

Tank, and can be expected to occur on the SLS.

The material models for the foam utilized constitutive relationships already available within LSDYNA. The PDL-1034 was modeled using MAT SIMPLIFIED RUBBER/FOAM, as PDL is an elastic 

foam, which will recover its original shape after compressive loading is removed, up to very large strains. 

The constant material model inputs used in this study are given in Table 4. The behavior of this material 

model is primarily dependent on input stress-strain curves, with a different curve for each defined strain 

rate. These strain rate dependent curves are shown in Figure 1.

TABLE 1.—ICE MATERIAL MODEL PROPERTIES

Mass density ....................................... 8.4×10–5 lb sec2/in.

4 (0.032 lb/in.3

)

Young’s modulus............................................................. 1.35×106 lb/in.

2

Initial compressive flow stress................................................ 2100 lb/in.

2

Initial tensile flow stress ...........................................................210 lb/in.

2

Plastic tangent modulus............................................................100 lb/in.

2

Poisson’s ratio.................................................................................... 0.33

Pressure cut-off in compression................................................715 lb/in.

2

Pressure cut-off in tension .......................................................62.8 lb/in.

2

TABLE 2.—STRAIN RATE SENSITIVITY OF ICE

Strain rate, 

sec–1

Stress scale factor

1.0 1.00000

10.0 1.25660

100.0 1.51320

200.0 1.59044

300.0 1.63562

400.0 1.66768

500.0 1.69255

600.0 1.71287

700.0 1.73005

800.0 1.74493

900.0 1.75805

1000.0 1.76979

1100.0 1.78042

1500.0 1.81498

10000.0 2.02639

TABLE 3.—EQUATION OF STATE LOADING

ln volumetric 

strain

Pressure,

lb/in.

2

Bulk modulus,

lb/in.

2

0.0 0 1.3×106

–7.693×10–3 1×104 1.3×106

–3.125×10–2 1×104 3.2×105

–10 1×104 1.0×103
NASA/TM—2015-218938 4

TABLE 4.—PDL-1034 FOAM MATERIAL MODEL PROPERTIES

Mass density ............................. 4.992×10–6 lb sec2/in.

4 (0.001927 lb/in.3)

Linear bulk modulus.............................................................. 1540. lb/in.

2

Damping coefficient .......................................................................... 0.05

Poisson’s ratio.................................................................................. 0.011

Failure strain (tension)....................................................................0.0677

Figure 1.—PDL-1034 foam model stress-strain curves.

TABLE 5.—NCFI FOAM MATERIAL MODEL PROPERTIES

Mass density ......................................... 3.597×10–6 lb sec2/in.

4 (0.001388 lb/in.3)

Elastic modulus (normal)......................................................................800 lb/in.

2

Elastic modulus (transverse).................................................................200 lb/in.

2

Elastic shear modulus (out of plane).....................................................400 lb/in.

2

Elastic shear modulus (transverse)........................................................100 lb/in.

2

Shear modulus................................................................................. 402.01 lb/in.

2

Bulk modulus................................................................................... 269.36 lb/in.

2

Damping coefficient ...................................................................................... 0.05

Minimum principle failure strain..............................100% = –0.9; 75% = –0.675 

Maximum principle failure strain ............................100% = 0.094; 75% =0.0705

The NCFI was modeled using MAT TRANSVERSELY ANISOTROPIC CRUSHABLE FOAM, as it 

does not recover its original shape after compression. The constant material model inputs used in this 

study are given in Table 5. The reason for the differing strain to failure values, 100 and 75 percent, will be 

discussed in the next section. The behavior of this material model is also primarily dependent on input 

stress-strain curves. Since the foam is anisotropic, direction specific stress-strain curves are required and 

are shown in Figure 2. The strain rate sensitivity used in this model is included by the scaling of the yield 

stress, as shown in Figure 3. 
NASA/TM—2015-218938 5

Figure 2.—NCFI foam model stress-strain curves.

Figure 3.—NCFI strain rate scaling on yield stress.

TABLE 6.—ALUMINUM MATERIAL MODEL PROPERTIES

Mass density ................... 2.5389×10–4 lb sec2/in.

4 (0.098 lb/in.3)

Young’s modulus............................................... 1.02×107 lb/in.

2

Poisson’s ratio.....................................................................0.330

Both the material models for ice and PDL-1034 were certified by the Space Shuttle Program System 

Integration Control Board and the Orbiter Configuration Control Board by the Space Shuttle Program. 

The NCFI 24-124 material model was not board certified. However, it was created using the same 

analytical methods and internal reviews as the PDL and ice models. The input to all of the constitutive 

material models is primarily based upon mechanical property test data.

The Al of the tank skin simulation was modeled as a simple elastic material, as no plastic deformation 

was expected or noted from any ice or foam impacts. The input parameters for this material model are 

given in Table 6.

3.0 Impact Model Verification

Modeling of ice and foam impacts, and subsequent damage to structure-insulating foam, requires 

complex, and not routinely used analysis. Before this analysis can be used for prediction, verification 

must be performed to insure that the modeling methodology is sound, and appropriate for use for the SLS 

application. Fortunately, as presented in Section 2.0, reliable ice and foam materials model were

developed, and subsequently used, during the Space Shuttle Program Return-to-Flight. Other analytical 
NASA/TM—2015-218938 6

parameters and techniques such as mesh sizes and contact algorithms must also be included in an overall 

analytical verification. For the Space Shuttle Program, impacts to the external tank and the orbiter were a 

major concern, and extensive work was performed to develop reliable impact analytical models, insuring

that these impacts would not jeopardize the vehicle integrity. The materials models, parameters, and other 

analytical techniques developed during the Space Shuttle Program were used in the verification 

performed for this study.

The verification consisted of comparing impact tests that were performed during the Space Shuttle 

Program Return-to-Flight (Refs. 3 and 4) with analysis modeling these specific tests. This current 

verification is a repetition of the Return-to-Flight verification; only using a current version of LS-DYNA,

final certified material models, and newly created meshes. (The meshes used in Return-to-Flight were no 

longer available.) Specific tests, out of the many which were conducted, were selected based upon 

projectile masses, velocities, and impact angles being most relevant to SLS. Both ice (described in 

Section 3.1) and PDL foam (described in Section 3.2) impact tests onto the acreage foam test panels were 

modeled.

The LO2 and LH2 acreage test panels were fabricated from NCFI 24-124 sprayed per STP 1535. Final 

foam thickness was 1.00 ±0.25 in. and were left in the net-sprayed condition. Foam was sprayed onto 

2219T-87 2- by 2-ft by 0.375-in. nominal thick Al substrates as shown in Figure 4. A finite element 

model of the acreage test panel was created and is shown in Figure 5. The element size used in this model 

was the same as that found by Lockheed Martin MAF to produce the most accurate analysis. Additional 

details of the test fixture are provided in the Reference 4.

Figure 4.—Acreage foam on Al plate test specimen drawing.
NASA/TM—2015-218938 7

Figure 5.—Finite element model of acreage test panel

In many of the test articles, including those that were used for the verification, the foam regularly 

failed at the Al and foam interface layer. It was also observed that the character of the NCFI foam in this 

region was slightly different than in the remainder of the panel, with the foam cell size being slightly 

smaller and less elongated. The correlation analysis for both the PDL foam and ice impacts did not 

originally duplicate the propensity that the NCFI foam showed for failing at this interface layer. As a 

result, a thin layer of foam elements was included between the foam and Al plate to model the adhesion 

between the foam and plate. A limited set of iterations was performed, and the failure strain in this layer 

of NCFI foam elements was reduced 75 percent from that of the acreage foam, as given in Table 5. No 

other physical properties were modified in this layer. The 75 percent reduction in failure strain is only an 

approximation of the reduced adhesion strain and/or strength, but it does appear to adequately model the 

interface behavior, as described in Section 3.1 and 3.2.

3.1 Ice Verification Results

The ice model is developed using the Arbitrary Lagrangian Eulerian (ALE) capabilities of the 

commercial analysis code, LS-DYNA. Details of this approach are provided elsewhere (Ref. 5); however 

for the present application, the acreage foam and the Al substrate are modeled as Lagrangian parts, and 

the ice is modeled as Eulerian. A void is created, and travels along with the ice impactor, and provides for 

a space for the ice to expand as the ice breaks up during the impact event (Figure 6). 

Table 7 shows the ice impact tests performed under the Return-to-Flight program (Ref. 3, Table 10), 

and the resulting area of foam effected. For the purpose of validating the present model, the final two 

cases (FF172 and FF174) were modeled, and the results of the model were compared to the test data. 

FF172 and FF174 were selected since they both were performed with shallow impact angles (15°), which 

is closer to the shallow impact angles expected for SLS. Just as important, these two tests used the 

smallest size projectiles, with weights closest to those expected for SLS. These two cases also represent 

two distinctly different sizes of ice projectiles. 
NASA/TM—2015-218938 8

Figure 6.—LS-DYNA ice on foam impact model.

