evaluation of in-plane shear test methods for composite material laminates

8/18/2019 Evaluation of in-plane Shear Test Methods for Composite Material Laminates

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Journal of Chongqing University: English Edition

Architecture & Civil Engineering

Vol. 6 No. 3 September 2007

Ar ticle ID: 1671-8224(2007)03-0221-06

To cite this article: WANG Yan-lei, HAO Qing-duo, OU Jin-ping. Evaluation of in-plane shear test methods for composite material laminates [J]. J Chongqing Univ:

Eng Ed (ISSN 1671-8224), 2007, 6(3): 221-226.

Evaluation of in-plane shear test methods for composite material laminates

WANG Yan-lei 1,a

, HAO Qing-duo 1, OU Jin-ping

1,2

1School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, P.R. China

2Dalian University of Technology, Dalian 116024, P.R. China

Received 31 December 2006; revised 25 February 2007

Abst ract: In-plane shear properties of composite material laminates are very important in structural design of composite

material. Four commonly used in-plane shear test methods were introduced in this paper. In order to study the differences of

various shear test methods, two ASTM standard in-plane shear test methods for composite material laminates were

experimentally investigated. They are ±45° tensile shear test (ASTM D3518) and V-notched rail shear test (ASTM D7078).

Five types of composite material laminates composed of E-glass fiber fabric and vinyl ester resin were utilized, whose stacking

sequences are [0]3s, [0/90]3s, [CSM/0/90]2s, [±45]3s and [(0/90)2/(±45)2/(0/90)2]s, respectively. The test results indicate

that the±45° tensile shear test can predict shear moduli of composite material laminates accurately. However, the predictions

of shear strength using ±45° tensile shear test are significantly lower than those of V-notched rail shear test.

Keywords: in-plane shear test; ±45° tensile shear test; V-notched rail shear test; composite material laminate

CLC number: TB332 Document code: A

1 Introduction a

Advanced composite materials have been widely

applied in military structures and civil engineering.

Therefore, the accurately experimental evaluation of

the mechanical properties of these composite

materials for use in design has become increasingly

important. The determination of composite materials

shear properties is one of the more difficult tasks,

because of the anisotropic nature of these materials

and their nonlinear response in shear. An ideal shear

test method should provide a region of pure and

uniform shear, be reproducible, require no special test

equipment, and provide the entire stress-strain

response to failure from a single specimen [1-2].

a WANY Yan-lei (王言磊): Male; Born 1978; PhD candidate;

Research interests: applications of composite material in civil

engineering; E-mail: [email protected].

* Funded by the Natural Science Foundation of China

(No.50308008) and Western Transportation Science and

Technology Foundation of China (No.200431882021).

Although many shear test methods have been

developed for use with composite materials over the

years, none of them completely satisfies all of these

criteria. Thus, there remains considerable confusion in

using the shear test methods.

Four most commonly used in-plane shear test

methods for composite material laminates were

described in this paper, viz. ±45° tensile shear, rail

shear, Iosipescu shear and V-notched rail shear. Two

ASTM standard in-plane shear test methods were

experimentally investigated to study their differences.

They were ±45° tensile shear test method (ASTM

D3518 [3]) and V-notched rail shear test method

(ASTM D7078 [4]). Five types of composite material

laminates composed of E-glass fiber fabric and vinyl

ester resin were used in this paper. .

2 Four in-plane shear test methods

2.1 ±45° tensile shear test method

In this shear test method, a [±45°]ns laminate is

loaded in axial tension to determine the in-plane shear


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222 Vol. 6 No. 3

properties. This test method is frequently used

because the specimens are easy to be fabricated and

no special test fixture is required [2]. It is a simple test

method for predicting in-plane shear modulus with an

acceptable precision [5]. However, the laminate is not

in a state of pure in-plane shear stress [6]. Thus the

calculated shear stress and strain values at failure

should only be used with caution. There are several

test standards/guides based on this test method, i.e.,

ASTM D3518 [3], BS EN ISO 14129 [7] and GB

3355 [8].

2.2 Rail shear test method

Rail shear test method is used to determine the in-

plane shear properties through two/three pairs of

loading rails (Fig.1), which are used to clamp the

specimen and introduce shear force in the specimen

[9]. The specimen is loaded on its faces, eliminating

the problem of edge crushing, and has a wide gage

region. There are three primary weaknesses of this

method. Firstly, slipping of the specimen in the rails

for the laminate with high shear strength may lead to

premature bearing failures as the bolts contact edges

of the specimen holes, thus it would nullify the test.

