Effect of the dynamic loading rate on the failure of bulk metallic glasses

Abstract

Abstract. The absence of structural ordering in bulk metallic glasses (BMGs) leads to plasticdeformation controlled by shear bands initiation, propagation, and interactions which differ mostlikely when quasi-static or dynamic loads are applied. Under quasi-static loading and high hydro-static stress, the shear band initiation and propagation process is stable which can result in largeplastic deformation in excess of 0.50. Under dynamic loading conditions, BMGs are brittle. Theobjective of the present study was to examine the influence of the dynamic loading rate on thefailure mechanisms of a Zr 57 Ti 5 Cu 20 Ni 8 Al 10 BMG. Dynamic compression tests were conducted witha direct impact compression apparatus over a wide range of dynamic strain rates from 570 to7760 s x1 . The decrease of the dynamic failure stress with the increase of strain rate was interpretedthrough the analysis of observed failure mechanisms. 1. INTRODUCTIONThe interest in developing new generations of bulk materials is not only with the objectives ofreaching isotropic and high strength properties but also with the goals to generate given failuremechanisms as to monitor fracture processes. Two new generations of materials respond to thesegoals, bulk nanomaterials and bulk metallic glasses (BMGs). The latter belongs to a class ofmaterialscalledbulkamorphousmaterials(BAM).Theobjectiveofthepresentpaperistoexploredynamic failure mechanisms of BMG. The mastering of the dynamic behaviour of materialsresponds to civil and military applications. The latter address kinetic ammunitions and armors.The absence of structural ordering in BMGs leads to plastic deformation controlled by shearbands initiation, propagation, and interactions, which differ when quasi-static or dynamic loadsare applied. Under quasi-static loading and high hydrostatic stress, the shear band initiation andpropagation process is stable. For specimen with elevated aspect ratio length over diameter, asingle shear band is generated associated to a low failure strain. For small aspect ratio, multipleshear bands are initiated which are interacted resulting in large plastic deformation in excess of0.50. In these conditions, experimental evidences show that shear bands developed are nonadiabatic [1–3].Under dynamic loading conditions, BMG undergo little plastic deformation with a decreaseof the strength with the increase of strain rate as observed by Bruck and al. [3] for aZr