Issue 48

M. Laredj et alii, Frattura ed Integrità Strutturale, 48 (2019) 193-207; DOI: 10.3221/IGF-ESIS.48.21 202 Figure (10-c) shows the variation of the plastic deformations zone as function of the yield strength. According to this figure we note that the yield strength increase results a small decrease of PDZ which is verified by the results of M. Su and al [31] by performing expansion by a numerical simulation for different degrees of expansion: 1.7, 3.4, 4.3, 5, and 6% on aluminium alloys 6082, 6005 and steel A42. They have demonstrate that crack initiation can be obtained by a lower number of cycles in the case of the yield strength increasing than by the increase of the degree expansion. Figure 10 : The plastic deformations zone In the last analysis we study the evolution of the maximum tension according to the three previous parameters. In figure (11-a) we observe that the decrease in the MT caused by increasing of thickness. Thus, the thicker structure presents the lower MT. On the other hand, in Figures (11-b) and (11-c) we observe that, an increase of the degree expansion and the yield strength leads to an increase of the maximum tension. This effect is more marked in the case of the expansion degree. Figure 11 : The variation of the maximum tension after the expansion In the first case of interactions, the parameters variation of residual stress profiles according to the three factors: (Ce), (Ys) and (t) is investigated. Therefore, the plan calculates the effects of both factors and their interaction using a regression model. In this study, we only present the prediction curves shown in the figures (12, 13) which show the influence of the most important points in the residual stress profile enumerated as following: • The maximum compressive residual stresses • The compressive residual stresses zone. Figure (12) shows the predicted response of the MCRS according to the variation of the three factors. The investigation of this curve shows that, to produce a maximum value of compressive residual stress (in absolute value) it is necessary to