Issue 46

A. Baltach et alii, Frattura ed Integrità Strutturale, 46 (2018) 252-265; DOI: 10.3221/IGF-ESIS.46.23 259 the vicinity of the exit face only. However, The entrance face present low compressive stresses surrounding the hole edge until a distance 2.25 mm, where after, the circumferential stresses become positive (tensile). Figure 11 : Residual stress distribution vs. the distance from the hole edge to the width border for the case of taper  =11.5 %: a) circumferential stresses and b) radial stresses. The radial stress resulting from the 11.5 % taper pin are always tensile near the entrance side of the hole edge, until 1.5 mm. Then, beyond this distance, it reaches the compressive values. After this point, the radial stresses are compressive through all the thickness of the plate (Fig. 11b). Higher residual compressive circumferential stresses are obtained for the 7.667 % tapered pin in the entrance and the exit face surrounding the hole edge compared to the ball and the 11.5 % taper pin expansion technique (see Fig. 12a). For this case, the maximum values of circumferential stress are always localized around the mid-thickness of the plate through the hole edge until 1mm distance, where the exit face presents the same value as the mid-thickness value. the compressive zone is broader on the side of the mandrel outlet, where it extends up to 3 mm away from the hole edge (see Fig. 12a). Fig. 12b shows the distribution of radial stresses around the hole, in the case of expansion with a conical mandrel of 7.667% taper. Figure 12 : Residual stress distribution vs. the distance from the hole edge to the width border for the case of taper  =7.667 %: (a) circumferential stresses and (b) radial stresses. A significant improvement can be noted in the inlet face, where the tensile stresses are reduced to only exist in the vicinity of the hole, but with a lesser peak compared with previous results. This indicates a positive effect of the decrease of the taper. However, the radial stresses in the middle and in the outlet side are not much affected by the taper degree. Fig. 13a and 13b compares the residual stress distribution through the plate thickness using the 3.833 % taper expansion model. Thus, as shown in Fig. 16a, enhancement appears at the entrance face. In fact, the 3.833 % taper model yields in a higher compressive residual stress for circumferential and radial stress components surrounding the entrance face (Fig. 13a an Fig. 13b). Fig. 13b indicates an increase of radial compressive stresses obtained at the entrance side location. Effectively, the radial stresses in the entrance face became similar to those surrounding the mid-thickness location. It is noted that, the exit face presents the higher values of compressive radial stress as all the first cases. For the 2.875 % tapered pin model, similar results are obtained but with lower compressive circumferential stresses surrounding the exit hole edge, as shown in Fig. 14a. While, around the exit side, there is a reduction in circumferential a) b) a) b)