Friction Coefficient Resistance Research Articles

Моделирование характеристик износа при скольжении композиционного материала на основе политетрафторэтилена (ПТФЭ), армированного углеродным волокном, в паре трения с SS304 (12Х18Н10Т)

Introduction. Over the last decade, composite materials based on polytetrafluoroethylene (PTFE) have been increasingly used as alternative materials for automotive applications. PTFE is characterized by a low coefficient of friction, hardness and corrosion resistance. However, this material has a high wear rate. A group of researchers attempted to improve the wear resistance of PTFE material by reinforcing it with different fillers. The purpose of the work: This study experimentally investigates the dry sliding wear characteristics of a PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. In addition, experimental mathematical and ANN models are developed to predict the specific wear rate, taking into account the influence of pressure, sliding speed, and interface temperature. The methods of investigation. Dry sliding experiments were performed on a pin-on-disk wear testing machine with varying the normal load on the pin, disk rotation, and interface temperature. Experiments were planned systematically to investigate the effect of input parameters on specific wear rates with a wide range of design space. In total, fifteen experiments were carried out at a 5-kilometer distance without repeating the central run experiment. Sliding velocities were obtained by selecting the track diameter on the disk and corresponding rotation of the disk. A feedforward back-propagation machine learning algorithm was used to the ANN model. Results and Discussion. This study finds better prediction accuracy with the ANN architecture having two hidden layers with 150 neurons on each layer. This study finds an increase in specific wear rates with normal load, sliding velocity, and interface temperature. However, the increase is more prominent at higher process parameters. The normal load followed by sliding velocity most significantly affects the specific wear rate. The results predicted by the developed models for specific wear rates are in good agreement with the experimental values with an average error close to 10%. This shows that the model could be reliably used to obtain the wear rate of PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. This study finds scope for further studies considering the effect of varying ANN architectures, different amount of neurons, and hidden layers on the prediction accuracy of the wear rate.

Microstructural characterization and enhanced tensile and tribological properties of Cu–SiC nanocomposites developed by high-pressure torsion

In this study, an attempt has been made to fabricate Cu–SiC nanocomposites by flake powder metallurgy and high-pressure torsion processing techniques at room temperature. Pure Cu and a mixture of Cu and nano-sized SiC powders were mechanically milled separately for 3 h and then green compacts were prepared by uniaxial pressing under 1 GPa pressure. The green compacts experienced 6-turn high-pressure torsion under a pressure of 6 GPa to prepare bulk Cu and Cu–SiC samples. The microstructures of the consolidated samples were characterized using an X-ray diffractometer and a high resolution scanning/transmission electron microscope, and the mechanical properties were evaluated by microhardness, tensile and wear tests. The results show that almost full density samples with ultrafine-grained (UFG) microstructure and well-dispersed nanoparticles in the metal matrix were obtained by the method used. The addition of the nanoparticles reduced the grain size and microstructural gradient between the center and edges of the disk samples. SiC nanoparticles improved copper microhardness by 35%, yield strength by 23% and tensile strength by 9% by implementing various strengthening mechanisms. The produced material showed a reduced coefficient of friction and high wear resistance. Delamination was determined as the major wear mechanism in HPTed Cu–SiC nanocomposite.

Experimental study on flat plate skin friction control by porous media based on global fluorescent oil film measurement technology

Skin friction is a primary source of total aircraft drag. It is important, therefore, in science and engineering, to achieve drag reduction control in a boundary layer. In this paper, under the experimental conditions of Reθ = 5909 (x/c = 0.55) and with a zero-pressure gradient, the drag reduction control of a plate boundary layer in porous media is studied. The global skin friction of the plate is measured using fluorescent oil film test technology. The results show that, in contrast with the downstream frictional resistance coefficient of a flat plate that possesses a smooth surface, the coefficient for porous media reduced significantly. Also, the lower the pores per inch (PPI) of the porous media, the greater the drag reduction effect. Among the three porous media with different PPI, porous media with ten PPI has the best drag reduction effect. With increasing distance from the porous media, the drag reduction effect decreases gradually. Porous media significantly increase the slope of the logarithmic region of the velocity profile of the downstream turbulent boundary layer, the dimensionless wall velocity u+ moves upward, and the velocity pulsation in the logarithmic region increases so as to reduce skin friction.

