Measurement of real contact area for rough metal surfaces and the distinction of contribution from elasticity and plasticity

TL;DR

This study introduces a new experimental method to measure the real contact area of rough metal surfaces and distinguishes the roles of elasticity and plasticity during contact, challenging previous assumptions.

Contribution

A novel apparatus based on frustrated total internal reflection is developed to measure contact area and analyze elastic and plastic contributions during loading and unloading.

Findings

Real contact area is linearly related to load during loading.

Both elasticity and plasticity are involved throughout the contact process.

A quantitative parameter indicates the contribution of plastic deformation.

Abstract

The measurement of real contact area between rough surfaces is one of most challenge problems in contact mechanics and is of importance to understand some physical mechanisms in tribology. Based on the frustrated total internal reflection, a new apparatus is designed to measure the real contact area. For brass samples with various surface topographies, the relation between normal load and real contact area is measured. Our experiments verify the linear relationship between load and real contact area during loading process. More importantly, the unloading process is firstly considered to distinguish the contribution of elasticity and plasticity in contact of rough surfaces. It is found that both elasticity and plasticity are involved throughout the continuous loading process, different from some present understanding and assumptions that they play at different loading stages. A quantitative parameter is proposed to indicate the contribution of plasticity. The present work not only provides an experimental method to measure real contact area but figure out how elastic and plastic deformation works in contact of rough surfaces.