Issue 48

M. Laredj et alii, Frattura ed Integrità Strutturale, 48 (2019) 193-207; DOI: 10.3221/IGF-ESIS.48.21 204 Hence, we note that the effect of the degree of expansion on the improvement of the service life is more significant than the yield strength and the thickness. From the obtained models we can determine the optimal values of the various factors (t), (Ce) and (Ys) to predict the residual stresses obtained from factor values. Figure 15 : Effects of factors on CRSZ. According to the analysis performed by the "modde5.0" software we can verify easily the optimal points of the responses. Consequently, according to the table (3) these values are obtained by maximizing the residual stress profile. The process can be carried out by the experiment which comprises the values of the thickness equal to 4.93 mm, the degree of expansion which is equal to 4.04  and the yield strength which is equal to 347.082 MPa. These findings are very close to the results of A. Amrouche and M. Su [32-31] showing through an experimental study that the existence of critical degree of expansion Ce = 4.3% increases the lifetime by about 3.5 times comparing to the drilling without expansion. On the other hand, beyond this critical value the expansion process becomes detrimental on lifetime and the crack propagation rate after its initiation. Thickness Ce % Ys CRSEH MCRS DMCRS DRSZ MT PDZ 6.6328 2.331 251.191 62.6207 156.727 1.2626 2.9075 13.5694 3.4623 6.3866 5.7463 313.173 52.3595 174.271 2.2156 3.999 51.4983 4.5646 4.8038 2.8226 358.838 143.368 248.403 0.9815 2.835 39.2896 3.3622 6.6137 5.876 311.975 45.0092 163.664 2.3023 4.0605 51.2529 4.6291 4.939 4.0448 347.082 115.912 241.729 1.4309 3.3315 48.4612 3.8708 7 5.5078 250.008 10.0388 112.273 2.5006 4.2592 34.2554 4.7822 5.5529 2.0674 368.755 161.045 239.242 0.6452 2.3531 32.5068 2.8971 4.5671 4.2187 357.05 109.586 -248.24 1.4403 3.2879 52.9058 3.869 Table 3 : Optimal values of residual stress profiles The validation of the models is done by comparing the results obtained by simulations and the predicted models. Table (4) illustrating the comparison of an expansion of a 5mm thick plate with a 4% degree of expansion made of aluminium alloy 6082-T6. Figure 16 shows a good correlation between residual stress profiles obtained by simulation and predicted models.