| The work described herein consists of two parts. In both parts a stress ratio parameter is used for studying the workability of metals. A rigid-viscoplastic formulation is used with the finite element analysis method to demonstrate a process for studying the plastic flow of metal during forming. Variations of the stress ratio g (mean stress/effective stress) in combination with the strain rate and with respect to time have been studied. The rate of change of the square of the g parameter with respect to the log of the strain rate allows a useful description of the material workability. In the first part, tension test simulations were run for strain rate sensitivity parameters in the range of 0.2-1.1. The compression test simulations were run for 0.2, 0.4, 0.8 strain rate sensitivity parameters and for 0.0, 0.001, 0.150, 0.800 friction factors. In the second part the stress-ratio parameter is used with similar analytical tools for studying the plastic flow of metals during extrusion through conical, constant-strain-rate and streamline dies. Various extrusion die geometries, billet materials and ram speeds with 9:1 as well as 4.4:1 reduction ratios were studied. Four different experimental process conditions were used with a streamline die to help confirm the results from the simulations. |