Analysis on flow resistance of two-phase ice slurry in pulsating flow

The pulsating flow plays a potential role in improving the heat transfer performance of ice slurry. However, the flow resistance characteristics of ice slurry in pulsating flow have not been fully understood. Therefore, the pulsating flow behavior of ice slurry is numerically investigated using the Eulerian-Eulerian multiphase model in the present study. The results showed that there is a phase lag between face-averaged velocity and pressure drop of ice slurry under pulsating flow, which changes from 0 to π/2. The phase lag increases with the increase of pulsating frequency, inlet ice volume fraction and pipe diameter. The instantaneous frictional resistance coefficient of ice slurry can be divided into two stages including acceleration and deceleration, which is larger than that at steady state in accelerating process and smaller than that at steady state in decelerating process. The cycle-averaged frictional resistance coefficient at low Reynolds number is obviously greater than that at steady state, while it is closer to the steady-state value at high Reynolds number. And the cycle-averaged frictional resistance coefficient increases with increasing the pulsating velocity amplitude, dimensionless frequency and inlet ice volume fraction. The pipe diameter has a significant influence on the cycle-averaged frictional resistance coefficient at low Reynolds number. In addition, the correlation is formed from the numerical results to predict the cycle-averaged frictional resistance coefficient of ice slurry.

Microstructure and Wear Resistance of a Composite Coating Prepared by Laser Alloying with Ni-Coated Graphite on Ti-6Al-4V Alloy.

Titanium alloys are widely used in high-tech fields, while its disadvantages such as low hardness, high coefficient of friction and poor wear resistance have restricted its applications. This study focuses on improving the friction and wear resistance of Ti-6Al-4V titanium alloys by means of laser surface alloying with Ni-coated graphite (G@Ni). The results suggest that Ni acts as a protective layer to hinder the direct contact and reaction of C and Ti in the molten pool. A part of graphite is unmelted and finally remains to form a self-lubricating wear-resistant composite coating with a compact structure. The average hardness of the coating is approximately four times that of the substrate owing to the TiC hard phase and compact microstructures as the reinforcing phase. The residual graphite in the coating plays a friction-reduction role during the wear test. The wear resistance is increased to 8.53 times that of the substrate according to wear mass loss. This study can effectively enhance the performance and expand the application of the titanium alloys by improving the wear resistance and reducing the friction.

Evaluating the Influence of Fracture Roughness and Tortuosity on Fluid Seepage Based on Fluid Seepage Experiments

The roughness and tortuosity of fractures are essential parameters affecting the fluid flow in a jointed rock mass. This paper investigates the influence of fracture roughness and tortuosity on fluid seepage behavior. A rough fracture surface was characterized by means of three-dimensional scanning and three-reconstruction technology, and the roughness and tortuosity of rock fractures were calculated. Hydraulic tests were conducted on deformed sandstone fractures with a self-made fracture seepage device, and the variation in the seepage flow was analyzed in rough fractures. The experimental results showed that the seepage flow of fluid decreased non-linearly with the increase in fracture roughness. Under different normal pressures, the friction resistance coefficient and tortuous resistance coefficient decreased with the increase in the Reynolds number. The friction resistance coefficient model and tortuous resistance coefficient model were used to quantitatively analyze the influence of fracture tortuosity and roughness on fluid flow, respectively. A modified model of the frictional resistance coefficient, considering fracture tortuosity and roughness, was established, which clearly expresses the law that with the increase in fracture tortuosity and roughness, the seepage flow of fluid decreases, and the head loss increases. The results of this research can provide a theoretical and experimental basis for studying fluid seepage behavior in deformed sandstone fractures.

Оцінка пластичності поверхневого шару металу при обкочуванні деталей циліндричної форми кулькою

