Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : October 07, 2017 - October 09, 2017
Effects of crystallographic orientation and grain boundary on Stage I fatigue crack propagations were investigated in a single crystal and a bi-crystal Ni-base superalloy. Fatigue crack propagation tests at room temperature were conducted using four types of single crystal CT specimens with different combinations of primary and secondary orientations. Stage I cracks in the single crystal superalloy were mixed mode with mode I, II and III components, and the <100> primary orientation or the <110> secondary orientation resulted in higher crack propagation rate. In order to interpret the effect of crystal orientations on the Stage I cracking, crystal plasticity finite element model was developed considering the 3-D geometry of the mixed mode crack plane. Damage parameter calculated from crack tip slip field provided reasonable explanations on the preferable crack paths and growth rate of Stage I cracks. Effect of grain boundary was also investigated using a bi-crystal finite element model involving two coarse grains. Analytical results proved that slip deformation was disturbed by the grain boundaries and resultant damage parameters were strongly affected by the crystal orientation of the grain ahead of the grain boundary.
