Effect of flow softening on ring test calibration curves

The application of the ring test to assess die–workpiece interface friction during forging of a flow softening material was investigated. Calibration curves were generated by conducting finite element method (FEM) simulations of ring forging with different friction factors. The method was validated by conducting isothermal, hot compression tests on rings of an α2 titanium aluminide alloy for both lubricated and unlubricated interface conditions. The FEM results for the flow softening material were compared to those generated assuming no flow softening. In all cases, the differences between the curves predicted for the flow softening and non-softening behaviors were quite small. Furthermore, for given values of the interface friction factor, the calibration curves were essentially independent of the strain rate sensitivity (m) and flow softening.