An investigation of residual stress gradient effects in FIB-DIC micro-ring-core analysis

In many cases residually stresses surface layers that are obtained by surface treatment or coating deposition contain significant stress gradients. These gradients affect the performance of component surfaces under the conditions of contact loading in service, such as impact, scratch and abrasion, wear, erosion, fretting fatigue, etc. The determination of residual stress in the close vicinity of sample surfaces, at the depths ranging from sub-micron to a few microns, is a challenging task that cannot be accomplished routinely using existing techniques. A challenging aspect of the problem of stress evaluation concerns the nature of weighting of the contributions from different depths below the surface within the gauge volume. In the present study we focus our attention on this issue, specifically, on the effects of sub-surface stress gradients on the apparent stress value obtained by FIB-DIC micro-ring-core analysis. The implications of this investigation are discussed in the concluding section.