TMM4175 Polymer Composites

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7. TEST METHODS¶

Tensile tests of unidirectional lamina¶

Uniaxial tensile tests are conducted on unidirectional laminae to determine the longitudinal and transverse Young's moduli $E_1$ and $E_2$, the Poisson's ratios $\nu_{12}$ and $\nu_{21}$ as well as the basic longitudinal and transverse strength parameters $X_T$ and $Y_T$.

Compressive tests of unidirectional lamina¶

The longitudinal compressive strength $X_C$ and the transverse compressive strength $Y_C$ are obtained by compressive tests of unidirectional lamina. Compression testing of composites is difficult because of the tendency for premature failure due to buckling. Techniques used to mitigate this problem are either based on a very short unsupported length, or some kind of support mechanisms (anti-buckling device).

Shear tests¶

There are several commonly used test methods for determining the shear modulus $G_{12}$ and the shear strength $S_{12}$:

Tensile testing of symmetric [$\pm$45] laminates and back calculating the shear stress and shear strain
Off-axis tensile testing: The testing is conducted on unidirectional laminae where the fiber orientation is oriented by a relatively small angel (about 10 degrees) relatively to the loading direction
Torque on thin-wall tubular hoop-wound specimen
Rail shear test
Arcan test
Iosipescu test.

Biaxial testing¶

Of the various methods that have been proposed, the tubular speciment appears to be the most versatile and offers the greatest potential. It offers the possibility of applying any desired biaxial state of stress by the the combination of axial load, internal or external pressure and torque.

Flexural testing¶

The two methods most usually used for the determination of flexural properties of laminates are the three-point and four-point tests.

Interlaminar fracture mechanical testing¶

Interlaminar crack propagation can occur in mode I, II and III corresponding to the fracture energies $G_{Ic}$, $G_{IIc}$ and $G_{IIIc}$. In TMM4175, the double cantilever beam (DCB) test for mode I, and the end-notch flexure (ENF) test for mode II will be discussed.

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