טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentZait Yuval
SubjectThe Effect of Contact Conditions and Material Properties on
the Unloading and Cyclic Loading of a Spherical
Contact
DepartmentDepartment of Mechanical Engineering
Supervisors Professor Emeritus Izhak Etsion
Dr. Yuri Kligerman
Full Thesis textFull thesis text - English Version


Abstract

The problem of the unloading as well as cyclic loading of a deformable hemisphere by a rigid flat is a fundamental problem in many engineering applications. It is used for example in the study of MEMS micro switches, thermal and electrical conductivity, gears and in the study of the contact of rough surfaces.

Most existing studies on the unloading and repeated loading of a spherical contact assume simple frictionless contact conditions and are relevant only to specific mechanical properties. In the present work, the spherical contact problem was studied using the finite element method under both perfect slip (frictionless) and full stick contact conditions, and a wide range of material properties. The effect of the contact conditions and material properties on the results was investigated.

For the single loading-unloading process it was found that the contact conditions have little effect on the behavior of the spherical contact problem provided a dimensionless solution and normalized material properties. Universal expressions for the global contact parameters during the unloading phase, such as contact load, contact area and flat displacements, were obtained for a wide range of material properties. Universal expressions for the residual deformations at the end of the unloading phase were also developed. The results were found to be in good agreement with existing experimental results.

For the cyclic loading problem, it was found that under full stick contact conditions the cyclic loading process does not become fully reversible following a single loading cycle (as is the case under frictionless contact conditions). Plastic yielding continues to occur during the first several loading-unloading cycles. Hence, several cycles are required in order to reach elastic shakedown. These findings support previous experimental findings.  

The findings of the present study may contribute to an improved design in cases where repeated loadings are applied, and in the study and analyses of mechanical failures of repeatedly contacting bodies.