13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- From the local strain development (Fig. 5), it is seen that deviation between local and global strains is more significant in IF steel and AA5754 comparing to AZ31. 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 Global strain Local strain IF steel AA5754 AZ31 Fig. 5 Local versus global strain in three alloys It is well known that in AA5754 deformed at room temperature at quasi-static strain rates, premature necking occurs due to the Portevin-Le Chatelier (PLC) effect (e.g. illustrated in the first three maps in Fig. 3 (c)) [1]. A simple model has been established to account for the effect of PLC band strain on reduction of uniform strain to UTS [1]. It is also reported that at a certain combination of temperature and strain rate (e.g. -50 °C and 6×10-4/s), the PLC effect and accompanying premature necking can be removed [1]. It is also reported that the formability of AA5754 can be improved by enhancing specific texture components (e.g. cubic texture) [10]. Traditionally, it is accepted that the higher plastic strain ratio, i.e. r-value, the better formability. In the discussion below, the relationship between plastic anaisotropy and formability is further examined in light of the above observations. Fig. 6 r-values development in three alloys When plotting the r-value evolution in the three materials used in the present study (Fig. 6), it is seen that the r-value in AZ31 is the highest (3.2). However AZ31 has the lowest formability in the uniaxial tensile deformation. Eq. (1) is derived with the assumption that material deforms in
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