Development of crystallographic-orientation-dependent internal strains around a fatigue-crack tip during overloading and underloading

In-situ neutron diffraction was employed to directly measure the crystallographic-orientation-dependent (i.e. hkl) internal strains as a function of distance from the crack tip on the pre-cracked Hastelloy C-2000 compact-tension specimen. Both in-plane (IP) and through-thickness (TT) strain evolutions for various grain orientations were examined during tensile overloading and compressive underloading cycles. After overloading, underloading and their combination loadings were applied and unloaded, the significantly different {hkl} residual strain profiles were obtained in the vicinity of the crack tip. The load responses of the {200} grain orientation in both the IP and TT directions were more significant than those of any other orientations. It is suggested that the different orientation-dependent strain distributions around the crack tip are caused by the combined effects of elastic and plastic anisotropy of each {hkl} reflection upon loading and the subsequent development of residual stresses generated near the crack tip during unloading as a result of the plastic deformation.