Damage Mechanics Approach to Material-Dependency of Fracture Toughness in Aluminum Alloys

Mixed-mode elastic-plastic fracture toughness in aluminum alloys,i.e., heat-treatable and non-heat-treatable alloys, depends on the hardening mechanism. Present investigation have been carried out to clarify the material dependency of the fracture toughness in aluminum alloys. Two kinds of alloys were regarded as particle reinforced composites which contain inclusions and dispersoids in different matrices. The matrix in the non-heat-treatable alloy has low yield stress and high strain hardening, while the matrix in the heat-treatable alloy has high yield stress and low strain hardening because it is hardened by shearable precipitates. Elastic-plastic analyses of mode I and mode II cracks were conducted for two alloys using finite element method based on Tohgo–Chou–Weng’s constitutive relation of particle-reinforced composites which describes the plasticity of the matrix and the debonding damage between the particles and matrix. From the numerical results for plastic zone and damage evolution around a crack tip, it is qualitatively explained that the heat-treatable alloy exhibits the crack initiation in brittle manner from mode I crack and in ductile manner from mode II crack, while in the non-heat-treatable alloy the crack initiation occurs in ductile manner from both cracks.