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sting is most often performed to measure the in-plane shear properties of a composite including in-plane shear modulus, in-plane shear strength or both [6]. Most common in-plane shear test methods are explained below.

2.3.1 ±450 Tensile Shear Test Method

In this test method, to determine the in-plane shear properties, the laminate is loaded in axial tension. For this test no special test fixture is required and the specimen is easy to fabricate, as a result this test method is frequently used. By using this test method the in-plane shear modulus is predicted with an acceptable precision. As the laminate will not be in a state of pure in-plane shear stress, the calculated shear stress and strain values at failure should be used with caution [5].

Based on the experimental results obtained in the study, the main advantages of ±450 tensile specimen are [11]

Good reproducibility

Easy to make

Is a conventional test

Economical in material

Requires simple data reduction

Easy to test at high or low temperature

The figure below shows the ±450 tensile specimen with load applied in the tensile direction. The fibre direction is also shown in the figure.

Fibber direction x

Load direction

Figure 2.9: ±450 Tensile Specimen [11].

2.3.2 100 Off-axis Tensile Test

The 100 Off-axis tension coupon is another simple specimen similar in geometry to the [±450] tension coupon. In this test the laminate is unidirectional with fibres oriented at 100 to the tensile load axis. When the 100 off-axis specimen is subjected to a uniaxial tensile load, a bi-axial stress state occurs. This bi-axial stress state consists of three stresses: longitudinal, transverse and in-plane shear on the 100 plane. The in-plane shear value will reach its critical value once the 100 off-axis tensile specimen fails. The 100 off-axis tensile specimen is used for measuring in-plane shear strength of unidirectional fibre composites. The main benefits of 100 off-axis specimen are as follows [11].

Specimen has uniform shear stress through the thickness.

It can be adapted to testing for environmental and elevated temperature effects.

It can be readily used for fatigue testing and dynamic and impact loading characterization.

Specimens are free of laminate residual stress

The in-plane shear strain reaches its maximum value when the angle between the load and fibre direction is about 100

As the 100 off-axis tensile specimen is very sensitive while calculating the in-plane shear stress, fibre direction, strain-gauge positioning and load alignment must be kept with ±10 to avoid disorientations errors. The 100 off-axis specimen is shown below.

Fibber direction X load direction

Figure 2.10: 100 Off-axis specimen [11].

2.3.3 Iosipescu test

Nicolne Iosipescu of Romania first proposed this test method in 1967 [11]. The iosipescu test applies an unvarying shear stress to the specimen. It is comparatively simple, precise and reproducible. This test is not limited to any kinds of special materials. It uses small, flat, easily prepared samples that do not require bonding to end-tabs [12].

By applying two counteracting moments