Thermo-mechanical criterion of generation of wear particles for volumetric stress
Journal Title: Вісник Тернопільського національного технічного університету - Year 2015, Vol 77, Issue 1
Abstract
The model of friction and wear surfaces is constructed based on theory of mechanical frictional interaction. The state of stress and kind of the surface layers fracture is analyzed. Longevity of mobile connections is estimated and critical conditions that lead to disruption of its normal function are defined. The ways to control friction and wear are discussed. The destruction of metal alloys in terms of friction accompanied by the separation of fine particles of a material called wear particles that are the parts of the metal matrix material. The current classification of the wear particles formed during the destruction of metal under the friction is briefly analysed. It is found that some of them can be identified as the structural elements of the surface layer. Thus, the two-point thermomechanical criteria of the appearance of wear particles for three-dimensional stress state in the surface layer of the tribological system is proposed. Thermomechanical wear criterion is based on the assumption that wear of the contact surfaces under mechanical and thermal load (frictional load) may occur due to the transition of the material at two points of the surface layer in the plastic state. Considered that the yield strength depends on the temperature. The distributions of the temperature and stresses in a half-space, caused by the temperature and normal pressure in the contact area, that moves with a constant speed, are used as input. Using this criteria, a close relationship between the microstructure of the alloy, size of wear particle and roughness of the surface layer counter-body is found. The size of the grain surface, under and above which under certain conditions material can pass in plastic state, may be defined from the size of contact spot (space of load of surface), which is formed from a single sliding frictional contact with a solid half-space inequalities can specify. Thus, there is the correlation between the size of a grain surface layer and the size of contact spot. For example, a map for the thermomechanical wear of the steel ShH15 is built.Comparison of critical load values in the case of one- and two-point criteria is done. The difference between the proposed criteria of wear and proposed previously by the authors one point criterion is that the critical stress is reached not only in some point in the friction surface, but in nearest to this point under the surface (such as grain size range).
Authors and Affiliations
Heorhiy Sulym, Sergiy Pyr'yev
Keywords
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