Dynamic Shear Band Propagation and Micro-structure of Adiabatic Shear Band

Meshfree Galerkin approximations in both two and three dimensions have been used in simulations of dynamic shear band propagation in an asymmetrically impact-loaded prenotched plate. Failure mode switching and failure mode transitions, which have been reported experimentally, are replicated in numerical computations. For intermediate impact speed (25 m=s < V 6 30 m=s), the numerical results show that a cleavage crack initiates from the tip of the dynamic shear band, indicating a dominance of brittle failure mode, and a failure mode switch (ductile-to-brittle: shearband-to-crack). For high impact velocities (V > 30 m=s), the numerical results show that a dynamic shear band penetrates through the specimen without trace of cleavage-type fracture, which is a ductile failure mode. Overall, with the increase of impact speed, the ®nal failure mode of the impacted plate transits from brittle failure to ductile failure. By introducing a multi-physics model to describe the stress collapse state of the shear band, it has been found that there is a non-uniform temperature distribution inside the adiabatic shear band. Strong evidences indicate that temperature distribution inside the shear band has periodic patterns in both space and time, con®rming the latest experimental results of P. Guduru et al. [Mech. Mater. (2000), submitted]. This suggests that there may exist a thermal±mechanical instability within the adiabatic shear band, reminiscent of hydrodynamic instability due to viscous heating.