ARMY RESEARCH LABORATORY 

Effect of an Angle-Ply Orientation 

‘on Compression Strength 

of Composite Laminates 

by Christopher P. R. Hopped 

and Steven J. De Teresa 

ARL-TIC2003 

Approved for public release; distribution is unlimited. 

DTIC QUALITY IN8PBC’rm 4 

June 1999 
.) 

The fiidings in this report are not to be construed as an official 

Department of the Amy position unless so designated by other 

authorized documents. 

Citation of mamfactmrss or trade names does not constitute an 

official endorsement or approval of the u&. thereof. 

Destroy this report when it is no longer rmded. Do not return 

it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-2003 June 1999 

Effect of an Angle-Ply Orientation 

on Compression Strength 

of Composite Laminates 

Christopher P. R. Hoppel 

Weapons and Materials Research Directorate, ARL 

Steven J. De Teresa 

Lawrence Livemore National Laboratory 

Approved for public release: distribution is unlimited. 
An experimental program was initiated to investigate the effect of angle-ply orientations on 

the compressive strength (XlC) of 0” plies in fiber-reinforced composite laminates. Graphite 

fiber-reinforced epoxy test coupons with the generic architecture [02/#] (where 8 varied 

between 0” and 90”) and for the quasi-isotropic architecture were evaluated. The effective 

compressive strength of the 0” plies varied considerably. The results were related to the 

Poisson’s ratios of the laminates, with high Poisson’s ratios leading to high transverse tensile 

strains in the test coupons and lower-than-expected strengths. Specimens with the [O,/BO] 

architecture had both the highest Poisson’s ratio and the lowest calculated ply-level compression 

strength for the 0” plies. 

This work has implications in the selection of composite failure criteria for compression 

performance, design of test coupons for acceptance testing and the selection of laminate 

architectures for optimum combinations of compressive and shear behavior. Two commonly used 

composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different 

laminate strengths depending on the Poisson’s ratio of the laminate. This implies that the biaxial 

stress state in the laminate needs to be carefully considered before backing out unidirectional 

properties. 

. 

ii 
Table of Contents 

. 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

List of Figures ...................... . ..................... . . . . . . . . 

List of Tables ...................... . ..................... . . . . ..a t . 

Introduction ...................................................... 

Analysis .......................................................... 

Experimental ..................................................... 

Results.. ......................................................... 

Discussion ........................................................ 

Conclusions....................................~ .................. 

References.. ...................................................... 

DistributionList ................................................... 

ReportDocumentationPage ......................................... 

m 

V 

vii 

1 

2 

6 

9 

12 

14 

15 

17 

29 

. . . 

111 
INTENTIONALLY LEFTBLANK. 

iv 
List of Figures 

Figure 

1. 

2. 

3. 

4. 

5. 

6. 

7. 

Effect of ply architecture on laminate strength for .a series of laminates with 

the generic architecture [0/0/-8/O],, (0 varies between 0” and 90”) and for 

the quasi-isotropic architecture [45/90/ -45/Olz . . . . . . . . . . . . . . . . . . . . . . . . . . 

Effect of ply architecture on v,, for a series of laminates with [8/O-8/0], 

(8 varies between 0” and 90”) and for the quasi-isotropic architectures . . . . . . . . 

Transverse stresses in the 0” ply at failure (based on the maximum stress 

failure criterion) for a series of laminates with the generic architecture 

[e/o/ - e/olB (e varies between 0” and 90”) and for the quasi-isotropic 

architecture [45/90/-45/O], . . . . . ,.....e.........,................... 

Schematic of tabbed compression specimen and fixture . . . . . . . . . . . . . . . . . . . . 

Failed specimens of i60, quasi-isotropic, and unidirectional laminates . . . . . . . . . 

Failed specimens of [30/0/-30/O], laminates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Backed-out compressive strengths for the [8/0/-8/O], and quasi-isotropic 

laminates . . . . . . . . . . . . . . . . . . . ..~................................. 

