13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- Fig. 1 shows the initial texture of IF steel, AA5754 and AZ31 sheets, the later having the basal texture while the former sheets exhibit typical rolling texture. (a) IF steel (b) AA5754 (c)AZ31 Fig. 1 Initial textures of the three alloys Fig. 2 Engineering stress – engineering strain curves of three alloys From the engineering stress-engineering strain curves of the three materials (Fig. 2), it is seen that the uniform strain to ultimate tensile stress is 29.6%, 18.0% and 15.8% for IF steel, AA5754 and AZ31, respectively. This is commonly accepted as the strain where diffuse necking is initiated in the materials. While only diffuse necking can be identified on stress-strain curves, the sequence of deformation occurring during tensile tests, especially the initiation and development of localized necking can be clarified for each material from tensile strain maps obtained from DIC measurements (Fig. 3). From Fig. 3, it is seen that both thinning and narrowing occurs in IF steel, only thinning in AA5754 and only narrowing in AZ31 following the diffuse neck formation. It is also seen in Fig. 3 (a) and (c) that localized necking occurs in both IF steel and AA5754 before fracture, however, no localized necking occurs in AZ31.
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