Analysis of Plane-strain Work Hardening in Sheet Alloys and Its Effect on Forming Limit

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Using commercial 70/30 brass, OFHC copper, and ll00-0 aluminum sheet alloys, the work hardening behavior and limit strain in plane-strain condition have been studied by means of the uniaxial and plane-strain tensile tests in relation to the effect of empirical work hardening law equation and yield function. The parameter m of Hill's non-polynomial yield function is confirmed to be the function of strain by applying Wagoner's rigorous method. The best-fit empirical work hardening law equation describing the relation between logarithmic work hardening rate and effective strain is Voce law equation (saturation law) for brass, Swift law equation (modified power law) for copper, and Hollomon law equation (power law) for aluminum. The results indicate that theoretical ε_<lc> of forming limit in plane-strain condition are almost independent of m-value and theoretical ε_<lc> based on best-fit work hardening law equation agree well with experimental ε_<lc>. The conditions which govern the m-value and the factors which influence the forming limit are discussed.