Keywords: asperity micro contacts, thermo-elastic-plastic deformation, fractal geometry, head-disk interface mechanics, finite element method.

Since there are significant variations in the size of the asperity micro contacts under typical contact situations, contact analyses using real surface topographies are necessary to obtain more accurate information about the contact stress and deformation fields. The previous studies provided useful knowledge about thermo mechanical analysis of semi-infinite medium in sliding contact with a rough surface. However, in all these studies, either the rough surfaces were not characterized with fractal geometry or the interactions between neighbouring asperities or the simultaneous effects of thermal and mechanical deformations were ignored. The main purpose of this study was, therefore, to develop thermo mechanical analysis of sliding contact between a computer hard disk and a magnetic head with realistic description of surface topographies as semi-infinite medium and rough slider, respectively. In order to achieve this purpose, magnetic head surface was first developed by using the fractal geometry. A two dimensional fully coupled thermo mechanical finite element model was then developed at the head-disk interface (HDI). The next requirement was to incorporate an equivalent surface topography of the HDI in a finite element model for analyzing the stress and strain fields occurring at the vicinity of the contact areas. The finite element simulations were performed to obtain temperature rise, subsurface stress/strain fields and contact pressure distribution for an elastic-plastic homogeneous medium. The effects of friction coefficient and surface interference on to deformation have also been investigated. Based on the results presented, it is shown that frictional heating increases not only the contact area but also the contact pressure and stresses. It is clear that frictional heating decreases the tensile stress while it increases the compressive stress at the surface of the semi-infinite medium. It also affects the location of the thermo mechanical curve by shifting it below to the mechanical curve. The maximum tensile stress in the thermo mechanical analysis occurs on the surface of the hard disk. The characteristics obtained for the pressure and stress are consistent with the results of finite element simulation of elastic and thermo elastic study of Gong and Komvopoulos [1]. The results of the present study are also consistent with elastic/plastic and thermo-elastic/plastic study presented by Boucly et al. [2] for the pressure distribution of the semi-infinite solid in contact with rigid sphere. In their study they found that the values obtained from thermal analysis were greater than those of only elastic and only elastic-plastic analysis, demonstrating the same trend as obtained in the presented study. It is clearly seen that increasing friction coefficient at the HDI increases profoundly the temperature at the surface of the semi-infinite medium. This is especially more evident for the high friction coefficient of 0.5. The results obtained showed that as the surface interference increases both the number of asperities which carries the load, and the contact area increase. Increasing in the contact area and in the number of asperities decreases the load carried by the each asperity since they share it. The plastic strains of thermo mechanical analysis are found to be higher than those of the mechanical analysis since there is greater temperature rise at the HDI due to the frictional heating which causes plastic deformation rather than elastic.

1

Gong, Z.-Q., and Komvopoulos, K., "Thermo mechanical Analysis of Semi-Infinite Solid in Sliding Contact with a Fractal Surface", ASME J. Tribology, 127, 331-342, 2005. doi:10.1115/1.1792691

2

Boucly, V., Nelias, D., Liu, S., Wang, Q.J. and Keer, L.M., "Contact Analysis for Bodies with Frictional Heating and Plastic Behaviour", ASME J. Tribology, 127, 355-364, 2005. doi:10.1115/1.1843851

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