DOT/FAA/AR-04/40,P1 

Office of Aviation Research 

Washington, D.C. 20591 

Explicit Finite Element Modeling of 

Multilayer Composite Fabric for 

Gas Turbine Engine Containment 

Systems 

Part 1: Static Tests and Modeling 

November 2004 

Final Report 

This document is available to the U.S. public 

through the National Technical Information 

Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration
NOTICE 

This document is disseminated under the sponsorship of the U.S. 

Department of Transportation in the interest of information exchange. The 

United States Government assumes no liability for the contents or use 

thereof. The United States Government does not endorse products or 

manufacturers. Trade or manufacturer's names appear herein solely 

because they are considered essential to the objective of this report. This 

document does not constitute FAA certification policy. Consult your local 

FAA aircraft certification office as to its use. 

This report is available at the Federal Aviation Administration William J. 

Hughes Technical Center's Full-Text Technical Reports page: 

actlibrary.tc.faa.gov in Adobe Acrobat portable document format (PDF). 
 Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-04/40,P1

2. Government Accession No. 3. Recipient's Catalog No.

5. Report Date

November 2004

4. Title and Subtitle 

EXPLICIT FINITE ELEMENT MODELING OF MULTILAYER COMPOSITE 

FABRIC FOR GAS TURBINE ENGINE CONTAINMENT SYSTEMS 

PART 1: STATIC TESTS AND MODELING 

6. Performing Organization Code

7. Author(s)

S. D. Rajan, Barzin Mobasher, Jignesh Sharda, Venkat Yanna, Chaitanya 

Deenadaylu, David Lau, and Dhaval Shah

8. Performing Organization Report No. 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

Department of Civil & Environmental Engineering 

Arizona State University 

Tempe, AZ 85287-5306 

11. Contract or Grant No. 

01-C-AW-ASU 

13. Type of Report and Period Covered

Final Report 

8/2001 – 5/2003

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration 

FAA William J. Hughes Technical Center 

Atlantic City International Airport, NJ 08405 

14. Sponsoring Agency Code

 ANE-100

15. Supplementary Notes

The FAA William J. Hughes Technical Center COTR was Donald Altobelli.

16. Abstract

Under the Federal Aviation Administration’s Airworthiness Assurance Center of Excellence and with support from the Aircraft 

Catastrophic Failure Prevention Program, the team consisting of Arizona State University, Honeywell Engines, Systems & 

Services, National Aeronautics and Space Administration Glenn Research Center, and SRI International collaborated to develop 

testing procedures and computational models for designing and evaluating ballistic fabric turbine engine containment structures. 

This report contains the details of the static tests and their finite element simulations carried out at Arizona State University.

17. Key Words 

Aircraft engine fragments, Containment, Zylon, Kevlar, 

Finite element analysis, Ballistic testing, Static testing

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS) Springfield, Virginia 22161.

19. Security Classif. (of this report)

 Unclassified 

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

 115

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized
ACKNOWLEDGEMENTS 

The investigators wish to thank Mr. William Emmerling, Mr. Donald Altobelli, Mr. Chet Lewis, 

and Dr. Xiaogong Lee of the Federal Aviation Administration for their technical and financial 

support. In order to meet the objectives of this project we have relied heavily on the technical 

collaborations with several other organizations that include Honeywell Engines & Systems

Phoenix, SRI International, and NASA Glenn Research Center. Some of the individuals who 

contributed immensely to this project include Dr. Shen Yeh Chen, Mr. Reha Gomuc, Mr. Wil 

Baker, and Mr. Jack Robinson of Honeywell; Dr. Don Shockey, Dr. Jeff Simons, and Mr. Dave 

Erlich of SRI International; and Mr. J. M. Pereira and Mr. Duane Revilock of NASA Glen

Research Center. Their support and cooperation in meeting the research objectives was greatly 

appreciated. 

iii/iv
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY xv 

1. INTRODUCTION 1-1 

1.1 Purpose 1-1 

1.2 Background 1-1 

2. TENSION TESTS 2-1 

2.1 Objectives 2-1 

2.2 Specimen Preparation Procedure 2-1 

2.2.1 Area Properties 2-1 

2.2.2 End Tabs 2-1 

2.2.3 End Plates 2-2 

2.3 Test Procedure and Results 2-3 

3. SPLICE TESTS 3-1 

3.1 Objectives 3-1 

3.2 Specimen Preparation Procedure 3-1 

3.3 Test Procedure 3-1 

3.4 Test Results 3-2 

4. STATIC TESTS 4-1 

4.1 Objectives 4-1 

4.2 Specimen Preparation Procedure 4-1 

4.3 Test Setup 4-3 

4.4 Test Procedure 4-7 

4.5 Test Results 4-8 

5. FINITE ELEMENT MODELING 5-1 

5.1 Objectives 5-1 

5.2 Tension Test Models 5-2 

5.3 Finite Element Analysis of Static Test Models 5-6 

5.3.1 One-Layer Kevlar Model 5-9 

5.3.2 Two-Layer Kevlar Model 5-12 

5.3.3 Four-Layer Kevlar Model 5-14 

5.3.4 Eight-Layer Kevlar Model 5-17 

v
5.3.5 Twenty-Four-Layer Kevlar Model 5-19 

5.3.6 One-Layer Zylon Model 5-22 

5.3.7 Two-Layer Zylon Model 5-26 

5.3.8 Four-Layer Zylon Model 5-30 

5.3.9 Eight-Layer Zylon Model 5-34 

5.3.10 Twenty-Four-Layer Zylon Model 5-38 

5.4 Energy Absorption Comparisons 5-42 

6. CONCLUSIONS 6-1 

7. REFERENCES 7-1 

APPENDIX A—STATIC TEST RESULTS 

vi
LIST OF FIGURES

Figure Page 

2-1 Zylon Specimens (T1) 2-2 

2-2 Kevlar Specimens (T1) 2-2 

2-3 Test Setup With Specimen 2-2 

2-4a End Plates for Gripping (T2) 2-3 

2-4b Side View (T2) 2-3 

2-4c Inner View of the Grip Assembly (T2) 2-3 

2-5a Load vs Actuator Stroke (KTest1) (Grip T1) 2-4 

2-5b Stress vs Strain Diagram (KTest1) (Grip T1) 2-4 

2-6a Load vs Actuator Stroke (KTest2) (Grip T1) 2-5 

2-6b Stress vs Strain Diagram (KTest2) (Grip T1) 2-5 

2-7a Load vs Actuator Stroke (KSwath1) (Grip T2) 2-6 

2-7b Stress vs Strain Diagram (KSwath1) (Grip T2) 2-6 

2-8a Load vs Actuator Stroke (KSwath2) (Grip T2) 2-7 

2-8b Stress vs Strain Diagram (KSwath2) (Grip T2) 2-7 

2-9a Load vs Actuator Stroke (ZTest1) (Grip T1) 2-8 

2-9b Stress vs Strain Diagram (ZTest1) (Grip T1) 2-8 

2-10a Load vs Actuator Stroke (ZTest2) (Grip T1) 2-9 

2-10b Stress vs Strain Diagram (ZTest2) (Grip T1) 2-9 

2-11a Load vs Actuator Stroke (ZSwath1) (Grip T2) 2-10 

2-11b Stress vs Strain Diagram (ZSwath1) (Grip T2) 2-10 

2-12a Load vs Actuator Stroke (ZSwath2) (Grip T2) 2-11 

2-12b Stress vs Strain Diagram (ZSwath2) (Grip T2) 2-11 

2-13 Stress vs Strain Diagrams for All Kevlar Specimens 2-12 

vii
2-14 Stress vs Strain Diagrams for All Zylon Specimens 2-12 

2-15 Kevlar Specimen (T2) 2-14 

2-16 Failure at Center (T2) 2-14 

2-17 Zylon Specimen (T2) 2-14 

2-18 Failure at the Edge (T2) 2-14 

3-1a Load vs Deflection (GTestk4_oe) (LVDT) 3-3 

3-1b Stress vs Strain Diagram (GTestk4_oe) (LVDT) 3-3 

3-2a Load vs Deflection (GTestk4_ne) (LVDT) 3-4 

3-2b Stress vs Strain Diagram (GTestk4_ne) (LVDT) 3-4 

3-3 Load vs Actuator Stroke (GTestk6_ne) (Actuator) 3-5 

3-4a Load vs Deflection (GTestz4_oe) (LVDT) 3-5 

3-4b Stress vs Strain Diagram (GTestz4_oe) (LVDT) 3-6 

4-1 Test Setup 4-1 

4-2a Mandrel for Specimen Preparation 4-2 

4-2b Specimen Transfer Ring 4-2 

4-3 Blunt Nose With Bearings 4-3 

4-4 Attachment of C-Clamps to the Specimen 4-4 

4-5 Top Plate With Bearings Orthogonal to Nose Bearings (Fixed-End Condition 

at Top) 4-5 

4-6a Schematic Diagram of the Test Setup 4-6 

4-6b Schematic of Test Setup With Clamps and Hinges to Remove Spurious Loads 4-6 

4-6c Revised Blunt Nose Housing Design (Fixed-Fixed Conditions) 4-7 

4-7 Load-Deformation Response of Single-Layer Kevlar Specimens Prior to 

Slack Adjustment 4-8 

4-8 Load-Deformation Response of Single-Layer Kevlar Samples After 

Slack Adjustment 4-9 

viii
4-9 Load-Deformation Response of 1-, 2-, 4-, 8-, and 24-Layer Kevlar Samples 4-10 

4-10 Load-Deformation Response of 1-, 2-, 4-, 8-, and 24-Layer Zylon Samples 4-11 

4-11 Energy-Absorbed/Areal Density Graphs of 1-, 2-, 4-, 8-, and 24-Layer Kevlar and 

Zylon Samples 4-12 

4-12 Energy-Absorbed/Areal Density Graphs of 1-, 2-, 4-, 8-, and 24-Layer Kevlar and 

Zylon Samples Normalized by Number of Layers 4-12 

4-13 Number of Layers vs Peak Load for All Tests 4-13 

4-14 Number of Layers vs Normalized Peak Load for All Tests 4-13 

4-15 Number of Layers vs Stiffness for All Tests (Actual and Linearly Extrapolated) 4-14 

4-16 Number of Layers vs Normalized Stiffness for All Tests (Actual and Linearly 

Extrapolated) 4-14

5-1 User-Supplied Piecewise Linear Stress-Strain Curve for Kevlar (KTest1) 5-3 

5-2a Piecewise Linear Stress-Strain Curve for Zylon (ZTest1, Grip T1) 5-4 

5-2b Piecewise Linear Stress-Strain Curve for Zylon (ZSwath1, Grip T2) 5-5 

5-3 Geometric Model Showing Quarter Model of the Static Test Setup 5-6 

5-4 Finite Element Mesh 5-7 

5-5 Details of the FE Mesh Showing the Blunt Nose, Steel Cylinder, and the Fabric 5-7 

5-6a Boundary Conditions Imposed on the Bottom of the Steel Cylinder and at the 

Position of the Clamps 5-8 

5-6b Boundary Conditions Imposed at the Bottom of the Blunt Nose 5-8 

5-7 Comparison of the Load-Displacement Graphs for a One-Layer Kevlar Test 5-9 

5-8 One-Layer Kevlar—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-11 

1 ε

5-9 One-Layer Kevlar—Plot of in-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-11 

2 ε

5-10 Comparison of the Load-Displacement Graphs for a Two-Layer Kevlar Test 5-12 

5-11 Two-Layer Kevlar—Plot of in-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-13 

1 ε

ix
5-12 Two-Layer Kevlar—Plot of in-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-14 

2 ε

5-13 Comparison of the Load-Displacement Graphs for a Four-Layer Kevlar Test 5-14 

5-14 Four-Layer Kevlar—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-16 

1 ε

5-15 Four-Layer Kevlar—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-16 

2 ε

5-16 Comparison of the Load-Displacement Graphs for an Eight-Layer Kevlar Test 5-17 

5-17 Eight-Layer Kevlar—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-18 

1 ε

5-18 Eight-Layer Kevlar—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step 5-19 

2 ε

5-19 Comparison of the Load-Displacement Graphs for a 24-Layer Kevlar Test 5-19 

5-20 Twenty-Four-Layer Kevlar—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step 5-21 

1 ε

5-21 Twenty-Four-Layer Kevlar—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step 5-21 

2 ε

5-22 Comparison of the Load-Displacement Graphs for a One-Layer Zylon Test 5-22 

5-23 One-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-24 

1 ε

5-24 One-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-24 

2 ε

5-25 One-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-25 

1 ε

5-26 One-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-25 

2 ε

5-27 Comparison of the Load-Displacement Graphs for a Two-Layer Zylon Test 5-26 

5-28 Two-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-28 

1 ε

x
5-29 Two-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-28 

2 ε

5-30 Two-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-29 

1 ε

5-31 Two-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-29 

2 ε

5-32 Comparison of the Load-Displacement Graphs for a Four-Layer Zylon Test 5-30 

5-33 Four-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-32 

1 ε

5-34 Four-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-32 

2 ε

5-35 Four-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-33 

1 ε

5-36 Four-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-33 

2 ε

5-37 Comparison of the Load-Displacement Graphs for an Eight-Layer Zylon Test 5-34 

5-38 Eight-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-36 

1 ε

5-39 Eight-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T1) 5-36 

2 ε

5-40 Eight-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-37 

1 ε

5-41 Eight-Layer Zylon—Plot of In-Plane Strain Superimposed on Deformation at 

the End of the Last Load Step (Grip T2) 5-37 

2 ε

5-42 Comparison of the Load-Displacement Graphs for a 24-Layer Zylon Test 5-38 

5-43 Twenty-Four-Layer-Zylon—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step (Grip T1) 5-39 