The article deals with the study of the peculiarities of the process of plastic deformation of the surface layer of cylindrical parts during rolling with a ball. The stress-strain state and the regularities of its change, depending on the process parameters in the surface layer of the part, were determined by the slip line method and the finite element method.The vast majority of parts of mechanisms and machines work in contact with the relevant parts, namely various friction pairs, shafts, rollers, gears or tools, product housings, strikers, and so on. Specific requirements for these parts are due to the peculiarities of the operation of the latter. As a rule, it is impossible to meet all the requirements when making parts from one material. This mainly applies to the requirements of combining the high strength characteristics of the material of the internal volume of the part and the significant hardness of the same material on its surface in contact with the corresponding part. In addition, the surface of the parts under certain conditions must have high wear resistance and low coefficient of friction (antifriction parts) or high coefficient of friction (friction parts), or self-changing surface layer, and sometimes the entire surface must have some porosity and sweat during operation .The slip line method can be attributed to the traditional methods for solving problems of the theory of plasticity. This method can be used to solve problems in which the equations of equilibrium and plasticity create a closed system of differential equations of hyperbolic type. Therefore, this method can be used for solving plane problems, and only in some cases for solving axisymmetric problems. The solutions that can be obtained if a certain area of slip lines is directly known are called straight lines. When information about the shape of the initial slip lines is insufficient, inverse and semi-inverse methods are used.A numerical study of the regularities of damage accumulation was carried out, calculations of the accumulated deformation, the stress state index, and the distributions of the used plastic resource over the volume of the plastic zone when rolling with a ball in the environment of a specialized software complex were carried out. The adequacy of the model is checked in comparison with the available experimental data.On the basis of the research carried out in the article, recommendations can be developed for the choice of processing modes that provide the most rational parameters of the state of the surface layer of parts such as bodies of revolution.

Analytical Penetration Solutions of Large-Diameter Open-Ended Piles Subjected to Hammering Loads

This paper proposes the penetration displacement solutions of large-diameter open-ended steel pipe piles (LOSPs) with the diameter exceeding 2 m subjected to hammering load. The ultimate forcing equilibrium relationships between LOSP and soil are analyzed, and the calculated formula for self-sinking depth is derived. Next, a partial differential equation of pile hammering by single blow in soft soil is developed based on wave equation incorporating the kinematic method. A dynamic coefficient of frictional resistance (DCFR) is implemented in the process of derivation, and then the displacement Fourier analytical expression of LOSP under hammering load is presented. The parameters sensitivity of the analytical solution is investigated, and the displacement curve is compared with the numerical result. The new method presented in this paper could be used to assess the penetration development of driven piles under impact loading to predict the punching through or hammer refusal during penetration.

Experimental study on thermal hydraulic characteristics of natural circulation loop under motion condition

• Comparatively studied thermal hydraulic characteristics of natural circulation loop under various motion conditions. • Obtained the periodic average frictional resistance coefficient and Nu. • Obtained the empirical relation of frictional resistance coefficient in turbulent region. • Under large flow rate conditions, rolling motion affects heat transfer characteristics mainly by affecting flow rate. • Some suggestions on the layout of marine natural circulation loop were given. In this present paper, an experimental research was carried out to investigate the influence of various motion conditions on the flow and heat transfer characteristics in natural circulation loops. A natural circulation loop was built on the six-degree-of-freedom motion experiment platform at Xi’an Jiaotong University (XJTU). First, it was found that the small acceleration heaving would not cause significant changes on flow rate of the natural circulation loop. Then, the influence mechanism of rolling motion on the natural circulation loop is different as the central axis of rolling is changed. The increase of additional inertial force along the coolant flow direction causes larger flow fluctuation. The periodic average frictional resistance coefficient under different working conditions is obtained, which is divided into flow fluctuation region ( Re < 5000) and turbulence region (5000 < Re < 35000). Last, according to the experimental data, a mathematical model to predict the periodic average frictional resistance coefficient which is suitable for the turbulent region is obtained, and the deviation between the predicted value and the experimental data is less than 20%. Beyond that, the period average Nu under different working conditions is also achieved. It shows that the rolling motion promotes the heat transfer with the small flow rate, while the rolling motion affects the heat transfer characteristics mainly by affecting the flow rate under the large flow rate conditions. Based on our research, some suggestions on the layout of marine natural circulation loop were given.

Influence of key geometry parameters on heat transfer and flow resistance properties of toothed internal spiral piece cracking furnace tube

Strengthening the heat transfer technology of the furnace tube in the radiant section of the cracking furnace is very important in the field of energy-saving and environmental protection. This research proposes a new type of open-tooth spiral to enhance heat transfer and increase ethylene productivity. The mathematical computation has been conducted to evaluate the thermal-hydraulic performance with an open-tooth spiral. The classical Ordinary tube was also investigated for comparison. At the same time, the vortex identification method based on the Q criterion reveals the enhanced heat transfer mechanism of the open-toothed spiral tube. Then use the field synergy principle to qualitatively judge the heat transfer performance, combined with the comprehensive heat transfer evaluation factor (PEC) to quantitatively evaluate the comprehensive heat transfer performance of the open-tooth spiral tube. The results show that although the Nusselt number of the open-tooth spiral is 8%-10% lower than that of the ordinary screw, the friction resistance coefficient of the spiral tube with an opening angle of 15° can be reduced by 33%∼43%. Its PEC value is between 1.15 and 1.25, with excellent comprehensive heat transfer performance. It can effectively improve key products, such as ethylene, propylene, etc.