Page 

4 

5 

6 

7 

11 

11 

12 
. 

I 

INTBNTIONALLY LEFTBLANK. 

. 

vi 
List of Tables 

Table Page 

1. Lamina Elastic Constants for IM7/8551-7 (Jiang and Tennyson 1989) ......... 3 

2. Lamina Failure Constants for IM7/855 l-7 (Jiang and Tennyson 1989) ......... 3 

3. Results of Laminate Compressive Tests and Backed-Out 0” Strengths ......... 10 

Vii 
IN'IENTIONALLY LEFTBLANK. 

. . . 

Vlll 
1. Introduction 

Angle-ply or axially biased composite laminates are an important class of laminates 

because they combine good properties in the axial and shear directions. The Army has been 

interested in these laminates for a variety of ballistic applications. However, the 

[30/o/-30/Ohs architecture, which offered one of the best combinations of axial and shear 

properties, had a much lower experimental compressive strength than that predicted using 

the maximum stress or maximum strain failure criteria. The present investigation was 

initiated to evaluate the cause of this low compressive strength and to evaluate the 

suitability of several failure criteria for predicting laminate compressive strength. 

Compression testing of composite laminates is important for establishing failure 

limits as well as material quality control. However, compression test results can vary 

significantly depending on the test method and the architecture of the laminate being tested 

(Camponeschi 1991). In general, unidirectional laminates give low compressive strengths 

due to instability during failure. There has been significant interest (Camponeschi and 

Hoyns 1991; Wilson et al. 1994; Welsh and Adams 1996 and 1997) in testing angle-ply or 

cross-ply composite laminates and “backing-out” the unidirectional strength of the material. 

The use of the back-out factor to calculate unidirectional strength assumes that the 

compressive failure is controlled by the axial stress state in the 0” ply. 

Several investigators have evaluated the use of angle-ply laminates to determine 0” 

compressive strength. Anquez (1994) proposed that the biaxial stress state in the composite 

laminates is important for evaluating compressive strengths. That work also proposed that 

optimum strength values could be obtained by backing out the 0” strength from a 0, /+ 60 

laminate, which has the same Poisson’s ratio as a unidirectional laminate. Welsh and 

Adams (1997) reached a similar conclusion after evaluating angle-ply laminates to obtain 

compressive strength. 

In the present study, the effect of material architecture on the compressive strength is 

evaluated. Experimental results are given for a range of angle-ply laminates, and the 

1 
backed-out unidirectional strengths are discussed in light of the biaxial stress state within 

the composite laminates. The lM7/8551-7 graphite fiber-reinforced epoxy material system 

is used for this evaluation. This material is of interest because it is used in a variety of 

Army applications. 

. 

2. Analysis 

A variety of failure’criteria exists for composite materials (Nahas 1986). Some of 

the most common are the maximum stress, the maximum strain, and the Tsai-Wu (Tsai 

1987; Tsai and Wu 1971). Of these, the maximum stress failure criterion does not account 

for any interaction between the stresses in the laminate but does identify the operative 

failure modes in the laminate. The maximum strain failure criterion provides some 

interaction between the stresses (due to Poisson’s effects) and also identifies the operative 

failure modes. The Tsai-Wu or tensor-polynomial criterion provides interaction between the 

stresses in the laminate but does not identify the specific failure mode. The Tsai-Wu 

equation is given in Equation 1, and the coefficients Fij are listed in Equations 2 through 7. 

Two other failure criteria, proposed by Hashin (1980) and Christensen (1988), differentiate 

between fiber and matrix failure modes. For the fiber-dominate failure mode, both of these 

failure criteria are similar to the maximum strain criterion. 

