Three Dimensional Effect Of Through-the-thickness Straight Crack For Ni Single Crystal

Nickel-base superalloy is a critical structure material employed as the hot and cold end of aero-engine. There exist most micro-cracks during the fabrication, which leads to deformation, crack propagation, and failure. Therefore, it is of great significance to study and analyse the three dimensional fracture at nanoscale. In this dissertation, based on EAM potential, the thickness effects and size effects on fracture of nickel crystal sheets at nanoscale are investigated by molecular dynamics. The main contents are listed below:(1)Thickness effects on fracture of nickel crystal sheets with through-the-thickness straight crack.Thickness effects are remarkable on fracture of nickel sheets in the simulations. For nanosheets with thickness of 2 nm, 8 nm and infinite under mode ? tensile loading, the 2-nm-sheet exhibits highest toughness and the 8-nm-sheet emits densest dislocations from the crack tip and significant lower toughness once entering the unstable crack growth stage, while the infinite sheet exhibits pure brittle fracture behavior. Similar to macroscale fracture, the three dimensional stress constraints raising around the crack tip decreases with decreasing thickness and is confined within a distance about the sheet thickness from the crack tip. Crack growth resistance represented by crack-tip-open-distance and crack-tip-open-angle is found to increase with decreasing thickness. Our results provide some insights into thickness effects on mechanical properties of cracked nanocrystals.(2)Size effects on fracture of nickel crystal sheets with through-the-thickness straight crack.Size effects are also outstanding on fracture of nickel sheets in the simulations. For nanosheets with different size under mode ? tensile loading, the stiffness and strength are depend on the size of nanosheets. The stiffness will increase with the increasing width; The strength will increasing with the increasing width or decreasing height. Particularly, width plays a dominant influence to the stiffness and strength. In addition, the dislocations will pile up and emit from crack tip more hardly with size increasing.