Measurement of the Effectiveness of Half Value Breadth of X-ray Diffraction Profile for Residual Stress Analysis using FEM Based on the Inherent Strain Methodology on the Cold-formed Part

Most cold forming processes are effective methods for improving the fatigue strength of large forged steel structures. However, these methods give rise to compressive residual stresses on the surface, while causing tensile residual stresses around the cold-formed parts. The inherent strain method using FEM is one of the most effective measures for predicting the internal residual stress distribution for large forged structures, because of the depth of the residual stresses. It was found that the conditions of the inherent strain area and the order of the inherent strain distribution functions, are very important for the accuracy of the predictions, when the efficient approach that combines the inherent strain method using FEM, X-ray stress measurement, and a new measurement procedure, was applied to the fillet portion of the axisymmetric shaft with flange after the cold forming process. In the cold-formed parts, the inherent strains are induced by plastic deformation, and there is a relationship between the half value breadth of X-ray diffraction profile and the plastic strains. By noting these points, this report confirms the relationship between the half value breadth of X-ray diffraction profile and the equivalent inherent strain. Moreover, we propose that it is important to set the conditions of the inherent strain area and the order of the inherent strain distribution functions while considering the half value breadth of the X-ray diffraction profile.