Finite element analysis of deformation and failure mechanisms in nanoscale hexagonal cellular structures of metallic glasses

Abstract

Cellular metallic glasses (MGs) have been found to be a potential candidate for structural and functional applications due to their attractive properties such as high strength to weight ratio, excellent energy absorption and enhanced plastic deformation. The experiments have shown transition in deformation mode from global failure caused by localization in a shear band to the local failure by damage confined to few cells with reduction in relative density of specimen from a large to moderate value. The mode of deformation again changes over to the collective buckling of ligaments through row by row collapse when the relative density is decreased to a sufficiently lower level. The atomistic simulations on nanoscale cellular MGs have also reported transition from localized but confined to few cells to almost homogeneous deformation with increasing cell size. They have also shown strain localization in a dominant shear band for cell spacing along diagonal direction above a threshold value which was correlated to shear bandwidth in monolithic MG. However, it is not clear as to why and how the shear band thickness in monolithic MG controls the threshold cell-spacing. Therefore, 2D plane strain finite element (FE) simulations of compressive loading are performed on nanoscale cellular MGs using thermodynamically consistent finite strain non-local plasticity model. The present FE simulations successfully predict the two transitions in deformation mode as observed in MD simulations and experiments. It is found that the interaction stress associated with the flow defects such as shear transformation zones (STZs) plays an important role in the deformation response of cellular MGs. Results show that the transition in deformation behavior is governed by the ratio of cell-wall thickness to the intrinsic material length associated with interaction stress. Also, the moderate change in sample size has marginal effect on the deformation response of MG cellular structure. The present work may provide guidelines for designing cellular MG structures capable of showing enhanced plastic deformation for practical engineering applications. © 2021 Elsevier Ltd