Adhesive Wear Based on Accurate FEA Study of Asperity Contact and n-Point Asperity Model

Adhesive Wear Based on Accurate FEA Study of Asperity Contact and n-Point Asperity Model

Ajay K. Waghmare (Department of Mechanical Engineering, Jadavpur University, Kolkata, India) and Prasanta Sahoo (Department of Mechanical Engineering, Jadavpur University, Kolkata, India)
DOI: 10.4018/IJSEIMS.2016010101
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Abstract

The paper describes a theoretical study of adhesive wear based on accurate finite element analysis (FEA) of elastic-plastic contact of single asperity and n-point asperity model. The wear model developed considers wear particle generation in whole range of deformation, ranging from fully elastic through elastic-plastic to fully plastic. Well defined adhesion index and plasticity index are used to study the prospective situations arising out of variation in load, material properties, and surface roughness. It is observed that the wear volume at particular level of separation increases with increase in plastic deformation and adhesion effect. Materials having higher tendency to adhesion show higher wear rate. Trend of the results obtained is found in line with the existing solutions which are modeled with conventional asperity concept. Inclusion of separate formulations for intermediate state of deformation of asperities which are based on accurate FEA study gives complete solution.
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Introduction

Loss of material from the surface of a solid is called as wear and is an important issue as it badly affects the performance, life and economic aspects of the system. Out of various mechanisms of wear, adhesive wear is considered as the dominant one in nano and micro scale systems. Archard (1957), based on Bowden and Tabor (1954) classical theory of adhesive friction, proposed adhesive wear theory and according to it wear takes place through the process of adhesion junction (cold weld) formation at asperity tips (contact spots of rough surfaces) and their subsequent shearing due to tangential force. Archard was the first to quantify adhesive wear for contact of rough surfaces. Thereafter, various works on adhesive wear are found in the literature (Rabinowicz, 1980; Qureshi & Sheikh, 1997; Sahoo & Chowdhury, 2002; Yin & Komvopoulos, 2010), which mainly studies the wear rate from the perspective of changes in sliding distance, sliding speed, contact area, applied load, interfacial conditions like adhesion/friction, material properties and scale dependence of topographic parameters. Few experimental studies on adhesive wear are also found in the literature (Schofer & Santer, 1998; Ando, 2000). As the plastically deformed asperities do not support tangential load so most of the earlier studies (like Sahoo & Chowdhury, 2002; Yin & Komvopoulos, 2010), assumed that the wear particles will be from plastically deformed asperities only. But studies like Schofer and Staner (1998) and Ando (2000), which are based on sophisticated experiments show occurrence of wear even at elastically deformed asperities. So present authors in earlier study (Waghmare & Sahoo, in press) have presented a wear model in which asperities from both the elastic and plastic zone of deformation are considered.

Present study intends to analyze adhesive wear in intermediate transition zone also. Transition from purely elastic to purely plastic zone of deformation doesn’t happen instantly and there exists a wide intermediate transition zone. According to Johnson’s (1987) study, the contact load causing fully plastic flow is almost 400 times the load causing initial yielding. Chang et al. (1987) first attempted to model the intermediate elastic-plastic zone of contact by using volume conservation of asperity tip concept. As this model introduced discontinuity in the contact load at transition, Zhao et al. (2000) tried to remove this discontinuity by using logarithmic and polynomial function. But the Zhao et al.’s attempt was based on mathematical, rather than physical, considerations. Kogut and Etsion (hence forth called KE) (2003), based on their accurate FEA results for a single asperity contact, have given analytical formulations to model contact load and contact area of this intermediate transition zone. Earlier studies (Sahoo et al., 2009; Mukherjee et al., 2004; Sahoo, 2006; and Ali & Sahoo, 2006), have successfully incorporated the KE (2003) analytical formulations to model rough surface contact situations in the elastic-plastic transition zone of deformations.

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