Ph.D Thesis

Ph.D StudentOvcharenko Andrey
SubjectExperimental Investigation of Junction Growth in Spherical
DepartmentDepartment of Mechanical Engineering
Supervisors PROFESSOR EMERITUS Izhak Etsion
DR. Gregory Halperin
Full Thesis textFull thesis text - English Version


An accurate knowledge of the evolution of the contact area of a spherical asperity under varying normal and tangential loading is important for studies involving many tribology and contact mechanics problems such as friction, adhesion, wear, electrical and thermal contact conductance to name a few. To investigate the behavior of such a contact a novel experimental test rig was developed to allow real time and in situ direct optical contact area measurement, synchronized with data acquisition of friction force and relative tangential displacement.

            The contact area is first studied under normal preload alone for both loading, loading-unloading and multiple loading cycles over a wide range of elastic-plastic deformations and for various materials and diameters of spherical specimens. Then the effect of adding tangential loading to a normally preloaded contact was studied. The evolution of the contact area as a result of adding gradually increased tangential loading revealed an essential growth of the contact area (junction growth), which depends on the magnitude of the normal preload, and appears to affect the static friction coefficient. Finally the effect of creep on the contact area under a constant normal load was also investigated. The experimental results correlate well with previous theoretical predictions based on the assumption of full stick contact condition. These results also reassured that proper normalization of the various contact parameters by their relevant critical values at yield inception provides a powerful universal similarity solution of the elastic-plastic contact problem.