DOT/FAA/AR-04/50 

Office of Aviation Research 

Washington, D.C. 20591

Comparative Testing to Assess 

the Equivalence of CEN and ASTM 

Test Methods for Composite 

Materials 

February 2005 

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-04/50

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

5. Report Date 

February 2005

 4. Title and Subtitle 

COMPARATIVE TESTING TO ASSESS THE EQUIVALENCE OF CEN AND 

ASTM TEST METHODS FOR COMPOSITE MATERIALS 6. Performing Organization Code

7. Author(s)

Daniel O. Adams 

8. Performing Organization Report No. 

10. Work Unit No. (TRAIS) 

 

9. Performing Organization Name and Address

Department of Mechanical Engineering 

University of Utah 

Salt Lake City, Utah 84112 

11. Contract or Grant No.

 

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

13. Type of Report and Period Covered

 Final Report

Office of Aviation Research 

Washington, DC 20591

14. Sponsoring Agency Code

 ACE-110

15. Supplementary Notes 

The FAA William J. Hughes Technical Center Technical Monitor was Peter Shyprykevich.

16. Abstract 

An initial assessment of equivalence between CEN and ASTM test methods was performed and documented in DOT/FAA/AR04/24. That study recommended additional test data to assess test method equivalency for four types of tests. The results of the 

four types of tests are contained in this report. First, lamina compression testing was performed to investigate the effects of 

different specimen gage lengths between either the prEN 2850–B and SACMA SRM 1 test methods (5 and 4.75 mm, 

respectively) and the AMS 2980 and 3970 specifications (12.5 mm). The results suggest that the gage length difference 

investigated (4.75 mm versus 12.5 mm) can produce significant differences in the apparent lamina compression strength. 

However, this difference is believed to be due to specimen buckling that occurred for specimens with longer gage lengths, which

is an unacceptable failure mode. Second, laminate compression tests were performed to investigate the method used to load the 

test fixture. The results suggest that the end-loaded test fixture shown in the SACMA SRM 3-94 test method is not suitable 

without additional clamping force applied near the specimen ends to prevent end-brooming failures. However, it is expected that 

through the modification of the existing test fixture to include more clamping bolts, an end-loaded test procedure can be produced 

that is capable of producing equivalent test results to the shear-loaded ASTM D 6484 test method. Third, in-plane shear testing 

was performed using ±45° type composite laminates loaded in tension to investigate laminate thickness effects. Test results 

showed that the 0.2% offset shear strength, the 5% shear strength measures, and the shear moduli calculated following the prEN 

6031/AMS and ASTM D 3518 test methods are in good agreement and independent of laminate thickness over the thickness 

ranges specified in the two test methods. Thus, these two shear test methods are believed to produce equivalent results when 

testing either tape or fabric laminates. Finally, constituent content was determined to compare procedures EN 2564 Method A 

and ASTM D 3171 Method I procedure B. The results showed that EN 2564 Method A and ASTM D 3171 Method I procedure 

B produced similar values for both the fiber volume percent and the matrix volume percent. However, the increased accuracy of 

the ASTM D 3171 test method due to the larger specimen size and the greater weighing accuracy produced more realistic values 

of void volume fraction than the EN 2564 Method A test method. 

17. Key Words 

Composite materials, Mechanical property testing, Test 

methods 

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 

 78 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized 
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY vii 

1. INTRODUCTION TO COMPARATIVE EVALUATION 1 

1.1 Background 1 

1.2 Comparative Evaluation of Test Methods 2 

1.3 Test Methods Recommended for Follow-On Testing 3 

1.3.1 Lamina Compression Tests: Effects of Gage Length 3 

1.3.2 Laminate Compression Tests: Effects of Loading Method 4 

1.3.3 In-Plane Shear Tests: Effects of Specimen Thickness 4 

1.3.4 Constituent Content Determination: Effects of Specimen Size and 

Weighing Accuracy 4 

2. GENERAL DESCRIPTION OF COMPARATIVE TESTS 4 

2.1 Materials 5 

2.2 Moisture Conditioning 5 

3. LAMINA COMPRESSION TESTS 6 

3.1 Test Description 6 

3.2 Lamina Compression Test Results 8 

4. LAMINATE COMPRESSION TESTS 10 

4.1 Test Description 10 

4.2 Laminate Compression Test Results 13 

5. IN-PLANE SHEAR TESTS 18 

5.1 Test Description 18 

5.2 In-Plane Shear Test Results 22 

6. CONSTITUENT CONTENT DETERMINATION 28 

6.1 Test Description 28 

6.2 Constituent Content Determination Results 30 

iii
7. SUMMARY OF RESULTS 32 

8. REFERENCES 34 

APPENDIX A—PHOTOGRAPHS OF FAILED SPECIMENS 

LIST OF FIGURES

Figure Page 

1 Test Fixture Used for the Lamina Compression Tests 6 

2 Lamina Compression Strengths From Tape and Fabric Laminates 9 

3 Test Fixture Used for the Laminate Compression Tests (End Loading) 10 

4 Shear Loading of Laminate Compression Test Fixture Using Hydraulic Grips 11 

5 Test Setup for End-Loaded Laminate Compression Tests With Additional 

Clamping Force 14 

6 Compression Strengths From Tape Laminates 17 

7 Compression Strengths From Fabric Laminates 18 

8 Test Setup Used for the In-Plane Shear Tests 20 

9 In-Plane Shear Strengths From Tape Laminates at RT/Ambient Conditions 25 

10 In-Plane Shear Strengths From Tape Laminates at 82oC/Wet Conditions 25 

11 In-Plane Shear Strengths From Fabric Laminates at RT/Ambient Conditions 26 

12 In-Plane Shear Strengths From Fabric Laminates at 82oC/Wet Conditions 26 

13 In-Plane Shear Modulus From Tape Laminates 27 

14 In-Plane Shear Modulus From Fabric Laminates 27 

15 Constituent Content Determinations From Tape and Fabric Laminates 32 

iv
LIST OF TABLES 

Table Page 

1 Summary of Lamina Compression Tests 7 

2 Lamina Compression Test Results 8 

3 Summary of Laminate Compression Tests 12 

4 Laminate Compression Test Results for 25/50/25 Tape Laminate 14 

5 Laminate Compression Test Results for 50/40/10 Tape Laminate 15 

6 Laminate Compression Test Results for 25/50/25 Fabric Laminate 15 

7 Laminate Compression Test Results for 40/20/40 Fabric Laminate 16 

8 Summary of In-Plane Shear Tests 19 

9 In-Plane Shear Test Results of Tape Laminates 23 

10 In-Plane Shear Test Results of Fabric Laminates 24 

11 Summary of Constituent Content Determinations 29 

12 Constituent Content Determination Results 31 

v
LIST OF ACRONYMS

c.v. Coefficient of variation 

CACRC Commercial Aircraft Composite Repair Committee 

CEN Comité Européen de Normalisation 

FAA Federal Aviation Administration 

prEN 6031/ASM prEN 6031 with ASM additions and changes 

RT Room temperature 

SACMA Suppliers of Advanced Composite Materials Association 

St. Dev. Standard deviation 

U.S. United States 

vi
EXECUTIVE SUMMARY 

An initial assessment of equivalence between CEN and ASTM test methods was performed and 

documented in the Federal Aviation Administration report DOT/FAA/AR-04/24. That study 

recommended four types of tests be done to provide additional test data to assess test method 

equivalency. The results of the four types of tests are contained in this report. First, lamina 

compression testing was performed to investigate the effects of different specimen gage lengths

between either the prEN 2850–B and SACMA SRM 1 test methods (5 and 4.75 mm, 

respectively) and the AMS 2980 and 3970 specifications (12.5 mm). The results suggest that the 

gage length difference investigated (4.75 mm versus 12.5 mm) can produce significant 

differences in the apparent lamina compression strength. However, this difference is believed to

be due to specimen buckling that occurred for specimens with longer gage lengths, which is an 

unacceptable failure mode. Second, laminate compression tests were performed to investigate 

the method used to load the test fixture. The results suggest that the end-loaded test fixture 

shown in the SACMA SRM 3-94 test method is not suitable without additional clamping force

applied near the specimen ends to prevent end-brooming failures. However, it is expected that 

through the modification of the existing test fixture to include more clamping bolts, an endloaded test procedure can be produced that is capable of producing equivalent test results to the 

shear-loaded ASTM D 6484 test method. Third, in-plane shear testing was performed using 

±45° type composite laminates loaded in tension to investigate laminate thickness effects. Test

results showed that the 0.2% offset shear strength, the 5% shear strength measures, and the shear 

moduli calculated following the prEN 6031/AMS and ASTM D 3518 test methods are in good 

agreement and independent of laminate thickness over the thickness ranges specified in the two

test methods. Thus, these two shear test methods are believed to produce equivalent results

when testing either tape or fabric laminates. Finally, constituent content was determined to 

compare procedures EN 2564 Method A and ASTM D 3171 Method I procedure B. The results 

showed that EN 2564 Method A and ASTM D 3171 Method I procedure B produced similar 

values for both the fiber volume percent and the matrix volume percent. However, the increased

accuracy of the ASTM D 3171 test method due to the larger specimen size and the greater 

weighing accuracy produced more realistic values of void volume fraction than the EN 2564 

Method A test method. 

vii/viii
1. INTRODUCTION TO COMPARATIVE EVALUATION. 

1.1 BACKGROUND. 

The original motivation for this comparative evaluation of United States (U.S.) and European 

test methods for composite materials dates back to the early 1990s. At that time, a composite 

materials characterization program was initiated to generate a dataset and subsequently qualify a 

composite material system for commercial aircraft repair [1]. The material to be qualified was a

wet lay-up composite material that was processed with a vacuum-only cure and used for airframe

repair. The material qualification program was performed according to SAE specification AMS

2980 [2] and Commercial Aircraft Composite Repair Committee (CACRC) requirements, which

used Committee for European Standardization, or Comité Européen de Normalisation (CEN), 

test methods. The mechanical tests performed included tension, compression, in-plane shear, 

open-hole tension, filled-hole tension, open-hole compression, filled-hole compression, bearing, 

compression after impact, tension-tapered joint, and tension-stepped joint tests. At the

completion of testing, the mechanical test results were processed into MIL Handbook 17-

acceptable form to provide statistical data. 

In the mid-1990s, a MIL Handbook 17 committee reviewed the test methods used in this material 

qualification program and compared them to the test methods recommended by MIL Handbook 

17 [3]. They noted that CEN test methods were used extensively in this qualification program, 

whereas MIL Handbook 17 focuses on ASTM test methods. The MIL Handbook 17 committee 

determined that the CEN and ASTM test methods differed in several aspects, raising concerns 

that the SAE-specified tests do not produce equivalent results to the MIL Handbook 17-

recommended test methods. The results of the MIL Handbook 17 committee review were 

published by email in October 1995 [4]. Following this review, discussions continued between 

MIL Handbook 17 and CACRC personnel. Although the CACRC continued using the CEN test

methods, similar ASTM test methods were added to the SAE specifications as an alternate for 

some tests. Additionally, for several types of tests included in both SAE AMS 2980 [2] (for wet

lay-up material) and SAE AMS 3970 [5] (for prepreg material), several parameters were 

specified that limited potential differences in test results between the CEN and ASTM test 

methods. For several types of tests, however, it remained unclear if the ASTM and CEN test 

methods would produce equivalent test results. 

