Creep damage and crack initiation behaviour of nickel-base single crystalline superalloys compact tension specimen with a void ahead of crack tip

摘要

Based on the meso- and microstructure change and damage characteristic of single-crystalline superalloys at high temperature, the paper presents a rate-dependent crystallographic creep constitutive theory coupled with a two-state-variable creep damage model, which takes the rafting damage and void damage into consideration simultaneously. Three-dimensional finite element analysis has been employed to investigate multiaxial creep damage and crack initiation behaviour of a single-crystalline compact-tension specimen containing a cylindrical void ahead of the crack-tip at high temperature for three crystallographic orientations: < 001>, <011> and <111>, taking octahedral and cubic slip systems into consideration. The emphasis is placed on the role of the effects of crystallographic orientation and the specimen geometry on creep damage and crack initiation as well as stress distribution along the thickness direction. The numerical simulation results show that the time to crack initiation depends strongly on the void location and crystallographic orientation, which also has considerable influence on the place of crack initiation (the notch or void surface). The resolved shear-stress along the thickness direction is nearly constant in the midsections and tends to decrease sharply near the free surfaces.