1 ε

5-44 Twenty-Four-Layer-Zylon—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step (Grip T1) 5-39 

2 ε

xi
5-45 Twenty-Four-Layer Zylon—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step (Grip T2) 5-40 

1 ε

5-46 Twenty-Four-Layer Zylon—Plot of In-Plane Strain Superimposed on 

Deformation at the End of the Last Load Step (Grip T2) 5-40 

2 ε

5-47 Energy-Absorbed/Areal Density Graphs for 1-, 2-, 4-, 8-, and 24-Layer 

Kevlar Samples 5-43 

5-48 Energy-Absorbed/Areal Density Graphs of 1-, 2-, 4-, 8-, and 24-Layer Kevlar 

Normalized by the Number of Layers 5-44 

5-49 Energy-Absorbed/Areal Density Graphs for 1-, 2-, 4-, 8-, and 24-Layer 

Zylon Samples 5-44 

5-50 Energy-Absorbed/Areal Density Graphs of 1-, 2-, 4-, 8-, and 24-Layer Zylon 

Normalized by the Number of Layers 5-45 

5-51 Energy-Absorbed/Areal Density Graphs for all Kevlar and Zylon Samples 5-45 

5-52 Energy-Absorbed/Areal Density Graphs for all Kevlar and Zylon Samples 

Normalized by the Number of Layers 5-46 

xii
LIST OF TABLES 

Table Page 

2-1 Basic Material Properties 2-1 

2-2 Summary of Test Results 2-13 

3-1 Kevlar Test Specimen Details 3-2 

3-2 Splice Test Results 3-2 

4-1 Summary of Static Test Conditions and Results 4-5 

5-1 Piecewise Linear Kevlar Stress-Strain Data 5-3 

5-2a Piecewise Linear Zylon Stress-Strain Data (T1) 5-4 

5-2b Piecewise Linear Zylon Stress-Strain Data (T2) 5-5 

5-3 Static Test—FEA Comparison for a One-Layer Kevlar Test 5-10 

5-4 Static Test—FEA Comparison for a Two-Layer Kevlar Test 5-12 

5-5 Static Test—FEA Comparison for a Four-Layer Kevlar Test 5-15 

5-6 Static Test—FEA Comparison for an Eight-Layer Kevlar Test 5-17 

5-7 Static Test—FEA Comparison for a 24-Layer Kevlar Test 5-20 

5-8 Static Test—FEA Comparison for a One-Layer Zylon Test 5-22 

5-9 Static Test—FEA Comparison for a Two-Layer Zylon Test 5-26 

5-10 Static Test—FEA Comparison for a Four-Layer Zylon Test 5-30 

5-11 Static Test—FEA Comparison for an Eight-Layer Zylon Test 5-34 

5-12 Static Test—FEA Comparison for a 24-Layer Zylon Test 5-38 

5-13 Summary of Energy Absorption Data (Prepeak) for Static Test and 

FE Simulations 5-43 

xiii
LIST OF ACRONYMS

AACE Airworthiness Assurance Center of Excellence 

ASU Arizona State University 

c/s Cross-section 

FAA Federal Aviation Administration 

FE Finite element 

FEA Finite element analysis 

GRC Glen Research Center 

Honeywell Honeywell Engines, Systems & Services 

ID Internal diameter 

NASA National Aeronautics and Space Administration

OD Outer diameter 

SRI SRI International 

xiv
EXECUTIVE SUMMARY

Modeling a multilayer fabric composite for engine containment systems during a fan blade-out 

event has been a challenging task. Nonlinear transient (explicit) finite element analysis (FEA) 

has the greatest potential of any numerical approach available to industry for analysis of these 

events. Significant research is still required to overcome difficulties with numerical stability,

material modeling (pre- and postfailure), and standardizing modeling methods to achieve 

accurate simulation of the complex interactions between individual components during these 

high-speed events. The primary focus of this research was to develop the methodology for 

testing, modeling, and analyzing a typical fan blade-out event in a multilayer fiber fabric

composite containment system. ABAQUS finite element code was used to verify the basic 

material model (prefailure state) developed through laboratory testing. LS-DYNA was the

primary modeling tool used in the explicit FEA of ballistic events. 

During the Fourth Federal Aviation Administration (FAA) Uncontained Engine Debris 

Characterization Modeling and Mitigation Workshop (held in May 2000 at SRI International,

Menlo Park, CA), a representative of Honeywell Engines, Systems & Services presented the 

capability of modeling complicated engine hub-burst and fan blade-out events, predicting most

of the event with high confidence was shown. At the same time, SRI presented their efforts on 

modeling the material characteristics within LS-DYNA and developing a new composite fiber 

material called Zylon that appeared to be stronger, lighter, and more temperature-resistant than

Kevlar. Both parties showed interest in each other’s work, and both agreed they could benefit 

from each other if collaborative mechanisms could be arranged. After the workshop, Honeywell 

and SRI contacted each other and began talks of a joint project. The FAA, National Aeronautics 

and Space Administration (NASA) Glenn Research Center (GRC), and Arizona State University

(ASU) were later invited into the discussion, resulting in this FAA-funded research under the

Aircraft Catastrophic Prevention Program and the Airworthiness Assurance Center of Excellence 

Program. 

The goal of this research was to use the technical strengths of Honeywell, SRI, and the ASU for

developing a robust explicit finite element analysis modeling methodology for the purposes 

mentioned above. Since the development of an experimental set of data to support the 

calibration of the finite element models was essential, various experimental methods to measure

material and structural response of the fabrics were conducted. NASA GRC, under the NASA 

Aviation Safety Program, conducted a series of engine containment ring tests that were used for 

modeling in this program. 

Each member of the team took a leadership role and developed a comprehensive report 

describing the details of the research task and the findings. The complete FAA report is 

comprised of the following four separate reports (parts 1 through 4). 

• 

• 

• 

Part 1: Static Tests and Modeling by Arizona State University Department of Civil 

Engineering 

Part 2: Ballistic Testing by NASA Glenn Research Center 

Part 3: Material Model Development and Simulation of Experiments by SRI International

xv
• Part 4: Model Simulation for Ballistic Tests, Engine Fan Blade-Out, and Generic Engine 

by Honeywell Engines, Systems & Services 

This report contains the details of the static tests and their finite element simulations carried out 

by ASU. 

xvi
1. INTRODUCTION.

1.1 PURPOSE. 

This research effort was undertaken as a direct result of discussions from the Fourth Federal 

Aviation Administration (FAA) Uncontained Debris Characterization Modeling and Mitigation

Workshop (held in May 2000 at SRI International). A teaming effort between academia, and 

industry was seen as an excellent opportunity to transition fabric modeling and testing research

that was being sponsored by the FAA Aircraft Catastrophic Failure Prevention Program.

1.2 BACKGROUND.

During the Fourth FAA Uncontained Engine Debris Characterization Modeling and Mitigation 

Workshop, a representative of Honeywell Engines, Systems & Services presented the capability 

of modeling complicated engine hub-burst and fan blade-out events. Predicting most of the

event with high confidence was shown. At the same time, SRI International presented their

efforts on modeling the material characteristics within LS-DYNA and developing a new 

composite fiber material called Zylon. Both parties showed interest in each other’s work, and 

both agreed they could benefit from each other if collaborative mechanisms could be arranged. 

It was especially attractive that Zylon seemed to be stronger, lighter, and had better endurance 

under high temperature compared to Kevlar. After the workshop, Honeywell and SRI 

contacted each other and began talks of a joint project. The FAA, National Aeronautics and

Space Administration (NASA) Glenn Research Center (GRC), and Arizona State University 

(ASU) were later invited into the discussion, resulting in this FAA-funded research. 

The goal of this research was to use the technical strengths of Honeywell, SRI, NASA GRC, and 

ASU for developing a robust explicit finite element analysis modeling methodology for the 

purposes mentioned above. Since the development of an experimental set of data to support the 

calibration of the finite element models is essential, various experimental methods to measure

material and structural response of the fabrics were conducted. Some of the specific program

objectives were as follows. 

1. Couple LS-DYNA modeling and the engine expertise of Honeywell with the material 

modeling capability of SRI, the ballistic test capability of NASA GRC and the

experimental facilities and finite element analysis/modeling capabilities of ASU. 

2. Incorporate the material model developed by SRI into the LS-DYNA modeling 

methodology developed by Honeywell for controlled laboratory hardware test, 

developing new methodologies if necessary. 

3. Develop methodologies for numerical simulation of engine fan blade-out events with 

composite fiber fabric wraps using SRI’s material model and Honeywell’s LS-DYNA 

modeling methodology. Calibrate the methodologies to the existing engine test results 

from Honeywell. 

4. Compare the efficiency of Kevlar and Zylon wraps by laboratory hardware test and LSDYNA for the test coupons. 

1-1
5. Explore the potential of Zylon for future engine containment systems. 

The reasons for including both Kevlar and Zylon in the project are as follows. 

• Quantify back-to-back comparison of the two materials. 

• Currently, there are no engine containment systems made of Zylon. However, Kevlar 

data are available from the existing hardware tests at Honeywell. For calibrating the

analysis model for Kevlar, basic modeling techniques for Kevlar will need to be 

investigated.

• Having both Kevlar and Zylon analyzed for engine containment systems will provide a

better understanding of the strength and weakness of both fabrics. 

The research was divided into four tasks: 

• Task 1: Static Tests and their FE modeling and simulation. 

• Task 2: Ballistic Tests. 

• Task 3: Finite element (FE) modeling and simulation of the Ballistic Tests. 

• Task 4: FE modeling and simulation of a fan blade out condition for a generic engine. 

This report deals with the details of the static tests. This entire report deals specifically with 

Kevlar 49 17x17 fabric and Zylon AS 35x35 fabric. Tension tests were conducted to develop 

the basic material properties, which are discussed in section 2. Section 3 presents the results 

from splice tests used in investigating the bond properties of the fabrics using different epoxies. 

The static tests of multiple-layer specimens wrapped around a ring and subjected to static load 

due to penetration of a blunt penetrator are discussed in section 4. This is followed by the finite 

element modeling and simulation of the static tests in section 5. A summary and suggestions for 

improvements are made in section 6. Additional photographs and load-deflection plots for the 

static tests are contained in appendix A. 

1-2
2. TENSION TESTS.

Tension tests are used in creating the stress-strain curve for a material. These curves can then be 

used as a basis of a material model suitable for use in a finite element analysis. 

2.1 OBJECTIVES.

The primary objective of these simple tension tests was to construct the engineering stress-strain 

diagram up to ultimate failure in the principal material direction for Kevlar 49 and Zylon AS 

fabrics. 

2.2 SPECIMEN PREPARATION PROCEDURE.

The specimens were custom-made with their sides stitched (Lincoln Fabrics LTD, Canada). The

dimensions and other properties of the specimens are provided in table 2-1. 

TABLE 2-1. BASIC MATERIAL PROPERTIES 

Material 

Yarn 

Count 

Bulk 

Density

(lb/in3) 

Linear 

Density 

(lb/in.) 

c/s Area per 

Yarn 

(in2

) 

Specimen Size 

(in.) 

Kevlar 49 17 x 17 0.00530516 9.457(10-7) 1.78(10-4) 2.5 x 12 

Zylon AS 35 x 35 0.00567358 3.175(10-7) 5.59(10-5) 2.5 x 12 

2.2.1 Area Properties.

The cross-section (c/s) area of each yarn was calculated by taking into account the linear density

of the yarn material and dividing it by its bulk density. The total c/s area of the specimen was 

defined as the cross-sectional area per yarn multiplied by the number of yarns per inch of fabric 

times the total width of the fabric. The calculated c/s area values are shown in table 2-1. 

2.2.2 End Tabs.

Initially, two Zylon specimens and two Kevlar specimens were tested. Flat, perforated, 

aluminum pieces, 2.5′′ long by 2.5′′ wide by 0.025′′ thick, were used as end tabs. These tabs

were attached to both the ends of the specimen using epoxy to ensure a firm grip in the testing 

machine. The arrangement is shown in figures 2-1 and 2-2. In the testing machine, these tabs

were held in place under hydraulic pressure, as shown in figure 2-3. An alignment setup was

prepared and used to ensure that the end pieces were aligned (parallel) and resulted in the same

thickness, avoiding any eccentricity. Commercial-grade 5-minute epoxy consisting of a twocomponent resin and hardener was mixed in equal proportion by volume and used to glue the end 

tabs. The specimen was left for 24 hours at room temperature to cure. Tests conducted with this 

end tab arrangement are denoted in this report as Grip T1. 

2-1
FIGURE 2-1. ZYLON SPECIMENS (T1) FIGURE 2-2. KEVLAR SPECIMENS (T1) 

FIGURE 2-3. TEST SETUP WITH SPECIMEN 

2.2.3 End Plates.

To ensure that slipping of the specimens (from the grips) did not influence the deflection values, 

a different gripping fixture was used as shown in figures 2-4a through 2-4c. Flat steel plates, 

2.5′′ wide, 2′′ long, 0.25′′ thick, are used to grip the specimen at both ends. At each end, one of 

the two pieces has a curved groove at the center of the plate throughout its width, which is half 

the thickness of the plate. The other plate has a V-notch cut in the same position about half the 

thickness of the plate. A round aluminum rod is cut along the length to the shape of the groove 

to match the existing grooves in the steel plate. Two shoulder pins are assembled at the top of 

the plates to keep the assembly intact and prevent any wobble of the plates, with respect to each 

2-2
other about the aluminum piece. The fabric was held between the V-notch and the aluminum

piece so that the notch pinches against the fabric and prevents it from slipping, with respect to

the end plates. The two plates were pressed with hydraulic grips, thereby ensuring uniform 

pressure application to minimize, if not prevent, any fabric slippage. The revised grip assembly 

is denoted as Grip T2. Two specimens of each fabric type were tested with the T2 gripping

fixture. 

