Photoelastic stress analysis of a V-shaped die for plastic work

The stress state in the V-shaped die for plastic compression was investigated by using a photoelastic stress analysis in which an Araldite in a glassy elastic state and a softened celluloid were used as model materials for the die and work specimen, respectively. It was found that the direction of the frictional shear stress is reversed at a certain point on the die surface. Because the frictional shear stress of the die mainly depends on the flow speed of the work material, the popular assumption that the coefficient of friction is a constant over the die surface such as in the case of Coulomb friction appears unrealistic.