**1. Introduction**

The Hole Drilling Method (HDM) and the Ring-Core Method (RCM) are semidestructive mechanical method widely used for the residual stress (RS) evaluation in mechanical components [1–12]. Each of two methods have a proper application field; respect to the more known HDM, the RCM is characterized by a higher stress relaxation that allows the user to extend the RS analysis up to about 5÷7 mm from the surface of the analysed component, whereas the HDM allows to analyse the RS up to about 1.5–2 mm. Although several applications have been performed in the various industrial fields along with a lot of research works for both the methods, the RCM has never been considered by standardization organisms, whereas the HDM has been standardised by the ASTM since the 80<sup>0</sup> . In practice, for both the methods, the most

accurate computational approach used for the evaluation of a generic non-uniform RS distribution, is the so called Integral Equation Method proposed by Schajer (HDM) [6, 7] and Ajovalasit et al. (RCM) [13]; such computational approaches has been included in the ASTM E837-13a standard [14]. However, the very different geometrical variation introduced by the RCM (annular groove) and the HDM (simple hole) involve the presence of different influence parameters on the the RS analysis. In the past the HDM has been used more widely than the RCM thank to its lower damaging and easier experimental procedure. However, the use of the RCM is increased in recent years, especially in Europe, also thank to new modern equipment commercially available [15]. The diffusion of both the methods is corroborated by the high number of special strain gauge rosettes sold in the world by the most famous strain gauge manufacturer as the American MM or the Germany HBM. Also, both the method attract again various research activities having the aim to improve the accuracy of such methods, see as an example the works devoted to the error and uncertainty analysis [16, 17], recently reported in literature.
