Transient analysis of sliding contact of layered elastic/plastic solids with rough surfaces

Abstract

Based on the boundary element method (BEM) and a variational principle, a numerical model is developed to analyze the time -transient sliding contact of two layered elastic/plastic solids. Two cases are considered: one is the loading/sliding/unloading of a rough surface on a smooth surface, and the other is of two rough surfaces. Contact statistics, contact pressure profile and stress distribution are predicted at each time step with updated surface roughness. The results are used to study the effect of surface roughness, physical properties of the layer and the substrate, and lubricant film thickness on friction, stiction, and wear. Discussion on the integration of this contact model into advanced tribological models, e.g., wear model, is also presented. IntroductionThe deposition of layers is an effective way to improve the tribological performance of elastic/plastic solids with rough surfaces. For example, the Diamondlike carbon overcoat is used in magnetic head-disk interface to prevent wear and corrosion. In order to achieve the optimum performance of the layered structure, its contact mechanism has to be studied. Analytical methods usually are not feasible due to the complex nature of the contact problem. Numerical models are widely used to simulate the contact with the variation of contact parameters, thus are effective ways to study the contact mechanics. A comprehensive review of contact models has been presented in [1].However, current numerical models focus more on the static contact mechanism, e.g., normal contact and quasisliding contact. The transient sliding contact of two layer solids with rough surfaces, as shown in Fig. 1, has rarely been studied. Although the static models can predict a general trend of layer effect and surface roughness on the contact performance, the results are lack of relationship with the time history and very difficult to be compared with the experimental results.In this paper we extend a three-dimensional static contact model [1-4] to include a time factor as well. This three-dimensional numerical model was developed to analyze the quasi-sliding contact of two layered elastic/perfectly plastic solids with rough surfaces (multi-asperity contact). By performing a series of quasi-sliding analyses in a time sequence, with updated contact parameters at each specific time point, the model is extended from quasisliding contact (static) analysis to sliding contact (transient) analysis. Transient response, such as time-varying displacements and stresses, are predicted. This analysis provides a new insight of the surface evolution during the sliding contact of two rough surfaces and is critical in problems such as ''wear-in'' process of the pseudo-contact magnetic recording. BEM contact analysis based on a variational principleIn order to perform numerical analysis, the solids need to be discretized into small elements so that no assumption concerning the roughness distribution is required. BEM employs a different discretization scheme from finite difference method and finite elem...

Multiple loading–unloading of an elastic–plastic spherical contact

“…It is found in various applications such as contact resistance in MEMS micro switches (Majumder et al, 2001(Majumder et al, , 2003, head-disk interaction in magnetic storage systems (Peng and Bhushan, 2003), and ultrasonic interfacial stiffness measurements (Kim et al, 2004) to name just a few. A solution of this problem can also be useful for rough surfaces wear studies (Kapoor et al, 2002) and for contact shakedown in various rolling elements, see e.g.…”

Unloading of an elastic–plastic loaded spherical contact

“…Repeated loading and unloading of rough surfaces is an important problem, especially in the technology of micro/nano-systems, such as MEMS microswitches (Majumder et al, 2001(Majumder et al, , 2003, for example, or headdisk interaction (Peng and Bhushan, 2003) in magnetic storage system. Hence, the interest in loading/ unloading of a sphere in contact with a flat, which can simulate a single asperity of a rough surface, is obvious.…”

Elastic–plastic modeling of heat-treated bimorph micro-cantilevers

“…The tip deflection of bimorph cantilevers is found to depend on the temperature conditions applied during the heat treatment process. However, in spite an elastic-plastic model was used to analyze layered solids with rough surfaces in ref (Peng and Bhushan 2003), previous studies generally did not consider the plastic characteristics of bimorph cantilevers. In micro-cantilevers manufacturing process, a gap is formed by etching sacrificial layers in surface micro-machining (Cui et al 2004) or by back-etching substrates in bulk micro-machining .…”