In May 2002, a joint meeting was held between CACRC and the MIL Handbook 17 Composite

Materials Handbook Committee. Following this meeting, Mr. Rich Fields reviewed the test 

methods in the initial release of SAE AMS 3970 [5] and wrote a summary of findings and 

conclusions [6]. Mr. Fields concluded that the results from some CEN test methods would not 

be expected to be equivalent to the results for the same properties obtained using MIL Handbook 

17-recommended test methods. Based on these events, an Federal Aviation Administration 

(FAA)-funded comparative investigation was initiated by the author. The first phase of the 

investigation focused on a detailed evaluation and comparison of the CEN and ASTM test 

methods. The results of the investigation, published in 2004 [7], are summarized in the

following section. For those tests where the significance of an important difference could not be 

determined, follow-on mechanical tests were proposed as a second round of investigation. The 

results of the follow-on mechanical tests are the focus of this report. 

1
1.2 COMPARATIVE EVALUATION OF TEST METHODS. 

In June 2004, the author prepared a detailed test method comparison [7] directed towards 

assessing the equivalence of the different test methods (primarily CEN and ASTM) referred to in 

the SAE AMS 2980 and 3970 specifications. Of interest was both a direct comparison of the test

methods as well as an investigation of the effects of additions and changes given in the AMS 

specifications. For several types of tests, both a CEN and an ASTM test method are referred to 

in the AMS specifications and were, therefore, used for comparison. In several other cases, 

however, only a CEN test method is referred to in the AMS specifications. For these cases, a 

similar ASTM test method was sought for comparison. For cases where no comparable ASTM 

test method existed, either a draft ASTM standard or a Suppliers of Advanced Composite

Materials Association (SACMA)-recommended method was selected. For the lamina 

compression test, the AMS specifications referred only to a SACMA-recommended method. For 

this case, a comparable ASTM standard was identified and used for comparison. Of the CEN 

test methods used for comparison, several of the standards are currently draft or preliminary 

standards and are denoted as prEN test methods. Other test methods, which have been approved 

by CEN, are denoted as EN test methods. In total, two test methods were reviewed and 

compared for a total of 16 different types of tests. 

For each type of test, the results of the comparative evaluation were arranged into three 

comparison tables. The first table focused on the geometric features of the test specimen and test 

fixture. Included in this table were important dimensions and tolerances associated with both the 

test specimen and fixture. The second table focused on the parameters associated with the test 

procedure. Included were parameters associated with specimen preparation and instrumentation; 

procedures for specimen preconditioning, loading, and testing; and accuracy requirements for 

measured quantities. The third table focused on the procedures for data reduction and reporting. 

Included were the procedures, formulas, and statistical methods used to calculate and report test 

quantities. 

In addition to a detailed comparison of test method parameters, the significance of the 

differences in parameters was assessed and included in the comparison tables. For every 

parameter compared, an assessment of the equivalence was made using the following rating 

scale: 

• 0—No difference, essentially the same, not expected to produce any effect on the results 

• 1—Insignificant difference, potential to produce an insignificant effect on the results 

• 2—Minimal difference, difference of minimal significance, potential to produce a 

minimal effect on the results 

• 3—Moderate difference, difference of moderate significance, potential to produce a 

moderate effect on the results 

• 4—Major difference, difference of major significance, potential to produce a major effect 

on the results 

2
For cases where an assessment of equivalence was not possible, a rating of not comparable was 

used. A brief summary of each test method comparison was provided, which emphasized the 

most significant differences between the test methods. 

Prior to publishing, an initial draft of these comparison tables was prepared by the author and 

distributed to the following group for evaluation. 

• Mr. Rich Fields, Lockheed Martin Orlando, Chairman of ASTM D 30 Committee and 

Co-Chairman of MIL Handbook 17 Testing Working Group 

• Mr. Peter Shyprykevich, Federal Aviation Administration 

• Dr. Donald F. Adams, president of Wyoming Test Fixtures, Inc. 

• Dr. John Tomblin, Director of the National Institute for Aviation Research at Wichita 

State University 

Following a review of the comparison tables, the author and evaluators met at Wichita State

University in August 2003 to discuss the comparison and assessment tables as well as to 

determine which tests would require follow-on testing to assess equivalence. As a result of this 

meeting, changes were made to both the format and the content of the comparison and

assessment tables. The final comparison tables, along with a brief summary of the comparison, 

were published for the 16 test methods in an FAA report in June 2004 [7]. The final section of 

this report listed and briefly discussed four types of tests that were identified as requiring followon testing in the second round of this investigation to assess equivalence. 

1.3 TEST METHODS RECOMMENDED FOR FOLLOW-ON TESTING. 

Based on the comparative assessments of equivalence performed in reference 7, four of the

sixteen types of tests were selected for follow-on testing to further assess test method 

equivalency. Note that these four tests only reflected the need for additional test data to assess

equivalency and was not a reflection of their degree of equivalency relative to other tests. The 

four types of tests selected for follow-on testing and the parameter(s) to be investigated are 

described briefly in the following sections. 

1.3.1 Lamina Compression Tests: Effects of Gage Length. 

The test method comparison for lamina compression testing revealed a potentially significant 

difference in specimen gage lengths. Although similar gage lengths are listed for the prEN 

2850-B and SACMA SRM 1 test methods (5 mm versus 4.75 mm, respectively), the AMS 2980 

and 3970 specifications specify a 12.5-mm gage length. It is not well understood how this 

difference in gage length (4.75 mm versus 12.5 mm) will affect the delivered compression 

strengths produced in lamina compression testing. Thus, follow-on testing was recommended to 

determine the effects of specimen gage length on delivered lamina compression strength. Tests 

were proposed using specimens with both 4.75- and 12.5-mm gage length specimens. 

3
1.3.2 Laminate Compression Tests: Effects of Loading Method. 

The two test methods compared for laminate compression testing followed procedures generated 

for open-hole compression testing, but used a specimen without a hole. The test fixture specified 

in these test methods, SACMA SRM 3 and ASTM D 6484, was very similar. However, the 

method used to load the test fixture differs significantly and may produce differences in 

delivered compression strengths. Whereas the ASTM D 6484 has traditionally required 

hydraulic wedge grips to grip the test fixture, the SACMA SRM 3 test method allowed the test

fixture to be end-loaded between two parallel platens of the test machine. It was noted that 

neither standard was intended for compression testing of specimens without a central hole. 

Further, in 2004, the ASTM D 6484 test method was modified to include both shear and end 

loading of the test fixture. Thus, follow-on testing was recommended to determine the effects of 

the loading method on the delivered compression strength of composite laminates. Testing was 

proposed with the test fixture gripped (hydraulic wedge grips) and end-loaded. 

1.3.3 In-Plane Shear Tests: Effects of Specimen Thickness. 

The test methods compared for in-plane shear testing both used ±45° type composite laminates 

loaded in tension. Although both the prEN 6031 test method and the AMS 2980 and 3970 

specifications require an 8-ply +45° laminate for either unidirectional tape or woven fabric, 

ASTM D 3518 requires 16-, 20-, or 24-ply unidirectional tape laminates and 8-, 12-, or 16-ply 

woven fabric laminates. Since specimen thickness effects on strength have been reported in the 

literature [8], follow-on testing was recommended using multiple-thickness specimens fabricated 

from both prepreg tape and prepreg fabric materials. 

1.3.4 Constituent Content Determination: Effects of Specimen Size and Weighing Accuracy. 

Both test methods compared for constituent content determination, EN 2564 Method A and 

ASTM D 3171 Method I procedure B, used an acid digestion procedure to determine the

constituent content of composite laminates. Two significant differences between the test

methods were proposed for investigation in follow-on testing. First, the effect of the differences 

in the required specimen size reported between the test methods was proposed for investigation. 

Whereas EN 2564 requires a 2-mm-thick, 200-mm2

 rectangular specimen, ASTM D 3171 

requires a minimum surface area of 625 mm2

 and specifies a minimum mass requirement. 

Second, the difference in the required weighing accuracy between the test methods was proposed 

for investigation. Although ASTM D 3171 requires that the weights be determined to the nearest 

0.1 mg, EN 2564 only requires accuracy to the nearest ±1 mg. Both unidirectional prepreg 

laminates and prepreg fabric laminates were recommended for evaluation. 

2. GENERAL DESCRIPTION OF COMPARATIVE TESTS. 

Four types of tests were performed in this portion of the research investigation to help assess

equivalency between the CEN and ASTM test methods. As stated earlier, the selection of these 

four tests for follow-on testing only reflected the need for additional test data to assess

equivalency and was not a reflection of their degree of equivalency relative to other tests. Prior 

to discussing the detailed testing procedures and presenting the results for each type of test in the

4
following sections, the materials tested and the method used for specimen conditioning are 

presented. 

2.1 MATERIALS. 

Tests were performed using two different carbon/epoxy composite materials. (1) A

carbon/epoxy unidirectional prepreg tape produced by Toray (America), Inc., designated as 

Toray T700G/#2510. This unidirectional prepreg tape had an areal weight of 150 g/m2

. (2) A 

carbon/epoxy woven prepreg fabric produced by FiberCote Industries, designated as T300/E765. 

This plain weave prepreg fabric had an areal weight of 190 g/m2. Cured panels constructed from 

each of these materials were supplied to Wichita State University and subsequently forwarded to

the University of Utah. Details on fabrication procedures used for the Toray T700G/#2510 tape 

laminates and the FiberCote T300/E765 fabric laminates are provided in references 9 and 10, 

respectively.

2.2 MOISTURE CONDITIONING. 

For each of the three types of mechanical tests performed (lamina compression, laminate 

compression, and in-plane shear), specimens were tested at room temperature (RT)/ambient as 

well as at elevated temperatures following moisture conditioning. This section describes the 

procedure followed for moisture conditioning of specimens prior to mechanical testing. 

The test methods governing moisture conditioning are ASTM D 5229, “Standard Test Method 

for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix Composite

Materials” [11], and prEN 2823, “Determination of the Effect of Exposure to Humid 

Atmosphere on Physical and Mechanical Characteristics” [12]. Additions and changes are 

specified in sections 6.2 and 6.3.4 of both AMS 2980 [2] and AMS 3970 [5]. Both test methods

require that the specimens be conditioned in their final form, following all machining and

tabbing operations. Traveler specimens are required if the actual test material cannot be properly 

weighed, as in the case where the specimens are tabbed. Whereas prEN 2823 requires the 

travelers to have a width and length greater than 25 mm and a mass of 1.5 grams, ASTM D 5229 

requires the travelers to weigh more than 5 grams. For both test methods, the travelers must 

come from the same panel as the test specimens. The travelers used for this investigation 

satisfied both sets of requirements. 

The test specimens and travelers were humidity-aged using a laboratory convection oven 

maintained at a temperature of 70 ±2°C. The test specimens and travelers were placed onto

plastic trays in covered plastic tubs with water placed in the tubs below the specimen racks. 

Using these covered plastic tubs resulted in a relative humidity of 85% ±5%, measured with a 

humidity sensor. For each set of test specimens, traveler specimens were used to monitor 

moisture absorption. When the maximum difference between two subsequent weighings divided 

by the maximum mass of the specimen was less than 5 × 10-4, the test specimens were properly 

conditioned. The weighings were performed at 168-hour (7-day) intervals. 

5
3. LAMINA COMPRESSION TESTS. 

3.1 TEST DESCRIPTION. 

The test methods followed for lamina compression testing, prEN 2850 [13] and SACMA SRM

1R-94 [14], are similar to the test methods for determining the compressive properties of

composite materials. Note that prEN 2850 describes two types of compression tests; this 

comparison is based on method B. Section 6.5.3 of AMS 2980 [2] and 3970 [5] specifications 

provide additions and changes only to prEN 2850-B; the SACMA SRM 1 standard is not 

referred to in either AMS specification. 

