Mechanics of crack propagation in delamination wear

A mathematical model of subsurface crack propagation in sliding contact is developed. It is shown that linear elastic fracture mechanics may be applied to such problems, even for elastoplastic solids. An equation to predict wear rates is derived, which should apply in delamination wear to materials in which crack nucleation is easy. Results of calculations of stress intensity factors for various subsurface cracks and coefficients of friction are presented. The numerical calculations were done only for coefficients of friction greater than 0.5.The calculations show that there is a characteristic crack propagation depth below the surface, which increases with increasing coefficient of friction. In addition, the change in stress intensity factor and hence the crack propagation rate, increases with increasing coefficient of friction. A comparison between these calculations and approximate crack growth rates in sliding wear shows that the results agree reasonably well.The model is used to explain the phenomenon that increased hardness sometimes increases wear. A possible explanation for seizure in geometrically constrained systems is advanced. The model may be used to predict wear rates from first principles in the near future.