Study of the structure and frictional properties of a new composite friction material

В статье приведены результаты исследования фрикционных свойств и структуры нового композиционного фрикционного материала (КФМ). В ходе исследования были разработаны восемь перспективных составов КФМ, полученных методом порошковой металлургии. Фрикционные испытания новых материалов проводились на испытательной машине на трение и износ ИИ5018, оснащённой программным комплексом Tester 3.0, позволяющим точно фиксировать изменение момента трения в течение испытания с построением графика и автоматическим расчётом параметров трения. Методика испытаний позволила имитировать условия фрикционного взаимодействия, возникающие в муфтах электроприводов, применяемых в наземном и морском транспорте. По результатам испытаний оценивались величина коэффициента трения и его стабильность на протяжении цикла испытания и в диапазоне рабочих регулировок электропривода, а также износостойкость КФМ. На основании исследований структуры поверхности трения и качественной оценки стабильности коэффициента трения был определён оптимальный состав КФМ, способный обеспечить стабильную и безопасную работу электропривода в диапазоне рабочих регулировок. The article presents the results of a study of the frictional properties and structure of a new composite frictional material (CFM). In the course of the study, eight promising CFM compositions were developed, obtained by the method of powder metallurgy. Friction tests were carried out on a friction and wear testing machine II5018, equipped with the software package Tester 3.0, which allows registering the change in friction moment during the test with plotting and automatic calculation of friction parameters. The test technique made it possible to simulate the conditions of frictional interaction arising in the couplings of electric drives used in land and sea transport. After the tests, the value of the friction coefficient, its stability during the test cycle and in the range of operating adjustments of the electric drive and the wear resistance of the CFM were evaluated. Based on the analysis of the structure of the friction surface and a qualitative assessment of the stability of the coefficient of friction, the optimal composition of the CFM capable of ensuring stable and safe operation of the electric drive in the range of operating adjustments was determined.

Stress-weighted spatial averaging of random fields in geotechnical risk assessment

Effects of spatial fluctuations of soil parameters are considered in a new context – considering variability of soil parameters in conjunction with non-uniform stress fields, which can locally amplify (or suppress) subsoil inhomogeneities. In this way, several design situations for the Coulomb frictional material with random tan(φ(x)) reveal a reduction of variance, which is less significant than for the standard volume averaging. When looking for an ‘effective’ random variable [tan(φ)]a – that is, a random variable, which is equivalent to the random field tan(φ( x )) – the Vanmarcke averaging by simple volume integrals is insufficient; it systematically overestimates effects of variance reduction, thus causing potentially unsafe situations. The new proposed approach is coherent, formally defined and more realistic.

Regularities of the influence of submicron ceramic powders TiO2, AlN, Cr2O3 on the tribological properties of a friction material

Friction units for automotive and special vehicles are designed to operate under boundary friction conditions. Modern vehicles contain friction assemblies that use friction materials. Currently, friction materials are actively used: based on thermosetting resins; pulp and paper-based materials; sintered powder materials; materials of carbon or carbon composition; materials with a ceramic matrix. The development of a unified understanding of the effect of the size and chemical nature of ceramic additives on the processes occurring in a friction material during friction is very important and can be obtained both on the basis of experimental and theoretical studies. The paper presents the results of a study of the effect of submicron TiO2, Cr2O3, AlN powders with a size of 0.2-0.5 microns on the tribotechnical properties of a frictional material based on copper intended for operation under boundary friction conditions. It was found that when using the addition of Cr2O3 powder, the greatest increase in the value of the friction coefficient is noted - from 0.042 to 0.082, a slightly smaller increase in the friction coefficient is shown by the use of AlN and TiO2 defects - 0.042-0.074 and 0.042-0.060, respectively. The least wear of the friction material was obtained when using 3.0 vol. % aluminum nitride additive - 2.1 microns / km. Increasing the addition of any of the submicron powders by more than 7 vol. % leads to a significant decrease in wear resistance. This is due to the formation on the surface of the friction material of a modified layer containing ceramic particles and the metallic phase of the friction material. For the friction material, an unstable value of the friction coefficient and increased wear were recorded

