Microscale Investigation of Transverse Tensile Failure of Fiber-Reinforced Polymer Composites

Abstract

In this study, two experimental approaches are used to understand fracture mechanisms that govern transverse tensile failure of fiber-reinforced polymer composites at the microscale. These observations are used to directly measure, and indirectly estimate, the magnitude and scatter of the transverse tensile strength, Y_T, and the associated effective flaw size, a₀. To this end, static three-point bend tests are performed on pristine and notched 90° unidirectional IM7/8552 carbon-epoxy samples. In the pristine specimen study, tensile microcracks are observed to initiate well before the ultimate failure load used to compute Y_T is reached. In the notched specimen study, a comparison is made between experimentally measured strengths with known notch lengths and a linear elastic fracture mechanics solution. The fracture mechanics solution significantly over-predicts the apparent Y_T for notch lengths less than a ply thickness, suggesting that this approach may not be appropriate for estimation of transverse tensile strength at the microscale. The observations made in this study suggest that Y_T may not be a true material property, but rather, a structural property dependent on specimen geometry and microstructural variability.