Effect of lateral tension and compression on plane strain flattening processes of surface asperities lying over a plastically deformable bulk

Abstract

Numerical simulation of flattening processes of surface micro-asperities is carried out by using an elastic-plastic finite element code which is capable of dealing with large plastic deformation. Frictionless flattening of a five-asperity model is compared with that of a previously described three-asperity model under a laterally free condition. An infinite-asperity model is also introduced with additional assumptions of periodicity and uniformity with respect to the boundary between surface asperities. Both new models confirmed the main features of deformation associated with bulk plasticity previously observed with the three-asperity model. The three-asperity model, in turn, gives indirect experimental support to the infinite-asperity model. Using the infinite-asperity model, the effect of lateral tension and compression is analysed. The lateral compression, which suppresses bulk plasticity, yields surface deformation of bulging at the non-contacting valleys, while lateral tension enhances bulk plastic deformation of lateral expansion, leaving the surface layer under non-contacting valleys substantially elastic until the latter stage of flattening as in a laterally free flattening process. Lateral tension greatly increases the real-to-apparent ratio of contact under given mean apparent contact pressures, while lateral compression decreases the ratio. This behaviour can be explained by a yield criterion of plasticity of workpiece material.