Finite element modelling of crack growth and wear particle formation in sliding contact

Abstract

Two steel surfaces in sliding contact are examined analytically and experimentally. The experiments are restricted to the reciprocating sliding of a relatively hard circular cylinder on a soft plane but the analytical model developed can be applied to general two-dimensional sliding contact situations. The surfaces are nominally smooth (smooth to the touch) but microscopic roughness is modelled as surface asperities having the form of randomly spaced cylindrical corrugations, which ideally represent plane strain conditions perpendicular to the direction of sliding. Under dry sliding conditions (high friction) it is known that crack growth and particle detachment can occur below the elastic limit. By applying finite element methods to linear elastic fracture mechanics, a model is developed, which simulates crack growth and wear particle detachment from an existing surface crack. A range of mixed mode stress intensity factors for cyclic loading is evaluated and related to crack extension by a Paris type equation. The maximum tensile stress criterion is used to determine the crack-turn-angle (crack path) during crack propagation under cyclic loading. It is found that eventually the crack extends and turns toward the surface of the plane to form a single wear particle. Estimated wear volume is calculated using surface statistics and integration. The predicted particle size and the estimated wear volume are in reasonable agreement with those obtained from experiments involving hardened steel sliding on steel. Some of the tested specimens were sectioned and examined in a scanning electron microscope. Two distinct types of crack were observed. Hardness tests on the section revealed significant work hardening in the near-surface layer.