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 ≤ 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 final 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, confirming 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.