 

FIGURE 2-4a. END PLATES FOR 

GRIPPING (T2) 

FIGURE 2-4b. SIDE VIEW (T2) 

 

FIGURE 2-4c. INNER VIEW OF THE GRIP ASSEMBLY (T2) 

2.3 TEST PROCEDURE AND RESULTS.

The tests were performed according to the Standard ASTM procedure, Tensile Testing of 

Polymer Matrix Composites—ASTM D 3039 “Standard Test Method for Tensile Properties of 

Fiber-Resin Composites.” 

Tests were conducted in a 55-kips servo-hydraulic test frame operated under closed-loop control. 

The test procedure was a displacement control test with the rate of displacement of actuator 

(stroke) set at 0.1′′/min. A digital data acquisition was used to collect data at every 0.5 second. 

2-3
The test was continued until complete failure of the specimen was achieved. The loaddeformation results were used to calculate the stress-strain response. The overall deformation of 

the specimen was measured by the stroke movement of the actuator. 

The various load-deflection and stress-strain graphs are presented in figures 2-5a through 2-12b. 

In the figures, K refers to the Kevlar specimens and Z refers to the Zylon specimens. 

0 0.1 0.2 0.3

Actuator Stroke, in

0

500

1000

1500

2000

2500

Load, lbs

FIGURE 2-5a. LOAD VS ACTUATOR STROKE (KTest1) (GRIP T1) 

0.00 0.01 0.02 0.03 0.04

Strain, in/in

0

100000

200000

300000

Stress, psi

FIGURE 2-5b. STRESS VS STRAIN DIAGRAM (KTest1) (GRIP T1) 

2-4
0 0.1 0.2 0.3

Actuator Stroke, in

0

500

1000

1500

2000

2500

Load, l

bs

FIGURE 2-6a. LOAD VS ACTUATOR STROKE (KTest2) (GRIP T1) 

0.00 0.01 0.02 0.03 0.04

Strain, in/in

0

100000

200000

300000

St

r

ess, psi

FIGURE 2-6b. STRESS VS STRAIN DIAGRAM (KTest2) (GRIP T1) 

2-5
0.0 0.1 0.2 0.3 0.4 0

Actuator Stroke, in

.5

0

500

1000

1500

2000

2500

Load, l

bs

FIGURE 2-7a. LOAD VS ACTUATOR STROKE (KSwath1) (GRIP T2) 

0.00 0.01 0.02 0.03 0.04

Strain, in/in

0

100000

200000

300000

St

ress, psi

FIGURE 2-7b. STRESS VS STRAIN DIAGRAM (KSwath1) (GRIP T2) 

2-6
0.0 0.1 0.2 0.3 0.4 0.5

Actuator Stroke, in

0

500

1000

1500

2000

2500

Load, l

bs

FIGURE 2-8a. LOAD VS ACTUATOR STROKE (KSwath2) (GRIP T2) 

0.00 0.01 0.02 0.03 0.04 0.05

Strain, in/in

0

100000

200000

300000

Stress, psi

FIGURE 2-8b. STRESS VS STRAIN DIAGRAM (KSwath2) (GRIP T2) 

2-7
0 0.2 0.4 0.6

Actuator Stroke, in

0

500

1000

1500

2000

2500

Load, lbs

FIGURE 2-9a. LOAD VS ACTUATOR STROKE (ZTest1) (GRIP T1) 

0.00 0.02 0.04 0.06 0.08

Strain, in/in

0

100000

200000

300000

400000

500000

St

ress, psi

FIGURE 2-9b. STRESS VS STRAIN DIAGRAM (ZTest1) (GRIP T1) 

2-8
0 0.2 0.4 0.6

Actuator Stroke, in

0

500

1000

1500

2000

2500

L

oad, lbs

FIGURE 2-10a. LOAD VS ACTUATOR STROKE (ZTest2) (GRIP T1) 

0.00 0.02 0.04 0.06 0.08

Strain, in/in

0

100000

200000

300000

400000

500000

St

ress, psi

FIGURE 2-10b. STRESS VS STRAIN DIAGRAM (ZTest2) (GRIP T1) 

2-9
0.0 0.2 0.4 0.6 0.8 1.0

Actuator Stroke, in

0

500

1000

1500

2000

2500

Load, lbs

FIGURE 2-11a. LOAD VS ACTUATOR STROKE (ZSwath1) (GRIP T2) 

0.00 0.02 0.04 0.06 0.08 0.10

Strain, in/in

0

100000

200000

300000

400000

St

r

ess, psi

FIGURE 2-11b. STRESS VS STRAIN DIAGRAM (ZSwath1) (GRIP T2) 

2-10
0.0 0.2 0.4 0.6 0.8

Actuator Stroke, in

0

500

1000

1500

2000

Load, l

bs

FIGURE 2-12a. LOAD VS ACTUATOR STROKE (ZSwath2) (GRIP T2) 

0.00 0.02 0.04 0.06 0.08

Strain, in/in

0

100000

200000

300000

400000

St

r

ess, psi

FIGURE 2-12b. STRESS VS STRAIN DIAGRAM (ZSwath2) (GRIP T2) 

2-11
The stress-strain curves are summarized for all the Kevlar specimens in figure 2-13 and for the 

Zylon specimens in figure 2-14. The results are summarized in table 2-2. 

0 0.02 0.04 0.06

Strain, (in/in)

0

100

200

300

Stress (

ksi)

KTest1 - 302 ksi

KTest2 - 272 ksi

KSwath1 - 283 ksi

KSwath2 - 257 ksi

FIGURE 2-13. STRESS VS STRAIN DIAGRAMS FOR ALL KEVLAR SPECIMENS 

0 0.02 0.04 0.06 0.08

Strain, (in/in)

0

100

200

300

400

500

St

r

ess (

ksi)

ZTest1 - 460 ksi

ZTest2 - 420 ksi

ZSwath1 - 440 ksi

ZSwath2 - 416 ksi

FIGURE 2-14. STRESS VS STRAIN DIAGRAMS FOR ALL ZYLON SPECIMENS 

2-12
TABLE 2-2. SUMMARY OF TEST RESULTS 

Energy Absorbed 

per Unit Volume

(lb-in/in3

) 

Test ID 

Peak 

Load 

(lb) 

Elongation 

(in.) 

Tensile 

Strength 

(psi)(a)

Ultimate 

Tensile 

Strain 

(%)(b)

Modulus 

of 

Elasticity 

(ksi)(c) En1*(d) En2*(e)

Kevlar Specimens 

KTest1 (T1) 2419 0.214 301950 3.06 17115 3650 3590 

KTest2 (T1) 2085 0.204 272453 2.92 18590 2584 2519 

KSwath1 (T2) 2166 0.322 282644 2.99 16345 3472 3340 

KSwath2 (T2) 2014 0.320 256911 3.05 15321 3539 3387 

Average 2171 0.265 278490 3.01 16843 3311 3209

Std. Dev. 177 0.065 18883 0.065 1377 490 473 

Zylon Specimens 

ZTest1 (T1) 2276 0.510 461550 7.27 18242 7923 6875 

ZTest2 (T1) 2064 0.472 419554 6.75 18960 7217 6188 

ZSwath1 (T2) 2088 0.501 439618 5.56 17166 10597 10366 

ZSwath2 (T2) 1975 0.554 415788 5.10 19868 6842 6735 

Average 2101 0.509 434128 6.17 18559 8145 7541

Std. Dev. 127 0.0340 21062 1.011 1142 1695 1907 

Notes: 

(a) Stress is obtained by dividing the peak load by the cross-section area as tabulated in table 2-1. 

(b) Ultimate tensile strain is obtained by dividing the elongation at peak load by the specimen gage length.

(c) Modulus of elasticity is taken as the maximum (linear) slope from the prepeak region of the stress-strain graph. 

(d) En1* - Energy absorbed by the fabric as calculated by total area under the stress-strain curve. 

(e) En2* - Energy absorbed by the fabric as calculated by linear approximation of the area under the stress-strain

curve extended from the modulus of elasticity slope. 

The initial portion of the load-deflection graph shows a large increase in displacement (actuator 

stroke) for a very small increase in load. In this portion, the load essentially straightens the yarns 

by removing the crimp. Woven fabrics inherently have crimp (or waviness). As the load 

increases, the yarns stiffen, as shown by the increase of the slope of the load-deflection graph. 

The graph of one specimen (figure 2-10a) exhibits a small nonsmooth behavior (or waviness) in 

the prepeak region. This is perhaps due to total or partial failure of yarn(s) in the specimen. This

behavior is much more pronounced in the postpeak region of Kevlar specimens (figures 2-5a, 2-

7a, 2-8a) and one Zylon specimen (Figure 2-12a). The failure of all the specimens is sudden 

(brittle behavior). 

Examination of the results showed that the scatter for the Kevlar tests was much smaller 

compared to the Zylon tests. The standard deviation for the (Kevlar) peak strain values of four

tests is 0.065%. In the case of Zylon, the peak strain values obtained using Grip T2 are less than

those obtained from Grip T1. This is probably due to less slippage occurring at the grips with 

2-13
Grip T2. The standard deviation of the peak strain for the four tests was 1.011%. The ultimate 

tensile strain was obtained by dividing the elongation at peak load by the specimen gage length. 

The gage length used for Grip T1 was determined based on the average distance of grip face to

grip face. The gage length used for Grip T2 was determined based on the average distance of 

groove edge to groove edge. The modulus of elasticity was measured as the maximum slope

within the linear range of the ascending portion of the stress strain curve. In addition, the curves 

were converted to piecewise linear responses, which were used in the finite element modeling. 

The average Young’s Modulus of Kevlar fabrics was measured as 16,843 ksi, and the average 

modulus for the Zylon fabrics was measured as 18,559 ksi. In addition, two different means of

measuring the energy absorbed were investigated. In the first method, the energy absorbed by 

the fabric was calculated from the total area under the stress-strain curve. This included the

initial nonlinear ascending portion of the curve. In the second method, the energy absorbed by 

the fabric was calculated by linear approximation of the area under the stress-strain curve 

extended from the modulus of elasticity slope. This in effect resulted in assuming that the 

response of the material was a linear elastic behavior. The differences between these two 

methods are insignificant as the energy absorbed for Kevlar measured 3311 lb-in. for the exact 

integration versus 3209 psi for the linearized case. For the Zylon material exact integration 

yields energy of 8145 lb-in. versus 7541 psi for the linearized case. This represents that the

modeling of the material by means of elastic or quasi elastic response results in 3.0% and 7.4% 

underestimation of the energy absorbed for Kevlar and Zylon respectively.

Some of the failure modes using Grip T2 are shown in figures 2-15 through 2-18. The failure 

(broken yarns) occurs at the middle of the specimen for the Kevlar specimen, while the failure

occurred near the grips for the Zylon specimen. 

FIGURE 2-15. KEVLAR SPECIMEN (T2) FIGURE 2-16. FAILURE AT CENTER (T2) 

 

FIGURE 2-17. ZYLON SPECIMEN (T2) FIGURE 2-18. FAILURE AT THE EDGE (T2)

2-14
3. SPLICE TESTS.

To conduct a valid single or multilayer static test, the Kevlar and Zylon fabrics must be wrapped 

around a steel cylinder. The implication is that the two ends of the continuous fabric wraps need 

to be anchored so that the fabrics would not unwrap when they are subjected to an external load. 

It was, therefore, decided to investigate how two different epoxies could provide the anchor by 

preparing and testing splice joints made of these epoxies and fabrics. 

3.1 OBJECTIVES.

The primary objective of the splice tests was to determine the bond strength of the epoxy and the 

suitability of using these epoxies in preparing the specimens for the static tests. 

3.2 SPECIMEN PREPARATION PROCEDURE.

Three Kevlar specimens and one Zylon specimen were tested. Two overlap lengths of 4′′ and 6′′

were investigated. The specimen sizes (lengths) were chosen in such a way that the final length 

after overlap was 12′′. The specimens were prepared as follows. 

• Epoxy was applied evenly on the overlap areas of the two fabrics. Heavy flat plates were 

placed on top of this area to apply an even pressure and facilitate the bonding process. 

The overlap was left 24 hours at room temperature for curing. 

• Aluminum tabs were attached to the two ends of the test specimen, similar to the

procedure used with the simple tension tests. This was done after ensuring that the total

specimen length was exactly 12′′. 

The specimens were gripped (in the test fixture) using Grip T1, as described in section 2. 

Two different epoxies were used in the tests. They are identified as Epoxy A (5-minute epoxy) 

and Epoxy B (Hardman® extra fast setting epoxy). The epoxies consisted of two parts (resin and 

hardener) to be mixed in equal proportions by volume. 

3.3 TEST PROCEDURE.

The tests were performed according to the Standard ASTM procedure—ASTM D 3039

“Standard Test Method for Tensile Properties of Fiber-Resin Composites.” A 55-kips servohydraulic test frame, operated under closed-loop control, was used. The test procedure was a

displacement control test with the rate of displacement of actuator (stroke) set at 0.1 in./min. 

Digital data acquisition was used to collect data at every 0.5 second. The test was continued 

until complete failure of the specimen was achieved. The load-deformation results were used to 

calculate the stress-strain graph. The overall deformation of the specimen was measured by the

stroke movement of the actuator. 

3-1
3.4 TEST RESULTS.

The details of the Kevlar test specimens are shown in table 3-1. 

TABLE 3-1. KEVLAR TEST SPECIMEN DETAILS 

Specimen ID Epoxy Type 

Overlap Length 

(in.) 

GTestk4_ne B 4

GTestk4_oe A 4

GTest6_ne B 6

In all three tests, failure occurs at the edge of the overlap region. The failure was sudden. 

