Neutron and X-ray Microbeam Diffraction Studies around a Fatigue-Crack Tip after Overload

Abstract

An in-situ neutron diffraction technique was used to investigate the lattice-strain distributions and plastic deformation around a crack tip after overload. The lattice-strain profiles around a crack tip were measured as a function of the applied load during the tensile loading cycles after overload. Dislocation densities calculated from the diffraction peak broadening were presented as a function of the distance from the crack tip. Furthermore, the crystallographic orientation variations were examined near a crack tip using polychromatic X-ray microdiffraction combined with differential aperture microscopy. Crystallographic tilts are considerably observed beneath the surface around a crack tip, and these are consistent with the high dislocation densities near the crack tip measured by neutron peak broadening.

A study on fatigue crack growth behavior subjected to a single tensile overload

“…the crack growth rate temporarily slows down), which increases the fatigue lifetime. There have been numerous efforts to account for the crack growth retardation phenomena, which include both experimental studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and computer simulation studies [17][18][19][20]. Among them, the plasticity-induced crack closure concept suggested by Elber [1] has been supported by many investigations [4][5][6][7][8][9][10][11][12]20].…”

“…Recently, neutron diffraction and high-energy synchrotron X-ray diffraction as a nondestructive evaluation technique have been employed to investigate the overload effects during fatigue crack growth [14,15,26,[33][34][35][36]. The deep-penetration and volume-averaging capabilities of these techniques enable the direct measurements of residual and internal strains/stresses in the bulk sample as a function of distance from the crack tip.…”

Neutron diffraction measurements of residual stresses around a crack tip developed under variable‐amplitude fatigue loadings

“…Nondestructive diffraction methods (e.g. high‐energy synchrotron X‐ray diffraction or neutron diffraction) are a powerful technique in the direct measurement of internal strains/stresses in the bulk sample 12–20 . Steuwer et al 15 .…”

“…high-energy synchrotron X-ray diffraction or neutron diffraction) are a powerful technique in the direct measurement of internal strains/stresses in the bulk sample. [12][13][14][15][16][17][18][19][20] Steuwer et al 15 investigated the imaging of fatigue cracks and associated crack-tip strain field using synchrotron X-ray diffraction and tomography. They observed a significant compressive zone at and behind the crack tip following a 100% overload.…”