This type of compression test, sometimes referred to as a modified ASTM D 695 compression 

test, features an end-loaded, face-supported specimen. When compression strength

determination specimens are tabbed, the short gage length between the tabs prevents the use of

strain gages for modulus determinations. Thus, a second set of untabbed specimens are required 

for modulus determination. These untabbed specimens are not suited for compression strength 

determination, since the specimen ends typically crush before compression failure occurs in the 

specimen gage section. The test fixture used for both test methods, shown in figure 1, was

obtained from Wyoming Test Fixtures, Inc. [15]. The fixture supports the face of the tabs on the 

tabbed specimen, but not the specimen gage length itself. The specimen is end-loaded through 

hardened steel plates. 

FIGURE 1. TEST FIXTURE USED FOR THE LAMINA COMPRESSION TESTS 

Comparison of specimen geometries from the two test methods [7] revealed several minor 

differences in dimensions and tolerances that were not expected to produce significant effects on 

results. However, a significant difference was identified in the specified gage lengths. Whereas 

similar gage lengths are listed for the prEN 2850-B and SACMA SRM 1 test methods (5 mm 

versus 4.75 mm, respectively, a result of round-off between U.S. Customary and SI units), the 

AMS 2980 and 3970 specifications, which modify the prEN 2850-B test method, specify a 

6
12.5-mm gage length. Since it is not well understood how this difference in gage length 

(4.75 mm versus 12.5 mm) will affect the delivered compression strengths produced in lamina 

compression testing, mechanical testing was performed using specimens with both 4.75- and 

12.5-mm gage lengths. Since the tabbed specimens used for strength determination were 

unsuitable for modulus determinations, only compression strength determinations were made in 

these tests. 

Both a unidirectional tape laminate and a fabric laminate with 100% of the plies in the (0o/90o) 

orientation were tested. As described in section 2.1, Toray T700G/#2510 unidirectional prepreg 

tape was used to produce the unidirectional tape laminate. This laminate was fabricated from

eight prepreg layers, resulting in a [0]8 laminate. The fabric laminate was fabricated from eight

0/90 layers of FiberCote T300/E765 plain weave prepreg, resulting in a [(0/90)]4s laminate. 

Testing was performed both at RT/ambient as well as at 82oC (180oF) following moisture 

conditioning (82oC/wet). A total of six specimens were tested per condition. Table 1 

summarizes the lamina compression tests performed in this investigation and provides the 

nominal thicknesses of the laminates used. 

TABLE 1. SUMMARY OF LAMINA COMPRESSION TESTS 

Number of Specimens Tested 

Test Method 

Test 

Condition 

Toray T700G/#2510 

Tape Laminate 

[0]8 

1.3-mm Nominal 

Thickness 

FiberCote T300/E765 

Fabric Laminate 

[(0/90)]4s 

3.0-mm Nominal 

Thickness 

prEN 2850 w/AMS RT/Ambient 6 6

Specifications 

(12.5-mm gage length) 

82oC/Wet 6 6

SACMA SRM 1R-94 RT/Ambient 6 6

(4.75-mm gage length) 82oC/Wet 6 6

Specimen tabbing was performed using 1.6-mm-thick G-10 glass-fabric/epoxy, following the 

recommended tabbing procedure developed at the University of Utah [16]. For specimens to be 

tested at RT/ambient conditions, Hysol 907 epoxy was used to adhesively bond the tabs. For

specimens that were moisture-conditioned and tested at hot/wet conditions, Loctite 9394 epoxy 

was used as the adhesive because it was determined that Hysol 907 epoxy had inadequate shear 

strength at 82oC/wet conditions. Two different gage lengths were produced in the test 

specimens: 4.75 and 12.5 mm. After tabbing, the specimens were cut from the tabbed panel 

using a water-cooled surface grinder equipped with a diamond blade. For specimens to be tested 

following the prEN 2850-B procedure, the nominal specimen dimensions were 80 mm in length 

and 12.5 mm in width. For specimens tested following the SRM 1R-94 procedure, the nominal 

length was also 80 mm, but the width was increased to 15 mm. Width and thickness 

measurements for the prEN 2850-B specimens were taken using a flat anvil micrometer. The 

same flat anvil micrometer was used for width measurements on the SRM 1R-94 specimens; 

however, a double-ball interface micrometer was used for thickness measurements. 

7
Tests were performed on a 100-kN capacity, computer-controlled MTS servo-hydraulic load 

frame. For the prEN 2850-B procedure, the specimen was clamped between the face supports 

using a bolt torque of 0.5 N-m. The SACMA SRM 1R-94 test method specifies a bolt torque 

between 0.7 and 1.0 N-m; a torque of 0.7 N-m was used. All tests were performed under a 

constant crosshead displacement rate of 1.0 mm/min, and all specimens were loaded to failure. 

For hot/wet testing, an Instron environmental chamber was placed into the load frame. The

environmental chamber was maintained at 82oC and wet towels were placed inside to increase 

the humidity within the chamber during testing. 

As discussed previously, the tabbed specimens used for strength determination were not suitable

for modulus determinations due to the short gage lengths between tabs. Thus, only the ultimate 

compressive strength was determined from these tests. The primary objective of these tests was 

to determine the effects of specimen gage length on the delivered compression strengths. 

3.2 LAMINA COMPRESSION TEST RESULTS. 

Table 2 presents the results of the lamina compression tests using both the Toray T700G/#2510 

unidirectional [0]8 carbon/epoxy tape laminate and the FiberCote T300/E765 [(0/90)]4s plain 

weave fabric laminate. The average compression strength, standard deviation, and coefficient of 

variation are shown for each of the test conditions. Additionally, lamina compression strengths 

obtained from the test methods are compared for each material and test condition in figure 2. 

Photographs of all failed lamina compression specimens are shown in figures A-1 through A-8 in 

appendix A. 

TABLE 2. LAMINA COMPRESSION TEST RESULTS 

Compression Strength 

Laminate 

Test 

Condition Test Method

Average 

(MPa) 

Standard 

Deviation 

(MPa) 

Coefficient 

of Variation

(%) 

prEN 2850-B 

12.5-mm gage length 837 33 3.9 RT/Ambient

SRM 1R-94 

4.75-mm gage length 976 87 9.0

prEN 2850-B 

12.5-mm gage length 715 49 6.8

Toray

T700G/#2510 

Tape Laminate 

[0]8

82oC/Wet 

SRM 1R-94 

4.75-mm gage length 858 60 7.0

prEN 2850-B 

12.5-mm gage length 701 61 8.6 RT/Ambient

SRM 1R-94 

4.75-mm gage length 716 46 6.5

prEN 2850-B 

12.5-mm gage length 340 40 11.8

FiberCote 

T300/E765 

Fabric Laminate 

[(0/90)]4s

82oC/Wet 

SRM 1R-94 

4.75-mm gage length 324 29 9.1

8
0

200

400

600

800

1000

1200

RT/Ambient 82o C/Wet 

C

o

m

pression Stren

gth, MP

a

prEN 2850-B

12.5 mm gage length

SRM 1R-94

4.75 mm gage length

RT/Ambient 82o C/Wet 

Toray T700G/#2510

Tape Laminate

FiberCote T300/E-765

Fabric Laminate

FIGURE 2. LAMINA COMPRESSION STRENGTHS FROM TAPE AND 

FABRIC LAMINATES

For the unidirectional [0]8 carbon/epoxy tape laminate tested at RT/ambient conditions, the SRM

1R-94 test method with the 4.75-mm gage length produced a 14% higher average compression 

strength than the prEN 2850-B test method with a 12.5-mm gage length. However, this 

difference in compression strength is suspected to be due to buckling of the specimens with the 

12.5-mm gage length, which is an unacceptable failure mode. Similarly, when tested at 

82oC/wet conditions, the SRM 1R-94 test method with the smaller 4.75-mm gage length 

produced a 17% higher average compression strength than the prEN 2850-B test method with a 

gage length of 12.5 mm.

For the [(0/90)]4s carbon/epoxy fabric laminate, similar compression strengths were obtained 

between the two test methods for both RT/ambient as well 82oC/wet conditions. The difference 

in average compression strengths between the two test methods was 2.1% for RT/ambient

conditions and 4.9% for 82oC/wet conditions.

In summary, these test results suggest that the gage length difference investigated (4.75 mm 

versus 12.5 mm) can produce significant differences in the apparent lamina compression 

strength. However, this difference is believed to be from specimen buckling that occurred in the 

specimens with longer gage lengths, which is an unacceptable failure mode. 

9
4. LAMINATE COMPRESSION TESTS. 

4.1 TEST DESCRIPTION. 

Laminate compression tests were performed following two test methods developed exclusively 

for open-hole compression testing, but using specimens without a central hole. The first test 

method, SACMA SRM 3-94 test method, “Open-Hole Compression Properties of Orientated 

Fiber-Resin Composites,” [17] is referenced in section 6.5.8 of both AMS 2980 [2] and AMS 

3970 [5] for laminate compression testing. Since the resulting test method is not similar to any 

ASTM compression tests without holes, a comparison was made to ASTM D 6484, “Standard 

Test Method for Open-Hole Compressive Strength of Polymer Matrix Composite Laminates,” 

[18], but using a specimen without a central hole. ASTM D 6484 is very similar to SACMA 

SRM 3-94 and therefore provided a good comparison. 

The test fixture specified for laminate compression testing in both test methods is commonly

referred to as the Boeing Open-Hole Compression Test Fixture, as it was originally developed by 

The Boeing Company. The particular test fixture used in this investigation, obtained from 

Wyoming Test Fixtures Inc. [15], is shown in figure 3. This test fixture supports the test 

specimen continuously along both faces, but includes a V-shaped gap designed into the adjacent 

ends of the fixture halves to prevent contact from occurring during loading. Guide plates are

used on each side of the fixture to maintain alignment of the assembly. 

FIGURE 3. TEST FIXTURE USED FOR THE LAMINATE COMPRESSION TESTS 

(END LOADING) 

Although this same test fixture is specified in the two test methods used, the method of load 

introduction differs significantly. The SACMA SRM 3-94 test method allows the assembled 

fixture, with specimen installed, to be end-loaded between two parallel platens, as shown in 

figure 3. Until 2004, ASTM D 6484 required the assembled fixture to be gripped at each end by 

10
hydraulic grips in the testing machine shown in figure 4 (shear loading). However, ASTM D 

6484 was modified in 2004 to include both shear loading and end loading. The primary focus of 

these tests was to investigate the effects of the loading method on the delivered compression 

strength of composite laminates. 

FIGURE 4. SHEAR LOADING OF LAMINATE COMPRESSION TEST FIXTURE

USING HYDRAULIC GRIPS 

In addition to the difference in loading method, minor differences in specimen dimensions also 

exist between the two test methods. Whereas ASTM D 6484 specifies an overall specimen 

length of 300 mm and a width of 36 mm, SACMA SRM 3-94 specifies slightly larger 

dimensions: an overall length of 305 mm and a width of 38.1 mm. The longer specimen length 

in the SACMA test method allowed for proper assembly of the fixture halves while ensuring that 

the specimen ends are flush with the ends of the assembled fixture, thus allowing proper end 

loading. In contrast, the slightly shorter ASTM specimens did not extend to the ends of the 

fixture halves when assembled. However, having the specimen ends flush with the fixture was 

not important for the ASTM test method since the specimens were shear-loaded using hydraulic 

grips. 

Two carbon/epoxy tape laminates and two fabric carbon/epoxy laminates were used for laminate

compression testing. The first tape laminate was a quasi-isotropic lay-up with 25% of the plies

orientated at 0° (the direction of loading), 50% of the plies orientated at ±45°, and 25% of the 

plies orientated at 90°. This laminate was referred to as the 25/50/25 laminate. The second tape

laminate had 50% of the plies orientated in the 0° direction, 40% of the plies orientated at ±45°, 

and 10% of the plies orientated at 90°, and was referred to as the 50/40/10 laminate. The first 

fabric laminate was quasi-isotropic with 25% of the fabric plies placed in the 0°/90° orientation,

50% of the plies in the ±45° orientation, and 25% of the fabric plies placed in the 90°/0° 

orientation. This quasi-isotropic fabric laminate was referred to as the 25/50/25 fabric laminate. 

