PLASTIC BEHAVIOR OF THE STEEL 20-MNMONI-5-5 AT TRANSIENT HIGH-VELOCITY LOADING

The dynamic deformation behaviour of the steel 20 MnMoNi 5 5 has been investigated using the Split Hopkinson Pressure Bar technique. Contrar y to the usual practice short loading pulses were used. In this way hi ghly transient loading conditions were attained with maximum strain ra tes in the range of 10(4) s(-1), which simulates the situation near ra pidly moving crack tips. One result is that the often used viscoplasti c material models of Bodner-Partom and Perzyna are not suited to descr ibe the transient response behaviour of the investigated steel. A mode l developed in the present work describes the observed response quite well. The model takes into account delayed yielding. Furthermore it is assumed that the density of mobile dislocations depends on the loadin g history.