F,cr, + F&r2 + c.r3) + F,,o; + F&,2 + cr;) + 2F,,o, ((7, + cr,) + 

2F2+r2cr3 + F,cr,2 + FM (cr; + of) = 1 

(1) 

Fl =m!e---!- 

XlT XlC 

F2 =L-.-iX2T X2C 

Fn= ’ 

(XlT)(XlC) 

F 1 

** = (X2T)(X2C; 

F44 = 2052 - F23 > 

2 

(2) 

(3) 

(4) 

(5) 
F 

1 

66 =- 

si 

(7) 

Jiang and Tennyson (1989) evaluated the elastic constants and failure allowables for 

the IM7/8551-7 material system in the principal directions. The results of their work are 

listed in Table 1 and Table 2. For the Tsai-Wu failure criterion, Hahn and Kallas (1992) 

determined the two interaction terms that require biaxial testing: Fr2 was reported as 

4.001*10-r’ ksiV2 (8.412*10T7 MPa-“), and F23 was reported as 6.1698*10-‘” ksi-’ (1.2972*10- 

5 MPa-‘). 

Table 1. Lamina Elastic Constants for IM7/8551-7 (Jiang and Tennyson 1989) 

El1 23.5 msi 

J322 1.21 msi 

GE 0.69 msi 

“I, 0.339 

162 GPa 

8.34 GPa 

4.79 GPa 

0.339 

Table 2. Lamina Failure Constants for IM7/8551-7 (Jiang and Tennyson 1989) 

XlT 351 2417 

XlC 150 1035 

X2T 11 73 

x2c 26 176 

s12 27 183 

Using the data reported by Jiang and Tennyson (1989) and Hahn and Kallas (1992), 

the predicted ,strengths were calculated for a series of angle-ply laminates using four 

different failure criteria. The strengths were calculated using LAM3D software (Bogetti, 

Hoppel, and Drysdale 1995), which uses a “smearing-unsmearing” theory (Chou, Carleone, 

and Hsu 1972) to calculate ply-level stresses in a laminate and apply a failure criterion to 

3 
each ply. The laminates had the generic form [O/O/-B/01, (with 8 varying between 0” 

and 90’) and for the quasi-isotropic architecture [45/ 90/- 45/0h, . The predictions do not 

include thermal stresses due to manufacturing the laminate or edge effects in the test 

specimens. The results are shown in Figure 1. LAM3D was also used to calculate the 

laminate Poisson’s ratios as well as the ply-level stress states at failure. 

. 

160 

Figure 1. 

I q Max Stress ’ 

/@I Tsai-Wu 

•i Max Strain 

la Christensen / 

50 60 

Theta (degrees) 

70 80 90 quasi 

Effect of ply architecture on laminate strength for a series of laminates with 

the generic architecture [6/O/- e/01, (0 varies between 0” and 90’) and for 

the quasi-isotropic architecture [45/90/-45/01,. 

From Figure 1, the four failure criteria show similar strength predictions when 8 

equals 0” or 60” and for the quasi-isotropic architecture; however, for other values of 8, the 

predictions differ significantly. The main reason for these differences is the biaxial stress 

state in the 0” ply for each of the architectures. 

The Poisson’s ratios are shown in Figure 2. The [60/0/-60/O], and 

[45/90/-45/o&, architectures both have Poisson’s ratios close to that of the unidirectional 

laminate. For values of 8 between 0” and 60”, the Poisson’s ratio is much greater than that 

of the unidirectional lamina; the maximum Poisson’s ratio is for the [30/O/- 30/OlS 

4 
architecture. When the Poisson’s ratios are greater than those of the unidirectional laminate, 

the 0“ plies are placed in transverse tension when the laminate is loaded in compression. 

The transverse tensile stresses in the 0“ plies in the center of the laminate at failure (based 

on the maximum stress failure criterion) were calculated using LAM3D and are plotted in 

Figure 3. The [30/O/- 30/ 01s laminate shows transverse tensile loads close to the 

maximum allowable (Table 2). The transverse stresses are compressive for values of 0 

greater than 60”. These compressive stresses may add stability to the laminate and delay the 

axial compressive failure. 

