טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRoman Goltsberg
SubjectContact Mechanics of Thin Film Coatings
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Etsion Izhak
Full Thesis textFull thesis text - English Version


Abstract

Coatings are widely used in various applications of contacting surfaces to enhance the tribological performance such as friction and wear reduction, electrical and thermal conductivity improvement and resistance to yield inception, to name a few. Proper selection of coatings can reduce energy consumption, prevent failures such as coating delamination and increase service life. However, the selection of the coating material and thickness is done so far mainly by trial and error and is not necessarily optimized for different applications, due to lack of scientific theory for coating design.

In this study a model for elastic coated spherical contact under normal loading is developed using a finite element method. The effect of mechanical properties of the coating and the substrate materials and the coating thickness on the tribological parameters such as load, interference and contact area is studied.

The first part of this study deals with the onset of plasticity in a coated spherical contact with hard coatings. It is found that, in general, hard coatings increase the resistance to plasticity (increasing the required load for plasticity onset) compared to the uncoated case. Also, an optimal coating thickness exists, which maximizes the resistance to plasticity for a given set of mechanical and geometrical properties. A range of very small coating thicknesses is observed where the coating actually weakens the coated system by reducing the resistance to plasticity compared to the uncoated case. This “weakening” effect is extensively investigated and characterized.

In the second part of the study a new method for normalizing of the dimensional contact parameters is introduced. This normalization enables universal relations between the various contact parameters and provides an effective modulus of elasticity for a coated spherical contact, which is load independent and therefore more realistic than previous approaches.

This study is a first step for developing a contact model for rough coated surfaces. Such contact model will enable the optimization of coating design for different tribological applications.