Some Issues of Rough Surface Contact Plasticity at Micro- and Nano-Scales

Abstract

Rough surface contact plasticity at microscale and nanoscale is of crucial importance in many new applications and technologies, such as nano-imprinting and nano-welding. This paper summarizes our recent progress in understanding contact plasticity from a multiscale point of view, and also presents our perspectives. We first discuss a contact model based on fractal roughness and continuum plasticity theory. Interestingly, our simple, elastic-plastic contact model of Weierstrass-Archard type gives rise to many practical scaling relations of contact pressure, contact compliance etc. The usefulness of those predictions is discussed for the experiments of indentation and measurements of thermal and electrical properties. A material length scale can be introduced by a nonlocal plasticity theory, or implicitly by dislocation mechanics model. The recent work on micro-plasticity of surface steps gives a variety of surface yielding and hardening behaviors, depending on interface adhesion, roughness features and slip systems. As a consequence, a rough surface contact at small scale can lead to the formation of a boundary layer with sub-layer dislocation structures, which cannot be predicted by existing strain gradient plasticity theories. The micromechanical analysis of surface plasticity could serve as the connection between microscale bulk dislocation plasticity and nanoscale atomistic simulations.

Finite element modeling of elasto-plastic contact between rough surfaces

“…7). A similar saturation value has been predicted in recent analytic studies of 2D plastic surfaces (Gao et al, 2004). Simple scaling relations were given that allow hpi to be estimated for any yield stress and hardening exponent (Eqs.…”

“…This is consistent with recent analytic studies of asperity interactions on self-affine surfaces in two-dimensions. Gao et al (2004) found that the contact pressure approached 6s y with decreasing yield stress. It is noteworthy that our three-dimensional numerical results (Fig.…”

“…Since Ho1, surfaces look smoother as the length scale increases. Conversely, the surface becomes singular at small scales unless the scaling is cutoff (Persson, 2001;Ciavarella et al, 2004;Gao et al, 2004). We take the small scale cutoff as our unit length and quantify the magnitude of the roughness by the rms slope in each lateral direction at this scale:…”