13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- (a) IF steel tensile strains (b) IF steel width strains (c) AA5754 tensile strains (d) AA5754 width strains (e) AZ31 tensile strains (f) AZ31 width strains Fig. 4 Line scan of cross section for post-necking strain development in three alloys Fig. 4 shows the line scans taken through the strain maps at different stages of the deformation. In Fig. 4 (a) and (c), correspondng to IF steel and AA5754, tensile strains become intense in a more and more narrow band while strain outside this area remains unchanged or even is slightly lowered. These are the typical signatures of localized necking in metallic materials. Together with Fig. 3 (a) and (c), it is concluded that localized necking occurs in IF steel and AA5754 sheet materials. However, when looking closely at AZ31 line scan data in Fig. 4 (e) and (f), one observes that both tensile and width strain keep evolving as the global strain increases. This indicates that no localized necking occurs in AZ31. Instead, it transits directly from diffuse necking into final fracture process [3, 14].
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