11
The second fabric laminate had 40% of its plies orientated at 0°/90°, 20% at ±45°, and 40% at

90°/0°, and was referred to as the 40/20/40 fabric laminate. For each laminate, six specimens 

were produced for each of the two test methods for both RT and hot/wet testing. As described in 

section 2.1, Toray T700G/#2510 unidirectional prepreg tape was used to fabricate the tape 

laminates, and FiberCote T300/E765 plain weave prepreg was used to fabricate the fabric 

laminates. Tests were performed both at RT/ambient as well as at elevated temperatures, 

following moisture conditioning (82oC/wet). Table 3 summarizes the laminate compression tests 

performed and provides the nominal thicknesses of the laminates tested. 

TABLE 3. SUMMARY OF LAMINATE COMPRESSION TESTS 

Number of Specimens Tested 

Toray T700G/#2510 

Tape Laminates 

FiberCote T300/E765 

Fabric Laminates 

Test Method 

Test 

Condition 

25/50/25 

3.6-mm 

Nominal 

Thickness 

50/40/10 

3.0-mm 

Nominal 

Thickness 

25/50/25 

3.4-mm 

Nominal 

Thickness 

40/20/40 

4.3-mm 

Nominal 

Thickness 

SACMA RT/Ambient 6 6 6 6

SRM 3-94 

w/o Hole 

(End-Loaded) 

82oC/Wet 

6 6 6 6

ASTM D 6484 RT/Ambient 6 6 6 6

w/o Hole 

(Shear-Loaded) 

82oC/Wet 6 6 6 6

Specimen tabbing was not required for the laminate compression tests. Specimens were cut from

each laminate using a water-cooled surface grinder equipped with a diamond blade. The width

and thickness measurements for all specimens were taken using a flat-face micrometer. 

Testing was performed on a 250-kN capacity computer-controlled MTS servo-hydraulic load 

frame equipped with hydraulic wedge grips. For testing performed according to the SACMA 

SRM 3-94 test method, the assembled fixture with the installed specimen was end-loaded using 

two parallel end plates with welded flanges that were gripped by the hydraulic wedge grips. The

raised, rectangular frames on the end plates were included as a safety precaution to provide

lateral constraint, so that the fixture would not slip from between the platens while being 

compression-loaded. As per the test procedure in SACMA SRM 3-94, the specimen was secured

between the assembled fixture halves by tightening the two bolts on each half of the fixture to a 

torque of approximately 0.6 N-m.

For laminate compression testing performed according to the ASTM D 6484 test method, the

assembled test fixture with installed specimen was shear-loaded using MTS hydraulic wedge 

grips, as shown in figure 4. Prior to loading in the hydraulic grips, the two bolts on each half of 

the fixture were torqued to 7 N-m.

12
All laminate compression testing was performed under a constant crosshead displacement rate of

1.0 mm/min, and all specimens were loaded to failure. For hot/wet testing of the end-loaded 

SACMA SRM 3-94 specimens, an Instron environmental chamber was placed into the load 

frame so that the entire length of the specimen as well as the end plates were contained within 

the environmental chamber. The environmental chamber was maintained at 82oC and wet towels

were placed inside to increase the humidity within the chamber during testing. Due to size and 

temperature considerations, the hydraulic grips used to shear load the ASTM D 6484 specimens

could not be enclosed in the environmental chamber. Thus, for the shear-loaded specimens, the

Instron environmental chamber was placed immediately behind the hydraulic grips and an 

insulated extension to the environmental chamber was constructed to enclose the region of the 

test specimen located between the hydraulic grips. A thermocouple mounted to the surface of 

the specimen ensured that the specimen was maintained at a temperature of 82oC. 

4.2 LAMINATE COMPRESSION TEST RESULTS. 

The initial test plan prescribed six specimens for both end loading and shear loading, as listed in 

table 3. As the testing of the end-loaded specimens commenced, however, brooming failures at 

the specimen ends occurred. This undesirable failure mode was believed to result from 

inadequate clamping pressure exerted on the specimen faces by the support fixture. As shown in 

figure 3, the end-loaded laminate compression specimen was clamped between the assembled 

fixture halves by two bolts on each fixture half. These two clamping bolts, located near the gage

section of the specimen, were subjected to a rather minimal torque of approximately 0.6 N-m,

per SACMA SRM 3-94 specifications. Efforts to prevent end-brooming failures by increasing 

the torque applied to the two bolts on each fixture half were not successful. An investigation into 

the test procedure used in the original Carbon Composite Wet Repair Qualification Program [1] 

revealed the use of two additional bolts in each fixture half located near the ends of the 

specimen, presumably to prevent end-brooming failures from occurring. Based on this 

observation, trial tests were performed using large C-clamps to apply additional clamping force 

to the fixture halves, as shown in figure 5. These trial tests yielded successful gage section

failures, and the original test plan was modified so that only three specimens were tested in the

original end-loaded configuration, according to SACMA SRM 3-94 specifications. The 

remaining three specimens were end-loaded with additional clamping force provided by the 

existing fixture bolts torqued to of 13.5 N-m and the added C-clamps torqued to 20 N-m. 

Laminate compression strengths obtained from the 25/50/25 and 40/20/40 tape laminates are

presented in tables 4 and 5, respectively. Compression strengths from the 25/50/25 and 50/40/10 

fabric carbon/epoxy laminates are presented in tables 6 and 7, respectively. In each table, the 

average compression strength, standard deviation, and coefficient of variation are shown for each

for the test conditions investigated. Photographs of all failed lamina compression specimens are 

provided in figures A-9 through A-24 in appendix A. 

13
FIGURE 5. TEST SETUP FOR END-LOADED LAMINATE COMPRESSION TESTS 

WITH ADDITIONAL CLAMPING FORCE 

TABLE 4. LAMINATE COMPRESSION TEST RESULTS FOR 25/50/25 

TAPE LAMINATE 

Compression Strength 

Laminate 

Test 

Condition Test Method

Number of 

Specimens 

Average

(MPa) 

Standard

Deviation 

(MPa) 

Coefficient 

of Variation 

(%) 

SACMA SRM 3-94 

(End-Loaded) 3* 426 13 3.1

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 539 4.1 0.8

RT/Ambient

ASTM D 6484 

(Shear-Loaded) 6 6003 40 8.6

SACMA SRM 3-94 

(End-Loaded) 3** 380 21 5.6

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 409 12 2.9

Toray T700G/#2510

Tape Laminate 

25/50/25 

82oC/Wet

ASTM D 6484 

(Shear-Loaded) 6 400 27 6.7

*All three specimens failed at specimen end. 

**One specimen failed at specimen end. 

14
TABLE 5. LAMINATE COMPRESSION TEST RESULTS FOR 50/40/10 

TAPE LAMINATE 

Compression Strength 

Laminate 

Test 

Condition Test Method 

Number of 

Specimens 

Average

(MPa) 

Standard

Deviation 

(MPa) 

Coefficient 

of Variation 

(%) 

SACMA SRM 3-94 

(End-Loaded) 3* 578 36 6.2

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3** 628 53 8.5

RT/Ambient

ASTM D 6484 

(Shear-Loaded) 6 659 21 3.1

SACMA SRM 3-94 

(End-Loaded) 3* 493 87 17.6

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 524 92 17.5

Toray T700G/#2510

Tape Laminate 

50/40/10 

82oC/Wet

ASTM D 6484 

(Shear-Loaded) 6 526 52 9.9

*All three specimens failed at specimen end. 

**Two specimen failed at specimen end. 

TABLE 6. LAMINATE COMPRESSION TEST RESULTS FOR 25/50/25 

FABRIC LAMINATE 

Compression Strength 

Laminate 

Test 

Condition Test Method

Number of 

Specimens 

Average

(MPa) 

Standard

Deviation 

(MPa) 

Coefficient 

of Variation 

(%) 

SACMA SRM 3-94 

(End-Loaded) 3* 493 12 2.4

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 529 2.3 0.4

RT/Ambient

ASTM D 6484 

(Shear-Loaded) 6 539 46 8.5

SACMA SRM 3-94 

(End-Loaded) 3 341 14 4.1

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 373 9.9 2.7

FiberCote 

T300/E765

Fabric Laminate 

25/50/25 

82oC/Wet

ASTM D 6484 

(Shear-Loaded) 6 349 17 4.8

*All three specimens failed at specimen end. 

15
TABLE 7. LAMINATE COMPRESSION TEST RESULTS FOR 40/20/40 

FABRIC LAMINATE 

Compression Strength 

Laminate 

Test 

Condition Test Method

Number 

of 

Specimens 

Average

(MPa) 

Standard

Deviation 

(MPa) 

Coefficient 

of Variation 

(%) 

SACMA SRM 3-94 

(End-Loaded) 3* 500 21 4.2

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 541 12 2.2

RT/Ambient

ASTM D 6484 

(Shear-Loaded) 6 555 14 2.5

SACMA SRM 3-94 

(End-Loaded) 3 418 7.7 1.9

SACMA SRM 3-94 

(End-Loaded)

With added clamping 

3 437 13 2.9

FiberCote T300/E765

Fabric Laminate 

40/20/40 

82oC/Wet

ASTM D 6484 

(Shear-Loaded) 6 403 18 4.5

* Two specimens failed at specimen end. 

Laminate compression strengths obtained from the two tape laminates are compared for the two

test methods in figure 6. For both laminates and at both test conditions, the end-loaded SACMA 

SRM 3-94 specimens exhibited the lowest compression strengths. For the 25/50/25 laminate 

tested at RT/ambient conditions, the average compression strength was 29% less than the 

average from the shear-loaded ASTM D 6484 specimens. As shown in appendix A, all three of

the end-loaded SACMA SRM 3-94 specimens had end-brooming failures, whereas all ASTM D

6484 specimens failed in the gage section. When tested at 82oC/wet conditions, however, the 

compression strengths obtained from the 25/50/25 tape laminate using these two test methods 

were within 5%. Whereas one of the three end-loaded SACMA SRM 3-94 specimens failed due 

to end brooming, all shear-loaded ASTM D 6484 specimens failed in the gage section. 

Similarly, the differences in compression strengths between the two test methods for the 

50/40/10 tape laminate were 12% at RT/ambient conditions and 6% for 82oC/wet conditions. 

For both test conditions, all three end-loaded SACMA SRM 3-94 specimens from the 50/40/10 

laminate failed due to end brooming. 

For both tape laminates, the additional clamping force on the end-loaded SACMA SRM 3-94 

specimens produced higher delivered compression strengths and more gage section failures than 

using the standard end-loading method in SACMA SRM 3-94. For specimens tested at 

RT/ambient conditions, the delivered compression strengths were improved to within 11% and 

12% of the shear-loaded compression strengths for the 25/50/25 and 50/40/10 tape laminates, 

respectively. All three of the specimens tested with additional clamping force from the 25/50/25 

laminate failed in the gage section, whereas two of the three 50/40/10 specimens failed due to 

end brooming. For tests performed with the two tape laminates at 82oC/wet conditions, the 

compression strengths obtained were equivalent to those obtained using the ASTM D 6484 

shear-loading test method, and gage section failures occurred in all specimens. 

