Strain-dependence of plastic strain ratio of deep-drawing aluminium-killed steel sheet

The change of width and length of an aluminium-killed (AK) steel sheet was measured in detail at various tensile strain levels. The effects of tensile strain on the conventional strain ratio, r(c)-value, and the instantaneous strain ratio, r(i)-value, were analyzed. It was shown that the strain ratio of the AK steel sheet had obvious strain-dependency. The individual r(c)-values for all tested directions tended to unity with increasing strain so that the planar anisotropy decreased with increasing strain. The r(i)-value had overall strain-denpendency similar to that of r(c)-value, though it was overly sensitive to the experimental errors and showed significant variation with strain. In the representation of average strain ratio, the linear regression strain ratio, r(r)-value, which was obtained by fitting a straight line to the epsilon(W) vs epsilon(T) curve, is preferable to the r(c)-value measured at some specfic extension.