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The fluctuation of J-integral, J, during high temperature fatigue crackpropagation, due to the microscopic inclination of crack shape and elastic anisotropy ofeach grain, is investigated by means of a series of finite-element-analyses on a crackedbody. The simulated material is a Nickel-based directionally solidified (DS) superalloy,where the DS, load, and crack propagation axes are set to be perpendicular to eachother. The magnitude of J is estimated using 2-dimensional models simulated after anexperimental result; (i) with the actual crack shape and grain arrangement, (ii) with theactual crack shape in the homogeneous body, and (iii) with the straight crack inhomogeneous body (averaged deformation behavior of the material). The microscopicinclination of crack propagation direction causes the sporadic drop of J at the pointwhere the crack direction is largely inclined from the direction normal to the load axis.The anisotropy of grain causes the stepwise change in the a (crack length) - Jrelationship. These directly relate to the change in the crack propagation rate in thetransgranular cracking. Then, J, which takes into accounts the factors, correlates wellwith the crack propagation rate in the transgranular cracking. The grain-boundarycracking possesses fluctuated J and shows weaker resistance against the propagationthan the transgranular one.