ANALISA DEFORMASI PLASTIS PADA KONTAK ANTAR ASPERITI: MODEL DAN EKSPERIMEN

Abstract

The discussion of friction, wear, and lubrication in micro-scale of an engineering surface incorporates the knowledge about the asperity deformation. Running-in is an effective way to adjust the engineering surface parameters between two contacted components in rolling and/or sliding situations. There are many chemical and mechanical parameters change on the micro-geometry of the surface during the running-in phase. In the study of mechanical parameter change on the engineering surface in running-in phase, there are two dominant mechanisms: plastic deformation and mild wear. During this phase, the higher peaks or asperity of the rough surface, produced by machining process, is reduced by plastic flow mechanism. The valleys are filled and the surface conformity is obtained. The understanding of the reducing/truncating the higher asperity in running-in phase is required in optimizing the surface topography and machining selection. In order to understand the aforementioned phenomena, the literature studies were conducted and some proposed models were found. Researchers investigated the contact situation between the hard-soft material and two deformable bodies. One of the researchers, Johnson and Shercliff concluded that the contact between two asperities with the same hardness number will produce the same plastic deformation without considering the geometries. This thesis explores the conclusion of Johnson and Shercliff by conducting the experiments and finite element modeling. Two brass hemispheres with seven different radius ratios (R1/R2) were contacted and loaded. The contacting loads were 8000 N and 11000 N and resulted plastic deformation. A non-linear curve which depicts the relation between plastic deformation of the contacted hemisphere and its radius ratio is performed. This curve does not agree with the conclusion of Johnson and Shercliff. The plastic deformation decreases when the radius ratio increases which describes that the plastic deformation of two contacted asperities is affected by the geometry of the asperities. Keywords: asperity, plastic deformation, contact mechanics, running-in