Spatial and temporal crack initiation prediction in steels based on residual stress tensor distribution monitoring

Abstract

We have developed a method and the corresponding instruments, able to provide the spatial and temporal determination of crack initiation in ferromagnetic steels and their welds. The method is based on the monitoring of the differential magnetic permeability µr along the length of the steel, since a sigmoid monotonical dependence of µr on residual stresses has been determined in the past. Thus, the magnetic stress calibration (MASC) curves can inform on the localized residual stresses. Therefore, the temporal stress monitoring at different areas of interest can inform about the status of residual stresses. Then, the tendency of the residual stress value can inform about reaching the positive (tensile) or negative (compressive) yield point of the steel. As an example, a quasi-parabolic temporal dependence of µr offers the tendency to determine the time, or the time window, required to reach yield point. This way, the temporal prediction of the crack initiation is provided for the given point in space, since reaching the yield point results in crack initiation.