Plane Strain Visioplasticity for Dynamic and Quasi-Static Deformation Processes

Abstract

The visioplasticity approach is developed to enable the complete stress history of any steady or nonsteady, quasi-static or impact, plane strain plastic deformation process to be determined from a record of the deformation pattern. The velocity field is determined experimentally, and, for dynamic conditions, high-speed photographs are taken of grid patterns marked on the end surface of the specimen. Digitization of the instantaneous grid node positions allows the velocity fields to be obtained at predetermined time intervals throughout the transient deformation period. Hence, the strain-rate, equivalent strain rate, equivalent strain, and finally stress fields can all be obtained. Plane strain upsetting tests, conducted at a speed of 0.1mm/s give results that agree closely with the well-documented “friction hill” type of normal stress distribution for quasi-static rates of strain. However, with a specimen deformed at a speed of 478.54 cm/s the normal stress distribution is radically different exhibiting a saddle-type distribution. The effect of strain rate on the interface and interior stresses will have significant bearing on a number of metal-forming operations.