Reduction of lateral constrain leads to plasticity in metallic glasses

Inserting a Teflon tape between a relaxed sample of a Zr 50 Cu 40 Al 10 metallic glass and a loading platen resulted in the emergence of a plastic strain of 1.5%–2% under compression. We determined the origin of plasticity from the evolution of the local internal strain/stress state (i.e., the local mechanical state) during compression. A real-time observation of the strain state by a digital image correlation (DIC) analysis revealed a large longitudinal-to-lateral strain ratio (–ε xx /ε yy ) near the contact area, suggesting that the Teflon tape enabled expansion of this region. A finite element method (FEM) analysis confirmed this hypothesis. The DIC analysis revealed the appearance of multiple shear bands, which were initiated in regions that were identified as yielding areas under the expansion contact condition in the FEM analysis. The induced inhomogeneous strain/stress distribution retarded the immediate penetration of shear bands/cracks, which may have led to the emergence of global plasticity.