TABLE 7.—ICE IMPACT TEST MATRIX AND AREA AFFECTED FROM REFERENCE 3 (TABLE 10)

Test Article Projectile Test Article

Part Back

-ing

plate,

in.

Test 

No.

TPS

Config.

Shape Substrate

Thickness,

in.

ImpactorShape Length

(approx.)

in.

Diam., 

in.

Sabot + 

ice,

grams

Sabot,

grams

Ice,

grams

Ice,

lb

Angle,

deg.

Velocity,

fps

Panel ID Area

affected,

in.

2

LO2/LH2

Acreage

1 FF157 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 141.39 100.55 40.84 0.090 45 868 JR1903 #4-2 166.5

LO2/LH2

Acreage

1 FF158 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 140.41 99.93 40.48 0.089 45 846 JR1903 #4-11 169.75

LO2/LH2

Acreage

1 FF160 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 140.4 99.89 40.51 0.089 30 973 JR1903 #2-4 188.25

LO2/LH2

Acreage

1 FF161 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 139.89 99.58 40.31 0.089 30 972 JR1903 #4-10 172.25

LO2/LH2

Acreage

1 FF162 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 139.98 99.57 40.41 0.089 15 995 JR1903 #3-3 95

LO2/LH2

Acreage

1 FF163 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 1.25 140.2 99.78 40.42 0.089 15 966 JR1903 #2-13 142.75

LO2/LH2

Acreage

1 FF165 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 114.95 100.62 14.33 0.032 15 865 JR1903 #3-11 73

LO2/LH2

Acreage

1 FF166 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 113.98 100.21 13.77 0.030 15 878 JR1903 #4-9 90.75

LO2/LH2

Acreage

1 FF167 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 114.82 100.56 14.26 0.031 30 813 JR1903 #4-12 85

LO2/LH2

Acreage

1 FF168 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 114.56 100.14 14.42 0.032 30 791 JR1903 #1-8 79.5

LO2/LH2

Acreage

1 FF169 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 114.25 100.19 14.06 0.031 45 793 JR1903 #2-2 86.25

LO2/LH2

Acreage

1 FF170 NCFI24-

124

Flat panel 0.375 Ice Cylinder 2.25 0.75 113.71 99.79 13.92 0.031 45 782 JR1903 #5-9 101.25

LO2/LH2

Acreage

1 FF172 NCFI24-

124

Flat panel 0.375 Ice Cylinder 1.125 0.75 106.65 99.93 6.72 0.015 15 865 JR1903 #1-1 86.9375

LO2/LH2

Acreage

1 FF174 NCFI24-

124

Flat panel 0.375 Ice Cylinder 0.72 0.75 103.64 99.82 3.82 0.008 15 872 JR1903 #1-4 35.815

Figure 7 shows the damaged foam and exposed Al for test FF174. For this test, the ice enters from the 

right side of the image and travels to the left. Near the center of the test plate, the ice fully penetrates the 
NASA/TM—2015-218938 9

foam, hits the Al plate, and then rebounds off the plate. During impact with the plate, the ice breaks into 

multiple pieces, and during rebound the expanded volume of ice damages a broader area of foam. 

Figure 8 depicts LS-DYNA results showing the ice projectile penetrating the foam layer. Four 

snapshots are shown progressing from time=0 to time=0.0006 sec. Beyond 0.0006 sec the ice travels 

below the surface of foam, and in this view cannot be seen, until after the ice rebounds off the Al plate 

and travels back up towards the surface of the foam. Up until near 0.0006 sec, the ice is not damaged by 

the foam, and the ice slices a relatively clean path through the foam layer.

Figure 7.—Damaged foam and exposed Al for test FF174

Figure 8.—LS-DYNA results showing ice projectile penetrating foam.
NASA/TM—2015-218938 10

Figure 9.—LS-DYNA cross section showing damaged foam.

Figure 9 shows a cross section with the progression of ice and the resulting damaged foam. As shown 

in the previous figure during initial ice entry into the foam a damaged path roughly the size and shape of 

the ice projectile is formed. After the ice impacts the Al plate, the ice begins to break apart, and rebounds 

off the plate. During rebound the damaged ice spreads out and the resulting damage to the foam is much 

broader than during ice entry. (Note that for Figure 8 and Figure 9, the ice travels from left to right in the 

simulations while in the actual tests the ice travels from right to left. This does not affect the results, 

merely the viewing of the results.)

Figure 10 shows a comparison between the FF174 test and LS-DYNA results. The damage is somewhat 

complex since the total damage is a combination of the damage through the thickness of the foam, as well as 

the surface area of the exposed Al plate. In practice, damage to the foam and exposure of the Al plate leads 

to thermal effects which produce the potential for higher stress levels in the underlying structures, and an 

increase in possible structural failures. For the present comparison, the combined damaged area is used as 

the measure to compare test to analysis. Figure 10(a) shows the damage in the top layer foam at the test 

completion. Exposed Al plate can be seen in the photo, however the extent of the exposure is not captured in 

the photo since there is separation between the foam and plate in areas where the top layer of foam is not 

damaged. Figure 10(b) shows the damage in the top layer of foam predicted from the LS-DYNA simulation. 

While the overall length of the damage is consistent with the test results, the LS-DYNA results do not show 

foam damage in the region where the ice projectile rebounds off the Al plate. Figure 10(c) shows the LSDYNA predicted exposure of the Al plate as a result of failure in the interface layer. In reality, the top foam 

layer cannot remain intact if the underlying layer has been damaged, so it is sensible to combine the damage 

to the top foam layer with the damage to the interface layer. Once these damage areas are combined, they

can be compared to the test results (Figure 10(d)). 

A quantitative comparison between test and analysis is made by approximating the damaged areas 

using an ellipsoid fit. Figure 11 shows the actual combined damage area for FF174, and an ellipsoid fit to 

that area. Once the ellipsoid is fit, then a quantitative approximation can be made for the length and width 

of the damaged area, and the area of the damage can be calculated.

Figure 12 shows the damaged foam and exposed Al for test FF172. For this test, the impact velocity 

is similar to test FF174; however the ice projectile is close to twice as large, leading to far more foam 

damage. Figure 13 shows a comparison between the FF172 test and LS-DYNA results. Figure 13(a) 

shows the damage in the top layer foam at the test competition. Similar to test FF174 exposed Al plate is 

produced as a result of the ice impact. Figure 13(b) shows the damage in the top layer of foam predicted 

from the LS-DYNA simulation while Figure 13(c) shows the LS-DYNA predicted exposure of the Al 

plate as a result of failure in the interface layer. Figure 13(d) shows the comparison between the area of 

foam damage in the test and the analysis. 
NASA/TM—2015-218938 11

Figure 10.—Test FF174: test and LS-DYNA results. (a) Impact test FF174 at 15°. (b) Damage in 1-in.-foam 

layer. (c) Damage in interface foam layer. (d) Combined damaged areas.

Figure 11.—Use of ellipsoid to estimate damages area
NASA/TM—2015-218938 12

Figure 12.—Damaged foam and exposed Al for test FF172.

Figure 13.—Test FF172: test and LS-DYNA results. (a) Impact test FF172 at 15°. (b) Damage 

in 1-in.-foam layer. (c) Damage in interface foam layer. (d) Combined damaged areas.
NASA/TM—2015-218938 13

While LS-DYNA predicts more damage for FF172 compared to FF174, LS-DYNA does not predict 

damage as extensive as exhibited in the actual test. It can be seen in Figure 12 that the region of foam loss 

in test FF172 extends to the edge of the acreage foam. Unfortunately, this means that both the foam edge 

and the boundary conditions of the Al substrate participate in the response of the panel to the projectile. In 

turn, this non-homogeneous condition can lead to highly varied foam loss. The variability is demonstrated 

by considering additional tests, documented in Table 7. For these additional tests, there were two tests 

performed for each projectile impact angle and ice weight. Repeatability of the damage for each specific 

set of conditions is lacking, i.e. repeat test conditions often produce dissimilar resulting damage. In 

particular, the 15° impacts showed the highest variability in the amount of acreage foam which was lost. 

Test results FF162 and FF163, which both had a 0.089 lb projectile impacting at 15°, are shown in 

Figure 14(a) and (b). As can be seen there is a significant difference in the amount of foam loss between 

the two tests, and that the damage extended to the edge of the foam. Test FF162 resulted in a foam loss of 

95 in.

2 and test FF163 resulted in foam loss of 143 in.2

, a difference of ~33 percent. Test results FF165

and FF166, which both had a ~0.030 lb projectile impacting at 15°, are shown in Figure 14(c) and (d).

Test FF165 resulted in a foam loss of 73 in.

2 and test FF165 resulted in foam loss of 91 in.2

, a difference 

of ~20 percent. It is evident that credible and precise analytical predictions of foam loss area in these low 

angle tests are not possible, given the large variability in the test results. 

