PREREQUISITES FOR THE DESTRUCTION OF THE SURFACE LAYERS OF DETAILS DURING THEIR FRICTION AND WEAR
DOI:
https://doi.org/10.18372/0370-2197.2(107).20165Keywords:
friction, wear, elastic deformations, elastic behavior of material, elastoplastic materials, metal creep, modulus of elasticity, shear modulus, reduced modulus, loss of stability, beam flexibility, residual deformations, deflection of flat sections, Euler's formulaAbstract
In the process of calculating friction and wear of surface layers, significant emphasis is placed on calculations for local stretching in the contact zone and the longitudinal stability of the material layers. Calculations are usually performed based on the classical laws of Hooke and Euler. For example, Hooke's laws are used for tensile calculations, where the stress is proportional to the strain , with . Additionally, the Euler formula is used for the stability calculations of the outer layers of the material. If , the outer layer material, associated with the base material of the part, loses its original shape, and elements of such a layer, supported by deeper plastic layers, can become brittle and lose longitudinal stability. In most loading cases, normal stresses in the zone under the stamp follow Hooke's law, and rupture stresses generally do not occur. In the zone ahead of the stamp, local stability of the layer is often lost under the same loads, leading to the formation of a corrugated surface. The change in the layer's shape indicates the presence of residual inelastic deformations.
Scattered literary sources containing data on different types of surface layers, mainly working under tension and compression, indicate that the material in the compression zone in front of the stamp behaves as an elastoplastic material. Consequently, deflection (initially flat cross-sections before deformation) and wave formation (corrugations) appear similar to initial geometrical micro-roughness after mutual shearing due to mechanical interaction. Such ambiguous material behavior during deformation suggests that instead of Hooke's and Euler's laws, their inelastic analogs manifest. Additionally, a thin surface layer due to strain hardening and re-hardening supported by the elastic base behaves like a rod with a low flexibility coefficient . In this case, local loss of stability of the surface layer may not occur, and brittle fatigue failure of the layer may occur. This process can end with the formation of local cracks.
Data from sources on different types of surface layer parameters, plastic, elastic, and elastoplastic, indicate that the conclusions obtained were confirmed by creating a mathematical model of the problem, reflecting the manifestations of the nonlinear properties of material parts after considering the geometric and physical nonlinearity of the deformed layer. In the mathematical model of the problem, the influence of brittle fracture of the outer layer, its cracking, and chipping on the deformation ridges can be established.
The results of the work can be refined by introducing a term describing the brittle fracture of the outer layers into the differential equation of the problem.
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