One Zylon specimen was tested with a 4′′ overlap using 5-minute epoxy. The load level 

reached was low, and the two Zylon layers peeled off. Zylon surface adhesion property is even

lower than a carbon surface. The test results are summarized in table 3-2. 

TABLE 3-2. SPLICE TEST RESULTS 

Kevlar Zylon

Test ID GTest4_oe GTestk4_ne GTestk6_ne GTestz4_oe 

Deflection at ultimate load (in.) 0.029 0.066 - 0.082 

Ultimate load (lb) 1998 1491 1650 627 

Ultimate load per yarn (lb) 51 48 43 7.7 

Ultimate strain 0.0077 0.0177 - 0.0218 

Ultimate stress per yarn (psi) 287,848 270,278 - 136,774 

The test results showed that the bond strength of the 5-minute epoxy, even for a 4′′ overlap, was 

more when compared to the 6′′ overlap strength provided by the fast-setting epoxy. 

The load-deflection and stress-strain graphs are shown in figures 3-1a through 3-4b. 

3-2
0.00 0.01 0.02 0.03 0.04 0.05

Deflection, in

0

500

1000

1500

2000

2500

Load, lbs

FIGURE 3-1a. LOAD VS DEFLECTION (GTestk4_oe) (LVDT) 

0.00 0.01

Strain, in/in

0

100000

200000

300000

St

r

ess, psi

FIGURE 3-1b. STRESS VS STRAIN DIAGRAM (GTestk4_oe) (LVDT) 

3-3
0.00 0.02 0.04 0.06 0.08

Deflection, in

0

400

800

1200

1600

Load, lbs

FIGURE 3-2a. LOAD VS DEFLECTION (GTestk4_ne) (LVDT) 

0.00 0.01 0.02

Strain, in/in

0

100000

200000

300000

St

r

ess, psi

FIGURE 3-2b. STRESS VS STRAIN DIAGRAM (GTestk4_ne) (LVDT) 

3-4
0.00 0.04 0.08 0.12 0.16

Deflection, in

0

400

800

1200

1600

2000

Load, l

bs

FIGURE 3-3. LOAD VS ACTUATOR STROKE (GTestk6_ne) (ACTUATOR) 

0.00 0.02 0.04 0.06 0.08 0.10

Deflection, in

0

200

400

600

800

Load, l

bs

FIGURE 3-4a. LOAD VS DEFLECTION (GTestz4_oe) (LVDT) 

3-5
0.00 0.01 0.02 0.03

Strain, in/in

0

40000

80000

120000

160000

Stress, psi

FIGURE 3-4b. STRESS VS STRAIN DIAGRAM (GTestz4_oe) (LVDT) 

The test results showed that while it is possible to generate a Kevlar splice joint with some

strength, the Zylon splice joints have little or no bond strength. Based on this observation, it was 

decided to clamp the Kevlar and the Zylon specimens to the steel ring at distances sufficiently far 

away from the point of application of the load. Details of this setup are discussed in section 4. 

3-6
4. STATIC TESTS.

4.1 OBJECTIVES. 

The primary objective of static tests is to simulate the penetration of the blunt object through the 

engine containment system assembly. A steel cylinder is used to simulate the engine housing, 

and the composite fabric is wrapped around this cylinder. The tests were conducted by applying 

the load in a quasi-static manner until failure, defined as full penetration of the blunt nose 

through the single or multilayer fabric. The load and deformation history were collected 

throughout the test, and the energy absorption capacity of the structure was calculated from this 

response. This test may ultimately be used as one of the key parameters in the determination of 

properties and design of the containment chamber. In this section the details of the static tests 

are presented. Relevant pictures and graphs are also presented to facilitate the understanding of

the test procedures and results. Additional information in the form of pictures and graphs can be 

found in appendix A. (A detailed data disk including the ABAQUS model, is available upon 

request from the FAA William J. Hughes Technical Center. 

4.2 SPECIMEN PREPARATION PROCEDURE.

The proposed plan for testing required determination of the load-deformation response of single 

and multilayer specimens for both Kevlar and Zylon wraps. The specimens were subjected to

outward penetration motion of a blunt nose assembly that was initially set up inside the steel 

ring. The specimen dimensions were 32′′ in diameter, 4′′ wide, and consisted of 1, 2, 4, 8, and 24 

layers wrapped around the outside of the steel cylinder, see figure 4-1. A small window was 

machined in the ring, allowing the penetration of the blunt nose assembly. 

FIGURE 4-1. TEST SETUP 

4-1
For the single-layer specimens, a 6′′ length of fabric overlap was used to glue the fabric onto 

itself. For multilayer specimens, the fabric was wrapped around the outside diameter of a 

custom-designed mandrel (figure 4-2a). The first layer was held on the mandrel by temporary 

glue. The last layer was glued to the previous layer using 5-minute epoxy. Overlap length for 

all specimens was 6′′. The specimen was cured for 24 hours before testing. To ensure proper 

alignment of the layers and cause minimal disturbance during the assembly process, a 32′′

diameter transfer ring (figure 4-2b) was manufactured. The rolled sample was slipped from the 

mandrel onto a transfer ring in order to transport it to the test fixture. The specimens were 

covered with opaque plastic sheeting to minimize the degrading effects of moisture and 

ultraviolet light. 

FIGURE 4-2a. MANDREL FOR SPECIMEN PREPARATION 

FIGURE 4-2b. SPECIMEN TRANSFER RING 

4-2
4.3 TEST SETUP.

A test fixture was manufactured by rolling a section of A36 mild steel to the inner diameter 

dimensions of the test setup. The ring dimensions are as follows: 

• Outer diameter (OD) 32′′

• Internal diameter (ID) 30′′

• Width 6′′

• 1′′ thick 

This ring was the main component of the loading fixture and was fabricated at Karlson 

Machinery, Phoenix, AZ. The complete loading fixture consisted of four major parts. The ring 

was assembled in two parts—as a large and a small arc at bottom to allow for installation of the 

fabric ring. The other components include the two side support plates and end plate to connect

the two ring components. A detailed view of the cylinder with side plates is shown in figure 4-1. 

The small arc that was cut out from the ring was connected at the bottom of the ring assembly 

and did not alter the geometry of the test setup. The size of the small arc corresponds to a 38°

angle. Using of the ring as two parts allowed easy installation of the specimen in the loading 

fixture. The specimens were first wrapped on an aluminum mandrel. Removal of the small arc

during the sample mounting stage facilitated the transfer of the test specimen from the transfer 

ring. The cylinder was attached to two side plates using 15-3/4′′ diameter, high-strength bolts 

connected along the ring’s perimeter. These side plates were connected to the base plate; hence, 

the ring had a clearance of 3′′ from the base plate. 

A blunt nose assembly (see figure 4-3) was used as the penetrator for all the tests in this

program. The steel nose was 2′′ wide by 5/16′′ thick. The top nose surface that was in contact 

with the fabric layer had a radius of 5/32′′ in the major direction and the corners. The crosssection of the base of the blunt nose was 2′′ by 2′′. 

FIGURE 4-3. BLUNT NOSE WITH BEARINGS 

4-3
The amount of load transferred through the lap (splice) joint and its potential failure were a 

major concern, especially in the one-layer tests. The tests conducted with the bond strength of 

Zylon indicated the difficulty in gluing the material and potential problems with interface 

failures. To avoid transferring the entire load to the end joint, it was decided to use clamps at 

points remote from the blunt head contact. The effect of clamping the specimen to the ring on

the integrity of the test results was studied using one-layer specimens. Specimens with and 

without clamps were tested, and the results are discussed in the following sections. For the 

multilayer Kevlar specimens and all the Zylon specimens, the tests were conducted with the 

clamps in place. Figure 4-4 shows the clamps placed on the side of the specimen. The clamps 

were placed at the same height on both sides of the ring to maintain symmetry and uniformity. 

The clamps are placed at 13.75′′ from the top of the base plate or at 10.75′′ from the bottom of 

the cylinder OD. 

FIGURE 4-4. ATTACHMENT OF C-CLAMPS TO THE SPECIMEN 

Another important parameter was the effect of fixing the blunt nose loading mechanism with

respect to the specimen, especially with large displacements expected throughout the test. It was 

expected that if the side loads were not removed through the use of hinges, a stiff system would 

be created, which would result in side loads. Alternatively, any rotation of the test assembly 

could result in loss of contact of the full length of the blunt nose with the fabric, thus increasing 

the contact pressure and premature failure of the specimen. Measurement of such second-order 

effects would be difficult, if not impossible. To make sure that the load applied is purely

uniaxial, one has to allow for at least two hinges to remove forces in the two minor directions. 

Based on the above, samples were tested with bearings placed at the nose and load cell. Both 

cases of parallel and orthogonal hinges were studied. However, the hinge-to-hinge conditions

were found to be unstable due to eccentricities in the test assembly. It was found necessary to fix

the end conditions at the top of the blunt nose housing by fixing the load cell bearings that were

placed orthogonal to the nose bearings, as shown in figure 4-5. It should be noted that the 

aluminum plates placed between the vertical shaft that is connected to the test machine crosshead

and the top plate of the blunt nose housing, restrict the ability of the housing to rotate under 

eccentric loads. This setup corresponds to the fixed-hinge end conditions shown in table 4-1. 

4-4
FIGURE 4-5. TOP PLATE WITH BEARINGS ORTHOGONAL TO NOSE BEARINGS 

(FIXED-END CONDITION AT TOP) 

TABLE 4-1. SUMMARY OF STATIC TEST CONDITIONS AND RESULTS 

Area Under the 

Curve (lb-in.)

Test ID 

No. of 

Layers Special Provisions

Peak 

Load 

(lb) 

Peak 

Stroke 

(in.) 

Stiffness 

(lb/in.) Prepeak Postpeak

Kevlar Specimens 

Kring1_2 1 Fixed-hinge, no clamps 1685 3.17 1503 1157 78

Kring1_3 1 Fixed-hinge, no clamps 1486 2.69 1115 993 507

Kring1_4 1 Fixed-hinge, no clamps 1522 2.39 1052 1062 721

Kring1_5 1 1571 3.10 1161 1260 203

Kring2_1 2 3429 3.30 2694 2371 590

Kring4_1 4 Preload: 250 lb 6625 3.23 4942 4503 889 

Kring8_1 8 Preload: 250 lb 13231 3.62 9463 9907 1036 

Kring24_2 24 Preload: 2000 lb 31131 3.35 16314 37434 5629 

Zylon Specimens 

Zing1_2 1 1730 4.69 1481 1323 162

Zring2_1 2 3408 4.47 2635 2906 143

Zring4_2 4 7363 4.39 5463 6105 56

Zring8_3 8 Preload: 1000 lb 12640 4.74 10006 9499 410 

Zring24_1 24 Preload: 2000 lb 34148 4.84 22704 32526 61 

Note: Unless otherwise mentioned under special provisions, the specimens were not preloaded, the blunt nose end 

conditions were fixed-fixed and clamps were used. 

4-5
It was furthermore observed through the preliminary tests that significant slack existed for the

multilayer Zylon samples. This can be verified through the analysis of the raw test data, which

indicated up to 2′′ of stroke travel under an insignificant amount of load (e.g., up to 250 lb). To 

relieve the slack, the specimens were pretensioned using an outward pressure applied at the

bottom portion of the ring. The pressure was applied by placing two steel spacer blocks between

the small arc of the ring and the spacer plate, and pushing the spacer plate outward by tightening 

the screws. Schematic diagrams of this setup are shown in figures 4-6a and 4-6b. This ensured 

some of the slack recovery. 

Data acq . System

Command signal generator

Feedback Signal

Error Signal

DIGITAL CONTROLLER

Personal Computer

Data Acquisition

System

Servo-Control valve

Command

Signal

Feedback

signal

specimen

load cell

FIGURE 4-6a. SCHEMATIC DIAGRAM OF THE TEST SETUP 

Steel Ring Fabric

Spacer plate

C-Clamp

Small arc

C-Clamp

FIGURE 4-6b. SCHEMATIC OF TEST SETUP WITH CLAMPS AND HINGES TO 

REMOVE SPURIOUS LOADS 

4-6
Even with the best-case efforts in ensuring that the test setup was exactly as discussed above, 

side loads were generated during the testing. The blunt nose assembly would start to tilt due to 

the hinge condition at the bottom of the blunt nose housing. To overcome this problem, a

revised housing (and blunt nose) was designed, as shown in figure 4-6c. This corresponds to the 

fixed-fixed end conditions shown in table 4-1. Additionally, a threaded rod was used in between

the blunt nose and the support plate to increase the length of the nose. 

FIGURE 4-6c. REVISED BLUNT NOSE HOUSING DESIGN 

(FIXED-FIXED CONDITIONS) 

4.4 TEST PROCEDURE.

Each sample was transferred from the wrapping mandrel to the test rig, then the side plates were 

attached. An MTS servo-hydraulic test machine with Digital Teststar2 controller software was

used for all the specimens. All the tests were conducted under actuator control using a constant 

rate of travel of 0.4 in./min. The test was conducted in a manner such that the load cell housing 

the blunt nose remained stationary throughout the test, while the actuator and, hence, the ring 

moved downward, thus loading the fabric against a stationary blunt nose. The data were 

collected using an automatic digital data acquisition system at a rate of 2 Hz. 

For certain specimens, the test was run in a single step and continued until failure occurred. For 

multilayer specimens (4-, 8-, 24-layer Kevlar and all Zylon), tests were performed in two steps. 

Since the maximum actuator travel length was limited to 4 inches, a readjustment of the position 

of the sample was necessary to extend the total displacement beyond the 4′′ expected in the 

multilayer and Zylon tests. During the first stage, the sample was loaded to 250 lb (see 

exceptions in table 4-1), and the test was placed on hold. At this point, the actuator was brought 

4-7
back to the zero position, while the crosshead was moved up to maintain the preload of the 

sample at 250 lb. At this point, the test was resumed and displacement was imposed until failure 

of the specimen. The adjustment of the crosshead was necessary to ensure enough travel was 

available for the sample to fail without causing any impact on the quality of the data obtained. 

