Translaminar fracture limit curves for U-notched glass/epoxy composite laminates with different layup configurations subjected to mixed mode- I/II loading

Characterization of FRP composite laminate subjected to mixed-mode loading is one of the challenging topics in fracture mechanics. In this study, numerous experiments are conducted on U-notched rectangular tension (UNRT) specimens of various tip radii made of E-glass/epoxy composite with various layup configurations for experimental measurement of the translaminar U-notch fracture toughness (TLUNFT) of the composite laminates under mixed mode-I/II loading conditions. Two fracture limit curves are developed based on a two-dimensional stress distribution around the notch for predicting the mixed mode TLUNFT taking advantage of the maximum tangential stress (MTS) and the mean stress (MS) criteria as well as the virtual isotropic material concept (VIMC). It is revealed that both two-dimensional new models, namely the translaminar U-notch maximum tangential stress (TLUN-MTS) and the translaminar U-notch mean stress (TLUN-MS) criteria, can well estimate the experimental results obtained from testing the UNRT specimens made of the unidirectional (${\left[0\right]}_{16}$) and quasi-isotropic (${\left[0/90/\pm 45\right]}_{2s}$) E/glass epoxy composites. It should be underlined that this is the first time that some fracture limit curves have been developed by using the notch fracture mechanics (NFM) for estimating the TLUNFT of laminated composites subjected to mixed mode loading. These curves can be accurately, rapidly, and conveniently utilized to predict the last-ply-failure load of U-notched composite laminates subjected to in-plane loading conditions.