Issue 48

M. Laredj et alii, Frattura ed Integrità Strutturale, 48 (2019) 193-207; DOI: 10.3221/IGF-ESIS.48.21 201 latter on CRSZ is insignificant. Consequently, an increase in the degree of expansion by 50% leads only to an increase of 7.46% of the compressive residual stresses zone. Figure 8 : The depth variation of the maximum compressive residual stress in Figure (9-c) illustrates the effect of the yield strength on CRSZ. Contrary to the other parameters, an increase in the yield strength leads to a decrease of the compressive residual stresses zone. In fact, a 72% increase in the yield point leads to a 20% decrease in the CRSZ. It had been demonstrated that the mechanical characteristics have an influence on the distribution of the circumferential residual stresses. Several investigations carried by Z. SEMARI and M. SU [29-31] have focused on the study of the effect of the mechanical characteristics on residual stress profiles. Therefore all studies agree that the increasing of the yield strength causes a decrease in CRSZ. Figure 9 : The variation of the compressive residual stresses zone The evolution of the plastic deformations zone as a function of the (t), (Ce) and (Ys) are presented respectively in the figures (10-a), (10-b) and (10-c) . Figure (10-a) illustrates the evolution of the plastic deformations zone with respect to the thickness. We note that the increase of the thickness causes a small increase of PDZ. These results are in agreement with the work of V. NIGRELLI [28]. Figure (10-b) illustrates the effect of the degree of expansion on the PDZ. We see that an increase of the expansion degree leads to an increase of the plastic deformations zone which provokes the deceleration of the propagation kinetics of the defects and thus the increase of the lifetime of the structures. These results are in accordance with the work results of Z. SEMARI [29].