Damage evolution and modeling of sintered metals under multi-axial loading conditions

• Quantitative description of damage process in sinter metals.
• Development of a continuum damage model for sinter metals.
• Verification of the damage model with multi-axial experiments.
• Prediction of fracture strain as a function of stress triaxiality.

Sintered powder metals have found extensive engineering applications in industry. The mechanical property of sintered metals is characterized by high porosity and micro-cracks. Inelastic behavior of the materials is coupled with micro-crack propagation and coalescence of open voids. In the present paper the damage evolution of the sintered iron under multi-axial monotonic loading conditions was investigated experimentally and computationally. The tests indicated that damage of the sintered iron initiated already at a stress level much lower than the macroscopic yield stress. The damage process can be divided into three stages: the primary stage with high growth rate in the elastic state, the secondary stage with stable growth rate in the elastic–plastic state and fracture where the growth rate is too large to measure. Based on the uniaxial tensile tests an elastic–plastic continuum damage model was developed which predicts both elastic damage and plastic damage in the sintered iron under general multi-axial monotonic loading conditions. Computational predictions agree with experiments with different multi-axial loading paths. The damage evolution in sintered metals can be reasonably predicted by the proposed damage model.