Measurement of the Constraining Stresses during Plane-Strain Compression Testing

A modification of the channel and anvil apparatus used to enforce plane-strain deformation conditions on rectangular specimens is described. This enables the constraining stress and the frictional stress on the channel walls to be measured simultaneously. Copper single crystals have been deformed in the channel both when frictional forces are high and when they are at a minimum. It is shown that irrespective of these external conditions the resolved shear stresses on each slip system predicted by the Bishop and Hill theory of crystal plasticity are similar. The increase in applied stress required when lubrication is poor is used to do work against friction. If an internal hardening mechanism, such as strengthening with a dispersed second phase, exists in the crystal, then the applied stress to deform the crystal increases. But in this instance when it is resolved there is an increase in the shear stress on each slip system in accordance with theory.