16
0

100

200

300

400

500

600

700

800

C

ompressio

n Stren

gth, M

P

a

SACMA SRM 3-94 End Loaded

SACMA SRM 3-94 With Clamping

ASTM D 6484 Shear Loaded

RT/Ambient 82o C/Wet RT/Ambient 82o C/Wet

25/50/25

Tape Laminate

50/40/10

Tape Laminate

0

100

200

300

400

500

600

700

800

C

ompressio

n Stren

gth, M

P

a

SACMA SRM 3-94 End Loaded

SACMA SRM 3-94 With Clamping

ASTM D 6484 Shear Loaded

RT/Ambient 82o C/Wet RT/Ambient 82o C/Wet

25/50/25

Tape Laminate

50/40/10

Tape Laminate

FIGURE 6. COMPRESSION STRENGTHS FROM TAPE LAMINATES 

A comparison of the laminate compression strengths obtained from the fabric laminates are 

presented in figure 7. For both fabric laminates tested at RT/ambient conditions, the end-loaded

SACMA SRM 3-94 specimens exhibited the lowest compression strengths. Compared to the 

average compression strength obtained using the shear-loaded ASTM D 6484 test method, the 

end-loaded SACMA SRM 3-94 test method produced compression strengths that were 9% and 

10% lower for the 25/50/25 and 40/20/40 laminates, respectively. All three of the 25/50/25 

specimens and two of the three 40/20/40 specimens that were end-loaded in accordance with 

SACMA SRM 3-94 specifications failed due to end brooming. In contrast, all specimens from

the fabric laminates that were shear-loaded following ASTM D 6484 specifications failed in the 

gage section. When tested at 82o C/wet conditions, however, the compression strengths obtained 

using the two test methods were within 4% for both fabric laminates. All of the end- and shearloaded fabric specimens tested at 82oC/wet conditions failed in the specimen gage section. 

For both fabric laminates tested at RT/ambient conditions, the additional clamping force on the 

end-loaded SACMA SRM 3-94 specimens produced average compression strengths that were 

within 2.5% of the corresponding shear-loaded ASTM D 6484 compression strengths. Further, 

the additional clamping force resulted in gage section failures for all fabric specimens tested. 

For the two fabric laminates tested at 82oC/wet conditions, the average compression strengths 

from the end-loaded specimens with additional clamping force were up to 4% higher than 

obtained from shear-loaded ASTM D 6484 specimens. 

17
0

100

200

300

400

500

600

700

C

o

mpressio

n Stre

n

gth, M

Pa

SACMA SRM 3-94 End Loaded

SACMA SRM 3-94 With Clamping

ASTM D 6484 Shear Loaded

RT/Ambient 82o C/Wet RT/Ambient 82o C/Wet

25/50/25

Fabric Laminate

40/20/40

Fabric Laminate

0

100

200

300

400

500

600

700

C

o

mpressio

n Stre

n

gth, M

Pa

SACMA SRM 3-94 End Loaded

SACMA SRM 3-94 With Clamping

ASTM D 6484 Shear Loaded

RT/Ambient 82o C/Wet RT/Ambient 82o C/Wet

25/50/25

Fabric Laminate

40/20/40

Fabric Laminate

FIGURE 7. COMPRESSION STRENGTHS FROM FABRIC LAMINATES 

In summary, these test results suggest that the test fixture shown in the SACMA SRM 3-94 test 

method is not suitable for end loading of laminate compression specimens without additional 

clamping force applied near the specimen ends to prevent end-brooming failures. Results from 

this investigation suggest that the addition of clamping force to the specimen near the ends can

reduce the occurrence of end-brooming failures, subsequently producing higher delivered 

compression strengths. Since the clamping force provided by C-clamps in this investigation

were not adequate to eliminate end-brooming failures in all cases, it cannot be concluded that 

end loading of the laminate compression test specimens produces equivalent results to shear 

loading. However, it is expected that through the modification of the existing test fixture to 

include more clamping bolts, an end loaded test procedure can be produced that is capable of

producing equivalent test results to the current shear-loaded ASTM D 6484 test method. 

5. IN-PLANE SHEAR TESTS. 

5.1 TEST DESCRIPTION. 

In-plane shear tests were performed following two test methods that used ±45° type laminates

loaded in tension: prEN 6031 [19] and ASTM D 3518 [20]. The prEN 6031 test method 

followed in these tests were performed using the additions and modifications given in section 

6.5.4 of both AMS 2980 [2] and AMS 3970 [5]. The test method comparison completed in 

Phase I of this investigation [7] revealed one potentially significant difference in the prescribed 

specimen thickness. Although both the prEN 6031 test method and the AMS 2980 and 3970 

18
specifications require an 8-ply ±45° laminate for either unidirectional tape or woven fabric, 

ASTM D 3518 requires 16-, 20-, or 24-ply unidirectional tape laminates or 8-, 12-, or 16-ply 

woven fabric laminates. As discussed in section 1.3.3, a specimen thickness effect on strength 

has been reported previously [8], resulting in lower delivered shear strengths from thinner ±45° 

specimens. To further investigate the effects of specimen thickness, mechanical testing was

performed using multiple-thickness specimens fabricated from both prepreg tape and prepreg 

fabric materials. 

In-plane shear tests were performed on three carbon/epoxy tape laminates and two carbon/epoxy 

fabric laminates, all with 100% of the fibers in the ±45o orientations. The three tape laminates

were 4-ply [±45]s, 8-ply [±45]2s, and 16-ply [±45]4s. The two fabric laminates were 4-ply 

[(±45)]s and 8-ply [(±45)]2s. As described in section 2.1, Toray T700G/#2510 unidirectional

prepreg tape was used to fabricate the tape laminates, whereas FiberCote T300/E765 plain weave 

prepreg was used to fabricate the fabric laminates. Testing was performed both at RT/ambient as 

well as at elevated temperatures, following moisture conditioning (82oC/wet). A total of six 

specimens were tested per condition. Table 8 summarizes the in-plane shear tests performed in

this investigation and provides the nominal thicknesses of the laminates used. 

TABLE 8. SUMMARY OF IN-PLANE SHEAR TESTS 

Number of Specimens Tested 

Toray T700G/#2510 

Tape Laminates 

FiberCote T300/E765 

Fabric Laminates 

Test 

Condition 

4-ply 

[±45]s 

0.6-mm 

Nominal 

Thickness 

8-ply 

[±45]2s

1.2-mm 

Nominal 

Thickness 

16-ply 

[±45]5s

2.5-mm 

Nominal 

Thickness 

4-ply 

[(±45)]s

0.9-mm 

Nominal 

Thickness 

8-ply 

[(±45)]2s

1.7-mm 

Nominal 

Thickness 

RT/Ambient 6 6 6 6 6

82oC/Wet 6 6 6 6 6

The tabbing of specimens, although optional in the ASTM D 3518 test method, was performed 

on all in-plane shear specimens tested. Specimen tabbing was performed using 1.6-mm-thick 

G-10 glass-fabric/epoxy, following the recommended tabbing procedure developed at the 

University of Utah [16]. For specimens tested at RT/ambient conditions, Hysol 907 epoxy was 

used to adhesively bond the tabs. For specimens that were moisture-conditioned and tested at 

hot/wet conditions, Loctite 9394 epoxy was used as the adhesive. 

After tabbing, the specimens were cut from the tabbed panel using a water-cooled surface 

grinder equipped with a diamond blade. The overall specimen dimensions were 230 mm in 

length and 25 mm in width, with a gage length of 130 mm. Although only one set of six 

specimens was tested for each condition, the final dimensions were measured twice, each time in

accordance with a specific test method. For ASTM D 3518, width measurements were taken

with a flat-face micrometer, and thickness measurements were taken with a double-ball interface 

micrometer. For prEN 6031, width measurements were taken with a vernier caliper, and 

19
thickness measurements were taken with a flat-face micrometer. The measurements that were 

taken according to each test method were subsequently used to calculate the material properties

as specified in each test method. In general, the area measurements taken using the different 

measurement devices were within 1%-2% for specimens from both the tape and fabric laminates. 

Strain gages were used on all specimens for modulus measurement. Two Measurements Group 

CEA-060250UW-350 strain gages were bonded to a single surface of each specimen using 

M-Bond 200 adhesive. One strain gage was aligned in the direction of the applied load 

(0° direction), and the other gage was oriented transversely to the loading direction

(90° direction). Both gages were centered across the specimen width and placed near the center 

of the gage length. 

Tests were performed on a 100-kN capacity, computer-controlled MTS servo-hydraulic load 

frame. A Measurements Group 2100 strain gage conditioner/amplifier system was used for

strain gage measurements. A test speed of 2 mm/min was used in all tests. Mechanical wedge

grips were used to grip the specimen as shown in figure 8. The grips were tightened on the 

specimen by manually turning a screw mechanism. A universal joint was used between the

upper grip and the load cell. For hot/wet testing, an Instron environmental chamber was placed

into the load frame. The environmental chamber was maintained at 82oC and wet towels were

placed inside to increase the humidity within the chamber during testing. 

FIGURE 8. TEST SETUP USED FOR THE IN-PLANE SHEAR TESTS 

20
Following testing, shear strains and shear stresses were calculated using the expressions 

i xi yi γ = ε −ε 12 (1)

and 

A

Pi

i 2

τ 12 = , (2)

where: 

12i γ = shear strain at i-th data point 

xi ε = longitudinal normal strain at i-th data point 

yi ε = lateral normal strain at i-th data point 

12 τ = shear stress at i-th data point 

Pi = load at i-th data point 

A = cross-sectional area 

In-plane shear strength and shear modulus properties were calculated according to the two test 

methods. For ASTM D 3518, the shear strength was defined as the maximum shear stress at or 

below 5% shear strain. An optional calculation of the 0.2% offset shear strength was performed 

for comparison purposes. The 0.2% offset shear strength was defined as the value of shear stress 

corresponding to the intersection of the shear stress versus shear strain curve and the shear

modulus offset by 0.2% shear strain. For prEN 6031 with the AMS additions and changes (prEN 

6031/AMS), three shear strength values were calculated. The first shear strength value, the 0.2% 

offset shear strength, was defined the same as for ASTM D 3518. Thus, the only source for the 

differences in the 0.2% offset shear strengths calculated from the two test methods were due to 

the different cross-sectional area measurements. The second measure, the shear strength at 5% 

strain, was defined as the shear stress achieved at 5% shear strain. The third measure, the 

ultimate shear strength, was defined as the maximum recorded shear stress recorded during 

testing. Note that since ASTM D 3518 defines the maximum shear stress as the maximum value 

at or below 5% shear strain, this value was expected to compare well with the shear strength at 

5% strain from the prEN 6031/AMS test method if the shear stress continued to increase up to 

5% shear strain. 

For the modulus determination, ASTM D 3518 specifies that the chord modulus be taken over a 

4000 ±200 με shear strain range with the lower strain point in the range of 1500 to 2500 με. In 

this study, the reference points of 2000 and 6000 με were used. For prEN 6031/AMS, the shear

modulus was calculated using strain reference points between 2000 and 6000 με. Thus, the 

method of shear modulus measurement between the two test methods was the same. As a result, 

the only differences in the calculated shear moduli between the two test methods would result 

from the different methods used to measure the cross-sectional area. 

21
5.2 IN-PLANE SHEAR TEST RESULTS. 

Tables 9 and 10 present the results of the in-plane shear tests of the Toray T700G/#2510 

carbon/epoxy tape laminates and the FiberCote T300/E765 plain weave fabric laminates,

respectively. The average shear strength and shear modulus values are listed, along with the 

standard deviation (St. Dev.) and coefficient of variation (c.v.) for each of the test conditions 

investigated. As described in section 5.1, two shear strength measures were calculated according

to ASTM D 3518 specifications and three shear strength measures from prEN 6031/AMS.

Photographs of all failed lamina compression specimens are shown in figures A-25 through A-34 

in appendix A. 

As noted in table 9, three of the six, four-ply tape specimens tested at RT/ambient conditions and 

one of the six, four-ply specimens tested at 82oC/wet conditions failed prior to achieving a 5% 

shear strain. For these two test conditions, the calculation of the prEN 6031/AMS shear strength 

at 5% strain was based on the remaining specimens. Of the remaining three tape specimens 

tested at RT/ambient conditions, two specimens experienced failure in one of the strain gages, 

therefore, the 5% shear strain reading was estimated based on the output of the one remaining 

strain gage. Since the specimens continued to load past the point of strain gage failure, these 

strain gage failures were believed to be produced by localized failures at the specimen surface. 