Secondly, the user must drill multiple holes in the

specimen, which may introduce interlamination

debonding. Thirdly, a uniform shear stress is not

developed within the specimen, and stress

concentrations are induced in the regions where the

rails are clamped onto the specimen [10-11]. ASTM

D4255 [12] is one of the test standards/guides based

on this test method.

2.3 Iosipescu shear test method

V-notched beam (Iosipescu) shear test method was

originally developed for isotropic materials by N.

Iosipescu [1]. The V-notched specimen is loaded by a

special test fixture (Fig.2a) for approaching the pure

shear state. This test specimen incorporates V-notches,

which results in a relatively uniform shear stress state

and fails within the gage section between the notches.

In general, Iosipescu shear test can obtain satisfyingresults. So this method was the most commonly used

shear test method in the past [9]. However, the

relatively small gage section is not well suited for

some textile composites with coarse fiber

architectures and large unit cell sizes. Another

weakness of the method is that the specimen is loaded

by concentrated forces on its edges. In some cases,

this may lead to edge crushing prior to shear failure.

These concentrated forces may also disturb the

uniform stress state within the gage section [1,11].

This test method has been adopted as ASTM D5379

[13] and HB 7237 [14] at present.

Fig. 1 Rail shear test fixture: (a) Two rails; (b) Three rails

2.4 V-notched rail shear test method

V-notched rail shear test is essentially a

combination of Iosipescu shear test and two-rail shear

test, eliminating certain weaknesses of each. It is

considered as the most promising shear test method so

far [11]. The ends of the V-notched specimen are

clamped by two pairs of loading rails and the rails

introduce shear forces into the specimen through the

specimen face. The special test fixture is shown in

Fig.2b. Compared with Iosipescu shear test method,

the present test method utilizes a specimen with alarger gage section, and face loading allows higher

shear forces to be applied to the specimen.

Additionally, this method eliminates the problem of

edge crushing. In contrast to two-rail shear test, the V-

notched rail shear test provides specimen gripping

without the need for holes in the specimen and

eliminates potential premature bearing failures

because of the slipping the specimen introducing the

contact between the bolts and the specimen [15]. Also,

this method can obtain more uniform shear stress statewithin the gage section of the specimen than two-rail

shear test [16]. ASTM D7078 [4] is the only test

a b


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223Vol. 6 No. 3

standard based on this test method at present.

Fig. 2 Test fixture of (a) Iosipescu shear; (b) V-notched rail shear

3 Specimens and tests

To ensure the typicality of the contrast test, five

types of composite material laminates composed of E-

glass fiber fabric and vinyl ester resin were selected in

the test, and the laminates were fabricated by hand

lay-up. The detailed parameters of the five types of

composite laminates are shown in Table 1. The five

types of composite laminates were among the most

commonly used composite laminates. The vinyl ester

resin with model of Swancor-901 provided by

Swancor Ltd was selected in the test. The fiber

volume fractions of the five composite laminates were

all about 30%. According to ASTM D3518 and

ASTM D7078, standard specimens were fabricated, as

shown in Fig.3. Three specimens were tested for each

type of composite material laminates.

Table 1 Parameters of five types of composite material laminates

Label Stacking sequence Type of fabric Thickness/mm

L700 [0]3s Unidirectional (0) fabric with weight of 700 g/m2 4.7

LT600 [0/90]3s Bidirectional (0/90) equally proportional fabric with

weight of 600 g/m2

4.5

EMK750 [CSM/0/90]2s Compound fabric with weight of 750 g/m2, which is

composed of chopped strand mat (CSM) with weight of

300 g/m2 and bidirectional (0/90) fabric with weight of

450 g/m2. The ratio of fiber in 0° and 90° direction for

bidirectional fabric is 2.

4.1

BX600 [±45]3s ±45° equally proportional fabric with weight of 600 g/m2 4.4

COM [(0/90)2/ (±45)2/(0/90)2]s 12 layers laminates composed of LT600 (0/90) and BX600

(±45) fabrics

8.7

a b

Fig. 3 Shapes and dimensions (unit: mm) of (a)±45° tensile

specimen; and (b) V-notched rail shear specimens

Back-to-back two-element strain gauges of Model

BE120-10AA in both longitudinal and transverse

directions were used in ±45° tensile shear specimens.

