Study On Mechanical Properties And Fracture Behaviors Of Nickel Nano-single-crystals With Semi-elliptical Surface Cracks

Nickel-based superalloy is a key structure material employed in the hot and cold regions of aero-engine. During manufacture process, micro-defects and micro-cracks appeared inevitably, which will deform, propagate under external load and lead to failure at last. Therefore, to analyze the three-dimensional stress state in atomic scale is of great engineering significance. We simulate the mechanical properties and behaviors of semi-elliptical surface cracked Ni single crystal under uniaxial tension. Furthermore, the constraint and size effects have been investigated. The main conclusions are listed below:(1) Mechanical properties and behaviors analysis of semi-elliptical cracked Ni single crystal under uniaxial tension.We have found the existence of semi-elliptical crack will lower the yield strength. During the process of crack propagation, the crack becomes sharp and deforms to triangle which is different from crack blunting in traditional continuum mechanics. When the loading rate changes from 1 to 100 m/s, the loading rate have little effect on the elasticity but have much effect on the plasticity, the lower loading rate, the better plasticity.(2) Constraint effects on mechanical and fracture properties of semi-elliptical surface cracked Ni single crystal.We have found at x-z period and x-z direction constraint boundary conditions, the specimen becomes much more sensitive to the crack, crack depth and crack width increase rapidly with strain. At x-z direction constraint boundary condition, the crack propagates along the slip plane and leads to final fracture. While at x-z period boundary condition, the crack propagates along the z direction, and adjacent cracks converge lead to final fracture.(3) Size effects on mechanical and fracture properties of semi-elliptical surface cracked Ni single crystal.We have found that increasing the depth or width of the crack will decrease the yield strength, while the elasticity modulus keeps the same, the plasticity decreases a little and the dislocation activity keeps the same. We also found increasing the width or thickness of the specimen will increase both the yield strength and elasticity modulus, but have little effect on the plasticity properties.