Elucidation of contact state on various rough surfaces via highly robust colorimetric optical interferometry

Tatsunori Tomota,Mamoru Tohyama,Kazuyuki Yagi

doi:10.1038/s41598-021-04104-y

Tatsunori Tomota, Mamoru Tohyama + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-04104-y

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Abstract

In this study, we developed and practiced colorimetric optical interferometry for the direct observation of contact states to clarify contact phenomena. We theoretically demonstrated that the effect of roughness diffuse reflection could be neglected using interferometric light intensity according to the relationship between the optical film thickness and hue. Then, we measured the static contact surfaces of spherical test pieces of different root mean square roughnesses. Results indicate that the nominal contact area is significantly larger than that obtained from the Hertzian theory of smooth contact as the surface roughness increases. The contact film thickness on the nominal contact area increases almost in proportion to the root mean square roughness. Our experiment supports the validity of the contact theory and contact simulation with very small roughnesses, which have been difficult to verify experimentally. The advantage of this measurement is that it can simultaneously capture the macroscopic contact area and microscopic film thickness distribution, which is expected to further expand the range of application.

Highlights

In this study, we developed and practiced colorimetric optical interferometry for the direct observation of contact states to clarify contact phenomena
We developed and verified a method for the direct observation of the contact state to clarify the effect of surface roughness on the contact phenomenon
Using the interferometric light intensity from three single-wavelength light sources, we calculated the relationship between the optical film thickness and hue, and theoretically demonstrated that the effect of roughness diffuse reflection can be neglected

Summary

Introduction

We developed and practiced colorimetric optical interferometry for the direct observation of contact states to clarify contact phenomena. Our experiment supports the validity of the contact theory and contact simulation with very small roughnesses, which have been difficult to verify experimentally The advantage of this measurement is that it can simultaneously capture the macroscopic contact area and microscopic film thickness distribution, which is expected to further expand the range of application. Changes in the frictional force significantly impact energy loss, thereby affecting the performance of mechanical parts, and changes in the degree of wear directly affect product life and reliability It is widely known from both empirical and theoretical predictions that a small gap exists on the contact surface of the joint in various sealed structures, and the amount of leakage from the gap varies depending on the surface finish[6,7,8]. Direct simulations have been actively conducted using finite element methods; they are not often compared with the experimental r esults[13,14,15]

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