DOT/FAA/AR-95/109 Comparative Evaluation of Failure ...

DOT/FAA/AR-95/109

Office of Aviation Research Washington, D.C. 20591

Comparative Evaluation of Failure Analysis Methods for Composite Laminates

May 1996 Final Report

This document is available to the U.S. public through the National Technical Information Service, 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: tc.its/act141/reportpage.html in Adobe Acrobat portable document format (PDF).

Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-95/109

4. Title and Subtitle

2. Government Accession No.

COMPARATIVE EVALUATION OF FAILURE ANALYSIS METHODS FOR COMPOSITE LAMINATES

3. Recipient's Catalog No.

5. Report Date

May 1996

6. Performing Organization Code

7. Author(s)

C.T. Sun, B.J. Quinn, J. Tao, Purdue University, D.W. Oplinger, William J. Hughes Technical Center

8. Performing Organization Report No.

9. Performing Organization Name and Address

School of Aeronautics and Astronautics Purdue University West Lafayette, IN 47907-1282

12. Sponsoring Agency Name and Address

U.S. Department of Transportation Federal Aviation Administration Office of Aviation Research Washington, D.C. 20591

15. Supplementary Notes

Analysis performed and report prepared by: Galaxy Scientific Corporation 2500 English Creek Ave., Building 11 Egg Harbor Township, NJ 08234-5562

10. Work Unit No. (TRAIS) 11. Contract or Grant No.

13. Type of Report and Period Covered

Final Report

14. Sponsoring Agency Code

AAR-431

FAA COTR: Donald Oplinger

16. Abstract

Over the last three decades, there have been continuous efforts in developing failure criteria for unidirectional fiber composites and their laminates. Currently, there exist a large number of lamina failure criteria and laminate failure analysis methods. In this project, a comprehensive and objective study of lamina and laminate failure criteria was performed. Comparisons among the commonly used failure criteria were made for failure in unidirectional composites under various loading cases. From these comparisons, the characteristics of these criteria were identified and discussed. Further, with the aid of some limited experimental lamina and laminate strength data available in the literature and new data generated by the authors, an attempt was made to select the failure criteria and laminate analysis methods that are mechanistically sound and are capable of accurately predicting lamina and laminate strengths for states of combined stresses. It was found that those lamina failure criteria which separate fiber and matrix failure modes most accurately predict lamina and laminate strength.

17. Key Words

Fiber composites, Strength Failure rules, Failure analysis

19. Security Classif. (of this report)

Unclassified Form DOT F1700.7 (8-72)

18. Distribution Statement

This document is available to the public through the National Technical Information Service (NTIS), Springfield, Virginia 22161.

20. Security Classif. (of this page)

21. No. of Pages

22. Price

Unclassified

132

Reproduction of completed page authorized

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1. INTRODUCTION

2. LAMINA FAILURE ANALYSIS

2.1 Lamina Failure Criteria

2.2 Comparison among Lamina Failure Criteria

2.2.1 Bidirectional Stress Plane

2.2.2 Off-Axis Loading

2.2.3 Pure Shear

2.3 Comparison with Experimental Data

2.3.1 Lamina Failure Criteria Comparison With Off-Axis Tension Data 2.3.2 Lamina Failure Criteria Comparison with Tubular Specimens

2.4 Analysis of the Physical Basis for Lamina Failure Criteria

2.4.1 Fiber Failure 2.4.2 Matrix Failure 2.4.3 Generation of Failure Envelopes in the Stress Planes 2.4.4 On the Maximum Strain Criterion 2.4.5 Dependence of Shear Strength on Compressive Normal Stress 22 2.4.6 Concluding Observations on Lamina Failure Criteria

3. LAMINATE FAILURE ANALYSIS

3.1 Stiffness Reduction

3.1.1 Parallel Spring Model 3.1.2 Incremental Stiffness Reduction Model

3.2 Laminate Failure Analysis Methods

3.2.1 Ply-By-Ply Discount Method 3.2.2 Sudden Failure Method 3.2.3 Hart-Smith Criterion: The Truncated Maximum Strain Envelope

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iii

3.3 Laminate Failure Analysis under Biaxial Loading

36

3.3.1 Comparison of Data for Biaxial Loading

41

3.3.2 Biaxial Failure in the Strain Plane

42

3.3.3 Biaxial Testing Data for Glass Woven Fabric Composite

44

3.4 Laminate Strength Analysis for Unidirectional Off-Axis Loading

44

3.4.1 Generation of Laminate Failure Curve for Off-Axis Loading

45

3.4.2 Selection of Laminates and Off-Axis Loading Angles

45

3.4.3 Consideration of Curing Stresses and In-Situ Lamina Strength

45

3.4.4 Laminate Coupon Specimens

46

3.4.5 Testing Procedure

48

3.4.6 Comparison with Test Data

50

3.5 Observations on Laminated Failure Criteria

56

4. CONCLUSIONS

58

5. RECOMMENDATIONS

59

6. REFERENCES

60

APPENDICES

AA List of Failure Criteria

BA Computer Code for Strength Analysis of Laminated Composites

iv

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