טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShai Ronen
SubjectElastic-plastic model for a coated sphere compressed
by a rigid flat under full stick contact
conditions
DepartmentDepartment of Design and Manufacturing Management
Supervisors Professor Emeritus Etsion Izhak
Dr. Roman Goltsberg
Dr. Kligerman Yuri
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, 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-plastic coated spherical contact, with hard coatings, under normal loading is developed using a finite element method. The effect of mechanical properties and coating thickness under stick contact condition on the tribological parameters such as load, interference and contact area is studied and compared with corresponding results under slip contact condition.

The first part of this study deals with the onset of plasticity in a coated spherical contact. It was found that the general behavior of the onset of plasticity under stick and slip is similar, showing a maximum resistance to yield inception at a certain peak dimensionless thickness. However, the Poisson's ratio in stick has a significant effect on the first yield inception.

In the second part the plasticity evolution under stick contact condition is investigated. It was found that the contact condition has a significant effect on the plasticity evolution mainly within the coating close to the contact interface. The stick contact condition had no effect on the plasticity evolution in the substrate. Hence, only the first yield inception, which occurs close to the contact area, is affected by the contact condition while the second yield inception within the substrate is not.

The third part of this study investigates the influence of the system mechanical and geometrical properties on the contact load and contact area in the elastic-plastic regime of the coated sphere. Here again, it is shown that in this regime the contact condition has almost no effect on the contact load and contact area. This study is a first step for developing a coated spherical contact model under combined normal and tangential loading which can be helpful in future research to model the effect of coating properties on friction and wear.