Figure 14.—Damaged foam and exposed Al from low angle ice impacts. (a) Test FF162 (0.089 lb 

ice). (b) Test FF163 (0.089 lb ice). (c) Test FF165 (0.032 lb ice). (d) Test FF166 (0.030 lb ice).
NASA/TM—2015-218938 14

TABLE 8.—SUMMARY ANALYTICAL RESULTS FOR ICE IMPACT VALIDATION TESTS, FF174 AND FF172

Test Ice projectile, 

in.

Ice projectile 

(test),

lb

Ice projectile 

(

a

LS-DYNA),

lb

Impact 

angle,

deg.

Velocity,

fps

L2/W2,

in.

Area,

in.

2

FF174 0.75 diam. by 0.72 length 0.008 0.010 15 872 11.25/3 26.5

35.8 test

FF172 0.75 diam. by 1.125 length 0.015 0.016 15 865 13.5/3.75 39.5

(86.9 test) a

0.0324 lb/in.

3

Table 8 shows summary results for LS-DYNA analysis of test cases FF174 and FF172. The ice model 

used in this analysis was the certified model discussed in Section 2.0, and the density was not adjusted to 

match the slightly lower density of the test projectiles. As can be seen, using a slightly higher ice density 

in the analysis did not result in greater damage than in the test. Considering both the variability in the area

of tested foam loss and that the damage in test FF172 extended to the edge of the foam, the analytical 

results represent a reasonable match to the test results. The difference between the analytical and test 

foam loss in FF174 was ~26 percent, less than the difference observed between tests FF162 and FF163.

3.2 PDL-1034 Foam Verification Results

Modeling foam projectiles impacting foam targets is somewhat more straightforward than modeling 

ice impacts, in that both the foam projectile and foam target can be modeling using Lagrangian meshes. 

However, in addition to the general impact analysis complexities, such as stability, contact and mesh size, 

with foam there are large distortions to the mesh, making test verification a requirement.

Table 9 shows the PDL foam impact tests performed under the Return-to-Flight program (Ref. 4, 

Table 3), and the resulting volume of NCFI foam removed. For the purpose of validating the present 

model, two cases (FF100 and FF109) were modeled, and the results of the model were compared to the 

test data. FF100 and FF109 were selected since they represent two distinct shallow impact angles (15°

and 30°), which are closest to the shallow impact angles expected for SLS. Modeling two distinct angles 

gives an additional layer of verification. All of the PDL foam impact tests were performed with the same 

nominal size projectile.

Figure 15 shows the damaged foam and exposed Al for test FF100. For this test, the PDL foam 

projectile enters from the right side of the image and travels to the left. Near the center of the test plate, 

the PDL foam fully penetrates the NCFI foam, hits the Al plate, and then rebounds off the plate. During 

impact with the plate, the PDL foam breaks into multiple pieces, causing a large area of NCFI foam to 

detach from the plate.

Figure 16 depicts LS-DYNA results showing the PDL foam projectile penetrating the NCFI foam. 

Four snapshots are shown progressing from time=0 to time=0.0015 sec, which shows both the PDL foam

projectile breaking apart and damage to the NCFI foam. There is damage to the NCFI foam which 

extends beyond that visible in Figure 16. This is shown in the cross section close-up of Figure 17, where 

the NCFI foam has been detached from the Al plate in an area larger than the immediate area around the 

impact.
NASA/TM—2015-218938 15

TABLE 9.—PDL FOAM IMPACT TEST MATRIX AND AREA AFFECTED FROM REFERENCE 4 (TABLE 3)

Test

No.

Projectile

material

Projectile

number

Projectile data Panel

material

Panel

ID

Substrate

thickness,

in.

Impact

angle,

deg.

Gun

pressure

psi

Velocity,

fps

Volume

removed,

in. Diam., 3

in.

Length,

in.

Mass,

gram

FF078 BX-265 1907BX265-8-01 2.957 4.987 18.2 NCFI24-124 1-16 0.375 15 20 1357 90

FF080 BX-265 1907BX265-8-15 2.957 4.987 18.2 NCFI24-124 1-12 0.375 15 20 1346 35

FF081 BX-265 1907BX265-8-26 2.961 4.769 18.21 NCFI24-124 1-15 0.375 15 20 1372 35

FF082 BX-265 1907BX265-8-28 2.964 5.02 18.25 NCFI24-124 1-11 0.375 15 20 1346 36

FF085 BX-265 1907BX265-8-06 2.965 4.657 18.16 NCFI24-124 2-07 0.375 30 19.7 1355 92

FF086 BX-265 1907BX265-8-07 2.961 4.6225 18.22 NCFI24-124 1-03 0.375 30 19.7 1367 121

FF087 BX-265 1907BX265-8-04 2.973 4.692 18.15 NCFI24-124 1-09 0.375 30 19.5 1354 80

FF088 BX-265 1907BX265-8-09 2.966 4.998 18.15 NCFI24-124 2-03 0.375 45 19.5 1350 118

FF089 BX-265 1907BX265-8-02 2.9613 4.985 18.23 NCFI24-124 2-06 0.375 45 19.5 1353 114

FF090 BX-265 1907BX265-8-12 2.9641 4.832 18.14 NCFI24-124 3-01 0.375 45 19.5 1382 111

FF091 BX-265 1907BX265-8-05 2.9652 4.629 18.19 NCFI24-124 2-14 0.375 45 19.3 1367 97

FF094 NCFI24-124 1855B-P7-189 2.9716 4.213 18.18 NCFI24-124 3-07 0.375 30 20 1325 73

FF095 NCFI24-124 1855B-P7-171 2.993 4.211 18.17 NCFI24-124 3-16 0.375 30 20.1 1365 84

FF096 NCFI24-124 1855B-P7-181 2.9833 4.233 18.17 NCFI24-124 1-07 0.375 30 20.1 1337 129

FF097 NCFI24-124 1855B-P7-169 2.9836 4.2325 18.19 NCFI24-124 3-13 0.375 30 20.1 1364 91

FF099 PDL-1034 PDL-12-02 2.486 3.745 18.18 NCFI24-124 2-16 0.375 30 20 1191 91

FF100 PDL-1034 PDL-12-07 2.4917 3.72 18.19 NCFI24-124 1-06 0.375 30 20.2 1023 76

FF101 PDL-1034 PDL-12-13 2.4868 3.675 18.16 NCFI24-124 3-10 0.375 30 22 1326 100

FF102 PDL-1034 PDL-12-04 2.4895 3.766 18.18 NCFI24-124 3-06 0.375 30 21 1285 84

FF103 PDL-1034 PDL-12-29 2.4908 3.777 18.14 NCFI24-124 2-01 0.375 30 20.5 1270 135

FF104 PDL-1034 PDL-12-01 2.4897 3.701 18.18 NCFI24-124 1-05 0.375 45 20 1258 113

FF105 PDL-1034 PDL-12-30 2.4928 3.6685 18.15 NCFI24-124 1-10 0.375 45 19.5 1261 129

FF106 PDL-1034 PDL-12-27 2.4901 3.6655 18.15 NCFI24-124 2-12 0.375 45 18.5 1224 133

FF107 PDL-1034 PDL-12-03 2.4875 3.702 18.19 NCFI24-124 2-11 0.375 15 22 1314 41

FF108 PDL-1034 PDL-12-14 2.487 3.711 18.17 NCFI24-124 2-15 0.375 15 21.5 1287 46

FF109 PDL-1034 PDL-12-06 2.487 3.679 18.18 NCFI24-124 1-13 0.375 15 21.5 1280 38

Figure 15.—Damaged foam and exposed Al for test FF100.
NASA/TM—2015-218938 16

Figure 16.—PDL foam projectile impacting NCFI foam covered Al plate.

Figure 17.—Cross section of panel showing damaged NCFI foam.

Figure 18 shows a comparison between the FF100 test and LS-DYNA results. As in the ice projectile 

verification, the combined damaged area is used as the measure to compare test to analysis. Figure 18(a)

shows the damage in the top layer foam at the test completion. Figure 18(b) shows the damage in the top 

layer of NCFI foam predicted from the LS-DYNA simulation. Figure 18(c) shows the LS-DYNA 

predicted exposure of the Al plate as a result of failure in the interface layer. As discussed previously, the 

top NCFI foam layer cannot remain intact if the underlying layer has been damaged, so the damage in the 

two layers is combined. Once these damage areas are combined, they can be compared to the test results 

(Figure 18(d)). 
NASA/TM—2015-218938 17

Figure 18.—Test FF100: test and LS-DYNA results. (a) Impact test FF100 at 30°. (b) Damage 

in 1-in.-foam layer. (c) Damage in interface foam layer. (d) Combined damaged areas.

For test FF109, the impact velocity is greater than test FF100 and the impact angle is shallower (15° 

versus 30° and 1280 fps versus 1023 fps). Figure 19 shows a comparison between the FF109 test and LSDYNA results. Figure 19(a) shows the damage in the top layer foam at the test competition. Similar to 

test FF100, exposed Al plate is produced as a result of the foam impact. Figure 19(b) shows the damage 

in the top layer of foam predicted from the LS-DYNA simulation while Figure 19(c) shows the LSDYNA predicted exposure of the Al plate as a result of failure in the interface layer. Figure 19(d) shows 

the comparison between the area of foam damage in the test and the analysis. 

