Notch failure in laminated composites under opening mode: The Virtual Isotropic Material Concept

Abstract

Experimental and theoretical fracture investigations are performed on laminated glass/epoxy composite specimens with different numbers of ply and lay-up configurations weakened by central U-shaped notches of various tip radii and loaded under pure opening mode. Since the main purpose of this research is to evaluate the load-carrying capacity (LCC) of the U-notched glass/epoxy composite specimens, it is experimentally recorded by the testing machine and the failure behavior of the specimens is carefully observed. To predict the experimentally obtained LCCs or the last-ply-failure (LPF) loads theoretically, a novel concept, called Virtual Isotropic Material Concept (VIMC), is proposed and linked to two well-known stress-based brittle fracture models in the context of the linear-elastic notch fracture mechanics (LENFM), namely the maximum tangential stress (MTS) and the mean stress (MS) criteria. It is shown that both VIMC-MTS and VIMC-MS combined criteria can predict the experimental results well without the need for ply-by-aply failure analysis, the first-ply-failure (FPF) prediction, and the progressive damage modeling (PDM) etc. Thanks to both VIMC and LENFM, the LPF prediction is direct, rapid, and convenient, because only two distinct fracture parameters, namely the ultimate tensile strength and the trans-laminar fracture toughness of laminate are necessary for LPF prediction.