NUMERICAL MODEL OF A LOCAL CONTACT OF A POLYMER NANOCOMPOSITE AND ITS EXPERIMENTAL VALIDATION

In the paper a model of a local contact of a polymer-based nanocomposite was developed within the method of a movable cellular automaton. The features of mechanical behavior of nanocomposite at the mesoscale level under dry sliding were studied with explicit account for the microprofile of the counterbody surface and the characteristic sizes of nanofiller. Factors that contribute to the conditions for the formation of a stable tribofilm of silica nanoparticles are analyzed. Two other parameters like sample geometry and the value of relative sliding velocity are also examined. It is shown that the thickness of tribofilm depends on stress conditions at the contact, and the friction coefficient decreases with increasing sliding velocity similar to one observed experimentally. To ensure the low friction properties of polymer nanocomposite, particles whose sizes are comparable with the characteristic size of the substrate microprofile are preferred. Results of numerical simulation are in good correlation with available experimental data

Sliding simulation of automotive brake primary contact with variable amounts of copper and graphite nanoparticles

Copper is one of the most important components in brake pads and its amount can reach up to 14%. In spite of a number of positive features copper usage in brake pad formulations has recently become the subject of considerable discussions, primarily due to concerns about potential risks related to environmental impacts of copper particles. So, for developing new pad formulations with possible replacements of copper content, it is very important to understand the functionality of copper additions to brake friction materials. In the paper theoretical investigation of the role of copper as a pad ingredient was carried out on the basis of modelling by the method of movable cellular automata (MCA). In the study the concentration of copper particles in a Fe3O4-matrix was varied. The sliding simulations were performed while assuming material properties at 500°C in order to assess the beneficial role of copper during severe braking conditions corresponding to fading cycles during dynamometer testing

Molecular dynamics modelling of boundary migration in bicrystals under nanoburnishing

The paper reports the molecular dynamics simulation results on the behavior of a copper crystallite in local frictional contact. The crystallite has a perfect defect-free structure and contains a high-angle grain boundary of type Σ5. The influence of the initial structure on the specimen behavior under loading was analyzed. It is shown that nanoblocks are formed in the subsurface layer. The atomic mechanism of nanofragmentation was studied. A detailed analysis of atomic displacements in the blocks showed that the displacements are rotational. Calculations revealed that the miso ientation angle of formed nanoblocks along different directions does not exceed 2 degrees

Application of symbiotic cellular automaton method to describe the contrast media

The method of symbiotic cellular automaton, which combines two approaches to describe the simulated media – the method of conventional cellular automaton and method of movable cellular automaton, has been developed for modeling and study of heterogeneous materials. Verification of the method has been carried out by comparing the simulation results of sorption of carbon dioxide in the lignite with experimental data. Possibilities of the method are exemplified by results of numerical study of the influence of the gas phase on strength and fracture of the lignite specimens

A study of the influence of soft particle size and concentration on strength and strain properties of ceramic composites

In the paper a theoretical study of the influence of particle distribution of soft inclusions-agglomerates in a ceramic composite sample on its strength and deformation characteristics was carried out. A movable cellular automaton method was used to simulate a uniaxial compression test of two-dimensional rectangle composite samples. It was found that the average size of inclusions agglomerate-while maintaining the volume fraction of the particles of the soft phase has little effect on the strength and deformation properties of the simulated samples. The simulation results can help to understand the mechanical properties of such objects within any generalized model

THE EFFECT OF ELECTRON-BEAM TREATMENT ON THE DEFORMATION BEHAVIOR OF THE EBAM TI-6AL-4V UNDER SCRATCHING

The effect of the continuous electron beam scanning (CEBS) post-treatment on the microstructure, mechanical properties and scratching behavior of the Ti-6Al-4V alloy samples produced by electron beam additive manufacturing was studied experimentally and by using molecular dynamics simulation. It was found that the CEBS post-treatment resulted in the transformation of the microstructure of the samples from the α′-martensite into the α+β structure. The evolution of the sample microstructure was shown to provide improved mechanical characteristics as well as enhanced deformation recovery after scratching. A mechanism was proposed based on the results of molecular dynamics simulation, which attributed to the improved recovery of the scratch groves after passing the indenter to reversible β→α→β phase transformations, which occurred in the vanadium alloyed Ti crystallites

Ab initio calculations for search optimization of multicomponent alloy configurations

The paper presents an algorithm for optimization of searching configurations of multicomponent alloys that have a predetermined value of physical and mechanical properties. Values obtained by Exact MT Orbitals (EMTO) were used for calculations. The algorithm efficiency is demonstrated on an example of estimating the bulk modulus of a three-component alloy based on Ti, Nb and Zr. It is shown that the use of the algorithm can in some cases reduce the amount of calculations by 10 times or more

Molecular-dynamics investigation of nanoburnishing process

It is well known that the burnishing process affects the surface characteristic, namely: surface roughness, surface hardness, wear resistance, fatigue resistance and increased maximum residual stress in compression. Unfortunately we still far from full understanding what parameters and mechanisms are responsible for the certain surface modification. That is why methods of computer modeling can be considered as useful tool to investigate surface changing during contact interaction as well as burnishing process. It is more essential if we consider processes are taking place at atomic scale level. In the paper we try to reproduce the details of burnishing process at nano-scale level. To investigate features of surface treatment we use the molecular dynamics simulation. Various pure crystalline materials were considered. Results of our modeling are very close to the experimental observatio