Shear strengths obtained from the prEN 6031/AMS and ASTM D 3518 test methods are 

compared in figures 9 and 10 for the tape laminates tested at RT/ambient and 82oC/wet 

conditions, respectively. For each test condition, the five shear strength measures are plotted for 

each of the three laminate thicknesses. As expected, the 0.2% offset shear strengths from the 

prEN 6031/AMS and ASTM D 3518 test methods were very similar. Since all 8- and 16-ply 

tape specimens achieved a shear strain of 5% prior to failure, the ASTM D 3518 shear strength 

(maximum shear stress at or below 5% shear strain) was similar to the prEN 6031/AMS 5% 

shear strength. Since some of the four-ply tape specimens failed to reach a shear strain of 5%

prior to failure, a comparison of these two shear strength values is less meaningful. For all cases

other than the four-ply tape specimens, the prEN 6031/AMS ultimate shear strength was

considerably higher than either the ASTM D 3518 shear strength or the prEN 6031/AMS 5%

shear strength, indicating a considerable increase in shear stress beyond a 5% shear strain. 

Shear strengths obtained for the fabric laminates tested at RT/ambient and 82oC/wet conditions 

are compared in figures 11 and 12, respectively. Similar to the results obtained for the tape

laminates, the 0.2% offset shear strengths from the prEN 6031/AMS and ASTM D 3518 test 

methods were very similar. Further, the prEN 6031/AMS 5% shear strength was within 2% of 

the corresponding ASTM D 3518 shear strength (maximum shear stress at or below 5% shear 

strain). As the thickness of the fabric laminate increased from four to eight plies, the prEN 

6031/AMS 5% shear strength and the ASTM D 3518 shear strength decreased slightly at 

RT/ambient conditions but increased slightly at 82oC/wet conditions. However, neither change

in these two shear strength measures was statistically significant. An increase in the prEN 6031 

ultimate shear strength of 7% and 10% was observed for the RT/ambient and 82oC/wet 

conditions, respectively, as the laminate thickness was increased from four to eight plies. 

22
TABLE 9. I

N-PLANE SHEAR TEST RESULTS OF TAPE LAMINATES 

Shear Strength Shear Modulus 

prEN 6031/AMS ASTM D 3518 

Test 

C

o

n

ditio

n

L

a

min

ate

0.2% Offset 

Strength 

(MPa) 

Strength at 

5% Strain 

(MPa) 

Ultimate 

Strength 

(MPa) 

0.2% Offset 

Strength 

(MPa) 

Shear 

Strength 

(MPa) 

ASTM 

D 3518 

Modulus 

(GPa) 

prEN 6031 

Modulus 

(GPa) 

A

v

g. 61.4

8

8.9** 8

5.9

6

2.0

81.7 4.52

4.4

7

St. Dev. 3.05 3.07** 11.8 3.00 

7.16

0.2

3

0.2

3 [±45]s (4 ply) c.v. (%) 5.0 3.5** 13.7 4.8 8.8 5.1 5.0 

A

v

g. 5

6.2

8

5.4 10

7

5

6.5

8

5.9 4.40

4.3

7

St. Dev. 1.72 1.28 1.92 1.72 1.16 0.05 0.05 [±45]2s (8 ply) c.v. (%) 3.1 1.5 1.8 3.0 1.4 1.2 1.2 A

v

g. 5

4.5

8

5.0 110

5

4.7

8

5.2 4.24

4.2

2

St. Dev. 1.04 1.77 14.2 1.12 1.76 0.10 0.10 

RT/Ambient 

[±45]4s 

(16 ply) c.v. (%) 1.9 2.1 12.9 2.0 2.1 2.4 2.4 

Avg. 35.2 48.6* 56.8 35.7 47.0 2.71 2.66 St. Dev. 0.97 0.97* 13.1 0.75 5.33 0.05 0.07 [±45]s (4 ply) c.v. (%) 2.8 2.0* 23.0 2.1 11.3 1.8 2.5 A

v

g. 3

3.6

4

8.6

7

2.7

3

3.9

4

8.8 2.74

2.71

St. Dev. 1.79 0.26 3.54 1.82 0.66 0.05 0.05 [±45]2s (8 ply) c.v. (%) 5.3 0.5 4.9 5.4 1.3 1.8 1.9 A

v

g. 3

3.2

4

6.1 7

5.2

3

3.4

4

6.0 2.71

2.7

0

St. Dev. 1.16 1.63 2.91 1.14 1.28 0.07 0.06 

82oC/W

et 

[±45]4s 

(16 ply) c.v. (%) 3.5 3.5 3.9 3.4 2.8 2.6 2.3 

23

*One of t

he si

x speci

mens failed prior to 5% shear strai

n; calculations were based on t

he remaining five speci

mens. 

**Three of t

he six s

peci

mens failed prior to 5% s

hear strai

n; calculations were based on the remaining three speci

mens. 
TABLE 10. IN-PLANE SHEAR TEST RESULTS OF FABRIC LAMINATES 

Shear Strength Shear Modulus 

prEN 6031/AMS ASTM D 3518 

Test 

Condition Laminate

0.2% Offset 

Strength 

(MPa) 

Strength at 

5% Strain 

(MPa) 

Ultimate 

Strength 

(MPa) 

0.2% Offset 

Strength 

(MPa) 

Shear 

Strength 

(MPa) 

ASTM 

D 3518 

Modulus 

(GPa) 

prEN 6031 

Modulus 

(GPa) 

Avg. 63.3 85.8 93.1 63.0 87.1 6.19 6.10St. Dev. 1.89 2.01 1.43 5.27 2.42 0.20 0.19 [±45]s (4 ply) 

c.v. (%) 3.0 2.3 1.5 8.4 2.8 3.3 3.0 

Avg. 65.3 89.2 99.2 65.7 89.8 6.43 6.38St. Dev. 0.44 4.28 2.33 0.56 4.22 0.18 0.17 

RT/Ambient 

[±45]2s 

(8 ply) c.v. (%) 0.7 4.8 2.3 0.8 4.7 2.7 2.6 

Avg. 29.2 43.1 58.6 29.4 43.4 2.44 2.42St. Dev. 2.00 1.79 1.85 1.88 1.55 0.12 0.12 [±45]s (4 ply) 

c.v. (%) 6.8 4.2 3.2 6.4 3.6 4.8 4.9 

Avg. 28.7 39.6 64.5 28.9 39.8 2.25 2.24St. Dev. 2.17 2.11 2.75 2.13 2.05 0.11 0.11 

82oC/Wet 

[±45]2s 

(8 ply) c.v. (%) 7.6 5.3 4.3 7.4 5.1 5.0 4.9 

24
0

20

40

60

80

100

120

140

Shear Strength, M

Pa

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

4 ply

Tape Laminate

8 ply

Tape Laminate

16 ply

Tape Laminate

0

20

40

60

80

100

120

140

Shear Strength, M

Pa

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

4 ply

Tape Laminate

8 ply

Tape Laminate

16 ply

Tape Laminate

FIGURE 9. IN-PLANE SHEAR STRENGTHS FROM TAPE LAMINATES AT 

RT/AMBIENT CONDITIONS 

0

10

20

30

40

50

60

70

80

90

Shear Strength, MPa

4 ply

Tape Laminate

8 ply

Tape Laminate

16 ply

Tape Laminate

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

0

10

20

30

40

50

60

70

80

90

Shear Strength, MPa

4 ply

Tape Laminate

8 ply

Tape Laminate

16 ply

Tape Laminate

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

FIGURE 10. IN-PLANE SHEAR STRENGTHS FROM TAPE LAMINATES AT 

82oC/WET CONDITIONS 

The results shown in figures 9-12 indicate, with the exception of the four-ply tape laminate, that 

the 0.2% offset shear strengths calculated according to the prEN 6031/AMS and ASTM D 3518 

specifications are equivalent. Further, these quantities do not change in a statistically significant 

manner as the thickness is increased. Similarly, with the exception of the four-ply tape laminate,

the ASTM D 3518 shear strength (maximum shear stress at or below 5% shear strain) is 

equivalent to the prEN 6031/AMS 5% shear strength for both the tape and fabric laminates. 

25
Since both prEN 6031/AMS and ASTM D 3518 specify minimum laminate thicknesses of eight 

plies, both the 0.2% offset shear stress and the shear strength at 5% strain (up to 5% shear strain 

for ASTM D 3518) are equivalent for the two test methods. 

0

20

40

60

80

100

120

Shear Strength, M

Pa

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

4 ply

Fabric Laminate

8 ply

Fabric Laminate

0

20

40

60

80

100

120

Shear Strength, M

Pa

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

4 ply

Fabric Laminate

8 ply

Fabric Laminate

FIGURE 11. IN-PLANE SHEAR STRENGTHS FROM FABRIC LAMINATES AT 

RT/AMBIENT CONDITIONS 

0

10

20

30

40

50

60

70

80

Shear Strength, MPa

4 ply

Fabric Laminate

8 ply

Fabric Laminate

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

0

10

20

30

40

50

60

70

80

Shear Strength, MPa

4 ply

Fabric Laminate

8 ply

Fabric Laminate

prEN 6031 0.2% Offset Strength

prEN 6031Strength at 5% Strain

prEN 6031 Ultimate Strength

ASTM D 3518 Strength

ASTM D 3518 0.2% Offset Strength

FIGURE 12. IN-PLANE SHEAR STRENGTHS FROM FABRIC LAMINATES AT 

82oC/WET CONDITIONS 

26
Shear moduli obtained from the prEN 6031 and ASTM D 3518 test methods are compared in 

figures 13 and 14 for the tape and fabric laminates, respectively. As discussed in section 2.5, the

method of shear modulus measurement between the two test methods was the same. Thus, any 

differences in the calculated shear moduli between the two test methods are a result of the 

different methods used to measure the cross-sectional area. For all laminates and test conditions,

the difference in shear modulus between the prEN 6031 and ASTM D 3518 test methods was 

less than 2%. 

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Shear Modulus, GPa

RT/Ambient 82o C/Wet

4 ply 8 ply 16 ply 4 ply 8 ply 16 ply

prEN 6031

ASTM 3518

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Shear Modulus, GPa

RT/Ambient 82o C/Wet

4 ply 8 ply 16 ply 4 ply 8 ply 16 ply

prEN 6031

ASTM 3518

FIGURE 13. IN-PLANE SHEAR MODULUS FROM TAPE LAMINATES 

0

1

2

3

4

5

6

7

Shear Modulus, GPa

prEN 6031

ASTM 3518

RT/Ambient 82o C/Wet

4 ply 8 ply 4 ply 8 ply

0

1

2

3

4

5

6

7

Shear Modulus, GPa

prEN 6031

ASTM 3518

RT/Ambient 82o C/Wet

4 ply 8 ply 4 ply 8 ply

FIGURE 14. IN-PLANE SHEAR MODULUS FROM FABRIC LAMINATES 

27
Referring to figure 13, a small decrease in the average shear modulus with increasing laminate 

thickness is observed for the tape laminates tested at RT/ambient conditions. Figure 14 shows a 

small increase in the average shear modulus with increasing laminate thickness for the fabric

laminates tested at RT/ambient conditions. Note, however, that neither change is statistically

significant. Similarly, the small decrease in shear modulus with increasing laminate thickness

for the fabric laminates tested at 82oC/wet conditions is not statistically significant. 

