Extension of the virtual isotropic material concept to mixed mode I/II loading for predicting the last-ply-failure of U-notched glass/epoxy laminated composite specimens

Abstract

The last-ply-failure (LPF) load in glass/epoxy laminated composite specimens weakened by U-notches of various root radii is investigated experimentally and theoretically under mixed mode I/II loading conditions. A newly proposed concept, called the Virtual Isotropic Material Concept (VIMC), accompanying with two well-known brittle failure models, namely the maximum tangential stress (MTS) and the mean stress (MS) criteria, is utilized for the first time for theoretical LPF load prediction under mixed mode I/II loading. According to VIMC, a real laminated composite material is theoretically equated with a hypothetical isotropic brittle material in order to avoid time-consuming and complex ply-by-ply failure analysis. To verify the validity of the proposed concept in combination with MTS and MS criteria under combined tension-shear loading, it is utilized to predict the LPF loads of numerous U-notched semi-circular bend (USCB) specimens made of E-glass/epoxy unidirectional composite laminate and loaded under mixed mode I/II. It is shown that both VIMC-MTS and VIMC-MS criteria can predict the experimental results accurately and rapidly.