Wedge indentation of elastic–plastic layered substrates: Designing against contact-induced plasticity

The present paper investigates the indentation of plastically graded substrates by wedge indenters. Substrates made of graded materials are often encountered in nature or are artificially produced. The variation of the plastic properties depends on micro-structural or compositional changes of the material with depth. The introduction of certain controlled gradients in plastic properties can minimize plasticity and promote resistance to the onset of damage at contact surfaces during tribological applications. Contact analysis of plastically graded surfaces can be particularly useful in the design of load-bearing devices such as gears, rollers and electric contacts found in many macro- and micro-electro-mechanical systems. A comprehensive parametric finite element study of the mechanics of indentation of plastically graded materials by a rigid wedge is presented in the present paper. Of particular interest in the current investigation is the variation of the elastic modulus and the yield strength, of the type E = E0 y0/y and σY = σY0 y0/y. This type of distribution is inspired from the material properties distribution of the human tooth. The results of this work show how surface modifications that result in certain plastic graded properties can strengthen substrates against contact-induced damage.