Facta Universitatis, Series: Mechanical Engineering

Solid viscoelasticity is one of the essential origins of sliding friction, as every solid exhibits energy dissipation due to it during deformation processes. In this paper, we first show theoretical solutions for one-dimensional (1D) problems of viscoelastic friction with a 1D viscoelastic foundation. Then, we extend the 1D model to a two-dimensional (2D) model to find theoretical solutions for 2D problems of viscoelastic friction. Finally, we apply the Method of Dimensionality Reduction (MDR) to the theoretical solutions for the 1D problems to discuss three-dimensional (3D) problems of viscoelastic friction.

Interfaces and surfaces play an important role in tribology, mechanics and materials science, causing plastic strain localization and stress concentration of different spatial scales. The interfacial inhomogeneity is highly pronounced in 3D printed materials due to thermo-cycling and layer-by-layer building. In this paper, the inlayer and interlayer structure of a eutectic Al-Si alloy fabricated by wire-feed electron-beam additive manufacturing is investigated by optical and electron microscopy. Model structures inheriting the experimental morphology are created, and their deformation and fracture are simulated using ABACUS/Explicit, with the user-defined subroutines being developed to describe the constitutive behavior of aluminum dendrite, silicon and eutectic materials. A two-scale computational approach is implemented to study the influence of the interlayer formed in the heat-affected zone on the dendritic structure strength.

The purpose of the study is to experimentally determine the dynamic coefficient of dry friction between different materials under vibrations due to the initial deflection. The principle of dry friction between the grillage and the foundation is used for the seismic isolation of buildings and structures. A measuring complex with corresponding strain-gauge measuring channels was prepared on the laboratory one-component shaking stand to record the relative and absolute displacements of two-mass systems. A theoretical solution to this nonlinear problem was obtained with the additional use of a special logical algorithm to determine the direction of the dry friction force between two masses. The value of the dynamic coefficient of dry friction was determined by comparing the numerical solution to the problem with experimental records by selecting the value of the dry friction coefficient. The values of the mass of rubbing elements with the surface treatment of the steel-on-steel contact and a separate option with lubrication of the contact surface with fluoroplastic 4-on-fluoroplastic 4 gaskets were changed in the experiment. The maximum velocity of the platform in experiments corresponds to a 9-point earthquake on the MSK-64 scale.

The interaction between a semi-infinite underground pipeline and the surrounding soil during longitudinal seismic wave propagation is examined in the article. The wave travels through the soil with its front perpendicular to the pipeline's axis, and the nonlinear laws of interaction (friction) on the surface of their contact, including the Amonton-Coulomb law, are used to solve related wave problems for the pipeline and soil. The method of characteristics and the finite difference method are sequentially used to solve these problems numerically. The implementation of the law of interaction (friction) processes is shown, depending on the parameters of the wave in soil and the mechanical characteristics of soil. It was determined that a wave in soil that involves the pipeline generates a powerful wave in the pipeline. The amplitude of this wave is many times greater than the amplitude of the wave in soil, and it propagates through the pipeline without attenuation. The dependences of the amplitude of this wave on the parameters of the law of friction, waves in soil, and the mechanical characteristics of soil are determined. 

This article demonstrates a multi-step process for forming a nominally flat surface with circumferential lubricating microcavities on a tribological assembly of an Х38CrSi steel shaft. The process includes finish turning, preliminary strengthening burnishing, deformation profiling of microcavities by a honing stone and smoothing of microprotrusions. The study determines the optimal technological parameters for each of the transitions based on microhardness and oil absorption power maximization, as well as roughness and periodic impact minimization. The process optimization is conducted using the Tagichi experiment design method. The optimal combination of technological parameters for hardening burnishing was discovered to be: normal force F = 200 N; feed rate f = 0.025 mm/rev and three tool passes. These burnishing parameters practically eliminate the influence of periodic impacts at spatial frequencies determined by the tool feed rate and the number of spindle rotations during turning. We determined suitable honing stone grit parameters and application force that yield microcavities 3.8 to 8.1 μm in depth, as well as the optimal parameters for smoothing of microprotrusions, resulting in a bearing area roughness of Sa = 0.15 µm and oil absorption power of 13.74×10–5 mm3/mm2.