A trans-scale model for size effects and intergranular fracture in nanocrystalline and ultra-fine polycrystalline metals

A trans-scale mechanics model considering both strain gradient and interface energy effects is presented for describing size effects in nanocrystalline and ultra-fine polycrystalline metals accompanying by intergranular fracture. A finite element method is developed which is suitable for describing the strain gradient and interface energy effects. Moreover, cohesive interface model is used to study the intergranular damage and fracture in polycrystalline metals with nanoscale and ultra-fine grains. A systematical study on the overall strength and ductility of polycrystalline aggregates which depend on both grain interiors and grain boundaries for different grain sizes and different interface properties is performed. The results show that the overall strength and ductility of polycrystalline aggregates with nanoscale and ultra-fine grains strongly depend on the grain size and grain hardening, interface energy density, grain boundary strength and toughness.