Translaminar notch fracture toughness expressions for composite laminates

Abstract

First, two different test specimens, namely the rectangular tension (RT) and semi-circular bend (SCB) specimens, weakened by U-notches of various notch tip radii and made of E-glass/epoxy composite laminates of different lay-up configurations, are considered for measuring experimentally the translaminar notch fracture toughness (TLNFT) of the composite material under pure mode I loading conditions. Then, two new closed-form expressions are proposed for the TLNFT, by taking advantages of the maximum tangential stress (MTS) and the mean stress (MS) criteria, as well as the recently proposed virtual isotropic material concept (VIMC), with the goal to estimate the experimental results. It is found that both criteria can well estimate the test results that locate always between the predictions of MTS and MS criteria. Taking into account that MTS criterion is more conservative and simpler than MS criterion, it is preferred in mechanical design of notched E-glass/epoxy composite structures.