טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLevy Shoham
SubjectPlastic Yield Inception of a Soft Coated Sphere
Compressed by a Rigid Flat
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus Izhak Etsion
Dr. Yuri Kligerman
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The yield inception in a spherical surface with a soft coating, loaded normally by a flat and rigid surface was investigated in the present work using finite elements.

This problem is significant in contact mechanics and its investigation allows deepening the body of knowledge for surfaces in presence of coatings and an additional step towards a full model predicting the behavior of coated surfaces.

Many applications include relative contact between two surfaces. Coatings are a common solution for improvement of mechanical properties. Despite the variety and prevalence of coatings, the coating thickness is chosen through trial and error. The coating thickness and the influence of the coating and substrate materials are unpredictable due to the lack of a general model based on tribological knowledge.

The investigation of the spherical coated contact was done numerically, in the finite element method with the Ansys software. To validate this model, its results for identical coating and substrate materials were compared to an existing model in the literature for flattening a homogeneous asperity.

A range of non-dimensional parameters was presented for medium-high thicknesses, and a parametrical investigation to characterize the influence of the coating thickness and the mechanical properties of the coating and substrate on the yield inception according to the Von-Mises criterion in presence of a soft coating was done. The mathematical dependence of these parameters on the contact area and the critical load was presented. The mathematical dependence was compared between the present work and additional research works dealing with the yield inception in indentation of a soft coated surface and flattening of a hard coated sphere.

The parameter range was increased for very low thicknesses, and the effects of strengthening and weakening for non-dimensional critical loading, which are connected with maximum and minimum resistance to the yield inception, were presented.