4.5 TEST RESULTS.

The data collected by the test generated the load-deflection curve for each test. The various loaddeflection results are presented in table 4-1. 

Figure 4-7 shows the response of single-layer Kevlar specimens tested without clamps. Note 

that the initial region of the response curve indicates a gradual increase in the load-carrying

capacity. This is considered to be the region dominated by slack recovery (there is some 

deformation because of the straightening of the yarns) and gradual loading of the specimen to

reach the stiffness of the fabric being loaded in tension. Finally, the ultimate load was reached in 

these samples in an abrupt manner after several yarns fracture. The fracture of some yarns

before the peak load was observed as the sudden jump in the load response. The load carried by 

the fractured yarns was being transferred to unbroken yarns. It was expected that the load 

redistribution after the fracture of a few yarns results in an excess load on the surviving yarns.

This excess load was sufficient to push the average stress on the yarns beyond the average 

ultimate tensile strength. There was an insignificant amount of postpeak response observed in 

these samples. This was partly due to the fact that once the failure takes place, the frictional 

pullout force of the yarns was insignificant compared to the overall load-carrying capacity of the

member. For example, a maximum level of 26% postpeak strength was observed in sample 

Kring1_4. A limiting deformation value of 4′′ was used in all one-layer tests. 

0.0 1.0 2.0 3.0 4.0 5.0

Actuator Stroke, in

0

400

800

1200

1600

2000

Load, l

bs

Kring1_2

Kring1_3

Kring1_4

FIGURE 4-7. LOAD-DEFORMATION RESPONSE OF SINGLE-LAYER KEVLAR 

SPECIMENS PRIOR TO SLACK ADJUSTMENT 

4-8
Figure 4-8 shows the load versus actuator stroke response of all one-layer Kevlar specimens after 

slack adjustment. For the unclamped specimens, this was achieved by shifting the raw loaddeformation curves along the x axis so that the stiffnesses of the curves were coincident at the 

250-lb load level. For the clamped specimen (Kring1_5), the shift was such that the maximum 

stiffness of the specimen was coincident with the unclamped specimens. Examination of figure 

4-8 indicates that the stiffnesses of the samples are quite comparable. The average value of the 

stiffness for the single-layer specimens is 1108 lb/in., with a standard deviation of 50 lb/in. The 

ultimate loads for the hinged specimens, labeled Kring1_2, Kring1_3, and Kring1_4, are 1685,

1486, and 1522 lb respectively. This represents an average of 1564 lb and a standard deviation 

of 106 lb. 

0.0 1.0 2.0 3.0 4.0

Actuator Stroke, in

0

400

800

1200

1600

2000

Load, l

bs

Kring1_2

Kring1_3

Kring1_4

Kring1_5

FIGURE 4-8. LOAD-DEFORMATION RESPONSE OF SINGLE-LAYER KEVLAR 

SAMPLES AFTER SLACK ADJUSTMENT 

Note that after the slack adjustments (to equalize the zero to 1-inch actuator stroke), all the 

specimens follow the same slack recovery pattern. Specimen Kring1_5 represents the only 

specimen in this category that was clamped, and exhibits a knee in the early loading response. 

The clamped sample during the initial loading stages starts to pick up the load much earlier than

the unclamped samples, indicating a reduced level of slack. This knee in the load-deformation 

response indicates the role of clamps. Between the 200- and 300-lb load, there are indications of 

sliding and loss of gripping at the clamps. This is shown by the increasing displacements at 

relatively the same level of load, which may indicate the slippage of the fabric at the grips.

Beyond this level, the specimen behaved quite similar to the other unclamped specimens. Test

results showed that the knee behavior is less noticeable with multilayer specimens. 

4-9
Figure 4-9 shows a summary response plot for 1-, 2-, 4-, 8-, and 24-layer Kevlar specimens after

slack adjustment (0.65, 1, 0.8, 1.1, and 0.3 in. in the 1-, 2-, 4-, 8-, and 24-layer specimens

respectively). Although the peak load seems to scale proportional to the number of layers (up to 

eight layers), these responses may be viewed as highly nonlinear due to the progressive 

mechanism of failure that is operational in these specimens. It was observed that the two-layer 

specimen deviated from the one-layer curve at about 1000 lb, approximately 65% of the ultimate 

strength of a single layer. The four-layer specimen deviated from the two-layer specimen at

about 1400 lb, and the eight-layer deviated from the four-layer specimen at about 2000 lb. This

indicates that the contribution of outer layers to the stiffness of the overall assembly does not 

directly start at the beginning of the loading cycle. Significant displacement of the inner layers 

must take place before the outer layers are able to carry the load. This also indicated the 

importance of parameters such as the coefficient of friction between the layers, which is

responsible for the mechanical interlock and, thus, the transfer of load from one layer to another. 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

5000

10000

15000

20000

25000

30000

35000

Load, l

bs

1 Layer

2 Layers

4 Layers

8 Layers

24 Layers

FIGURE 4-9. LOAD-DEFORMATION RESPONSE OF 1-, 2-, 4-, 8-, AND 24-LAYER 

KEVLAR SAMPLES 

Figure 4-10 represents the response of 1-, 2-, 4-, 8-, and 24-layer Zylon samples after the slack 

adjustment (1, 0.47, 0.5, 0, and 0 in. in the 1-, 2-, 4-, 8-, and 24-layer specimens respectively). 

The amount of slack in these specimens was significant to the level of up to 3′′ of travel distance.

The use of clamps aided with the transfer of the load, as shown by the knee in the response; 

however, the stiffnesses of the material did not seem to be different during the early stages of 

loading. The one- and two-layer samples have almost the same stiffness up to the ultimate 

strength of the first layer. This indicates that the two-layer Zylon was not twice as stiff as the 

4-10
single-layer specimens, and the sample had to be loaded to a significantly high level of its single 

load-carrying level for the second and subsequent layers to participate in load sharing. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

5000

10000

15000

20000

25000

30000

35000

Load, l

bs

1 Layer

2 Layers

4 Layers

8 Layers

24 Layers

FIGURE 4-10. LOAD-DEFORMATION RESPONSE OF 1-, 2-, 4-, 8-, AND 

24-LAYER ZYLON SAMPLES 

Figures 4-11 and 4-12 show the energy absorbed/areal density and normalized energy 

absorbed/areal density graphs, respectively, for both the Kevlar and Zylon samples. The Zylon 

results showed more energy absorption capacity than the corresponding Kevlar specimens. The 

energy-absorbed graphs predict the fabric capacities as near linear in nature, but the normalized

energy absorbed capacity show that there is no consistency in the energy absorption capacity of 

the fabrics. Figure 4-13 shows the peak load versus the number of layers for Kevlar and Zylon, 

and figure 4-14 shows the peak load normalized by areal density of both Kevlar and Zylon. 

Figure 4-15 shows the stiffness versus the number of layers as well as linearly extrapolated 

stiffness values for Kevlar and Zylon. Figure 4-16 shows the same with the peak load value 

normalized with the areal density of the respective material.

4-11
0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

1.6x109

Ene

rgy abso

rbed /

a

r

e

al de

nsit

y

([l

b-i

n] / [l

b/in

2])

KEVLAR

ZYLON

FIGURE 4-11. ENERGY-ABSORBED/AREAL DENSITY GRAPHS OF 1-, 2-, 4-, 8-, AND 

24-LAYER KEVLAR AND ZYLON SAMPLES

0 4 8 12 16 20 2

No. of L

4

ayers

0x100

2x107

4x107

6x107

8x107

E

n

e

r

gy a

bso

r

b

e

d / a

r

e

al d

e

nsit

y / lay

e

r

([l

b-i

n] / [l

b/in2])

KEVLAR

ZYLON

FIGURE 4-12. ENERGY-ABSORBED/AREAL DENSITY GRAPHS OF 1-, 2-, 4-, 8-, AND 

24-LAYER KEVLAR AND ZYLON SAMPLES NORMALIZED BY NUMBER OF LAYERS 

4-12
0 4 8 12 16 20 24

No. of Layers

0

10000

20000

30000

40000

Pe

a

k L

o

a

d, l

bs

KEVLAR

ZYLON

FIGURE 4-13. NUMBER OF LAYERS VS PEAK LOAD FOR ALL TESTS 

0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

1.6x109

Pe

a

k Lo

a

d / a

r

e

al density, i

n2 (lbs/l

bs/in2

)

KEVLAR

ZYLON

FIGURE 4-14. NUMBER OF LAYERS VS NORMALIZED PEAK LOAD FOR ALL TESTS

4-13
0 5 10 15 20 25

No. of Layers

0

10000

20000

30000

Stiffn

ess, lbs/in

Kevlar - Static Test

Kevlar - 1 Layer Extrapolation

Zylon - Static Test

Zylon - 1 layer Extrapolation

FIGURE 4-15. NUMBER OF LAYERS VS STIFFNESS FOR ALL TESTS 

(ACTUAL AND LINEARLY EXTRAPOLATED) 

0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

1.6x109

Stiffn

ess /

a

r

e

al d

e

nsit

y, in (lbs/in / lbs/in

^

2)

Kevlar - Static Test

Kevlar - 1 Layer Extrapolation

Zylon - Static Test

Zylon - 1Layer Extrapolation

FIGURE 4-16. NUMBER OF LAYERS VS NORMALIZED STIFFNESS FOR ALL TESTS 

(ACTUAL AND LINEARLY EXTRAPOLATED) 

4-14
5. FINITE ELEMENT MODELING.

To develop and validate a numerical model of the two fabrics used in this research project, the 

FE method is used. The FE modeling of the fabrics and the static tests is discussed in this 

section along with the comparison of the FE response with those obtained experimentally, as

discussed in section 4. 

5.1 OBJECTIVES.

There are two major objectives. 

1. To develop a material model for Kevlar and Zylon fabrics using results from the simple 

tension tests, for use with FE analysis. 

2. To use the material model from objective 1. in the FE models of the static tests, and 

compare the FE results with the experimentally obtained values. The focus is on 

capturing the behavior of the fabrics up until the peak response. 

One can look at the Kevlar and Zylon fabrics as exhibiting orthotropic material behavior. The

material modeling starts with the strain-stress relationship expressed as 

ε =Sσ (5-1)

where is the vector of strains and is the vector of stress and the two areas related to 

each other via the following material matrix 

6 1 ε × σ 6×1





































































− −

− −

− −

× =

13

23

12

2 3

23

1

13

3

32

1 2

12

3

31

2

21

1

6 6

1 0 0 0 0 0

0 1 0 0 0 0

0 0 1 0 0 0

0 0 0 1

0 0 0 1

0 0 0 1

S

G

G

G

E E

v

E

v

E

v

E E

v

E

v

E

v

E

 (5-2) 

The modulus of elasticity, E , Poisson’s Ratio, ν , and shear modulus, G , are directionaldependent. Because of symmetry, there are a total of nine independent material constants:

1 2 3 12 23 13 12 E E, ,E G, ,G ,G , , ν ν 23 , and ν 13 . It should be noted that the material compliance matrix, 

S, is inverse of the material stiffness matrix, E. 

5-1
In the current study, a simplified approximation is made. The results from the simple tension 

tests are used to obtain the major modulus of elasticity value, , and the rest of the material

constants are suitably adjusted as explained later in this section. When the material behavior of 

orthotropic material is extended beyond the elastic regime, one needs to define the appropriate 

failure criterion. In the current study, (principal) strain is used to determine when the initial 

material failure takes place. The limiting value is obtained from the simple tension tests that

were discussed in section 2. 

E1

In the following sections, the FE models that are used to generate the various models have the

following characteristics.

1. The ABAQUS/Standard FE program [1] is used. 

2. The FE analysis involves static loads (load control), nonlinear stress-strain material 

behavior with smooth, finite sliding between the various contact surfaces, and uses large 

displacement theory. 

3. Linear solid elements (eight-noded hexahedral and four-noded tetrahedral elements) are 

used throughout the model. The use of ABAQUS/Standard [1] precludes the use of shell 

elements to model the fabrics. Contact definition between shell and solid elements is

difficult to capture in ABAQUS/Standard. The use of higher-order elements (20-noded 

hexahedral and 10-noded tetrahedral elements) is also not encouraged due to the 

underlying contact problem. Convergence studies using the developed model show that 

the linear elements are adequate in providing the required results. 

The following section explains how the user-defined material model is developed. The static test 

FE models are discussed in section 5.3. 

5.2 TENSION TEST MODELS.

A nonlinear stress-strain material behavior in the context of an FE analysis using ABAQUS 

requires a user-defined subroutine. The UMAT (user subroutine to define a material’s 

mechanical behavior) feature is used. The major features of this user subroutine [2] are as 

follows: 

1. It can be used to define the mechanical-constitutive behavior of a material. 

2. It can be used with any procedure that includes mechanical behavior. 

3. Solution-dependent state variables can be used. 

4. The subroutine must update the stresses and solution-dependent state variables to their 

values at the end of the increment for which it is called. 

5. The subroutine must provide the material Jacobian matrix, ∂∆σ ∂∆ε , for the 

mechanical-constitutive model. 

5-2
A piecewise linear approximation to the nonlinear stress-strain relationship obtained from the 

simple tension tests for Kevlar is shown in figure 5-1. The experimentally obtained curve 

(KTest1) is approximated by nine linear segments. Table 5-1 shows the limiting strain value in 

each segment and the corresponding modulus of elasticity. In the FE simulations, the strainsoftening zone is not implemented. The steep negative slope leads to convergence problems.

Beyond the peak, the slope of the stress-strain curve is taken as 1/10th of the largest slope. The

slope of the compressive stress-strain curve is also assumed to be the same as the postpeak 

tensile stress-strain curve. 