HIGH-PERFORMANCE METHOD OF PRODUCTION OF POWDER FRICTIONAL PRODUCTS ON FE-BASIS WITH HIGH TECHNOLOGICAL AND OPERATIONAL PROPERTIES

Physical and technological bases of DHP-PFM method for production of dry friction powder friction articles on Fe-base with high technological and operational indices for a wide range of practical use have been developed. The DHP-PFM method is that the dynamic hot pressing (DHP) provides production of the new powder frictional materials (PFM) through an underlayer from carbonyl iron between frictional material and a basis (framework) with electroplated nickel coating. Friction lining compaction is made of charge of ФМК-79 type and has high hardness and low porosity. Processes of the choice of composition of furnace charge, formation of structure and properties of new powder frictional materials on Fe-to a basis are investigated. The method is characterized by high productivity, energy saving, simplified technology and provides the possibility to use existing technological equipment for making structural powder products. Method of DHP-PFM manufacturing of dry friction powder friction linings can be used for manufacturing of friction units of transmissions of light track machines with high specific power. The friction material received by this method from furnace charge of FMK-79 type can be used as unified for such frictional units as the main friction clutch, an onboard friction clutch, tape and disk brakes.

Experimental Study of Fiber Orientation Effect on Frictional Material Properties and Tribology Performance

The objective of this work is to study the fiber orientation effect on frictional material properties and tribology performance. Effects of orientation on hardness, maximum load capacity under bending, the friction coefficient and surface wear of the composites were investigated. In this research, 3D printing technique was used to create workpieces in order to control fiber arrangement which is random, 0, 45, and 90 degrees. The results suggested that the fiber direction insignificantly affects material hardness with all specimen showing similar value of average hardness of approx. 90 HRC. However, the fiber orientation had a strong influence on material bending strength. The specimen with forced fiber orientation showed lower bending resistance compared to that with random fiber orientation. This may be caused by the non-uniform distribution of fiber which could promote fracture initiation site in some area with low fiber density. The coefficient of friction of the composite material was found to strongly related to it wear behavior, i.e. higher wear rate results in higher value of friction coefficient. The wear resistance was found to be controlled by both the fiber direction and fiber interface. With fiber oriented at 90 degree to sliding direction, higher coefficient was observed. However, as surface wear took place, the effect of wear debris results in an increase in friction coefficient. For 3D printed specimen, wear was increased with fiber interface density resulting in higher wear rate of specimen with 0-degree fiber orientation compared to those with 45-and 90-degree orientation during. Hence, the specimen with 0 degree fiber direction showed similar value of coefficient of friction to those with random and 90 degree fiber orientation.

The applicability of analytical elasto-plastic solutions and issues of the formation of shear bands zones

