Finite element calculations for correction of residual stress profiles of coated and uncoated materials measured by X-ray diffraction

Abstract

Residual stresses can cause a severe reduction of the lifetime of components exposed, for example, to varying loads which lead to fatigue. Measuring residual stresses is therefore of vital importance. X-ray diffraction is one of the techniques which can be used for this purpose. This method has the advantage of measuring stresses to a depth of only a few micrometres (in steel approximately 10 μm). Therefore it is possible to determine stress gradients within the material but, in order to do so, material must be removed before each measurement. When material containing or subjected to internal stresses is removed, the stress distribution in the remaining material is changed and it is therefore necessary to correct the measured stresses. Two correction methods are available for this purpose. The first and simplest is based on elastic beam theory and the second, which is developed by the present authors, is based on calculations with the finite element method (FEM). The latter is discussed in this paper together with the results of the calculations. The results show a significant difference between the corrections calculated by the two methods. It is particularly important to use the FEM-based method when considering measurements of residual stresses in coatings with elastic properties differing from those of the substrate material.