0.00 0.01 0.02 0.03 0.04 0.05

Strain, in/in

0

100000

200000

300000

400000

St

r

ess, psi

Static Test

L1

L2

L3

L4

L5

L6

L7

L8

Post Peak

FIGURE 5-1. USER-SUPPLIED PIECEWISE LINEAR STRESS-STRAIN CURVE 

FOR KEVLAR (KTest1) 

TABLE 5-1. PIECEWISE LINEAR KEVLAR STRESS-STRAIN DATA

Identification 

Limiting 

Strain Value

Slope, 

(psi) 

E

L1 0.0008 0.5354(106) 

L2 0.0017 0.6637(106) 

L3 0.0035 3.0000(106) 

L4 0.0061 6.0000(106) 

L5 0.0071 9.0000(106) 

L6 0.0291 1.0000(107) 

L7 0.0302 8.0000(106) 

L8 0.0307 1.0000(106) 

Postpeak > 0.0307 1.0000(106) 

5-3
Two piecewise linear approximations to the nonlinear stress-strain relationship obtained from the 

simple tension tests for Zylon are shown in figures 5-2a and 5-2b. The graphs represent results 

obtained from the two sets of grips (ZTest1:T1 and ZSwath1:T2). The experimentally obtained 

curves are approximated by five linear segments. Tables 5-2a and 5-2b show the limiting strain 

value in each segment and the corresponding modulus of elasticity that is the slope of the 

segment. 

0.00 0.02 0.04 0.06 0.08 0.10

Strain, in/in

0

100000

200000

300000

400000

500000

St

ress, psi

Static Test

L1

L2

L3

L4

Post Peak

FIGURE 5-2a. PIECEWISE LINEAR STRESS-STRAIN CURVE FOR ZYLON 

(ZTest1, GRIP T1) 

TABLE 5-2a. PIECEWISE LINEAR ZYLON STRESS-STRAIN DATA (T1) 

Identification 

Limiting 

Strain Value

Slope, 

(psi) 

E

L1 0.0282 1.2814(106) 

L2 0.0403 8.164686(106) 

L3 0.0480 5.841931(106) 

L4 0.0671 1.3277577(107) 

Post Peak > 0.0671 5.00000(105) 

In the FE simulations, the strain-softening zone is not implemented. The steep negative slope 

leads to convergence problems. Beyond the peak, the slope of the stress-strain curve is taken as 

a small fraction of the previous slope value. The slope of the compressive stress-strain curve is 

also assumed to be the same as the postpeak tensile stress-strain curve. 

5-4
0.00 0.02 0.04 0.06 0.08 0.10

Strain, in/in

0

100000

200000

300000

400000

500000

Stress, psi

Static Test

L1

L2

L3

L4

Post Peak

FIGURE 5-2b. PIECEWISE LINEAR STRESS-STRAIN CURVE FOR ZYLON 

(ZSwath1, GRIP T2) 

TABLE 5-2b. PIECEWISE LINEAR ZYLON STRESS-STRAIN DATA (T2) 

Identification 

Limiting 

Strain Value

Slope, 

(psi) 

E

L1 0.02429 3.11356 (105) 

L2 0.02957 3.495549 (106) 

L3 0.03208 1.159249 (107) 

L4 0.05413 1.743572 (107) 

Postpeak > 0.05413 5.00000 (105) 

To verify the user-developed material modeling subroutine for both Kevlar and Zylon, the 

displacement control approach was used in the FE analysis, and the results from the FE analysis 

matched the experimental values obtained from the simple tension tests up until the peak

response. 

In the absence of a more sophisticated procedure, the material values used in the material model 

are assumed as follows. The motivation was that the fabric in the static tests would primarily be

loaded in the (warp) direction; the direction used in the simple tension tests to generate the 

stress-strain diagram for the two fabrics. 

1. The in-plane tensile moduli are taken as . E E 1 2 = = E

2. The out-of-plane tensile modulus is taken as . 3 E E = 0.05

3. The in-plane shear modulus is taken as G . Similarly, the rest of the shear

moduli are also taken as G G . 

12 = 0.2

= 0.2E

E

13 = = 23 G12

5-5
4. All the Poisson’s ratios are considered to be negligible and are taken as 0.01 to avoid 

numerical problems. 

5.3 FINITE ELEMENT ANALYSIS OF STATIC TEST MODELS.

Because of the inherent symmetry (figure 5-3) of the geometry and the loading, the analysis is

performed on a quarter symmetry model. The static test FE model contains the following 

components: 

1. The A-36 steel cylinder—outer diameter 32 in., width 6 in. (z direction), and thickness 

1 in. The cylinder contains an opening or window that is in the circumferential direction. 

2. A cold-rolled steel blunt nose (or penetrator) dimensions are 2 by 8.5 by 5/16 in. The 

nose is constrained to move in radial direction, passes through the window in the 

cylinder, and pushes the fabric, thereby loading it. 

3. One concentric layer of finite elements representing the fabric (either Kevlar or Zylon) 

wrapped circumferentially around the cylinder. It should be noted that in the actual tests, 

the multilayer fabric assumes the shape of a spiral. The dimensions of the fabric

specimen that is modeled as a cylinder are as follows: 

• Radius = 16 in. 

• Thickness of each layer (Kevlar) = 0.003024 in. 

• Thickness of each layer (Zylon) = 0.00194532 in. 

• Width = 4 in. 

The steel cylinder and the blunt nose are modeled with elastic, isotropic material properties. 

• Modulus of elasticity = 29(106) psi 

• Poisson’s Ratio = 0.3 

FIGURE 5-3. GEOMETRIC MODEL SHOWING QUARTER MODEL OF THE 

STATIC TEST SETUP 

5-6
The fabric is modeled using the user-defined stress-strain relationship discussed in section 5-2. 

The FE mesh (figure 5-4) of the quarter symmetry model has 4909 nodes (14,727 degrees of

freedom), and 2255 elements. Linear hexahedral (eight-noded, fully integrated) elements were

used to mesh the cylinder, fabric strip, and the blunt nose. The region in the vicinity of the blunt 

nose tip and the window in the cylinder has a substantially higher grid density than the other

regions (figure 5-5). Convergence studies showed that the displacements had converged with the 

mesh density shown in the figures. 

FIGURE 5-4. FINITE ELEMENT MESH 

FIGURE 5-5. DETAILS OF THE FE MESH SHOWING THE BLUNT NOSE, 

STEEL CYLINDER, AND THE FABRIC 

5-7
The loads and boundary conditions applied during the experiment are replicated on the FE model 

(figures. 5-6a and 5-6b)—the line of nodes corresponding to the location of the clamps were

constrained from moving in all directions. In addition, the blunt nose is constrained to move in 

the radial (or 2) direction. The nodes at the bottom of the cylinder are also constrained from

moving in all directions. 

FIGURE 5-6a. BOUNDARY CONDITIONS IMPOSED ON THE BOTTOM OF THE 

STEEL CYLINDER AND AT THE POSITION OF THE CLAMPS

FIGURE 5-6b. BOUNDARY CONDITIONS IMPOSED AT THE BOTTOM OF 

THE BLUNT NOSE 

5-8
Two sets of contact surfaces are defined and used in the model. The first is between the fabric 

and the steel cylinder. The second is between the blunt nose and the fabric. A finite-sliding 

interaction, which is the most general and allows for arbitrary separation, sliding, and rotation of 

the participating surfaces, is assigned in both contact cases. The formulation is well-suited to 

geometrically nonlinear analysis. No friction between the contact surfaces is considered. 

The loading from the blunt nose is applied as uniformly distributed loading on the bottom of the

blunt nose. The loading is applied in increments to track and construct the load versus blunt nose 

tip displacement graph. 

In the following sections, the results from the FE analyses are presented and compared to the 

experimentally obtained values that contain an unknown amount of slack. As a result, the 

experimental load-deflection graphs are shifted horizontally so that the linear portion of the 

experimental and FE simulation graphs are close to each other. 

5.3.1 One-Layer Kevlar Model.

Figure 5-7 and table 5-3 show the comparison between the static test and the results obtained 

from the FE analysis (FEA). 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

400

800

1200

1600

2000

Lo

a

d, lbs

Kevlar - 1 Layer

Static Test

FEA

FIGURE 5-7. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR

A ONE-LAYER KEVLAR TEST 

5-9
TABLE 5-3. STATIC TEST—FEA COMPARISON FOR A ONE-LAYER KEVLAR TEST 

Static Test Kring1_5 FEA

Peak load (lb) 1571 1782 

Displacement at peak load (in.) 2.35 2.51 

The experimental curve was slack-shifted by 0.65′′. 

Observations for one-layer Kevlar simulation: 

1. Largest strain range (%) 

• Tensile 8 to 10 

• Compressive 2 to 6 

2. Reason for termination of the analysis 

• Overclosure of contact surfaces of the fabric and blunt nose, convergence judged 

unlikely. 

3. Strain ranges (%) 

• Near the blunt nose 6 to 10 

• Near the clamps 1.3 to 2.5 

• In between 1.3 to 2.5 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 299.7 

• Arc length of contact (in.) 83.7 

The FE and experimental peak load and displacement values are quite close. The FE loaddeflection graph follows the experimental graph very closely, except for the initial portion. The 

FE simulation overpredicts the peak load. This behavior occurs with some of the simulations

and is due to the fact that the finite elements where the ultimate strain has been exceeded are still 

a part of the FE model. Since these elements are not deleted, they still provide some finite 

stiffness to the overall response. However, it should be noted that these strain zones are very 

localized (see figures 5-8 and 5-9). 

5-10
FIGURE 5-8. ONE-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

1 ε

FIGURE 5-9. ONE-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

2 ε

5-11
5.3.2 Two-Layer Kevlar Model.

Figure 5-10 and table 5-4 show the comparison between the static test and the results obtained 

from the FEA. The two layers of Kevlar are modeled with one layer of finite elements with the

thickness twice that of one layer of Kevlar fabric. 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

1000

2000

3000

4000

Lo

a

d, l

bs

Kevlar - 2 Layers

Static Test

FEA

FIGURE 5-10. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A TWO-LAYER KEVLAR TEST 

TABLE 5-4. STATIC TEST—FEA COMPARISON FOR A TWO-LAYER KEVLAR TEST 

Static Test Kring2_1 FEA

Peak load (lb) 3360 3125 

Displacement at peak load (in.) 2.41 2.35 

The experimental curve was slack-shifted by 0.9′′. 

Observations for two-layer Kevlar simulation: 

1. Largest strain range (%) 

• Tensile 7.6 to 12.4 

• Compressive 0.8 to 2 

5-12
2. Reason for termination of the analysis 

• End of load steps, analysis completed successfully. 

3. Strain ranges (%) 

• Near the blunt nose 6.4 to 12.4 

• Near the clamps 1.6 to 2.7 

• In between 1.6 to 2.7 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 301.3 

• Arc length of contact (in.) 84.1 

Once again, the FE and experimental peak load and displacement values are quite close. As with

the one-layer model, the FE load-deflection graph follows the experimental graph very closely 

except for the initial portion. However, the FE simulation under predicts the peak load. This is 

because the FE model is inherently stiff. See figures 5-11 and 5-12. 

FIGURE 5-11. TWO-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

1 ε

5-13
FIGURE 5-12. TWO-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

2 ε

5.3.3 Four-Layer Kevlar Model.

Figure 5-13 and table 5-5 show the comparison between the static test and the results obtained 

from the FEA. The four layers of Kevlar are modeled as one layer of finite elements with the

thickness four times that of one layer of Kevlar fabric. 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

2000

4000

6000

8000

Lo

a

d, lbs

Kevlar - 4 Layers

Static Test

FEA

FIGURE 5-13. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A FOUR-LAYER KEVLAR TEST 

5-14
TABLE 5-5. STATIC TEST—FEA COMPARISON FOR A FOUR-LAYER KEVLAR TEST 

Static Test Kring4_1 FEA

Peak load (lb) 6624 5875 

Displacement at peak load (in.) 2.41 2.29 

The experimental curve was slack-shifted by 0.8′′. 

Observations for Kevlar four-layer simulation: 

1. Largest strain range (%) 

• Tensile 8 to 15 

• Compressive 0.7 to 2.1 

2. Reason for termination of the analysis 

• Overclosure of contact surfaces of the fabric and nose, convergence judged 

unlikely. 

3. Strain ranges (%) 

• Near the blunt nose 4 to 15 

• Near the clamps 0.7 to 0.73 

• In between 0.7 to 0.73 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 302 

• Arc length of contact (in.) 84.3 

The four-layer model follows the trends exhibited with the one- and two-layer models. The FE 

and experimental peak load and displacement values are quite close. The FE load-deflection

graph follows the experimental graph very closely, including the initial portion of the

experimental graph where there is less of a knee. The FE simulation underpredicts the peak load. 

See figures 5-14 and 5-15. 

5-15
FIGURE 5-14. FOUR-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

1 ε

FIGURE 5-15. FOUR-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

2 ε

5-16
5.3.4 Eight-Layer Kevlar Model.

Figure 5-16 and table 5-6 show the comparison between the static test and the results obtained 

from the FE analysis. The eight layers of Kevlar are modeled as one layer of finite elements

with the thickness eight times that of one layer of Kevlar fabric. 

0.00 1.00 2.00 3.00

Actuator Stroke, in

0

4000

8000

12000

16000

Load, l

bs

Kevlar - 8 Layers

Static Test

FEA

FIGURE 5-16. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

AN EIGHT-LAYER KEVLAR TEST 

TABLE 5-6. STATIC TEST—FEA COMPARISON FOR AN EIGHT-LAYER 

KEVLAR TEST 

Static Test Kring8_1 FEA

Peak load (lb) 13231 11375 

Displacement at peak load (in.) 2.52 2.28 

The experimental curve was slack-shifted by 1.1′′. 