1.5 , 

0 lo 20 30 40 46 50 60 70 60 90 quasi 

Theta(degrees) 

Figure 2. Effect of ply architecture on v,, for a series of laminates with [e/O/- e/01, 

(0 varies between 0” and 90”) and for the quasi-isotropic architectures. 

The interactive failure criteria show significant effects due to the transverse stress 

state. The Tsai-Wu failure criterion predicts lower laminate strengths than the other failure 

criteria for laminates with high Poisson’s ratios. For laminates with low Poisson’s ratios, 

the Tsai-Wu criterion predicts higher strengths. The maximum strain and Christensen’s 

failure criteria both predict laminate strengths similar to the maximum stress failure 

criterion, with the only exception being the prediction for the [30/O/- 30/O],, using 

Christensen’s failure criterion. For this laminate, Christensen’s criterion predicts a matrix 

dominated failure mode and a lower strength than the maximum stress or maximum strain. 

5 
Theta (degrees) 

Figure 3. Transverse stresses in the 0” ply at failure (based on the maximum stress 

failure criterion) for a series of laminates with the generic architecture 

[e/o/- e/01, (8 varies between 0” and 90’) and for the quasi-isotropic 

architecture [45/90/- 45/Ol,. The transverse stresses are tensile for values 

of 8 between 0” and 60”, compressive for values of 8 between 60” and 90”, 

and close to 0 for the 0” [60/O/- 60/01, and quasi-isotropic architectures. 

3. Experimental 

A series of laminates from the family [e/O /- 6/O],, with 8 = O”, 30”, 4S”, 60”, and 

90” were made from IM7/8551-7 unidirectional prepreg. A laminate made from the widely 

used [45/90 /- 45/ Olzs quasi-isotropic layup was also fabricated. Square 12-in panels were 

autoclave cured following the manufacturer’s recommended layup procedure and cure cycle. 

Cured panels were examined using ultrasonic C-scans and were found to be free of any 

gross porosity or delaminations. The average thickness of the cured ply was 0.0056 in. 

All compression tests were conducted using a variant of the Boeing-modified ASTM 

D695 specimen. These were 0.5-in-wide x 3.2-in-long strips of composite with either 

fiberglass or carbon fiber composite tabs adhesively bonded at each end to form a gauge 

length of 0.4 in. Carbon fiber tabs were used for the unidirectional specimens after it was 

6 
found that the weaker fiberglass would prematurely fail at the ends. The specimen is shown 

in Figure 4. It was selected because of its widespread use and compact size. Modifications 

to the standard specimen were made following the work by Haberle and Matthews (1994). 

Their work has shown that improved unidirectional strengths and reduced scatter are 

obtained when the high shear stresses near the tab end are relieved by eliminating the 

adhesive bond in this area. This unbonded area is made in a controlled manner by covering 

an area slightly greater than the gauge section of the specimen with a release-coated tape 

prior to bonding the tabs. In the present study, the stress-relief preparation was used for 

both uni- and multidirectional laminates. For comparison, a set of unidirectional specimens 

was prepared without the release tape to give fully bonded tabs. 

Adhesive H 

Kaptan - 

tape 

. 

1.4” 

Campasite s 

specrm en 

U, Cmpmite 

specrm en 

[gagesectirm: 

?I-- Ste el ins e 

_Sel 3crew 

. Figure 4. Schematic of tabbed compression specimen and fixture. 

Specimens were prepared from 6-in x 3.5-in composite plates that were cut from the 

panels using a diamond saw under flood coolant. The gauge area was covered with %-inwide Kapton tape that had a release backing. With this width tape, the final specimens have 

an intentional 0.18-in unbonded length at the tab ends. The bonding surfaces were lightly 

7 
abraded, then cleaned with acetone and isopropanol. Tabs 6 in long by 1.5 in wide were 

bonded to the composite using a O.OlO-in-thick film adhesive (3M AF-126-2). An 

aluminum alignment fixture was used during the adhesive cure to maintain the position of 

the tabs. The adhesive was cured in a press under 50-psi pressure for 1.0 hr at 250“ F. 

