Use of Hybrid Methods (Hole-Drilling and Ring-Core) for the Analysis of the RS on Welded Joints

The hybrid methods (HMs) for the residual stress (RS) analysis, such as the well-known hole-drilling method (HDM) and the ring-core method (RCM), have been widely developed since 80’. They are mechanical methods based on the partial relaxation of the RSs that occur when a proper geometry variation of the analysed component is introduced by drilling a hole (HDM) or a proper annular groove (RCM). The RS computation is performed by measuring the strains relaxed on surface and then by combine properly such measured strains with the influence coefficients previously computed accurately by using a numerical codes that consider the geometry of the particular component to be examined. In such a manner, the HMs can be potentially applied to any RS distribution independently from the cause that have caused them. In more detail, the HMs can be used for the analysis of the RS on welded joint by using both classical welding methods, as MIG or TIG processes, or modern methods as friction stir welding, etc. In the present chapter, after a brief presentation of the theory of the HMs, their application to various cases of welding joints are treated, and the possible limitation are discussed.