Measurement of mixed-mode cohesive laws of a UD composite undergoing delamination with large-scale bridging

Abstract

Cohesive zone modelling is often regarded as one of the most advanced tools to simulate fracture of composite materials. Conceptually, cohesive zone modelling enables the simulation of both crack initiation and propagation in an efficient manner e.g., without the need for initial crack, and without the need for re-meshing. These and other advantages have led to the development of many advanced CZM capable of modelling complex loading (e.g., mixed-mode and cyclic). However, most of these CZMs rely on idealised cohesive laws formulated as simple functions, where their traction separation relationship is defined a priori using simple functions (e.g., bi-linear softening, trapezoidal and exponential). This means that the functional form (and shape) of the cohesive laws is not determined experimentally but assumed instead. Since the shape of cohesive laws provides a “footprint” of the damage mechanisms within a real fracture process zone, an accurate measurement of the shape of cohesive laws has great scientific value to study the fundamentals of fracture. The type of cohesive laws which derives its functional form (shape) from a potential function are known as potential-based cohesive laws. If cohesive laws are to be understood as constitutive equations for surfaces (interfaces), then, the parameters describing these laws need to be determined experimentally for each different interface or material. As such, there is a great practical and scientific need for efficient procedures to experimentally determine cohesive laws of different material interfaces