Mo¨ssbauer effect measurement in single crystal iron subjected to cyclic stress

Abstract

High purity single crystal iron specimens, in the form of rectangular strips with appropriate stress concentrators in the midplane, were cyclically fatigued in the stress range of (3–7) kg/mm 2 and their backscattered Mo¨ssbauer spectra recorded at different fatigue levels. From the data on hyperfine spacing, it is observed that the effective field increased by about 1% per 2 × 10 6 fatigue cycles. This roughly equivalent to an order of magnitude increase in the interstitial impurity in solid solution in the region of stress concentration. This change in H (effective) at the absorber nuclei is accompanied by a corresponding line broadening from the superposition of spectra due to several nonequivalent absorber nucleus sites as well as inhomogeneous quadrupole interaction. It thus appears that this technique can be used to follow (measure) the interstitial impurity increase which is presumed to be the eventual cause of fatigue crack initiation and metal failure.