The variability in damage area resulting from the PDL foam impacts onto the NCFI acreage foam 

plates was not as great as that observed in the ice impacts. This is partially because the damage did not 

extend to the edge of the acreage foam. Even so, significant variability did occur in these tests. For 

example, Figure 20 shows a comparison between the damage resulting from test FF109, FF108, and 

FF107. Tests FF107 and FF108 used the same PDL foam projectile size and impact angle as FF109. In 

Reference 4, the volume of foam loss reported for FF107 was 41 in.

3

, for FF108 was 46 in.

3

, and for 

FF109 was 38 in.

3

. Obviously, the sample size in this test series is not large enough to perform reliable 

statistical analysis on the variability of foam loss. So, simply comparing the largest foam loss in FF108 to 

the smallest in FF109 shows a difference of ~17 percent.
NASA/TM—2015-218938 18

Figure 19.—Test FF109: test and LS-DYNA results. (a) Impact test FF109 at 15°. (b) Damage 

in 1-in.-foam layer. (c) Damage in interface foam layer. (d) Combined damaged areas.

Figure 20.—Damaged foam and exposed Al from low angle foam impacts. (a) Test FF107. (b) Test FF108. (c) Test 

FF109.

Table 10 summarizes both the ice and PDL foam projectile validation comparisons between test and 

analysis. The damage area measurements for the PDL foam analysis results were performed in the same 

manner as for the ice tests. Only the volume of the NCFI foam damage in the tests was given in Reference 

4, and not the area. So the area was calculated based upon the photographic documentation. As a result, 

the test damaged areas in Table 10 are approximate. The difference between the analytical and test foam 

loss in FF100 was ~8 percent, less than the difference observed between tests FF108 and FF109. The 
NASA/TM—2015-218938 19

TABLE 10.—SUMMARY RESULTS FOR BOTH ICE AND PDL FOAM IMPACT VALIDATION TESTS

Test Projectile, 

in.

Impact angle,

deg.

Velocity,

fps

L2/W2,

in.

Area,

in.

2

FF172 Ice 0.75 diam by 1.125 length 15 865 13.5/3.75 39.5

(86.9 test)

FF174 Ice 0.75 diam by 0.72 length 15 872 11.25/3 26.5

35.8 test

FF100 PDL 2.5 diam by 3.72 length 30 1023 13.5/3.75 69.7

(86.9 test)

FF109 PDL 2.5 diam by 3.72 length 15 1280 13/3 30.6

(~38 test)

difference between the analytical and test foam loss in FF109 was ~19 percent, approximately the same 

difference observed between tests FF108 and FF109. For both PDL foam and ice impacts to the NCFI 

acreage foam plates, considering the variability in the test results, the analytical results represent an 

acceptable match to the tests.

4.0 Impact Assessment Results

For this study, two allowable damage criteria are utilized; both the total damaged surface area, and 

exposed substrate below foam. Total damaged surface area is defined as the surface area damage in the 

top surface of the top layer of foam combined with the area of damage to the interface layer of foam. As 

discussed previously, in many cases the projectile burrows below the top layer of foam and damages the 

interface layer without damage to the top layer just above the location of the projectile. In these cases, 

while the simulation predicts the top foam layer remaining intact, it is not reasonable to expect that the 

top layer retains structural integrity in this region, so this region is considered as damaged area. The limit 

for allowable total foam loss is 16.0 in.

2

, and was derived from Return-to-Flight limits for the external 

tank (Ref. 4). For Return-to-Flight it was determined that beyond 16.0 in.

2 of foam loss, thermal effects 

would lead to exceeding allowable stress limits in the underlying structures.

The second criteria; exposed substrate is determined by measuring the area of the damaged interface 

layer of foam sandwiched between the top layer of foam and the Al plate. Once this layer is damaged, it is 

assumed that all of the foam in the top layer will lose its structural integrity, and the underlying Al plate 

will be exposed to the outside environment. The limit for exposed substrate is 1.7 in.

2

, and similarly to the 

total foam loss limit, was derived from Return-to-Flight limits for the external tank (Ref. 4). For Returnto-Flight it was determined that beyond 1.7 in.

2 of exposed substrate, thermal effects would lead to 

exceeding allowable stress limits in the underlying structures. 

The allowable damage criteria based on Shuttle limits is a reasonable starting point for SLS, however, 

the specific limits for SLS may differ from Shuttle. Therefore, SLS limits will need to be determined 

before the results of this study may be applied to SLS.

Two different impact angles were used for both the ice and PDL foam SLS impact study; 5° and 10°. 

For SLS, it is expected that the impact angles on acreage foam will be small because the vehicle generally 

possesses a smooth contour in the direction of flight. Therefore, impact angles greater than 10° were not 

evaluated.
NASA/TM—2015-218938 20

TABLE 11.—SLS ICE IMPACT CONDITIONS

Impact angle, 

deg.

PDL foam cylinder

Diameter,

in.

Length, 

in.

Weight,

lb

10 0.75 0.72 0.011

10 0.946 0.907 0.021

10 1.189 1.142 0.041

10 1.499 1.4387 0.082

5 0.75 0.72 0.011

5 0.946 0.907 0.021

5 3.547 5.25 0.041

5 1.502 1.440 0.082

4.1 Ice Impact Results

To determine ice impact limits which can be used by the SLS project, damage predicted by LSDYNA for combinations of impact angles, projectile size, and projectile velocities, is compared to the 

allowable limits, and the boundary of impact conditions that do not exceed the limits can be generated. 

The combinations of size and angle which were analyzed are reported in Table 11. The damaged area of 

acreage foam due to ice impact for each of these conditions is also reported.

The small ice projectile size was initially used, and then the projectile size was increased until 

projectile size did not affect the maximum allowable impact velocity. Once the ice projectile diameter 

becomes larger than the thickness of the top foam layer, increasing the projectile size has little effect on 

the damaged area. 

It is important to mention that only cylindrically shaped ice projectiles were studied. The same 

dimension cylinder that was used for the FF174 was used for the smallest SLS projectile (0.011 lb). For 

subsequent ice projectile sizes, the ratio of diameter to length was held constant, and the size was 

increased so the mass of the ice was double that of the previous size projectile. Projectile shape will have 

some effect of damage, however it was not practical, at this time, to study multiple projectile shapes.

Another important item to note is that for the results presented below, the LS-DYNA simulations were 

sometimes terminated before the projectile completed its trajectory, and before all of the damage was 

completed. The reason for this was that once the allowable damage limits were exceeded, the runs were 

sometimes terminated to free up computer resources to enable subsequent impact conditions to be 

analyzed. Performing the analysis in this way did not affect the resulting impact limits; however for the 

runs that were terminated early, the actual damage may have been underestimated.

Figure 21 to Figure 26 show the LS-DYNA results for the 0.011 lb projectile impacting with a 10°

impact angle. For the 872 fps impact velocity (Figure 21), both the exposed substrate, and the total foam 

loss, exceeds the allowable values, and the impact velocity must be reduced to determine the allowable 

Impact velocity limit. At 700 fps, both limits are still exceeded (Figure 23), and the impact velocity is 

further reduced. At 500 fps, only the exposed substrate limit is exceeded, and once again, the impact 

velocity is reduced. It is not until 400 fps that neither the exposed substrate nor the total foam loss limits 

are exceeded, and the maximum allowable impact velocity is identified. 
NASA/TM—2015-218938 21

Figure 21.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 872 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss.

Figure 22.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 700 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss.
NASA/TM—2015-218938 22

Figure 23.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 500 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss. 

Figure 24.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 450 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss.
NASA/TM—2015-218938 23

Figure 25.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 425 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss.

Figure 26.—Ice projectile: 0.75-in.-diameter by 0.72-in.-length, 10° impact angle, 400 fps impact velocity. 

(a) Damage in 1-in.-thick foam layer. (b) Interface foam (exposed Al plate). (c) Total foam loss.

Figure 27 shows a summary for the 0.75-in.-diameter by 0.72-in.-length. Ice projectile, 10° impact 

angle. As discussed above, the total damaged area criterion is exceeded when the impact velocity is 

greater than 540 fps. The exposed substrate criterion is exceeded at only 425 fps, and therefore dictates 

the critical impact velocity. In general there is less damaged foam and exposed substrate as the impact 

velocity is decreased; however the trend is not completely linear. At the lowest impact velocities, minimal 

amounts of the projectile reach the substrate, limiting the creation of exposed substrate. This trend is 

largely linear, and exposed substrate is required to create large amounts of damage. This effect minimizes 

the non-linear pattern at the lowest velocities. 
NASA/TM—2015-218938 24

Figure 27.—Summary for 0.75-in.-diameter by 0.72-in.-length ice projectile, 10° impact angle.

