Strain concentrations in tensile, fatigue and fracture behaviour

Abstract

A critical survey has been made of tensile, fracture, shear banding and fatigue measurements and their interpretations reported for different types of materials and test conditions. The mechanical properties of the materials are shown to be largely determined by microscopic plastic strain concentrations which depend on the inhomogeneity of the material microstructure, especially including importantly inhomogeneity of the dislocation substructure. Understanding this inhomogeneity is shown to provide a number of connections between seemingly disparate phenomena. The evolution of the dislocation substructure and its relationship to crystallography and various levels of microstructure are critically important. Professor Cottrell made seminal contributions to understanding the fundamental mechanisms involved in determining such strain concentrations. His work continues to provide clarity and guidance to current research accomplishments.

Fracturing across the multi-scales of diverse materials

“…Plastic flow considerations enter into both the nucleation of cracks and the nature of crack extensions, in the latter situation, no matter how brittle the material may appear to be. Thus, the crystal dislocation based plasticity theory co-invented just earlier in the twentieth century by Taylor [26], Orowan [27] and Polanyi [28] has been carried forward with important relevance to fracture, for example, in the work of Orowan [29], Petch [30], Cottrell [31,32], Crussard and co-workers [33,34], Yokobori et al [35], Nabarro [36], Kochendorfer et al [37], Friedel et al [38] and Hirsch et al [39], among many other colleagues. Current developments include such computational 'code' calculations as mesoscale cracking simulations to elucidate material deformation and cracking behaviours [40].…”