טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentCohen Dvir
SubjectA Model for Contact and Static Friction of Nominally Flat
and Spherical Rough Surfaces in Full Stick
DepartmentDepartment of Mechanical Engineering
Supervisors Dr. Yuri Kligerman
Professor Emeritus Izhak Etsion
Full Thesis textFull thesis text - English Version


Abstract

A model for elastic-plastic, nominally flat and spherical, contacting rough surfaces under combined normal and tangential loading, with full stick contact condition, is developed. The model incorporates the results of accurate finite element analysis for elastic-plastic contact and sliding inception of a single asperity, with statistical representation of surface roughness.

A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties and surface roughness are presented and compared with some limited available experimental results.

The model allows evaluating the effect of surface roughness on the real contact area, static friction and junction growth under small normal loads. It is shown that as the normal load approaches a certain threshold value, which depends on the plasticity index, the results of the present rough surface model approach these of previous corresponding models for smooth sphere and a rigid flat. At normal load values below the threshold load the correlation of the present results and published experimental results is much better in comparison with the results of the smooth surface models.