In summary, the 0.2% offset shear strength, the 5% shear strength measures, and the shear 

moduli calculated following the prEN 6031/AMS and ASTM D 3518 test methods were in good 

agreement and independent of laminate thickness over the thickness ranges specified in the two

test methods. Thus, these two shear test methods are believed to produce equivalent results

when testing either tape or fabric laminates. 

6. CONSTITUENT CONTENT DETERMINATION. 

6.1 TEST DESCRIPTION. 

The two test methods followed for constituent content determinations, EN 2564 Method A [21] 

and ASTM D 3171 Method I procedure B [22], both used an acid digestion method for removing 

the matrix material, thus allowing for the determination of the fiber and matrix content (by 

weight or volume) as well as the void volume fraction. Of the two AMS specifications

considered, only AMS 3970 [5] includes constituent content determination. Further, only EN

2564 is referred to in the AMS 3970 specification. Other than specifying the laminate lay-up, 

however, SAE 3970 does not provide any additions or changes to EN 2564. ASTM D 3171 

Method I procedure B was selected for comparison based on its similarity to EN 2564 Method A. 

Reference 7 of the two test methods for constituent content determination revealed two 

significant differences that were believed to have the potential to produce moderate effects on the 

constituent content determinations. First, the two test methods required different specimen sizes. 

Whereas EN 2564 requires a 2-mm-thick, 20- by 10-mm (200-mm

2

)-rectangular specimen,

ASTM D 3171 requires a minimum surface area of 625 mm2

 and specifies a minimum mass 

requirement. Second, the required weighing accuracy is significantly different between the two 

test methods. ASTM D 3171 requires that weights be determined to the nearest ±0.1 mg,

whereas EN 2564 only requires accuracy to the nearest ±1 mg. Thus, constituent content 

determinations were performed to assess the effects of both the size and weighing accuracy on

the test results. 

Constituent content determinations were performed using both a [±45]2s carbon/epoxy tape

laminate and a [(±45)]s carbon/epoxy fabric laminate. As described in section 2.1, Toray 

T700G/#2510 unidirectional prepreg tape was used to fabricate the tape laminate, whereas 

FiberCote T300/E765 plain weave prepreg was used to fabricate the fabric laminate. A total of 

six specimens were tested per condition. Table 11 summarizes the constituent content 

determinations performed. 

28
TABLE 11. SUMMARY OF CONSTITUENT CONTENT DETERMINATIONS 

Number of Specimens Tested 

Test Method 

Toray T700G/#2510 

Tape Laminate 

[±45]2s

FiberCote T300/E765 

Fabric Laminate 

[(±45)]s

EN 2564 Method A 6 6 

ASTM D 3171 

Method I procedure B 6 6

Specimens were cut from each laminate, to the minimum size as specified by each test method, 

using a water-cooled surface grinder equipped with a diamond blade. Next, density 

determinations were made. For ASTM D 3171, density measurements were made in accordance 

with ASTM D 792 [23]. For EN 2564, densities were measured in accordance with ISO 1183 

Method A [24]. Both methods required the specimen to be weighed first in air, and then 

weighed immersed in water. The relative density of each specimen was determined using the 

expression 

Relative density = a/(a – b) (3) 

where: 

a = mass of specimen in air 

 b = mass of specimen immersed in water

The specimen density was calculated next using the expression 

Density = Relative density * 0.9975 (4) 

For acid digestion of the matrix material, ASTM D 3171 Method I procedure B required that the 

specimen be heated in 20 ml of sulphuric acid until it began to fume, then 35 ml of hydrogen 

peroxide was added. The mixture was cooled and filtered, and the fibers were washed three

times with distilled water, with a final acetone wash. After drying at 100°C for 1 hour, the fibers 

were allowed to cool and were weighed to the nearest 0.1 mg. 

The procedure for EN 2564 also required heating the specimen in 20 ml of sulphuric acid until 

the mixture reached 160 ±10°C, when it began to fume. Hydrogen peroxide was added slowly to 

the mixture until the solution remained clear. The solution was cooled and added to a beaker 

containing 100 ml of distilled water. The fibers were filtered through a sintered glass crucible 

and washed with acetone. After drying at 120°C for at least 45 minutes, the fibers were cooled

and weighed to the nearest 1 mg. 

29
The fiber weight percent was calculated for each specimen using the expression 

initial specimenmass

mass of residual fiber Wf =100× (5)

Knowing the fiber density, the fiber volume percent Vf may be calculated using the expression 

fiber density

specimen density Vf = Wf × (6) 

Similarly, the matrix volume percent Vm and the void volume percent Vo may be calculated

using the expressions 

matrix density

specimen density Vm = (100 −Wf )× (7) 

Vo =100 −Vf −Vm (8)

The fiber and matrix densities for the two composite materials were obtained from previous

AGATE investigations [9 and 10]. For the Toray T700G/#2510 prepreg tape laminates, the fiber 

density Vf was 1.79 g/cc and the matrix density Vm was 1.266 g/cc. For the Fibercote 

T300/E765 prepreg fabric laminates, the fiber density Vf was 1.759 g/cc, and the matrix density 

Vm was 1.23 g/cc. 

6.2 CONSTITUENT CONTENT DETERMINATION RESULTS. 

Table 12 shows the results of the constituent content determinations performed using both a 

Toray T700G/#2510 [±45]2s tape laminate and a FiberCote T300/E765 [(±45)]s fabric laminate. 

The average value, standard deviation, and coefficient of variation are shown for each of the

calculated quantities. Additionally, fiber volume percents, matrix volume percents, and void 

volume percents obtained from the two test methods are compared for the two materials in 

figure 15. The results show that the two methods give similar results for both the fiber volume

percent and the matrix volume percent. For both the tape and the fabric laminates, the average 

values of the fiber volume and matrix volume percents are higher for the EN 2564 Method A test 

method than the ASTM D 3171 test method. However, none of the differences were statistically 

significant. Note that the higher values of fiber volume and matrix volume percents determined 

using the EN 2564 test method produced negative values of void volume percents, an indication 

of inaccuracies in the procedure. In contrast, the void volume percents calculated using the 

ASTM D 3171 procedure were positive for both the tape and fabric laminates. 

30
TABLE 12. CONSTITUENT CONTENT DETERMINATION RESULTS 

31 

Laminate Test Method

Composite 

Density 

(g/cc)

Fiber 

Content 

(wt %) 

Resin 

Content 

(wt %) 

Fiber 

Volume

(vol %) 

Resin 

Volume

(vol %) 

Void 

Volume

(vol %) 

Avg. 1.585 64.8 35.2 57.4 44.1 -1.5St. Dev. 0.010 1.24 1.24 1.18 1.56 0.78

EN 2564 Method A 

c.v. (%) 0.65 1.92 3.5 2.0 3.5 -54 

Avg. 1.540 65.0 35.0 56.0 42.5 1.5St. Dev. 0.010 0.55 0.55 0.74 0.55 0.52

Toray T700G/#2510 Tape Laminate [±45]2s

ASTM D 3171 Method I procedure B 

c.v. (%) 0.63 0.84 1.6 1.32 1.30 35

Avg. 1.523 61.8 38.2 53.5 47.3 -0.8St. Dev. 0.006 0.89 0.89 0.82 1.1 0.47

EN 2564 Method A 

c.v. (%) 0.38 1.44 2.3 1.5 2.3 -59 

Avg. 1.506 61.9 38.1 53.0 46.6 0.4St. Dev. 0.004 0.98 0.98 0.91 1.2 0.36

FiberCote T300/E765 Fabric Laminate [(±45)]s ASTM D 

3171 Method I procedure B 

c.v. (%) 0.27 1.59 2.6 1.7 2.5 93.4 
0

10

20

30

40

50

60

70

V

olu

me Percent (%)

prEN 6031

ASTM 3816

Fiber

Volume

Resin

Volume

Void

Volume

Fiber

Volume

Resin

Volume

Void

Volume

Toray T700G/#2510

Tape Laminate

FiberCote T300/E-765

Fabric Laminate

0

10

20

30

40

50

60

70

V

olu

me Percent (%)

prEN 6031

ASTM 3816

Fiber

Volume

Resin

Volume

Void

Volume

Fiber

Volume

Resin

Volume

Void

Volume

Toray T700G/#2510

Tape Laminate

FiberCote T300/E-765

Fabric Laminate

FIGURE 15. CONSTITUENT CONTENT DETERMINATIONS FROM TAPE AND 

FABRIC LAMINATES

In summary, EN 2564 Method A and ASTM D 3171 Method I procedure B produced similar 

values for both the fiber volume and matrix volume percents. The small differences observed in

the average values of these quantities were not statistically significant. However, the increased

accuracy of the ASTM D 3171 test method due to the larger specimen size and the greater 

weighing accuracy produced more realistic values of void volume fraction than the EN 2564 

Method A test method. 

7. SUMMARY OF RESULTS. 

Following the comparative assessments of equivalence performed previously, four types of tests 

were done to provide additional test data to assess test method equivalency. The conclusions are 

presented below for each of the four types of tests. All testing was performed using both Toray 

T700G/#2510 carbon/epoxy tape laminates and FiberCote T300/E765 carbon/epoxy plain weave 

fabric laminates. Mechanical testing was performed at room temperature/ambient conditions and 

at 82°C/wet conditions. 

Lamina compression tests were performed to investigate the effects of different specimen gage 

lengths. Although similar gage lengths are listed for the prEN 2850-B and SACMA SRM 1 test

32 
methods (5 mm versus 4.75 mm, respectively), the AMS 2980 and 3970 specifications specify a 

12.5-mm gage length. Thus, the lamina compression tests were performed using specimens with 

both 4.75- and 12.5-mm gage lengths. The results suggested that the gage length difference

(4.75 mm versus 12.5 mm) can produce significant differences in the apparent lamina 

compression strength. However, this difference is believed be due to specimen buckling that 

occurred in the specimens with longer gage lengths, which is an unacceptable failure mode. 

Laminate compression tests were performed to investigate whether the method used to load the 

test fixture affected the compression strength. The SACMA SRM 3 and ASTM D 6484 test 

methods, developed for open-hole compression tests, were followed using specimens without a 

hole. Whereas the ASTM D 6484 method has traditionally required hydraulic wedge grips to

grip the test fixture, the SACMA SRM 3 test method allows the test fixture to be end-loaded 

between two parallel platens of the test machine. Thus, follow-on tests were recommended to 

determine the effects of the loading method on the delivered compression strength of composite

laminates. The results suggested that the test fixture of the SACMA SRM 3-94 test method was 

not suitable for end loading of laminate compression specimens without an additional clamping 

force applied near the specimen ends to prevent end-brooming failures. Limited testing 

performed with additional clamping force, using C-clamps, was not adequate to eliminate endbrooming failures in all cases. Thus, it could be concluded that end loading the laminate 

compression test specimens did not produce equivalent test results to shear loading. However, it 

is expected that through the modification of the existing test fixture to include more clamping 

bolts, an end-loaded test procedure can be amended that is capable of producing equivalent test 

results to the shear-loaded ASTM D 6484 test method. In 2004, the ASTM D 6484 test method 

was modified to include both shear and end loading of the test fixture. 

Two test methods were compared for in-plane shear testing using ±45° type composite laminates 

loaded in tension. Although both the prEN 6031 test method and the AMS 2980 and 3970 

specifications require an 8-ply +45° laminate for either unidirectional tape or woven fabric, 

ASTM D 3518 requires 16-, 20-, or 24-ply unidirectional tape laminates and 8-, 12-, or 16-ply 

woven fabric laminates. Since specimen thickness effects on strength have been reported in the 

literature, follow-on tests were performed using multiple-thickness specimens fabricated from

both tape and fabric materials. The results showed that the 0.2% offset shear strength, the 5%

shear strength measures, and the shear moduli calculated following the prEN 6031/AMS and 

ASTM D 3518 test methods were in good agreement and independent of laminate thickness over 

the thickness ranges specified in the two test methods. Thus, the two shear test methods are 

believed to produce equivalent results when testing either tape or fabric laminates. 