TABLE 12.—LS-DYNA RESULTS FOR 0.946-in. DIAMETER BY 0.907-in. LENGTH

(0.021 lb) ICE PROJECTILE, 10° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

In.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

In.

2

- 0.946 diam. by 0.907 length 10 300 0/0 0

OK

1.7 9.3/1.0 7.3

OK

16.1

- 0.946 diam. by 0.907 length 10 325 7.8/2.0 12.2

NG

1.7 13.1/1.5 15.4

OK 

16.1

- 0.946 diam. by 0.907 length 10 350 8.3/1.6 10.4

NG

1.7 12.4/2.0 19.5

NG

16.1

- 0.946 diam. by 0.907 length 10 400 7.6/1.7 10.1

NG

1.7 12.9/1.3 13.2

OK

16.1

- 0.946 diam. by 0.907 length 10 1.7 16.1

Figure 28.—Summary for 0.946-in.-diameter by 0.907-in.-length (0.021 lb), 10° impact angle.

The next step was to maintain the impact angle, and to double the weight of the ice projectile. Table 

12 shows a summary of the LS-DYNA results for 0.946-in.-diameter by 0.907-in.-length (0.021 lb) ice 

projectile. At an impact velocity of 400 fps, the exposed substrate criterion was exceeded while the total 

foam loss was within the allowable limit. When the speed was reduced to 350 fps, both the exposed 

substrate and total foam loss criteria were exceeded. The total foam loss actually increased at the slower 

speed because at the slower speed the ice projectile did not travel directly to the substrate. Instead, the 

projectile was ‘caught’ in the foam layer, began to tumble, and did more damage to the foam top layer 

than at the higher impact velocity. The impact velocity had to be lowered to 300 fps before both the 
NASA/TM—2015-218938 25

exposed substrate and total foam loss were both within the allowable criteria. Figure 28 shows the results 

of Table 12 graphically.

The ice projectile weight was doubled, once again, and the resulting LS-DYNA predictions are shown 

in Table 13 and Figure 29. As expected, the impact velocity had to be lowered even further to meet the 

damage criteria compared to the smaller sized ice projectiles. At first look, it is surprising that the damage 

incurred at 200 fps is greater than the damage predicted at 300 fps. After closer examination (Figure 30), 

it was observed that at the higher velocity, the ice projectile slices a longer path through the foam, but less 

of the ice breaks-up, so the path is narrower than for the 200 fps impact. For the 200 fps impact, the ice 

projectile does not travel as far, but the ice breaks up more extensively, so the damage done to the foam is 

broader. It is important to note that the exact quantitative value for damage for the 200 and 300 fps 

conditions is not overly critical since both impact conditions exceed the allowable limits. What is more 

important is the velocity where the damage is equal to the limit since this velocity defines the critical 

impact velocity. Regardless of the actual damage values for the 200 and 300 fps impacts, so long as these 

conditions exceed the allowable, the critical velocity would still be reasonably close to 180 fps.

TABLE 13.—LS-DYNA RESULTS FOR 1.189 in. DIAMETER BY 1.142 in. LENGTH

(0.041 lb) ICE PROJECTILE, 10° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 1.189 diam. by 1.142 length 10 150 0/0 0

OK

1.7 9.6/1.0 7.5

OK

16.1

- 1.189 diam. by 1.142 length 10 175 0/0 0

OK

1.7 12.5/1.1 10.8

OK

16.1

- 1.189 diam. by 1.142 length 10 200 7.6/6.8 40

NG

1.7 7.6/6.8 40

NG

16.1

- 1.189 diam. by 1.142 length 10 300 9.1/2.4 17.2

NG

1.7 9.1/2.4 17.2

NG

16.1

Figure 29.—Summary for 1.189-in.-diameter by 1.142-in.-length (0.041 lb) ice projectile, 

10° impact angle.
NASA/TM—2015-218938 26

The weight of the fourth and final ice projectile size that was investigated was 0.082 lb. It was only 

necessary to run two conditions to locate the critical impact velocity, and as expected since this was the 

largest projectile size, the critical impact velocity was less than for the previous ice projectile sizes. These 

results are shown in Table 14 and Figure 31.

Figure 30.—Exposed substrate for 1.189-in.-diameter by 1.142-in.-length 

(0.041 lb) ice projectile, 10° impact angle.

TABLE 14.—LS-DYNA RESULTS FOR 1.499-in.-DIAMETER BY 1.4387-in.-LENGTH

(0.081 lb) ICE PROJECTILE, 10° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 1.499 diam. by 1.4387 length 10 150 0/0 0

OK

1.7 12.5/1.4 13.7

OK

16.1

- 1.499 diam. by 1.4387 length 10 200 12.5/3.3 32

NG

1.7 16.8/2.5 33

NG

16.1

Figure 31.—Summary for 1.499-in.-diameter by 1.4387-in.-length (0.081 lb) ice projectile, 

10° impact angle.
NASA/TM—2015-218938 27

After completion of the 10° impact analyses with a range of ice projectile sizes, the impact angle was 

reduced to 5°, and the analyses were repeated with the same size projectiles. The LS-DYNA results for 

the smallest, 0.011 lb, projectiles are shown in Table 15 and Figure 32. For this shallow impact angle, and 

small sized ice projectile, the projectile never caused enough damage to exceed the allowable, regardless 

of the impact velocity. At higher impact velocities, the ice tends to inflict slightly more damage to the top 

layer of foam, but, at higher velocities the ice also breaks up faster which tends to limit the total amount 

of damage. Regardless of the impact velocity, the ice projectile never penetrates through to the substrate, 

so there is never any damage to the exposed substrate.

TABLE 15.—LS-DYNA RESULTS FOR 0.75-in.-DIAMETER BY 0.72-in.-LENGTH

(0.011 lb) ICE PROJECTILE, 5° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 0.75 diam. by 0.72 length 5 500 0/0 0

OK

1.7 8/1.5 9.4

OK

16.1

- 0.75 diam. by 0.72 length 5 600 0/0 0

OK

1.7 14/.8 8.8

OK

16.1

- 0.75 diam. by 0.72 length 5 700 0/0 0

OK

1.7 15.4/.9 10.9

OK

16.1

- 0.75 diam. by 0.72 length 5 800 0/0 0

OK

1.7 15.6/.95 11.5

OK

16.1

- 0.75 diam. by 0.72 length 5 1000 0/0 0

OK

1.7 12.7/.94 9.4

OK

16.1

- 0.75 diam. by 0.72 length 5 1200 0/0 0

OK

1.7 12.7/1.1 11

OK

16.1

- 0.75 diam. by 0.72 length 5 1800 0/0 0

OK

1.7 13.6/1.1 11.7

OK

16.1

- 0.75 diam. by 0.72 length 5 2500 0/0 0

OK

1.7 14.4/1.1 12.4

OK

16.1

Figure 32.—Summary for 0.75-in.-diameter by 0.72-in.-length (0.011 lb) ice projectile, 5° impact angle.
NASA/TM—2015-218938 28

Table 16 and Figure 33 show the LS-DYNA results for the 0.946-in.-diameter by 0.907-in.-length 

(0.021 lb) ice projectile at 5° impact angle. For these impact conditions, and the range of impact velocities 

examined, the total foam loss never exceeds the allowable limit. Up until close to 1900 fps impact 

velocity, the ice projectile does not penetrate all the way to the substrate so there is no exposed substrate. 

At the critical velocity of 1950 fps, the exposed substrate just reaches the allowable limit. Figure 34

shows the total damage in the foam layer and exposed substrate. 

TABLE 16.—LS-DYNA RESULTS FOR 0.946-in.-DIAMETER BY 0.907-in.-LENGTH

(0.021 lb) ICE PROJECTILE, 5° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 0.946 diam. by 0.907 length 5 800 0/0 0

OK

1.7 16.7/.95 12.5

OK

16.1

- 0.946 diam. by 0.907 length 5 1500 0/0 0

OK

1.7 17.2/1.2 16.2 16.1

- 0.946 diam. by 0.907 length 5 1750 0/0 0

OK

1.7 17.4/1.1 15.0

OK

16.1

- 0.946 diam. by 0.907 length 5 1900 0/0 0

OK

1.7 17.8//1.1 15.4

OK

16.1

- 0.946 diam. by 0.907 length 5 2000 1.4/1.9 2.1

NG

1.7 17.9/1.1 15.5

OK

16.1

Figure 33.—Summary for 0.946-in.-diameter by 0.907-in.-length (0.021 lb) ice projectile, 5° impact angle.

Figure 34.—Damage in foam layer and exposed substrate for 0.946-in.-diameter by 0.907-in.-length 

(0.021 lb) ice projectile, 5° impact angle.
NASA/TM—2015-218938 29

Table 17 and Figure 35 show the LS-DYNA results for the 1.192-in.-diameter by 1.1428-in.-length 

(0.041 lb) ice projectile at 5° impact angle. For this size projectile, the damage is highly nonlinear in that 

the damage does not decrease linearly with impact velocity. Instead, the damage is maximum at an 

intermediate impact velocity (~600 fps), and is less at higher and lower impact velocities. The critical 

impact velocity is 350 fps. 

