Discussion on X-ray and HDM residual stress measurements

The stress field remaining in some materials without application of external sources of stress is known as residual stress. These residual stresses are produced in almost all manufacturing processes or may occur during the life of structures. They have a fundamental role in welded joints because they affect the way to design structures (e.g. the safety coefficients), their fatigue life and their corrosion resistance. Quantify, as well as possible, the residual stress field is one of main issues for mechanical engineers. To this purpose, in the last decades, several techniques have been developed. Hole Drilling Method (HDM) and X-Ray Diffractometry (XRD) are two of the most diffused and the only standardized techniques to measure the stress field in depth on welded structures. Although both methods declare to make an accurate measurement of the stresses, few comparisons of these techniques applied on the same structure are described in scientific literature. The aim of the present work is to compare the residual stress measurement between HDM and XRD on Ti-6Al-4 V (Grade 5) laser butt-welding joints to understand if a significant difference exists between the results obtained by the two methods or they may be considered comparable.