Dynamic fracture predictions of microstructural mechanisms and characteristics in martensitic steels

A dislocation-density-based multiple-slip crystalline plasticity formulation, and an overlapping fracture method were used to investigate the effects of carbide precipitates, M23C6, and martensitic block size on dynamic fracture in martensitic steels. The interrelated effects of dislocation-density evolution, orientation relations (ORs), adiabatic heating, and heat conduction on fracture behavior were investigated. Precipitates interfaces are shown to be the sites of crack nucleation due to dislocation-density impedance. Dislocation-densities are also shown to relieve tensile stresses and blunt crack propagation. These predictions indicate that the size refinement of martensitic blocks increases crack deflection at block/packet boundaries, which can significantly improve fracture toughness.