TABLE 17.—LS-DYNA RESULTS FOR 1.192-in.-DIAMETER BY 1.1428-in.-LENGTH

(0.041 lb) ICE PROJECTILE, 5° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 1.192 diam. by 1.1428 length 5 300 0/0 0

OK

1.7 15/1.2 14.1

OK

16.1

- 1.192 diam. by 1.1428 length 5 350 0/0 0

OK

1.7 17.2/1.2 16.2

NG

16.1

- 1.192 diam. by 1.1428 length 5 400 6.8/2.6 13.9

NG

1.7 18.8/1.1 16.2

NG

16.1

- 1.192 diam. by 1.1428 length 5 600 13.9/3.7 40.4

NG

1.7 22.5/1.2 21.2

NG

16.1

- 1.192 diam. by 1.1428 length 5 800 4.1/1.9 6.1

NG

1.7 12.4/1.3 12.7

OK

16.1

- 1.192 diam. by 1.1428 length 5 1000 13.7/1.8 19.4

NG

1.7 24.2/1.1 20.9

NG

16.1

- 1.192 diam. by 1.1428 length 5 1500 8.5/.83 5.5

NG

1.7 21.6/1.6 27.1

NG

16.1

Figure 35.—Summary for 1.192-in.-diameter by 1.1482-in.-length (0.041 lb) ice 

projectile, 5° impact angle.
NASA/TM—2015-218938 30

Table 18 and Figure 36 show the LS-DYNA results for the 1.502 in. diameter x 1.440 in. length 

(0.082 lb) ice projectile at 5° impact. For this size projectile the damage to the foam and the quantity of 

exposed substrate is extensive above an impact velocity of 400 fps. Both types of damage decrease below 

400 fps, and reach an allowable impact velocity at 275 fps.

Table 19 shows the ice summary results for both the 10° and 5° impact angles and the four sizes of 

projectiles. Figure 37 shows the Ice projectile critical velocity vs. projectile size. As expected, the critical 

impact velocity decreases as the size of the projectile increases, and the steeper impact angle (10° has 

lower critical velocities than the more shallow (5°) impact angle. As mentioned earlier, the critical impact 

velocity levels off for larger ice projectiles since the diameter of the larger size projectile exceeds the 

thickness of the top layer of foam, so part of the projectile does not make contact with the foam. It is also 

interesting to note that for all but one impact condition, the exposed Al (exposed substrate) criteria drives 

the allowable impact velocity since this criteria is exceeded before the total foam loss criteria is reached. 

TABLE 18.—LS-DYNA RESULTS FOR 1.502-in.-DIAMETER BY 1.440-in.-LENGTH

(0.082 lb) ICE PROJECTILE, 5° IMPACT

Test Ice projectile,

in.

Impact 

angle,

deg.

Velocity,

fps

Interface foam 

(exposed Al plate)

Total foam loss

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

Combined 

foam

L2/W2,

in.

Area,

in.

2

π/4 (L2*W2)

Target 

area,

in.

2

- 1.502 diam. by 1.440 length 5 250 0 0

OK

1.7 13.9/1.3 14.2

OK

16.1

- 1.502 diam. by 1.440 length 5 275 0 0

OK

1.7 15.4/1.3 15.7

OK

16.1

- 1.502 diam. by 1.440 length 5 300 0 0

OK

1.7 16.7/1.4 18.8

NG

16.1

- 1.502 diam. by 1.440 length 5 400 6.4/2.9 14.6

NG

1.7 19.3/1.2 18.2

NG

16.1

- 1.502 diam. by 1.440 length 5 600 16.5/5 65

NG

1.7 25/3.75 74

NG

16.1

Figure 36.—Summary for 1.502-in.-diameter by 1.440-in.-length (0.082 lb) ice projectile, 

5° impact angle.
NASA/TM—2015-218938 31

Figure 37.—Ice projectile critical velocity versus projectile size.

TABLE 19.—ICE PROJECTILE SUMMARY RESULTS

Impact angle,

deg

Ice cylinder Critical impact 

velocity,

fps

Criteria Exceeded

Diameter,

in.

Length ,

in.

Weight ice, 

oz.

Exposed Al Total foam loss 

surface area

10 0.75 0.72 0.011 425 Yes ---

10 0.946 0.907 0.021 305 Yes ---

10 1.189 1.142 0.041 180 Yes ---

10 1.499 1.4387 0.082 155 Yes ---

5 0.75 0.72 0.011 No limit --- ---

5 0.946 0.907 0.021 1950 Yes ---

5 1.192 1.1428 0.041 350 Yes ---

5 1.502 1.440 0.082 275 --- Yes

4.2 PDL Foam Impact Results

PDL foam impact results for SLS are determined for combinations of impact angles, projectile size, 

and projectile velocities, then compared to the allowable limits, so the boundary of impact conditions that 

do not exceed the limits can be generated. 

TABLE 20.—SLS PDL FOAM IMPACT CONDITIONS

Impact angle, 

deg.

PDL foam cylinder

Diameter,

in.

Length, 

in.

Weight,

lb

10 1.646 2.437 0.010

10 2.5 3.72 0.035

10 3.547 5.25 0.100

5 1.646 2.437 0.010

5 2.5 3.72 0.035

5 3.547 5.25 0.100

5 4.47 6.614 0.200
NASA/TM—2015-218938 32

The combinations of size and angle which were analyzed are reported in Table 20. The damaged area 

of acreage foam due to PDL foam impact for each of these conditions is also reported.

It is important to mention that, as in the ice assessment, only cylindrically shaped PDL foam 

projectiles were studied. The medium weight projectile (0.035 lb) that was assessed had the same 

dimensions as the cylindrical projectile used in the verification tests. For the other projectile sizes, the 

ratio of diameter to length was held constant, while the size was varied. Projectile shape will have an 

effect on damage. In particular, with foam masses of 0.1 lb and greater, not all of the foam in a cylindrical 

or square projectile would necessarily interact with the NCFI acreage foam. A higher aspect ratio 

rectangular foam projectile shape, with the same larger mass, will remove more acreage foam than the 

geometry studied. However, as in the ice assessment, it was not practical to study multiple projectile 

shapes.

The general procedure for measuring damaged areas and selecting velocities to analyze is essentially 

the same as discussed previously in the ice impact assessment. Table 21 shows a summary of LS-DYNA 

results for 1.646-in.-diameter by 2.437-in.-length (0.01 lb) PDL foam projectile impacting at a 10° angle.

For the 1600 fps impact velocity, both the exposed substrate, and the total foam loss, exceeds the 

allowable values, and the impact velocity must be reduced to determine the allowable impact velocity 

limit. At 1250 fps, only the exposed substrate limit is exceeded, and once again, the impact velocity is 

reduced. At 1100 fps neither the exposed substrate nor the total foam loss limits are exceeded, and the 

maximum allowable impact velocity is identified. In general there is less damaged foam and exposed 

substrate as the impact velocity is decreased; however the trend is clearly not linear. Figure 38 shows the 

results of Table 21 graphically. 

TABLE 21.—LS-DYNA RESULTS FOR 1.646-in.-DIAMETER BY 2.437-in.-LENGTH (0.01 lb)

PDL FOAM PROJECTILE, 10° IMPACT

Velocity, 

fps

10° impact angle PDL foam mass 0.01 lb Diameter = 1.646 in. Length = 2.437 in.

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer 

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

750 7.30 1.77 10.15 OK 0.00 0.00 0.00 OK 0.24

900 9.36 1.77 13.02 OK 0.00 0.00 0.00 OK 0.19

1000 7.92 1.77 11.02 OK 0.00 0.00 0.00 OK 0.25

1100 7.86 1.90 11.75 OK 0.00 0.00 0.00 OK 0.19

1250 8.22 1.87 12.08 OK 2.81 2.64 5.83 Exceeds 0.00

1500 9.48 1.90 14.13 OK 5.36 1.25 5.27 Exceeds 0.00

1550 10.11 1.90 15.12 OK 7.26 2.72 15.53 Exceeds 0.00

1600 11.18 1.91 16.74 Exceeds 3.09 1.97 4.79 Exceeds 0.00

1650 10.81 1.91 16.17 Exceeds 6.92 2.88 15.66 Exceeds 0.00

1700 11.93 1.90 17.84 Exceeds 8.16 2.49 15.95 Exceeds 0.00

1800 12.06 1.97 18.61 Exceeds 4.37 1.32 4.52 Exceeds 0.00
NASA/TM—2015-218938 33

Figure 38.—Summary for 1.646-in.-diameter by 2.437-in.-length (0.01 lb) PDL foam projectile, 10° impact angle.

