Abstract: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，rⁱ-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 rⁱ-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 ε_W VS ε_T  curve，is preferable to the r^c -value measured at some specfic extension

Key words: plastic strain ratio   anisotropy     tension