Dynamically Growing Shear Bands in Metals: A Study of Transient Temperature and Deformation Fields

Abstract

The objective of our work is (1) to establish the critical conditions for initiation and growth of shear bands in pre-notched plates subjected to asymmetric impact loading (dynamic mode II, see Fig. 1); and (2) to investigate and characterize the transition in the modes of failure when such plates are subjected to a variety of loading rates (impact velocities). These failure modes which may feature either dynamic shear band growth, dynamic crack propagation or both, (see Fig. 1), have been observed in structural materials such as the high strength steels and heat-resistant titanium alloy considered in the present work. The approach is to study both the dynamic mechanical deformations and the processes of heat generation and thermal softening. This necessitates the simultaneous use of high speed optical and infrared diagnostics in the experiments. In parallel to the experimental study, full-scale thermomechanical finite element simulations are conducted to assist the development of criteria for shear band initiation and propagation. The calculations make use of constitutive parameters measured in house through material testing in a variety of strain rates. Such a combined experimental and numerical approach enables us to make direct comparisons between measurements and predictions obtained using various material constitutive and failure models.