Issue 46

A. Baltach et alii, Frattura ed Integrità Strutturale, 46 (2018) 252-265; DOI: 10.3221/IGF-ESIS.46.23 262 conical part of the mandrel. This explains the incontestable effect of the taper on the distribution of residual stresses in the entrance face. Figure 17 : Axial force reaction of the mandrel during penetration through the hole. Figure 18 : Comparison of the resulted radial stresses obtained by different mandrel shapes for: a) Entrance face, b) exit face and c) Mid-thickness plane. Since the entrance face presents the lower residual stress, it can be noted that equilibrium between the latter and the exit face is obtained by using a conical mandrel with a taper λ = 2.875 % (see Fig. 14a). The same thing can be said for the outlet side, wherein Fig. 16b shows an improvement of residual stresses as a function of the taper. Much more, a taper of 3.833% optimizes the circumferential residual stresses. Regarding the radial residual stresses, the same finding is raised to the inlet face. Fig. 18a shows the effect of the mandrel shape on the radial residual stresses distribution surrounding the entrance face. It is evident in this figure that lower degree a) b) c)