Shims were used in the alignment fixture to yield an adhesive bondline that was nominally 

0.005 in thick. 

All four edges of the tabbed panel were trimmed with the diamond saw using a 

previously marked panel edge for reference. The ends and the surfaces of the tabs were then 

ground flat and parallel under flood coolant using a surface grinder. 

panel was sectioned into OS-in-wide specimens using the diamond saw 

0.480-in widths using the surface grinder. 

After grinding, the 

and then ground to 

The compression test fixture shown schematically in Figure 4 is also based on some 

of the work due to Haberle and Matthews (1994). Like their design, ours utilizes two 

independent fixtures (only one is shown in the figure) and is thus free of any of the friction 

forces that are present in the standard D695 fixture. The ends of the specimen are fully 

contained in the fixture, which reduces the chance of end failures. It is designed for use in a 

high-pressure vessel for study of the effects of superimposed pressure on the failure of fiber 

composites. The two fixtures were machined from annealed 350 CVM maraging steel with 

precision rectangular holes. The holes are 0.380 in thick and 0.500 in wide, which leaves 

room for lateral Poisson’s expansion of the 0.480-in-wide specimens. This expansion is 

significant in the +30 and ~45 laminates and could lead to premature failure if constrained 

by the fixture. The thickness of the hole was designed Q accommodate different tabbed 

specimens while leaving space for the steel insert as shown in the figure. A “grip” 

compression is applied to the tabs through the steel insert via two setscrews on the side of 

the fixture. This force has been shown beneficial in preventing premature tab failures in 

compression tests (Haberle and Matthews 1994). Shims were used to center the 0.480-inwide specimen in the 0.500-in-wide slots of the fixtures. These shims were left in place 

until after the setscrews were tightened to a torque of 50 in-lb. The alignment between the 

two fixtures is maintained by inserting the whole assembly inside a precisely bored guide 

8 
tube. All tests were conducted at a stroke rate of 0.05 in/min using an MTS servo-hydraulic 

test machine. 

4. Results 

The results of the laminate compression tests are listed in Table 3. Figure 5 gives 

some examples of failure in the +60, quasi-isotropic, and unidirectional laminates. The 

failure surfaces of most of the laminates were shear-type fractures, oriented at about 70” 

with respect to the load direction (the 0” direction) or a brooming-type failure. These 

fractures were confined to the gauge section with many appearing to have occurred at one 

tab end. Both the stress-relieved and fully bonded unidirectional specimens also appeared to 

have failed at one end of the gauge section. Despite this similarity, there was a noticeable 

improvement in strength for the specimens that were stress-relieved. This result is similar 

to the findings of Haberle and Matthews (1994). The average strength of the stress-relieved 

unidirectional specimen was 231 ksi. For comparison, manufacturer’s data for this 

composite system claim a unidirectional compression strength in the range 243-252 ksi 

(Hercules Aerospace Products Group 1985), significantly higher than the results reported by 

Jiang and Tennyson (1989). 

In contrast, the &30 laminates failed almost cleanly along one of the 30” directions, 

leaving the fibers in the opposing 30” plies and the 0” plies completely severed, indicating a 

different failure mode than the other specimens. Examples of this failure mode are shown 

in Figure 6. The failure propagated well into the tab area but appeared to have initiated in 

the gauge section near the tab. 

The 0” strengths were backed-out of the experimental laminate strengths using two 

different methods. The maximum stress failure criterion method is the same as the back-out 

factor used in other studies (Camponeschi and Hoyns 1991). The backed Tsai-Wu strength 

was found by solving equations 1 through 7 for XlC (the lamina compressive strength), 

assuming 0, = o4 = 6, = 0, = 0. This approximation was made based on the macroscopic 

stress-state predicted .with LAM3D software. LAM3D uses a “smearing” methodology to 

model global laminate properties but does not model the intra-ply stresses. The backed-out 

9 
strengths are shown in Figure 7. The Tsai-Wu equation solved for XlC is given in equation 

8: 

2 

-- 

XlC= XlT G1 

l-&4&-;)- (x1;(2C~ -2F,g3p2 ’ 

Table 3. Results of Laminate Compressive Tests and Backed-Out 0” Strengths 

[45/90/-45/ 012, 96 6.5 267 267 

10 

(8) 
. 