<p><strong>Key Words:</strong> numerical modelling, elasto-plastic analytical solutions, shear bands, geomechanics.</p><p>The correct analysis of wellbore stability in unconventional reservoirs receives much interest from the industry as shale rock and tar sands demonstrate perceptible plastic behavior which influences the estimation of rock failure. To tackle this problem the 3D finite element code has been developed for computing the stress-strain state in the elastoplastic medium near a borehole. The accuracy of the results, obtained due to the application of the finite element technique, can be affected by various numerical effects. Since the theory of plasticity assumes infinitesimal load increments, errors associated with finite increments are almost inevitable. The accuracy of the numerical solution can be verified by comparing the numerical results with the analytical solutions. Elasto-plastic analytical solutions [1], [2] stand out among others because they are the only ones among many others, mentioned in the cited monographs, that consider analytical solutions under conditions of non-hydrostatic loading.</p><p>In this study, the numerical and analytical solutions were verified and relative errors were calculated for different loading paths. It turned out, for example, that Galin’s analytical solution works well not only in the field of its applicability, but also outside of it, despite different errors. This work discusses questions related to the influence of the increment of the applied load on the structure of a stationary elasto-plastic solution, including in the case of the formation of zones of localized plastic deformation. The issue of the appearance of shear bands zones is also considered: these bands develop directly around the hole under certain boundary conditions or gradually grow out of the zones of elliptical plastic deformation.</p><p>The first, third and fifth authors acknowledge support of research by Geosteering technologies company within the scope of Geonaft project sponsored by Skolkovo foundation, Russia.</p><p>The second and fourth authors acknowledge support of research by Government of Russian Federation under grant 2019-220-07-9139.</p><p><strong>REFERENCES</strong></p><p>[1] Detournay, E. (1986). An approximate statical solution of the elastoplastic interface for the problem of Galin with a cohesive-frictional material. International Journal of Solids and Structures, 22(12), 1435–1454.</p><p>[2] Galin, L.A. (1946). Plane elastoplastic problem. Applied Mathematics and Mechanics, 10 (3), 365–386.</p>

Deformation and Failure Characteristics of Soil-Rock Mixture considering Material Composition and Random Structure

The soil-rock mixture is a cohesive-frictional geomaterial subjected to impacts of composition and structure seriously. When it suffers from gravity or other kinds of loadings, the loss of its bearing capacity always appears a progressive failure. In this study, the ultimate criterion of the frictional material changing from the deformation stage to the failure stage is analyzed first and then the deformation and failure characteristics of the soil-rock mixture with different compositions and structures are discussed by the discrete element method. The results indicate that the deformation and failure of the soil-rock mixture under axial pressure appear a significant phenomenon of detouring around rock blocks. The bond failure zones and the ultimate shear strain increase with the increase of rock block proportion. The distribution of the bond failure zones always has a good uniformity with the inclination of rock block inclinations. The increase of cementation degree between particles expands the distribution of the bond failure zones but minifies the ultimate shear strain.

Optimisation of hybridised cane wood–palm fruit fibre frictional material

A brake pad has been developed employing a hybrid of cane wood and palm fruit fibre as filler material. The filler materials were extracted and processed; however, the palm fruit fibre was further treated with NaOH to remove oil remnants. After proper drying, the filler materials were ground and sieved into 150 µm particle size. The experimental design was set up using Central Composite Design in Design Expert software. The design varied the percentage composition of the filler materials and the binder. At constant press time of 8 min, press temperature of 160 ℃ and curing time of 2 h, 20 test samples were produced and tested for mechanical and physical properties. These include hardness, wear rate and water absorption. The Fourier transform infrared analyses showed that both cane wood and palm fruit fibres have active alcohol (O–H) and amine (C–N) functional groups. The experimental results were analysed and optimised using response surface methodology and validated using the analysis of variance tool of the Design Expert software. An optimal 30% resin, 3.48% palm fruit fibre and 6.52% cane wood composition by mass was developed, which gave a product with 98.25 MPa hardness, 4.13 mg/m wear rate and 0.494% water absorption. This result indicated that hybridised cane wood–palm fruit fibre is a good filler material for brake pad production.

Seismic Fragility Analysis of Base-Isolated LNG Storage Tank for Selecting Optimum Friction Material of Friction Pendulum System

The objective of this study is to establish a system for selecting the optimum friction material to meet the seismic performance requirements of a liquefied natural gas tank with a friction pendulum system (FPS). A methodology for determining the optimum frictional material using seismic fragility analysis is suggested, and it is applied to materials with various frictional coefficients for FPS. Seismic fragility curves with two different limit states are developed to determine the optimum friction material, and a methodology for combining fragility curves is proposed. The analysis shows that a lower friction coefficient for FPSs is more appropriate for preventing failure in FPSs and the superstructure investigated in this study.