Observations for eight-layer Kevlar simulation: 

1. Largest strain range (%) 

• Tensile 4 to 18 

• Compressive 1.5 to 3 

5-17
2. Reason for termination of the analysis 

• Overclosure of contact surfaces of the fabric and nose, convergence judged 

unlikely. 

3. Strain ranges (%) 

• Near the blunt nose 2 to 18 

• Near the clamps 0.3 to2 

• In between 0.3 to 2 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 302.2 

• Arc length of contact (in.) 84.4 

The eight-layer model follows the previous trends exhibited with the one-, two- and four-layer

models. The FE and experimental peak load and displacement values are quite close. As with

the four-layer model, the FE load-deflection graph follows the experimental graph very closely, 

including the initial portion of the experimental graph where there is less of a knee. The FE 

simulation underpredicts the peak load. It appears that not only the required amount of slack 

adjustment to bring the two graphs close to each other increases with the number of fabric layers, 

but also that there is less of a discrepancy between the two curves in the initial portion of the 

graph. See figures 5-17 and 5-18. 

FIGURE 5-17. EIGHT-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

1 ε

5-18
FIGURE 5-18. EIGHT-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

2 ε

5.3.5 Twenty-Four-Layer Kevlar Model.

Figure 5-19 and table 5-7 show the comparison between the static test and the results obtained 

from the FEA. The twenty-four layers of Kevlar are modeled as three layers of finite elements 

with the thickness of each layer eight times that of one layer of Kevlar fabric. 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

10000

20000

30000

40000

Load, l

bs

Kevlar - 24 Layers

Static Test

FEA

FIGURE 5-19. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A 24-LAYER KEVLAR TEST 

5-19
TABLE 5-7. STATIC TEST—FEA COMPARISON FOR A 24-LAYER KEVLAR TEST 

Static Test Kring24_2 FEA

Peak load (lb) 31131 31875 

Displacement at peak load (in.) 3.04 2.28 

The experimental curve was slack-shifted by 0.3′′. 

Observations for 24-layer Kevlar simulation: 

1. Largest strain range (%) 

• Tensile 7 to 21 

• Compressive 0.4 to 4 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, and the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 3 to 21 

• Near the clamps 3.2 to 6.8 

• In between 3.2 to 6.8 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 302.1 

• Arc length of contact (in.) 84.4 

The 24-layer model follows some of the previous trends exhibited with the one-, two-, four-, and 

eight-layer models. The FE and experimental load and displacement values are quite close till 

about 15,000 lb. While the peak loads are close, the FE peak displacement is much less than the 

experimentally obtained value. Since the FE is much stiffer in this case, the FE results show that 

a larger value of load is needed to achieve the same level of deformation. The amount of slack 

adjustment to bring the two graphs close to each other is much less in this case, since in the

experimental setup, the fabric was directly wrapped on the steel ring. See figures 5-20 and 5-21. 

5-20
FIGURE 5-20. TWENTY-FOUR-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

1 ε

FIGURE 5-21. TWENTY-FOUR-LAYER KEVLAR—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST LOAD STEP 

2 ε

5-21
5.3.6 One-Layer Zylon Model.

Figure 5-22 and table 5-8 show the comparison between the static test and the results obtained 

from the FEA. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

400

800

1200

1600

2000

Load, l

bs

Zylon - 1 Layer

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-22. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A ONE-LAYER ZYLON TEST 

TABLE 5-8. STATIC TEST—FEA COMPARISON FOR A ONE-LAYER ZYLON TEST 

Static Test Zring1_2 Grip T1 FEA Grip T2 FEA 

Peak load (lb) 1730 1344 1500 

Displacement at peak load (in.) 3.69 3.59 3.31 

The experimental curve was slack-shifted by 1′′. 

Observations for one-layer Zylon simulation: 

Grip T1 FEA model: 

1. Largest strain range (%) 

• Tensile 7 to 30 

• Compressive 0 to 0.4 

5-22
2. Reason for termination of the analysis 

• End of load steps, analysis completed successfully. 

3. Strain ranges (%) 

• Near the blunt nose 6.7 to 30 

• Near the clamps 6.7 to 9.3 

• In between 6.7 to 9.3 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 289.5 

• Arc Length of contact (in.) 80.9 

Grip T2 FEA model: 

1. Largest strain range (%) 

• Tensile 7 to 12 

• Compressive 0 to 0.4 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 4 to 12 

• Near the clamps 0.6 to 3 

• In between 3 to 6 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 291.5 

• Arc length of contact (in.) 81.5 

The FE and experimental peak load and displacement values as well as the load-deflection 

graphs are quite close for Grip T1 model. Both the FE simulations underpredict the peak load. 

Once again, this is because the FE model is inherently stiff. The fabric-draping effect is much 

more pronounced with these models when compared to the Kevlar models. Figures 5-23 and 

5-24 show FEA results of Grip T1. Figures 5-25 and 5-26 show FEA results of Grip T2. 

5-23
FIGURE 5-23. ONE-LAYER ZYLON—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T1) 

1 ε

FIGURE 5-24. ONE-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T1) 

5-24
FIGURE 5-25. ONE-LAYER ZYLON—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T2) 

1 ε

FIGURE 5-26. ONE-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T2) 

5-25
5.3.7 Two-Layer Zylon Model.

Figure 5-27 and table 5-9 show the comparison between the static test and the results obtained 

from the FEA. The two layers of Zylon are modeled as one layer of finite elements with the 

thickness twice that of one layer of Zylon fabric. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

1000

2000

3000

4000

Load, l

bs

Zylon - 2 Layers

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-27. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A TWO-LAYER ZYLON TEST 

TABLE 5-9. STATIC TEST—FEA COMPARISON FOR A TWO-LAYER ZYLON TEST 

Static Test Zring2_1 Grip T1 FEA Grip T2 FEA 

Peak load (lb) 3408 3125 2813 

Displacement at peak load (in.) 4.00 3.92 3.33 

The experimental curve was slack-shifted by 0.47′′. 

Observations for two-layer Zylon simulation: 

Grip T1 FEA model: 

1. Largest strain range (%) 

• Tensile 12 to 25 

• Compressive 0.03 to 0.6 

5-26
2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 8 to 24 

• Near the clamps 6 to 8 

• In between 6 to 8 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 286.9 

• Arc length of contact (in.) 80.1 

Grip T2 FEA model: 

1. Largest strain range (%) 

• Tensile 9 to 16 

• Compressive 0 to 0.6 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 5 to 16 

• Near the clamps 2.2 to 5 

• In between 3.7 to 5 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 291.8 

• Arc length of contact (in.) 81.5 

Once again, the FE and experimental peak load and displacement values are quite close with the

Grip T1 model. The Grip T2 model is stiffer. Less slack adjustment is required to match the 

initial linear slopes of the experimental and the FE graphs compared to the corresponding Kevlar 

models. Figures 5-28 and 5-29 show FEA with Grip T1. Figures 5-30 and 5-31 show FEA with 

Grip T2. 

5-27
FIGURE 5-28. TWO-LAYER ZYLON—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T1) 

1 ε

FIGURE 5-29. TWO-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T1) 

5-28
FIGURE 5-30. TWO-LAYER ZYLON—PLOT OF IN-PLANE STRAIN SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T2) 

1 ε

FIGURE 5-31. TWO-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε SUPERIMPOSED 

ON DEFORMATION AT THE END OF THE LAST LOAD STEP (GRIP T2) 

5-29
5.3.8 Four-Layer Zylon Model.

Figure 5-32 and table 5-10 shows the comparison between the static test and the results obtained

from the FEA. The four layers of Zylon are modeled as one layer of finite elements with the 

thickness four times that of one layer of Zylon fabric. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

2000

4000

6000

8000

Lo

a

ds, lbs

Zylon - 4 Layers

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-32. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A FOUR-LAYER ZYLON TEST 

TABLE 5-10. STATIC TEST—FEA COMPARISON FOR A FOUR-LAYER ZYLON TEST

Static Test Zring4_2 Grip T1 FEA Grip T2 FEA 

Peak load (lb) 7363 6563 5938 

Displacement at peak load (in.) 3.88 3.85 3.31 

The experimental curve was slack-shifted by 0.50′′. 

Observations for four-layer Zylon simulation: 

Grip T1 FEA model: 

1. Largest strain range (%) 

• Tensile 9 to 33 

• Compressive 0 to 1.8 

5-30
2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 7 to 33 

• Near the clamps 7 to 10 

• In between 7 to 10 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 287.5 

• Arc length of contact (in.) 80.3 

Grip T2 FEA model: 

1. Largest strain range (%) 

• Tensile 8 to 30 

• Compressive 0.004 to 3 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge, and there are distorted elements near the blunt nose. 

3. Strain ranges (%) 

• Near the blunt nose 5 to 30 

• Near the clamps 3 to 5 

• In between 3 to 5 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 291.7 

• Arc length of contact (in.) 81.5 

The trends observed with the one- and two-layer models continue. The FE and experimental

peak load and displacement values are quite close with the Grip T1 model. The Grip T2 model 

is stiffer. Once again, there is less slack adjustment that is required to match the initial linear

slopes of the experimental and the FE graphs compared to the corresponding Kevlar models.

Figures 5-33 and 5-34 show FEA with Grip T1. Figures 5-35 and 5-36 show FEA with Grip T2. 

5-31
FIGURE 5-33. FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T1) 

1 ε

FIGURE 5-34. FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T1) 

2 ε

5-32
FIGURE 5-35. FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

1 ε

FIGURE 5-36. FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

5-33
5.3.9 Eight-Layer Zylon Model.

Figure 5-37 and table 5-11 show the comparison between the static test and the results obtained 

from the FEA. The eight layers of Zylon are modeled as one layer of finite elements with the

thickness eight times that of one layer of Zylon fabric. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

4000

8000

12000

16000

Loads, lbs

Zylon - 8 Layers

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-37. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

AN EIGHT-LAYER ZYLON TEST

TABLE 5-11. STATIC TEST—FEA COMPARISON FOR AN EIGHT-LAYER 

ZYLON TEST 

Static Test Zring8_2 Grip T1 FEA Grip T2 FEA 

Peak load (lb) 13290 13250 11000 

Displacement at peak load (in.) 3.72 3.84 3.26 

The experimental curve was slack-shifted by 0.84′′. 

Observations for eight-layer Zylon simulation: 

Grip T1 FEA model: 

1. Largest strain range (%) 

• Tensile 10 to 35 

• Compressive 0 to 2.3 

5-34
2. Reason for termination of the analysis 

• End of load steps, analysis completed successfully. 

3. Strain ranges (%) 

• Near the blunt nose 7 to 35 

• Near the clamps 7 to 10 

• In between 7 to 10 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 287.5 

• Arc length of contact (in.) 80.3 

Grip T2 FEA model: 

1. Largest strain range (%) 

• Tensile 9 to 20 

• Compressive 1.5 to 2 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge. 

3. Strain ranges (%) 

• Near the blunt nose 5 to 20 

• Near the clamps 2 to 5 

• In between 3.5 to 5.5 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 292.3 

• Arc length of contact (in.) 81.6 

The trends observed with the one-, two-, and four-layer models continue. The FE and 

experimental peak load and displacement values are quite close with the Grip T1 model. The 

Grip T2 model is stiffer. Figures 5-38 and 5-39 show FEA with Grip T1. Figures 5-40 and 5-41 

show FEA with Grip T2. 

5-35
FIGURE 5-38. EIGHT-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T1) 

1 ε

FIGURE 5-39. EIGHT-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T1) 

5-36
FIGURE 5-40. EIGHT-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

1 ε

FIGURE 5-41. EIGHT-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

5-37
5.3.10 Twenty-Four-Layer Zylon Model.

Figure 5-42 and table 5-12 show the comparison between the static test and the results obtained 

from the FEA. The twenty-four layers of Zylon are modeled with three layers of finite elements 

with the thickness of each layer being eight times that of one layer of Zylon fabric. The 

experimental curve was slack-shifted by 0.2′′. Both Grip T1 and Grip T2 FEA underpredicted 

the peak load. This was because of the limitations of the nonlinear FEA that is discussed at the 

end of this section. See figures 5-43 through 5-46. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

10000

20000

30000

40000

Loads, lbs

Zylon - 24 Layers

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-42. COMPARISON OF THE LOAD-DISPLACEMENT GRAPHS FOR 

A 24-LAYER ZYLON TEST 

TABLE 5-12. STATIC TEST—FEA COMPARISON FOR A 24-LAYER ZYLON TEST 

Static Test Zring24_1 Grip T1 FEA Grip T2 FEA 

Peak load (lb) 34149 21250 31875 

Displacement at peak load (in.) 4.64 4.03 4.17 

5-38
FIGURE 5-43. TWENTY-FOUR-LAYER-ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T1) 

1 ε

FIGURE 5-44. TWENTY-FOUR-LAYER-ZYLON—PLOT OF IN-PLANE STRAIN 2 ε

SUPERIMPOSED ON DEFORMATION AT THE END OF THE 

LAST LOAD STEP (GRIP T1) 

5-39
FIGURE 5-45. TWENTY-FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

1 ε

FIGURE 5-46. TWENTY-FOUR-LAYER ZYLON—PLOT OF IN-PLANE STRAIN 2 ε

SUPERIMPOSED ON DEFORMATION AT THE END OF THE LAST 

LOAD STEP (GRIP T2) 

5-40
Observations for 24-layer Zylon simulation: 

Grip T1 FEA model:

1. Largest strain range (%) 

• Tensile 16 to 20 

• Compressive 1.5 to 4.4 

2. Reason for termination of the analysis 

• Overclosure of contact surfaces, convergence judged unlikely. 