..I _’ 

“. :- : 

I 

:, ?‘. 

..’ 

..‘.. .I 

: 

1,. :; 

., 

2; i 

.,:: : ,- . .. 

,i, ;’ _. 

. . 

z- 

[60/O/- 60/O],, [45/90/- 451 Olzs I?& (Tape) lo],, (No Tape) 

Figure 5. Failed specimens of 60, quasi-isotropic, and unidirectional laminates. 

Figure 6. Failed specimens of [30/O/- 30/01, laminates. 

11 
320 

s 300 

S. 

.K 

G 

g 260 

F 

‘8 

8 k 260 

E 

S 

0 

0 = 240 

6 

s 

S 

m 220 

200 

45 60 

Theta (degrees) 

90 quasi 

Figure 7. Backed-out compressive strengths for the [e/O/- e/01, and quasi-isotropic 

laminates. 

5. Discussion 

From the results in Table 3 and Figure 7, it can be seen that the backed-out 

unidirectional strengths for composite laminates can differ significantly depending on the 

laminate architecture as well as the method used to back out the strength. Using the TsaiWu failure criterion to back out the unidirectional strength as was done here is probably 

inappropriate for most applications because it assumes failure is dominated by the 0” axial 

compressive strength (whereas the Tsai-Wu failure criterion assumes failure is due to the 

multiaxial stress-state). However, it was done in this paper to illustrate the importance of 

the biaxial stress state in the failure of the laminate. For angle-ply laminates with Poisson’s 

ratios greater than the unidirectional lamina, the tensile transverse stresses in the 0” plies 

may contribute to lower axial compressive strengths than in other architectures. Likewise, 

for cross-ply laminates, the compressive transverse stresses that develop in the 0” plies may 

contribute to higher axial compressive strengths than in other architectures. In either case, 

12 
backing out the unidirectional strength from these laminates using the maximum stress 

failure criterion ignores the biaxial stress state and can create misleading results. The 

laminates with the same Poisson’s ratios as the unidirectional lamina (such as 

[60/0/-60/O],, or [45/90/-45/O],,) remove the biaxial stress state and are more 

appropriate for backing out the unidirectional strengths. In the present analysis, these 

architectures gave the same backed out strengths for either maximum stress or Tsai-Wu 

back out factors. 

It should be noted that all of the compressive strengths measured and calculated in 

this study were significantly higher than the 150-ksi compressive strength originally 

reported by Jiang and Tennyson (1989) and used for the comparison in Figure 1. This 

demonstrates that differences in compressive test methods can also significantly affect 

strength predictions. The laminate compressive strengths were recalculated using the 231- 

ksi unidirectional strength found in this study, and the laminate strengths increased 

proportionally. One significant difference occurred: for the [30 / 0 /- 30 / OL5 laminate with 

the 231-ksi unidirectional axial strength, the maximum stress and maximum strain failure 

criteria predicted a transverse tensile failure mode, which is supported by the difference in 

failure mode seen in this study. 

It should also be noted that the “backed-out” Tsai-Wu strengths calculated from 

equation 8 use the other failure constants from Jiang and Tennyson as listed in Table 2. 

Since these constants all have some variability, it adds to the total variability of the backedout Tsai-Wu strengths. 

As discussed in the introduction, there are two main reasons for compression testing 

composite laminates: establishing failure limits and material quality control. The main 

focus of this paper has been the risks associated with backing unidirectional strengths out of 

angle-ply laminates for establishing failure limits. While the authors do not recommend 

using a Tsai-Wu backed-out strength as was done here, it illustrates the importance of the 

biaxial stress state in compressive failure. This method of backing out unidirectional 

strengths may prove to be an effective method for comparing different failure criteria. A 

13 
. 

measure of the success of a particular failure criterion may be how consistently the same 

unidirectional strength can be backed-out for different laminates. 

