D1 Mechanical Testing of Laminates

Topic

The mechanical tests for this model are standards specific to composite laminates; together, they address two distinct aspects of mechanical behavior: the tensile test and the short-beam shear test. Since each test is designed to induce a different failure mode in the laminate, they collectively cover both tensile behavior and interlaminar shear strength.

Of the two, the tensile test measures the laminate's longitudinal tensile strength and tensile modulus: a specimen loaded along the fiber direction is subjected to increasing tension until failure. The applied load results in a proportionally greater deformation during the initial section of the resulting curve—a ratio that defines the tensile modulus—while the maximum load the specimen withstands just before breaking determines the longitudinal tensile strength.

In contrast, the short-beam shear test measures the laminate's interlaminar shear strength. Unlike the tensile test, the specimen here is deliberately short relative to its thickness and is subjected to three-point bending with a very short span. This short span concentrates shear stress between the laminate layers, causing the specimen to fail via interlaminar shear before flexural failure occurs—which is precisely what this test aims to measure. For this reason, the experimental data from the two mechanical tests used to initiate this model feed into two distinct models within the overall framework: one describing the laminate's elastic properties—using the tensile modulus and longitudinal tensile strength measured by the tensile test—and another describing laminate delamination—using the interlaminar shear strength measured by the short-beam shear test, which that second model employs specifically to evaluate whether its delamination propagation criterion is met.

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