Toughening a bulk metallic glass through mode II fracture under mode I loading

High fracture toughness is vital for resisting catastrophic fracture of engineering structural materials which break through cavitation instability. We report a new toughening mechanism which totally suppressed cavitation through pure mode II fracture which was induced by pivoting around circular arc shear bands in a bulk metallic glass under mode I loading. We demonstrated that the mode II crack propagated along the outmost circular arc shear band along Prandtl slip line which is the orientation of maximum shear stress ahead of crack tip. Our theoretical investigation revealed that enhanced critical hydrostatic tension for cavitation which changed the stress field ahead of fatigue crack tip would be the trigger for pivoting which would increase energy dissipation and prevent hydrostatic tension ahead of crack tip from increasing. The present work would assist in guiding microstructure design to produce monolithic and composite materials with enhanced fracture toughness.