Given the highly non-linear nature of the physics, including the non-linear material behavior of the 

foams (Figure 1 and Figure 2), it is expected that the damage area versus velocity trends would also not 

be linear. The non-linear nature of these trends has been clearly visible in the ice impact results. However, 

the degree of sensitivity that foam loss in the interface layer shows to small changes in velocity is extreme 

(Figure 38). The PDL projectile foam has a similar density and strength as the NCFI acreage foam. As a 

result, it does not burrow into the NCFI foam while remaining largely intact as the ice does. Therefore, 

whether or not the NCFI foam interface layer fails depends on the velocity of the complex shock waves 

traveling through the foam, and whether or not they are in in-phase with the reflection from the Al 

backing plate. In other words, the foam on foam impact may create a non-linear resonance condition. 

When the resonance condition is created, the interface layer failure area is large. When not in resonance, 

the interface layer area is smaller. This behavior is also seen in the 5° tests with the 0.035 lb PDL 

projectile (Figure 42), and the 5° tests with the 0.1 lb PDL projectile (Figure 43).

The next step was to maintain the impact angle, and to increase the weight of the PDL foam 

projectile. Table 22 shows a summary of LS-DYNA results for 2.5-in.-diameter by 3.72-in.-length 

(0.035 lb) PDL foam projectile impacting at a 10° angle. The total foam loss exceeded the allowable 

value at very velocity analyzed, and the exposed substrate allowable was exceeded when the velocity was

at or greater than 750 fps. Figure 39 shows the results of Table 22 graphically. 
NASA/TM—2015-218938 34

TABLE 22.—LS-DYNA RESULTS FOR 2.5-in.-DIAMETER BY 3.72-in.-LENGTH

(0.035 lb) PDL FOAM PROJECTILE, 10° IMPACT

Velocity, 

fps

10° impact angle PDL foam mass 0.035 lb Diameter = 2.5 in Length = 3.72 in

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer 

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

250 13.07 2.80 28.74 Exceeds 0.00 0.00 0.00 OK 0.13

500 15.55 2.79 34.07 Exceeds 0.00 0.00 0.00 OK 0.07

600 14.42 2.79 31.60 Exceeds 0.00 0.00 0.00 OK 0.07

650 13.86 2.79 30.37 Exceeds 0.00 0.00 0.00 OK 0.07

700 13.92 2.79 30.50 Exceeds 0.00 0.00 0.00 OK 0.07

725 14.23 2.80 31.29 Exceeds 0.00 0.00 0.00 OK 0.07

750 14.86 2.64 30.81 Exceeds 5.24 1.62 6.67 Exceeds 0.00

1000 13.65 2.80 30.02 Exceeds 10.68 2.34 19.63 Exceeds 0.00

1500 14.85 2.95 34.41 Exceeds 9.67 1.97 14.96 Exceeds 0.00

Figure 39.—Summary for 2.5-in.-diameter by 3.72-in.-length (0.035 lb) PDL foam projectile, 10° impact angle.

The weight of the PDL foam projectile was increased again to 0.1 lb Table 23 shows a summary of 

LS-DYNA results for 3.547-in.-diameter by 5.25-in.-length (0.1 lb) PDL foam projectile impacting at a 

10° angle. The total foam loss exceeded the allowable value at every velocity analyzed, and the exposed 

substrate allowable was exceeded when the velocity was at or greater than 725 fps. Note that while the 

velocity at which the exposed substrate criterion was exceeded does not vary significantly from the 

0.035 lb assessment, the area of damage is much greater with the larger, 0.1 lb projection. Figure 40

shows the results of Table 23 graphically. 
NASA/TM—2015-218938 35

TABLE 23.—LS-DYNA RESULTS FOR 3.547-in.-DIAMETER BY 5.25-in.-LENGTH

(0.1 lb) PDL FOAM PROJECTILE, 10° IMPACT

Velocity, 

fps

10° impact angle PDL foam mass 0.1 lb Diameter = 3.547 in. Length = 5.25 in.

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer 

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

500 17.32 3.53 48.01 Exceeds 0.00 0.00 0.00 OK 0.19

600 17.55 4.14 57.06 Exceeds 0.25 0.17 0.03 OK 0.00

700 17.36 4.06 55.32 Exceeds 0.00 0.00 0.00 OK 0.07

710 16.67 3.79 49.60 Exceeds 1.65 0.88 1.14 OK 0.00

725 17.16 3.87 52.19 Exceeds 6.54 1.97 10.14 Exceeds 0.00

750 23.61 6.28 116.51 Exceeds 17.05 6.28 84.14 Exceeds 0.00

1000 20.36 4.05 64.73 Exceeds 14.60 4.05 46.40 Exceeds 0.00

1500 25.25 4.07 80.78 Exceeds 19.59 3.96 60.93 Exceeds 0.00

2000 25.22 7.22 143.08 Exceeds 13.36 7.22 75.76 Exceeds 0.00

2500 24.21 5.01 95.32 Exceeds 12.06 5.01 47.47 Exceeds 0.00

3000 27.17 4.76 101.60 Exceeds 14.85 4.76 55.54 Exceeds 0.00

Figure 40.—Summary for 3.547-in.-diameter by 5.25-in.-length (0.1 lb) PDL foam projectile, 10° impact angle.

After completion of the 10° impact analyses with a range of PDL foam projectile sizes, the impact 

angle was reduced to 5°, and the analyses were repeated with the same size projectiles. The LS-DYNA 

results for the smallest, 0.01 lb, projectile is shown in Table 24 and Figure 41. For this shallow impact 

angle, and small sized PDL foam projectile, the projectile never caused enough damage to exceed the 

exposed substrate allowable, regardless of the impact velocity. 
NASA/TM—2015-218938 36

TABLE 24.—LS-DYNA RESULTS FOR 1.646-in.-DIAMETER BY 2.437-in.-LENGTH

(0.01 lb) PDL FOAM PROJECTILE, 5° IMPACT

Velocity,

fps

5° impact angle PDL foam mass 0.01 lb Diameter = 1.646 in. Length = 2.437 in.

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer 

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

1700 12.27 1.77 17.03 Exceeds 0.00 0.00 0.00 OK 0.38

1800 13.49 1.77 18.75 Exceeds 0.99 0.89 0.69 OK 0.00

1850 13.74 1.77 19.09 Exceeds 0.00 0.00 0.00 OK 0.45

2000 13.56 1.83 19.53 Exceeds 0.00 0.00 0.00 OK 0.45

2200 15.04 1.90 22.45 Exceeds 0.00 0.00 0.00 OK 0.46

2500 15.48 1.78 21.59 Exceeds 0.00 0.00 0.00 OK 0.45

2800 14.78 1.91 22.12 Exceeds 0.00 0.00 0.00 OK 0.54

3000 13.43 1.90 20.08 Exceeds 0.00 0.00 0.00 OK 0.46

3500 13.22 1.90 19.76 Exceeds 0.00 0.00 0.00 OK 0.46

4000 14.09 1.97 21.79 Exceeds 0.00 0.00 0.00 OK 0.53

Figure 41.—Summary for 1.646-in.-diameter by 2.437-in.-length (0.01 lb) PDL foam projectile, 5° impact angle.

As in the 10° analyses, the weight of the PDL foam projectile was increased to 0.035 lb Table 25

shows a summary of LS-DYNA results for 2.5-in.-diameter by 3.72-in.-length (0.035 lb) PDL foam 

projectile impacting at a 5° angle. The total foam loss exceeded the allowable value at every velocity 

analyzed, and the exposed substrate allowable was exceeded when the velocity was at or greater than 

1050 fps. There is some sensitivity in the interface layer foam loss to specific dynamic conditions. This 

can be seen in the results of the 1150 and 1151 fps impact results, where the stress waves produced by the 

PDL foam projectile at these specific velocities did not couple with the response of the NCFI foam to 

produce complete insulating foam loss in any small area. This degree of general sensitivity was also seen 

in the test results, although not enough tests were conducted at these shallow angles to demonstrate this 

exact result. Figure 42 shows the results of Table 25 graphically. 
NASA/TM—2015-218938 37

TABLE 25.—LS-DYNA RESULTS FOR 2.5-in.-DIAMETER BY 3.72-in.-LENGTH (0.035 lb)

PDL FOAM PROJECTILE, 5° IMPACT

Velocity, 

fps

5° impact angle PDL foam mass 0.035 lb Diameter = 2.5 in Length = 3.72 in

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer 

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

700 13.91 2.05 22.40 Exceeds 0.00 0.00 0.00 OK 0.26

900 14.17 1.97 21.92 Exceeds 0.00 0.00 0.00 OK 0.31

1000 13.10 2.11 21.71 Exceeds 0.00 0.00 0.00 OK 0.25

1025 13.40 2.04 21.47 Exceeds 0.84 0.86 0.57 OK 0.00

1050 12.91 2.05 20.79 Exceeds 7.19 1.97 11.12 Exceeds 0.00

1075 13.16 2.04 21.09 Exceeds 4.19 2.27 7.47 Exceeds 0.00

1100 13.60 2.11 22.54 Exceeds 9.26 2.16 15.71 Exceeds 0.00

1125 13.92 2.13 23.29 Exceeds 9.92 2.89 22.52 Exceeds 0.00

1150 13.41 2.11 22.22 Exceeds 0.00 0.00 0.00 OK 0.25

1151 14.04 2.12 23.38 Exceeds 0.00 0.00 0.00 OK 0.31

1175 13.10 2.11 21.71 Exceeds 9.12 2.42 17.33 Exceeds 0.00

1200 13.78 2.18 23.59 Exceeds 4.86 1.78 6.79 Exceeds 0.00

1300 14.62 2.50 28.71 Exceeds 10.19 2.12 16.97 Exceeds 0.00

Figure 42.—Summary for 2.5-in.-diameter by 3.72-in.-length (0.035 lb) PDL foam projectile, 5° impact angle.

