Study of three- and four-point shear testing of unidirectional composite materials

Both the three- and four-point shear test methods for unidirectional composite materials were studied using a three-dimensional elastic-plastic finite element analysis. The span-to-thickness ratios of the test specimens were varied to study the shear stress distributions. Specimens with lower span-to-thickness ratios were found to yield higher apparent interlaminar shear strengths. This prediction coincides with many available experimental results. The dependence of apparent interlaminar shear strength on span-to-thickness ratio, confirmed by both analytical and experimental studies, shows that both the three- and four-point shear test methods should be used with caution in this regard when measuring the interlaminar shear strength of unidirectional composite materials.