A UNIAXIAL CYCLIC PLASTICITY MODEL INCLUDING TRANSIENT MATERIAL BEHAVIOUR

Abstract— A phenomenological uniaxial material model, which is a one‐dimensional equivalent to a two‐surface multiaxial plasticity model, is presented. The model takes into account the transient effects cyclic hardening/softening and mean stress relaxation by means of exponential relationships that are functions of number of reversals. The parameters describing these relationships are obtained from the strain‐life curve and the cyclic stress‐strain curve. The hysteresis loops are assumed to be bounded by two parallel, straight lines in tension and compression, i.e. bounding lines. The stress‐strain curve approaches these lines with increasing strain through a nonlinearly decreasing plastic modulus. The transient effects are simulated by increasing/decreasing the distance between the lines for cycling hardening/softening at each stress or strain reversal. A positive mean stress yields translation downwards of the bounding lines if the material is subjected to strain control, and translation in the opposite direction if the mean stress is negative. Dynamic creep is simulated when the material is subjected to stress control and mean stress. The test data was obtained from an experimental programme on St52–3N, which is a normalized structural steel. The specimens were loaded in strain or stress control. The comparison between tests and simulations shows that the model described simulates the cyclic transient material behaviour quite well. The main inaccuracy is due to using parallel bounding lines, as the tests show that these lines are not completely parallel for the present steel material.