Fracture in layered plates having property mismatch across the crack front

Abstract

Layered structures are used in protection systems such as personal and heavy armor, windshields and also in thermal barriers. Such materials have mismatch in the properties, both elastic and fracture, from layer to layer. The focus of this study is to understand the behavior of cracks in such systems, especially when the crack orientation is such that there are property changes along the crack front. Plates comprising of layers of epoxy and PMMA were prepared by bonding together sheets of 6 mm nominal thickness with an epoxy adhesive. Single edge notched (SEN) specimens were loaded in bending. The thickness averaged stress intensity factor (SIF) was obtained through photoelasticity. Subsequently the behavior of crack-propagation in these materials was also investigated by loading SEN specimen dynamically. The crack tip fields were recorded using high-speed imaging coupled with dynamic photoelasticity, from which the thickness averaged fracture parameters are extracted.