The weight of the PDL foam projectile was increased to 0.1 lb Table 26 shows a summary of LSDYNA results for a 3.547-in.-diameter by 5.25-in.-length (0.1 lb) PDL foam projectile, impacting at a 5°

angle. The total foam loss exceeded the allowable value at every velocity analyzed, and the exposed 

substrate allowable was exceeded when the velocity was at or greater than 760 fps. As in the 0.035 lb

PDL foam impact at 5°, there is some interesting dynamic sensitivity in the results. At 3000 fps, the 

projectile’s contact time with the target was short enough that stress waves which would cause interface 

foam damage were not created. Figure 43 shows the results of Table 26 graphically. 
NASA/TM—2015-218938 38

TABLE 26.—LS-DYNA RESULTS FOR 3.547-in.-DIAMETER BY 5.25-in.-LENGTH (0.1 lb)

PDL FOAM PROJECTILE, 5° IMPACT

Velocity, 

fps

5° impact angle PDL foam mass 0.1 lb Diameter = 3.547 in. Length = 5.25 in.

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

700 20.77 3.71 60.48 Exceeds 0.00 0.00 0.00 OK 0.13

750 20.92 3.20 52.54 Exceeds 0.00 0.00 0.00 OK 0.19

760 24.11 5.41 102.47 Exceeds 16.82 5.41 71.48 Exceeds 0.00

775 21.80 5.52 94.53 Exceeds 17.97 5.52 77.95 Exceeds 0.00

800 17.32 3.53 48.01 Exceeds 11.29 2.95 26.16 Exceeds 0.00

900 24.03 4.52 85.27 Exceeds 16.62 4.52 58.99 Exceeds 0.00

1000 20.59 3.03 49.05 Exceeds 13.51 2.42 25.64 Exceeds 0.00

1500 30.13 3.63 85.87 Exceeds 11.61 2.57 23.40 Exceeds 0.00

2000 29.77 3.79 88.62 Exceeds 15.81 2.58 31.97 Exceeds 0.00

2500 34.48 3.96 107.29 Exceeds 15.00 2.20 25.92 Exceeds 0.00

3000 34.78 3.96 108.23 Exceeds 0.00 0.00 0.00 OK 0.19

Figure 43.—Summary for 3.547-in.-diameter by 5.25-in.-length (0.1 lb) PDL foam projectile, 5° impact angle.

As the ice projectile mass was increased, the critical velocity did not decrease significantly, 

approaching convergence (Figure 38). Comparing the critical velocities for 10° PDL foam projectile, the 

same trend is evident, with the critical velocity of the 0.035 lb projectile at 750 fps and that of the 0.1 lb

projectile at 725 fps. At 5°, the critical velocity of the 0.035 projectile is 1050 fps and the critical velocity 

of the 0.1 lb projectile is 760 fps. Therefore, the weight of the PDL foam projectile was increased to

0.2 lb, to determine if the trend holds for the PDL foam impacting at 5°. Table 27 shows a summary of 

LS-DYNA results for a 4.469-in.-diameter by 6.615-in.-length (0.2 lb) PDL foam projectile, impacting at 

a 5° angle. With the critical velocity of 675 fps, the critical velocity has ceased decreasing significantly. 

Figure 44 shows the results of Table 27 graphically. 
NASA/TM—2015-218938 39

TABLE 27.—LS-DYNA RESULTS FOR 4.469-in.-DIAMETER BY 6.615-in. LENGTH

(0.2 lb) PDL FOAM PROJECTILE, 5° IMPACT

Velocity, 

fps

5° impact angle PDL foam mass 0.2 lb Diameter = 4.469 in. Length = 6.615 in.

Total damaged area Critical total damage 

area = 16.1 in.

2

Removed interface layer

area (exposed Al)

Critical removed interface 

area = 1.69 in.

2

Min 

remaining 

foam 

thickness,

in.

Length,

in.

Width,

in.

Damage 

area,

in.

2

Failure 

criteria

Length,

in.

Width ,

in.

Interface 

area,

in.

2

Failure 

criteria

600 29.97 4.15 97.61 Exceeds 0.00 0.00 0.00 OK 0.07

650 29.29 4.52 104.07 Exceeds 0.19 0.17 0.02 OK 0.00

675 29.54 3.97 92.01 Exceeds 12.19 3.80 36.32 Exceeds 0.00

700 30.86 4.15 100.58 Exceeds 14.63 1.58 18.09 Exceeds 0.00

750 26.98 4.07 86.33 Exceeds 13.55 4.76 50.63 Exceeds 0.00

Figure 44.—Summary for 4.469-in.-diameter by 6.615-in.-length (0.2 lb) PDL foam projectile, 5° impact angle.

A summary of the critical velocities for the PDL foam, at both the 10° and 5° impact angles, and for 

the assessed projectile masses is shown in Figure 45. As in the ice study, the critical impact velocity 

decreases as the size of the projectile increases, and for the steeper impact angle. (The 10° impacts have

lower critical velocities than the more shallow, 5° impacts.) Also as in the ice study, the critical impact 

velocity levels off with larger PDL foam projectiles. Here too, the diameter of the larger size PDL foam 

projectiles exceeds the thickness of the top layer of insulting foam, so part of the projectile does not make 

contact with the foam. As a result, some of the PDL cylindrical foam mass is not an effective projectile, 

and other projectile geometries might yield larger damage areas for the same mass and impact velocity.
NASA/TM—2015-218938 40

Figure 45.—PDL foam projectile critical velocity versus projectile size.

Figure 46.—Ice and PDL foam projectile critical velocity versus

projectile size.

4.3 Impact Results Summary

A summary of the critical velocities for both the ice and the PDL foam projectiles, and at both the 10° 

and 5° impact angles, versus the assessed projectile masses is shown in Figure 46. As shown in this 

figure, the same trend of critical impact velocity leveling off with larger mass projectiles occurs with both 

ice and PDL foam projectiles. 
NASA/TM—2015-218938 41

The difference in critical velocity for the same mass and impact angles between ice and PDL foam is 

also demonstrated in Figure 46. Here, the greater density of ice results in a lower critical velocity than the 

same mass projectile of less dense PDL foam. This effect of density, along with the previously discussed 

effects of projectile shape and localized dynamics, demonstrate why simple ice and foam impact 

assessments, using limited formulas such as kinetic energy, do not yield reliable results.

5.0 Summary

A large amount of testing and analysis were conducted with both ice and PDL foam impacts on NCFI 

acreage foam for the Space Shuttle Project (SSP) External Tank (ET). Test verified material models and 

techniques that resulted from this testing were utilized for this study to perform a parametric study for the 

Space Launch System (SLS) to determine critical impact velocities for given projectile weights

The testing, test verified material models and techniques were reviewed in Section 2.0. In Section 3.0, 

an updating repetition of the test verification analysis was presented. In Section 4.0 impact assessments of 

both ice and PDL foam impacts for NCFI acerage foam for multiple projectile masses, and for 5 and 10°

impacts were documented. The presented damage areas and comparisons to SSP ET critical areas can be 

used by SLS to assess potential damage due to debris. In addition, should additional analysis be required, 

the presented results can serve as an accuracy benchmark for any subsequent studies.

The allowable damage criteria based on Shuttle limits is a reasonable starting point for SLS, however, 

the specific limits for SLS may differ from Shuttle. Therefore, SLS limits will need to be determined 

before the results of this study may be applied to SLS.

References

1. Carney, K., Melis, M., Fasanella, E., Lyle, K., Gabrys, J., Material Modeling of Space Shuttle 

Leading Edge and External Tank Materials For Use in the Columbia Accident Investigation, 8th 

International LS-DYNA User’s Conference, 2004.

2. Carney, K.S., et al, ‘A phenomenological high strain rate model with failure for ice’, International 

Journal of Solids and Structures 43 (2006) 7820-7839.

3. Ice Impact Damage Test & Assessment to ET Systems to Support Physics Based Modeling –

Lockheed Martin Space Systems Company - Test Report 809-9804.

4. Impact Damage Test and Assessment to External Tank Thermal Protection System to Support Physics 

Based Modeling – Lockheed Martin Space Systems Company - Test Report 809-9473.

5. Hallquist, John O., editor, LS-DYNA 971 R6.1.0 Keyword Manual, August 2012.