6. Conclusions 

The influence of architecture on the compressive behavior of angle-ply composite 

laminates is evaluated. The analytic predictions and experimental results presented in this 

paper both show that the biaxial stress state that develops in angle-ply composite laminates 

has a significant effect on the axial compressive strength. Laminates with high Poisson’s 

ratios, such as the [30 / 0 /- 30 /Ohs , produce transverse tensile strains when they are loaded 

in axial compression and consequently have lower strengths than predicted using a 

maximum stress-type failure criterion. Similarly, laminates with low Poisson’s ratio, such 

as the [90/ OL, , produce transverse 

compression and may give artificially 

strengths. 

compressive strains when they are loaded in 

high estimates of the unidirectional compressive 

This work has implications in the selection of composite failure criterion for 

compression performance, design of test coupons for acceptance testing, and the selection of 

laminate architectures for optimum combinations of compressive and shear behavior. Two 

commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict 

significantly different lamina strengths depending on the Poisson’s ratio of the laminate. 

Compressive strength is ultimately dependent on the materials, architecture, loading 

conditions, and structural geometry. At this point, the best way to evaluate the strength of 

composite structures is to test those structures in the architectures and loading state that they 

will experience. When this is not possible, the designer needs to acknowledge the 

uncertainties in their backed-out stress and increase their factor of safety accordingly. 

14 
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15 
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Analytical and Experimental Evaluation of O/90 Laminate Tests for Compression 

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pp. 146-153, 1994. 

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STE 0944 2800 POWDER MILL RD 

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WDAMICO 

AMSRLWM BR 

J BORNSTEIN 

AMSRLWMTE 

ANJILER 

AMSRL WM BF 

J LACETERA 

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I 

: I 

28 
Composite Laminates 

622618AH80 

Christopher P. R. Hoppel and Steven J. De Teresa* 

REPORT NUMBER 

KS. Army Research Laboratory 

AT-IN: AMSRL-WMMB ARL-TR-2003 

Aberdeen Proving Ground, MD 210055069 

3. SPONSORlNG/MONlTORlNG AGENCY NAMES(S) AND ADDRESS 10.SPONSORING/MONITORlNG 

AGENCY REPORT NUMBER 

Il. SUPPLEMENTARY NOTES 

*Lawrence Livermore National Laboratory 

Liver-more, CA 94550 

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE 

Approved for public release; distribution is unlimited. 

13. ABSTRACT(Maximum 200 words) 

An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive 

strength (XlC) of 0” plies in fiber-reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with 

the generic architecture [O@] (where 8 varied between 0” and 90”) and for the quasi-isotropic architecture were 

evaluated. The effective compressive strength of the 0” plies varied considerably. The results were related to the 

Poisson’s ratios of the laminates, with high Poisson’s ratios leading to high transverse tensile strains in the test coupons 

and lower-than-expected strengths. Specimens with the [0#30] architecture had both the highest Poisson’s ratio and 

the lowest calculated ply-level compression strength for the 0” plies. 

This work has implications in the selection of composite failure criteria for compression performance, design of 

test coupons for acceptance testing and the selection of laminate architectures for optimum combinations of compressive 

and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict 

significantly different laminate strengths depending on the Poisson’s ratio of the laminate. This implies that the biaxial 

stress state in the laminate needs to be carefully considered before backing out unidirectional properties. 

14. SUBJECT TERMS 15. NUMBER OF PAGES 

34 

composites, compression, failure criteria 16. PRICE CODE 

17. SECURITY CLASSIFICATION 16. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT 

OF REPORT OF THIS PAGE OF ABSTRACT 

UNCLASSIFIED UNCLASSIFIED UNCLASSFJED UL 

ISN 7540-01-2605500 

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