Failure analysis of round-tip V-notched laminated composite plates under mixed mode I/II loading

Abstract

The purpose of this research is twofold. First, to predict the experimental results of the last-ply-failure (LPF) load of blunt V-notched composite laminates tested under mixed mode I/II loading conditions, and second, to analyze the fracture surfaces and the failure evidences to identify the types of macroscopic and microscopic failures. Rectangular E-glass/epoxy laminated composite specimens with the unidirectional ([0]8) and cross-ply ([0/90/0/90]s) lay-up configurations containing central rhombic holes with blunt V-shaped corners are fabricated and utilized for conducting the fracture tests. To predict the experimentally recorded LPF loads of the blunt V-notched laminated composite samples, two combined criteria are proposed and implemented. The most recently 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 employed for the first time under mixed mode I/II loading conditions for theoretical LPF load predictions. A good agreement is shown to exist between the theoretical predictions of both criteria and the experimental results for various notch opening angles and different notch tip radii. Macroscopic failure analysis of the specimens shows the notch induced delamination (NID), matrix cracking, and fiber breakage, while the microscopic analysis displays some clear evidences of the matrix micro-cracking, shear bands, fiber pull out, and fiber breakage.