Surface asperity deformation in metal forming processes

Abstract

The crushing of surface asperities by a frictionless die is examined under conditions of bulk deformation of the underlying material. For one-dimensional (ridge-like) asperities aligned perpendicularly to the direction of bulk strain, a slip-line field has been found which enables the growth of real area of contact with bulk strain to be calculated. For asperities aligned in the direction of the bulk strain, an approximate energy method due to Wilson and Sheu has been developed further [W. R. D. Wilson and S. Sheu, Real area of contact and boundary friction in metal forming. Int. J. Mech. Sci. 30, 475–489 (1988)]. Both theories predict a large increase in contact area with bulk strain and a reduction in the load needed for bulk yielding. The theories give reasonable agreement with experiments.