Dynamic experimental verification of void coalescence criteria

Void coalescence criteria were discussed. Thomasonʹs (Th.) and Brown–Emburyʹs (B.–E.) instantaneous criteria for a void cluster were, respectively, localized in a region surrounding voids to describe the void coalescence process. A stress triaxiality and strain rate (STSR) dependent failure criterion was presented to describe the dynamic void coalescence. A series of tension tests for pure copper sheets (PCS) containing laser-drilled voids of different configurations were carried out on tensile split Hopkinson bar (TSHB) tests. The deformation of PCS and evolution of drilled voids on PCS under multi-tension in TSHB tests were recorded by a high speed camera. The validity of void coalescence criteria was assessed using comparison between the experimental void evolution post coalescence at a certain average strain of PCS and the numerically simulated results which involve void coalescence criteria. The void coalescence process was revealed: localized strain was found near the center of region between the voids when the stress triaxiality and the strain rate increased to an extreme value rapidly, where the STSR dependent failure criterion was met; then the failure extended from the center region to each void. The whole process of void coalescence could also match localized Th. criterion and B.–E. criterion for a void cluster to a certain extent.