Constituent content was determined to compare procedures EN 2564 Method A and ASTM D 

3171 Method I procedure B. Although both procedures use the acid digestion method to 

determine the constituent content, two significant differences were examined: the required

specimen size and the required weighing accuracy. The results showed that EN 2564 Method A 

and ASTM D 3171 Method I procedure B produced similar values for both the fiber volume and 

the matrix volume percents. The small differences observed in the average values of these 

quantities were not statistically significant. However, the increased accuracy of the ASTM D

3171 test method due to the larger specimen size and the greater weighing accuracy produced 

more realistic values of void volume fraction than the EN 2564 Method A test method. 

33 
8. REFERENCES. 

1. Carbon Composite Wet Repair Qualification Program Report to the Commercial Aircraft 

Composite Repair Committee: Tenax HTA 5131 200tex f3000 / Epocast 52 A/B, Report 

No. 2192-JRL-140901/Q077-1, Tenax Fibers GmbH, Wuppertal, Germany, May 2002. 

2. SAE International Aerospace Material Specification (AMS) 2970, “Technical 

Specification: Carbon Fiber Fabric and Epoxy Resin Wet Lay-Up Repair Material,” 

November 1996. 

3. MIL Handbook 17 Revision F, Composite Materials Handbook. 

4. “ASTM/MIL-HDBK-17/SACMA Review of Selected AECMA Test Methods,” October 

10, 1995, Rich Fields, editor (email). 

5. SAE International Aerospace Material Specification (AMS) 3970, “Technical 

Specification: Fiber Fabric Repair Prepreg, 125°C (250°F) Vacuum Curing,” December

1999. 

6. Fields, R.E., “Survey of the Test Methods Within SAE AMS 3970,” unpublished report, 

June 2002. 

7. Adams, Daniel O., “A Comparison of CEN and ASTM Test Methods for Composite 

Materials,” FAA report DOT/FAA/AR-04/24, June 2004. 

8. Kellas, S., Morton, J., and Jackson, K.E., “Damage and Failure Mechanisms in Scaled

Angled-Ply Laminates,” Fourth Composites Symposium on Fatigue and Fracture, ASTM 

STP 1156, American Society for Testing and Methods, 1993, pp. 257-280. 

9. Tomblin, J., Sherraden, J., Seneviratne, W., and Raju, K.S., “A-Basis and B-Basis Design

Allowables for Epoxy-Based Prepreg—TORAY T700GC-12K-31E/#2510Unidirectional 

Tape,” AGATE-WP3.3-033051-135, October 2002. 

10. Tomblin, J., Seneviratne, W., Sherraden, J., and Seneviratne, N., “Laminate Design

Allowables for Epoxy-Based Prepreg—FiberCote Graphite Fabric T300 3KPW/E765,” 

AGATE-WP3.3-033051-109, September 2002. 

11. ASTM D 5229, “Standard Test Method for Moisture Absorption Properties and 

Equilibrium Conditioning of Polymer Matrix Composite Materials,” ASTM International,

West Conshohocken, PA, 1998. 

12. prEN 2823, “Determination of the Effect of Exposure to Humid Atmosphere on Physical 

and Mechanical Characteristics,” European Association of Aerospace Industries 

(AECMA), 1998. 

34 
13. prEN 2850, “Carbon Fiber Thermosetting Resin Unidirectional Laminates—Compression

Test Parallel to Fiber Direction,” European Association of Aerospace Industries

(AECMA), 1997. 

14. SACMA SRM 1R-94, “Test Method for Compressive Properties of Orientated FiberResin Composites,” Suppliers of Advanced Composite Materials Association, Arlington, 

VA, 1994. 

 

15. Wyoming Test Fixtures, Inc., Laramie, WY, www.wyomingtestfixtures.com.

16. Adams, Daniel O. and Adams, Donald F., “Tabbing Guide for Composite Test 

Specimens,” FAA report DOT/FAA/AR-02/106, October 2002. 

17. SACMA SRM 3-94, “Open-Hole Compression Properties of Orientated Fiber-Resin 

Composites,” Suppliers of Advanced Composite Materials Association, Arlington, VA,

1994. 

18. ASTM D 6484, “Standard Test Method for Open-Hole Compressive Strength of Polymer

Matrix Composite Laminates,” ASTM International, West Conshohocken, PA, 1999.

19. prEN 6031, “Determination of In-Plane Shear Properties (±45o Tensile Test),” European 

Association of Aerospace Industries (AECMA), 1995. 

20. ASTM D 3518, “Standard Test Method for In-Plane Shear Response of Polymer Matrix 

Composite Materials by Tensile Test of ±45o Laminate,” ASTM International, West 

Conshohocken, PA, 2001. 

21. EN 2564, “Carbon Fiber Laminates—Determination of the Fiber, Resin, and Void 

Contents,” European Association of Aerospace Industries (AECMA), 1998. 

22. ASTM D 3171, “Standard Test Method for Constituent Content of Composite Materials,” 

ASTM International, West Conshohocken, PA, 1999. 

23. ASTM D 792, “Standard Test Method for Density and Specific Gravity (Relative 

Density) of Plastics by Displacement,” ASTM International, West Conshohocken, PA, 

2001. 

24. ISO 1183, “Plastics—Methods for Determining the Density and Relative Density of NonCellular Plastics.” 

35/36 
APPENDIX A—PHOTOGRAPHS OF FAILED SPECIMENS

FIGURE A-1. LAMINA COMPRESSION T700G/#2510 TAPE SPECIMENS TESTED 

ACCORDING TO CEN prEN 2850-B/AMS SPECIFICATIONS (12.5-mm GAGE LENGTH) 

AT ROOM TEMPERATURE/AMBIENT CONDITIONS

A-1 
FIGURE A-2. LAMINA COMPRESSION T700G/#2510 TAPE SPECIMENS TESTED 

ACCORDING TO SACMA SRM 1R-94 SPECIFICATIONS (4.75-mm GAGE LENGTH) AT 

ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-2 
FIGURE A-3. LAMINA COMPRESSION T700G/#2510 TAPE SPECIMENS TESTED 

ACCORDING TO CEN prEN 2850-B/AMS SPECIFICATIONS (12.5-mm GAGE LENGTH) 

AT 82oC/WET CONDITIONS 

A-3 
FIGURE A-4. LAMINA COMPRESSION T700G/#2510 TAPE SPECIMENS TESTED 

ACCORDING TO SACMA SRM 1R-94 SPECIFICATIONS (4.75-mm GAGE LENGTH) 

AT 82oC/WET CONDITIONS 

A-4 
FIGURE A-5. LAMINA COMPRESSION T300/E-765 FABRIC SPECIMENS TESTED 

ACCORDING TO CEN prEN 2850-B/AMS SPECIFICATIONS (12.5-mm GAGE LENGTH) 

AT ROOM TEMPERATURE/AMBIENT CONDITIONS

A-5 
FIGURE A-6. LAMINA COMPRESSION T300/E-765 FABRIC SPECIMENS TESTED 

ACCORDING TO SACMA SRM 1R-94 SPECIFICATIONS (4.75-mm GAGE LENGTH) AT 

ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-6 
FIGURE A-7. LAMINA COMPRESSION T300/E-765 FABRIC SPECIMENS TESTED 

ACCORDING TO CEN prEN 2850-B/AMS SPECIFICATIONS (12.5-mm GAGE LENGTH) 

AT 82oC/WET CONDITIONS 

A-7 
FIGURE A-8. LAMINA COMPRESSION T300/E-765 FABRIC SPECIMENS TESTED 

ACCORDING TO SACMA SRM 1R-94 SPECIFICATIONS 

(4.75-mm GAGE LENGTH) AT 82oC/WET CONDITIONS

A-8 
FIGURE A-9. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 TAPE 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-9 
FIGURE A-10. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 TAPE 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT ROOM 

TEMPERATURE/AMBIENT CONDITIONS

A-10 
FIGURE A-11. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 TAPE 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT 82oC/WET CONDITIONS 

A-11 
FIGURE A-12. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 TAPE 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) 

AT 82oC/WET CONDITIONS 

A-12 
FIGURE A-13. LAMINATE COMPRESSION SPECIMENS FROM 50/40/10 TAPE 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-13 
FIGURE A-14. LAMINATE COMPRESSION SPECIMENS FROM 50/40/10 TAPE 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-14 
FIGURE A-15. LAMINATE COMPRESSION SPECIMENS FROM 50/40/10 TAPE 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT 82oC/WET CONDITIONS 

A-15 
FIGURE A-16. LAMINATE COMPRESSION SPECIMENS FROM 50/40/10 TAPE 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

82oC/WET CONDITIONS 

A-16 
FIGURE A-17. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 FABRIC 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-17 
FIGURE A-18. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 FABRIC 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-18 
FIGURE A-19. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 FABRIC 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT 82oC/WET CONDITIONS 

A-19 
FIGURE A-20. LAMINATE COMPRESSION SPECIMENS FROM 25/50/25 FABRIC 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

82oC/WET CONDITIONS 

A-20 
FIGURE A-21. LAMINATE COMPRESSION SPECIMENS FROM 40/20/40 FABRIC 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 SPECIFICATIONS 

(END-LOADED) AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-21 
FIGURE A-22. LAMINATE COMPRESSION SPECIMENS FROM 40/20/40 FABRIC 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-22 
FIGURE A-23. LAMINATE COMPRESSION SPECIMENS FROM 40/20/40 FABRIC 

LAMINATE TESTED ACCORDING TO SACMA SRM 3-94 (END-LOADED) AT 

82oC/WET CONDITIONS 

A-23 
FIGURE A-24. LAMINATE COMPRESSION SPECIMENS FROM 40/20/40 FABRIC 

LAMINATE TESTED ACCORDING TO ASTM D 6484 (SHEAR-LOADED) AT 

82oC/WET CONDITIONS 

A-24 
FIGURE A-25. IN-PLANE SHEAR SPECIMENS FROM FOUR-PLY TAPE LAMINATE 

TESTED AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-25 
FIGURE A-26. IN-PLANE SHEAR SPECIMENS FROM EIGHT-PLY TAPE LAMINATE 

TESTED AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-26 
FIGURE A-27. IN-PLANE SHEAR SPECIMENS FROM 16-PLY TAPE LAMINATE 

TESTED AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-27 
FIGURE A-28. IN-PLANE SHEAR SPECIMENS FROM FOUR-PLY TAPE LAMINATE 

TESTED AT 82oC/WET CONDITIONS 

A-28 
FIGURE A-29. IN-PLANE SHEAR SPECIMENS FROM EIGHT-PLY TAPE LAMINATE 

TESTED AT 82oC/WET CONDITIONS 

A-29 
FIGURE A-30. IN-PLANE SHEAR SPECIMENS FROM 16-PLY TAPE LAMINATE 

TESTED AT 82oC/WET CONDITIONS 

A-30 
FIGURE A-31. IN-PLANE SHEAR SPECIMENS FROM FOUR-PLY FABRIC LAMINATE 

TESTED AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-31 
FIGURE A-32. IN-PLANE SHEAR SPECIMENS FROM EIGHT-PLY FABRIC LAMINATE 

TESTED AT ROOM TEMPERATURE/AMBIENT CONDITIONS 

A-32 
FIGURE A-33. IN-PLANE SHEAR SPECIMENS FROM FOUR-PLY FABRIC LAMINATE 

TESTED AT 82oC/WET CONDITIONS 

A-33 
FIGURE A-34. IN-PLANE SHEAR SPECIMENS FROM EIGHT-PLY FABRIC LAMINATE 

TESTED AT 82oC/WET CONDITIONS 

A-34