3. Strain ranges (%) 

• Near the blunt nose 7 to 20 

• Near the clamps 6 to 7 

• In between 6 to 7 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 286 

• Arc length of contact (in.) 79.9 

Grip T2 FEA model: 

1. Largest strain range (%) 

• Tensile 14 to 30 

• Compressive 0 to 3 

2. Reason for termination of the analysis 

• Negative eigenvalues appear at the end of the load step, the solution starts to

diverge, and distorted elements occur near the blunt nose. 

3. Strain ranges (%) 

• Near the blunt nose 6 to 30 

• Near the clamps 6 to 10 

• In between 6 to 10 

4. Contact between the fabric and the ring at the end of the simulation 

• Angle of contact (°) 285 

• Arc length of contact (in.) 79.6 

5-41
For all the Kevlar and Zylon simulations, the following observations were made. 

1. The maximum tensile strain in the fabric occurs at the area in contact with the edge of the 

blunt nose. This is consistent with the failure mode that is observed (during the static 

tests) to initiate at and around the blunt nose contact region. The strain gradient is very 

high near the edges of the blunt nose and decreases very rapidly away from the blunt 

nose. Strain values greater than the ultimate strain value are found in all the FE 

simulations. This is because finite elements are not deleted when the ultimate strain

values are exceeded. However, this high strain zone is very localized. 

2. The highest compressive strains occur in the fabric at (a) the end diametrically opposite 

to the blunt nose and (b) at the edge of the fabric near the blunt nose. These compressive 

strains are prominent only after the postpeak stiffness value was reached. A fabricdraping effect is seen in the deformed plot that is more prominent with Zylon specimens 

than with Kevlar specimens. 

3. The FE load-displacement curves track the experimentally obtained curve quite nicely, up 

until the peak load. In the case of Zylon, the stress-strain curve from the T1 test performs

better than the T2-generated curve. When the multiple-layer results are compared to the 

FE-obtained curves, the FE results indicate a stiffer model or behavior. This is probably 

because, in the FEA, only one equivalent fabric layer is modeled. 

4. Termination of the FEA takes place when the (a) solution starts diverging due to the 

presence of negative eigenvalues in the system stiffness matrix (matrix is not positive 

definite) or (b) contact surface between the fabric and the blunt nose cannot be resolved 

at large displacement values. 

5.4 ENERGY ABSORPTION COMPARISONS.

The energy absorption data obtained from the analysis of static tests and FE simulation are 

tabulated in table 5-13. It should be noted that the energy-absorbed values only represent the 

load-deflection curve until the peak load, as the simulation cannot be carried beyond the peak

load. 

5-42
TABLE 5-13. SUMMARY OF ENERGY ABSORPTION DATA (PREPEAK) FOR

STATIC TEST AND FE SIMULATIONS 

Energy-Absorbed Data (lb-in.) 

Specimen No. of Layers Static Test FEA Simulation 

Kevlar 17x17 1 1260 1227 

2 2371 1992

4 4503 3611

8 9907 6877

24 37434 19548

Zylon 35x35 Grip T1 Grip T2 

1 1323 1048 574

2 2906 2520 1039

4 6105 5577 2250

8 9499 11178 3954

24 32526 24390 14120

The differences in the energy absorption values are mainly due to (1) premature termination of 

the FEA before the peak load value is reached and (2) the FE model being inherently stiffer.

Figures 5-47 to 5-52 show the comparison of the energy-absorbed values of static tests and the 

simulations.

0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

E

ner

g

y

A

bsorbed (lb-in) / areal density per la

yer (lb/in2

)

Static Test

FEA

FIGURE 5-47. ENERGY-ABSORBED/AREAL DENSITY GRAPHS FOR 1-, 2-, 4-, 8-, AND 

24-LAYER KEVLAR SAMPLES 

5-43
0 5 10 15 20 25

No. of Layers

0.0x100

2.0x107

4.0x107

6.0x107

E

nerg

y a

bsorbed (lb-in) / are

al density (l

b/in2) / No

of layers

Static Test

FEA

FIGURE 5-48. ENERGY-ABSORBED/AREAL DENSITY GRAPHS OF 1-, 2-, 4-, 8-, AND 

24-LAYER KEVLAR NORMALIZED BY THE NUMBER OF LAYERS 

0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

1.6x109

E

nerg

y

A

bsorbed (lb-in) / areal densit

y per la

yer (lb/in2

)

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-49. ENERGY-ABSORBED/AREAL DENSITY GRAPHS FOR 1-, 2-, 4-, 8-, AND 

24-LAYER ZYLON SAMPLES 

5-44
0 5 10 15 20 25

No. of Layers

0.0x100

4.0x107

8.0x107

1.2x108

E

nergy 

a

bsorbed (lb-in) / areal

density (lb/in2

) / No of layers

Static Test

Grip T1 FEA

Grip T2 FEA

FIGURE 5-50. ENERGY-ABSORBED/AREAL DENSITY GRAPHS OF 1-, 2-, 4-, 8-, AND 

24-LAYER ZYLON NORMALIZED BY THE NUMBER OF LAYERS

0 5 10 15 20 25

No. of Layers

0.0x100

4.0x108

8.0x108

1.2x109

1.6x109

E

nerg

y A

bsorbed (lb-in) / areal densit

y per la

yer (lb/in2

)

Zylon Static Test

Zylon Grip T1 FEA

Zylon Grip T2 FEA

Kevlar Static Test

Kevlar FEA

FIGURE 5-51. ENERGY-ABSORBED/AREAL DENSITY GRAPHS FOR ALL KEVLAR 

AND ZYLON SAMPLES 

5-45
0 5 10 15 20 25

No. of Layers

0.0x100

4.0x107

8.0x107

1.2x108

E

nerg

y a

bsorbed (lb-in) / areal densit

y (lb/in2) / No of layers

Zylon Static Test

Zylon Grip T1 FEA

Zylon Grip T2 FEA

Kevlar Static Test

Kevlar FEA

FIGURE 5-52. ENERGY-ABSORBED/AREAL DENSITY GRAPHS FOR ALL KEVLAR 

AND ZYLON SAMPLES NORMALIZED BY THE NUMBER OF LAYERS 

The following deficiencies exist in the FE modeling and simulations. 

1. The material model is essentially driven by the results from simple tension tests. The 

modulus of elasticity along the principal material direction was obtained from the tests, 

and all the other material constants were adjusted based on this value. Tests could be 

conducted to obtain additional material constants. This approach can then be combined 

with more sophisticated analytical/numerical approaches in constructing the material 

model for different weaves and ply counts without resorting to expensive testing 

procedures. Bridging the gap between the microfabric model and the macrofabric model

suitable for use in an FEA was a challenge. 

2. The FEA does not account for damage accumulation and progressive failure. It would be 

desirable to delete elements from the model that represent broken yarns. This may 

explain why some of the FE results overpredicted the strength of the test specimen. 

3. Dry fabrics do not have any appreciable compressive strength. However, the compressive 

behavior was taken to be similar to the last linear segment tensile behavior. 

4. The FE results for the 8 and 24 layers indicated that the FE model is stiffer than the

experiments. This was to be expected, since FE models are inherently stiff to begin with. 

Modeling changes could be made to improve the results such as using a finer mesh, etc. 

While the results obtained in this research program were extremely encouraging, further 

improvements to the FE modeling are recommended. 

5-46
6. CONCLUSIONS.

The simple tension tests were performed on a number of Kevlar and Zylon fabrics to

determine the stress-strain relationship in the principal material direction. Response of fabrics to 

adhesion was determined in the splice tests. It was found that adhesion was a problem especially 

for Zylon. Hence, it was decided to clamp the fabric specimens to the steel ring in the static ring

tests. These tests facilitated an understanding of the performance in terms of strength, stiffness, 

and energy absorption capacity for Kevlar and Zylon in terms of single- and multiple-layers of

fabrics. User-defined materially nonlinear, large displacement, multiple-contact surface finite 

element analyses were carried out in ABAQUS to compare the finite element simulation results 

with those obtained experimentally. 

The finite element modeling and the results are extremely encouraging. This is the first time 

large-scale experimental results (mimicking the use of dry fabrics in engine containment

systems) have been compared to results obtained from a finite element analysis. However, as

noted earlier in the report, there is a need for improvements both in the experiments and the finite 

element simulations. 

6-1/6-2
7. REFERENCES.

1. ABAQUS, INC., ABAQUS Version 6.2, Providence, R.I., 2002. 

2. ABAQUS, INC., ABAQUS/Standard User Manual, Volume III, Providence, RI, 2002. 

7-1/7-2
APPENDIX A—STATIC TEST RESULTS

Additional graphs (load-deflection curves) and pictures of the specimens after the tests are 

shown in figuresA-1 through A-30. 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

200

400

600

800

1000

1200

1400

1600

Load, l

bs

Kring1_5

1571 lbs

FIGURE A-1. LOAD DEFORMATION RESPONSE OF A ONE-LAYER

KEVLAR SAMPLE 

FIGURE A-2. FAILURE AROUND THE BLUNT NOSE CONTACT POINT, PARTIAL 

PENETRATION OF NOSE AT TOP (Kring1_5) 

A-1
FIGURE A-3. REMOTE FAILURE AT THE CLAMP POSITION (Kring1_5) 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

500

1000

1500

2000

2500

3000

3500

Load, lbs

Kring2_1

3429 lbs

FIGURE A-4. LOAD DEFORMATION RESPONSE OF A TWO-LAYER 

KEVLAR SAMPLE 

A-2
FIGURE A-5. FAILURE AROUND THE BLUNT NOSE CONTACT POINT, PARTIAL 

PENETRATION OF NOSE AT THE TOP (Kring2_1) 

FIGURE A-6. REMOTE FAILURE AT CLAMP POSITION (Kring2_1) 

A-3
0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

1000

2000

3000

4000

5000

6000

7000

Load, lbs

Kring4_1

6625 lbs

FIGURE A-7. LOAD DEFORMATION RESPONSE OF A FOUR-LAYER 

KEVLAR SAMPLE 

FIGURE A-8. FAILURE AROUND THE BLUNT NOSE CONTACT POINT, PARTIAL 

PENETRATION OF NOSE AT THE TOP (Kring4_1) 

A-4
FIGURE A-9. REMOTE FAILURE AT CLAMP POSITION (Kring4_1) 

0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

4000

8000

12000

16000

Load, lbs

Kring8_1

13231 lbs

FIGURE A-10. LOAD DEFORMATION RESPONSE OF AN EIGHT-LAYER 

KEVLAR SAMPLE 

A-5
FIGURE A-11. FAILURE AROUND THE BLUNT NOSE CONTACT POINT, PARTIAL 

PENETRATION OF NOSE AT THE TOP (Kring8_1) 

FIGURE A-12. REMOTE FAILURE AT CLAMP POSITION (Kring8_1) 

A-6
0.00 1.00 2.00 3.00 4.00

Actuator Stroke, in

0

10000

20000

30000

40000

Load, l

bs

Kring24_2

31131 lbs

FIGURE A-13. LOAD DEFORMATION RESPONSE OF A 24-LAYER KEVLAR SAMPLE 

FIGURE A-14. FAILURE AROUND THE BLUNT NOSE CONTACT POINT PARTIAL 

PENETRATION OF NOSE AT THE TOP (Kring24_2) 

A-7
FIGURE A-15. REMOTE FAILURE AT CLAMP POSITION (Kring24_2) 

Zring1_2

1730 lbs

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Actuator Stroke, in

0

400

800

1200

1600

2000

Load, l

bs

FIGURE A-16. LOAD DEFORMATION RESPONSE OF A ONE-LAYER 

ZYLON SAMPLE 

A-8
FIGURE A-17. COMPLETE NOSE PENETRATION (Zring1_2) 

FIGURE A-18. YARN PULLOUT ALONG THE CIRCUMFERENCE AT THE EDGE OF 

THE NOSE (Zring1_2) 

A-9
0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

1000

2000

3000

4000

Load, l

bs

Zring2_1

3408 lbs

FIGURE A-19. LOAD DEFORMATION RESPONSE OF A TWO-LAYER 

ZYLON SAMPLE 

FIGURE A-20. COMPLETE NOSE PENETRATION (Zring2_1) 

A-10
FIGURE A-21. OVERLAP PEEL-OFF (Zring2_1) 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

2000

4000

6000

8000

Load, l

bs

Zring4_2

7363 lbs

FIGURE A-22. LOAD DEFORMATION RESPONSE OF A FOUR-LAYER 

ZYLON SAMPLE 

A-11
FIGURE A-23. COMPLETE NOSE PENETRATION (Zring4_2) 

FIGURE A-24. OVERLAP PEEL-OFF (Zring4_2) 

A-12
0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

4000

8000

12000

16000

Load, l

bs

Zring8_3

12640 lbs

FIGURE A-25. LOAD DEFORMATION RESPONSE OF AN EIGHT-LAYER 

ZYLON SAMPLE 

FIGURE A-26. COMPLETE NOSE PENETRATION (Zring8_3) 

A-13
FIGURE A-27. FORMATION OF 2′′ WIDE BAND VISIBLE ALONG THE EDGE OF THE 

NOSE THROUGHOUT THE CIRCUMFERENCE (Zring8_3) 

0.00 1.00 2.00 3.00 4.00 5.00

Actuator Stroke, in

0

10000

20000

30000

40000

Lo

a

d, l

bs

Zring24_1

34148 lbs

FIGURE A-28. LOAD DEFORMATION RESPONSE OF A 24-LAYER ZYLON SAMPLE 

A-14
FIGURE A-29. COMPLETE NOSE PENETRATION (Zring24_1) 

FIGURE A-30. FORMATION OF 2′′ WIDE BAND VISIBLE ALONG THE EDGE OF THE 

NOSE THROUGHOUT THE CIRCUMFERENCE (Zring24_1) 

A-15/A-16