Back-to-back two-element (±45°) strain gauges of

Model BE120-6AA were mounted to the loading axis

and centered between the notches in V-notched rail

shear specimens. The notches on the V-notched rail

shear specimens were required to be aligned with the

loading center to obtain a true shear stress in the

region between two notches. The special test fixture

for V-notched rail shear test was the same as that

shown in Fig. 2b. All the tests were conducted by

universal material testing machine of Model Instron-

5500R. A head displacement rate of 2 mm/min wasused in all specimens. Strain data was acquired by a

strain data recording device of Model DH5935.

4 Test results and analysis

The in-plane shear properties of five composite

material laminates using 2 shear test methods are

listed in Table 2. Compared with V-notched rail shear

test, the errors of shear moduli obtained by ±45°

tensile shear test are all within 7%. Therefore, it can be concluded that ±45° tensile shear test can predict

the shear moduli of composite material laminates

250

50 2 5

45°

90°

5 6

r =1.3

76

3 0 . 6

1 2 . 7

1 2 . 7

25.3 25.325.4

a b


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224 Vol. 6 No. 3

accurately. However, the predictions of shear strength

by ±45° tensile shear test have big errors. The shear

strengths obtained in ±45° tensile shear test are 12%

to 39% smaller than the results obtained in V-notched

rail shear test. Past test results also showed this

tendency, and it is concluded that ±45° tensile shear

test may lead to an error as much as 30% to 40% in

shear strength [6].

Typical shear stress-shear strain curves of five

composite material laminates using 2 shear test

methods are shown in Figs. 4 to 8. Results from the

two tests have a very good agreement until shear

strain reaches about 0.6% in general. The curves

obtained in ±45° tensile shear test gradually fall

behind the curves obtained in V-notched rail shear test

when shear strain is bigger than 0.6%. However, the

whole curves of BX600 laminate have a relatively

good agreement. Moreover, the prediction of ultimate

shear strain using ±45° tensile shear test is also small.

5 Discussions

In ±45° tensile shear test, a [±45°]ns laminate is

loaded in axial tension. The in-plane axial tensile

force induces a shear stress τ 12 and longitudinal and

transverse normal tensile stress, σ 1 and σ 2, in each

lamina (ply). From classical lamination theory, the

lamina shear stress and shear strain induced by the

axial force are respectively [5]

2/12 x

σ τ ±= , (1)

y x ε ε γ −=12 , (2)

Table 2 In-plane shear strengths (τ 12,I and τ 12,II) and shear moduli (G12,I and G12,II) of five composite laminates by respectively I, ±45° tensile,

and II, V-notched rail shear methods

Laminate τ 12,I/MPa τ 12,II/MPa12,I

12,II

%τ

τ G12,I/GPa G12,II/GPa12,I

12,II

%G

G

L700 31.78 48.37 66 2.32 2.49 93

LT600 39.74 47.04 84 2.31 2.40 96

EMK750 55.35 91.18 61 2.89 3.08 94

BX600 139.68 159.45 88 6.94 6.52 106

COM 88.26 120.97 73 3.52 3.67 96

Fig. 4 Shear stress-shear strain curves of typical L700 laminate Fig. 5 Shear stress-shear strain curves of typical LT600 laminate

Fig. 6 Shear stress-shear strain curves of typical EMK750 laminate Fig. 7 Shear stress-shear strain curves of typical BX600 laminate

Shear strain/%

S h e a r s t r e s s / M P a

±45° tension

V-notched rail

0

1 2 3 4 5 6

10

20

30

40

0

50

Shear strain/%


±45° tensionV-notched rail

0

0

1 2 3 4 5 6

10

20

30

40

50

Shear strain/%


±45° tension

V-notched rail

0

1 2 3 4 5 6

20

40

60

0

80

100

Shear strain/%

S h e a r s t r e s s / M P a ±45° tension

V-notched rail

0

0.51.0 1.5

2.02.5 3.0

30

60

90

150

0.0

180

120


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225Vol. 6 No. 3

Fig. 8 Shear stress-shear strain curves of typical COM laminate

where τ 12 is lamina shear stress (ply material

coordinate axis); γ 12 is lamina shear strain; σ x is

laminate axial stress (laminate coordinate axis); ε x is

laminate axial strain; and ε y is laminate transverse

strain.

