Effect of self heating on the torque vs. equivalent tensile strain plot in high temperature torsion of visco-plastic material

In hot forming as simulated by the torsion test, a temperature rise due to self heating is simulated within a FEM approach. The numerical results allow for a “natural” explanation of the maximum experimentally observed for the torque vs. equivalent tensile strain plot. There is no longer any need for assumptions of microstructurally conditioned strain softening during the test. With increasing cumulated strain (time) the radial temperature gradient in a cross section of the useful centre part of the test specimen is shown to change in sign; in the beginning the temperature is highest at the surface and at the end the temperature maximum is at the centre.