Wear predictions for a simple-cam including the coupled evolution of wear and load

摘要

Predictions of wear based on the forces and slip velocities calculated using the unworn first cycle geometry will not accurately predict a mechanism's useful life. This is because there is a coupling between the contact conditions and the geometry of the components, which are changing as they wear. The ability to accurately predict how a mechanism will perform over an extended number of cycles requires knowledge of how the components are changing during operation. Using an Archard's wear constant, a closed form expression describing the coupled evolution of the contact loads and wear for a circular-cam with a flat-faced follower is developed. Further: these closed form expressions for load and wear: which are given in terms of the number of cam-cycles n, are non-dimensionalized by the cam eccentricity, width, and the Archard's wear constant. The non-dimensional wear and load are functions of the number of cycles and the non-dimensional group termed wear-compliance, which is the product of the Archard's wear constant and the spring constant over the cam width. Non-dimensional closed form equations are also developed for an uncoupled evolution of geometry and wear, and the predictions in useful life are compared for the coupled and uncoupled equations, The uncoupled wear predictions always over predict wear, and greatly over predict wear under conditions of high spring stiffness, low wear resistance, narrow cam widths and large numbers of cycles. It is suggested that a coupling of the evaluation of geometry and contact conditions must be accounted for when making life predictions of wearing mechanisms based solely on wear.