The lamina shear modulus, G12, is determined by

dividing Eq. (1) by Eq. (2).

121212/ γ τ =G (3)

However, the laminae are not in a state of pure

shear. In-plane normal stresses exist that are a

function of the applied axial stress σ x and the shear

stress τ xy induced in each ply. The normal stresses forthe +45° plies are [1]

2/)(1 xy x

τ σ σ += , (4)

2/)(2 xy x

τ σ σ −= . (5)

The sign of the induced shear stress, τ xy, must be

reversed in Eqs. (4) and (5) to describe the normal

stresses in −45° plies.

All angle-ply laminates also have interlaminar

stresses near the free edges of the laminates [9]. These

typically become negligible beyond about one

laminate thickness from each edge. The only non-zero

interlaminar stress in a [±θ ]ns angle-ply laminate is the

stress τ xz, stresses τ yz and σ z being equal to zero. The

stress τ xz is a maximum for [±11.5°]ns laminates and is

approximately one-fourth this magnitude for [±45°]ns

laminates [1].

When the intent is to determine the in-plane shear

properties (τ 12) in ±45° tensile shear test, interlaminar

shear (τ 13) is also present in the specimen (associatedwith the scissoring action of the ±45° laminate under

load), along with axial (σ 1) and transverse (σ 2) tensile

stresses in each ply [1]. Although the axial tensile

stresses may not be particular detrimental because of

the high stiffness and strength in this (fiber) direction,

the transverse tensile stresses can be quite detrimental

because of the typically low strength of the material in

this direction. The effect of transverse tensile stresses

on a given ply is minimized by the fiber reinforcement

of the neighboring piles. Moreover, the surface plies

of a given specimen being constrained by only one

neighboring ply (as opposed to interior plies, which

are constrained by a ply on each side) represent the

weakest link in a ±45° specimen. During the tensile

loading of this test specimen, the first ply failures

consist primarily of tensile stresses (or mixed mode)

failures, rather than pure shear failures. Because of

this, the actual material shear strength can not be

obtained from this test. Except for the case of

materials capable of sustaining large axial test

specimen strains (greater than about 3.0%), the shear

stress at failure is believed to underestimate the actual

material shear strength [3].

The result is that the test specimen actually fails

under a combined stress state, with the failure mode

depending upon the relative magnitudes of the in-

plane shear, interlaminar shear, and transverse tensile

strength of the particular composite material being

tested. Thus, sometimes the in-plane shear strength

presumably being measured agrees well with other in-

plane shear test results, but sometimes it may be

considerably lower.

6 Conclusions

Five types of E-glass fiber fabric/vinyl ester resin

laminates were fabricated by hand lay-up, and tested

by two ASTM standard in-plane shear test methods:

±45° tensile shear test (ASTM D3518) and V-notched

rail shear test (ASTM D7078). Typical shear stress-

shear strain curves of the five composite material

laminates were obtained. Compared with V-notched

rail shear test, ±45° tensile shear test can predict shear

moduli of composite material laminates accurately

with the biggest error of 7%. However, the prediction

of shear strength using±

45° tensile shear test has a

bad precision with the error as much as 12% to 39%.

Moreover, the predictions of shear strain in the state

Shear strain/%


±45° tension

V-notched rail

0

1 2 3 4 5 6

20

40

60

0

140

100

80

120


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226 Vol. 6 No. 3

of high shear stress using ±45° tensile shear test also

have some errors. ±45° tensile shear test provides a

simple test method for predicting in-plain shear

modulus with an accepted precision. However, the

laminate is not in a state of pure in-plane shear stress,

because an in-plane normal stress component is

present through the gage section and a complex stress

field is present close to the free edges of the laminate.

Thus the calculated shear stress and strain values at

failure should only be used with caution.

Acknow ledgements

This work was partially funded by the Natural

Science Foundation of China (No.50308008) and

Western Transportation Science and Technology

Foundation of China (No.200431882021).

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Edited by ZHAO Jing

evaluation of in-plane shear test methods for composite material laminates

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