INCREASING THE WEAR RESISTANCE OF ROAD TRANSPORT PARTS IN THE AGRO-INDUSTRIAL COMPLEX BY APPLICATION OF LASER DEPOSITION

In this work, we studied the effect of laser melting and alloying elements (ТаВ, МоВ, B4C) on the friction coefficient and wear rate of plasma coatings of automotive parts in the agro-industrial complex under friction conditions both without lubricant and with lubricant. Under friction without lubrication, the main factors that determine the wear resistance of the part are the hardness of the alloyed layer and its chemical composition. The content of molybdenum, tantalum and boron carbide borides in the surface layer, which provide the formation of secondary structures separating the friction surfaces, has a favorable effect on the coefficient of friction, and, consequently, on the operational characteristics of the surface. As a result of the research, the following trend was revealed: coatings with a lower coefficient of friction also have the least weight wear and are the most wear-resistant. Alloying with tantalum boride increases the heat resistance of coatings, leads to grain refinement in them, and an increase in microhardness. Therefore, this coating can be recommended for operation in conditions of friction without lubricant and high pressures. Studies have shown that the wear resistance of coatings is affected by laser processing modes, contact load, the method of reflow of a gas-thermal coating, as well as its chemical composition. The choice of laser processing modes provides control over the structure and properties of coatings, and also affects their wear. Also, as a result of studies under friction conditions with a lubricant, it was determined that the coating after laser alloying with molybdenum boride has the lowest coefficient of friction and wear resistance. This can be explained by the fact that laser doping of iron-based coatings with molybdenum boride increases their heat resistance. This is important at increased loads on the test sample. In addition, molybdenum, interacting with atmospheric oxygen and lubricant, forms molybdenum oxide, which further reduces the coefficient of friction. Therefore, the coating after laser alloying with molybdenum boride can be recommended for operation under conditions of friction with a lubricant at elevated pressures.

Spark Plasma Sintering of Copper-Niobium-Graphite Composites, and the Investigations of Their Microstructure and Properties

The microstructures and properties of ternary copper-niobium-graphite (Cu-Nb(nano)10-C4, and Cu-Nb(micron)10-C4) composites produced via spark plasma sintering (SPS) technique have been investigated for their potential use as electrical connection materials at high-temperature application. Nowadays, there is much activity in the development of such material all over the world. This study was aimed to compare the effect of adding the nano and micron particles sizes of Nb powders in the microstructures and properties of Cu-Nb-C composites sintered at 700 and 650 °C temperatures. The investigated materials have been produced via the SPS method. The microstructures were observed by electron microscopy technique, the wear test was observed by Anton-Paar TRB3 tribometer, thermal diffusivity was observed by LFA427 NETzschlaser flash device within the temperature of 100–900 °C, and the corrosion test was performed by potentiodynamic polarization. The discoveries have been presented in the manuscript and were discussed with reference to the microstructure development, the composite with nanoparticles sintered at 650 °C displayed closed thermal stabilities as temperature increased, and it recorded a low coefficient of friction and suitable corrosion resistance, which correspond to requirements for electrical contacting materials. The SPS method of production of the composites caused initial microstructure refinement and improved the properties of the composites.

Effect of iron addition on the structure and properties of copper-based friction powder material used under friction conditions with lubrication

Machines and mechanisms contain units responsible for their movement and stopping, and such units use friction materials. These units include oil-cooled brakes, hydromechanical transmissions, and clutches. They use mainly copper-based friction materials providing the high coefficient of friction and wear resistance. These materials feature by effective heat dissipation since a large amount of heat is released in these areas for a short period of time. The paper presents the results of studies into the effect of iron addition into a frictional powder material based on BrO6 and BrO12 bronze on its structure, mechanical and tribotechnical properties. It was shown that the introduction of iron contributes to an increase in the coefficient of friction from 0.034 to 0.055 for the BrO6-based friction material and from 0.042 to 0.073 for the BrO12-based friction material. It was determined that the ultimate compression strength of the BrO12-based friction material is 340 MPa without iron addition, 310 MPa at 10 vol.% of iron, and 180 MPa at 50 vol.% of iron. This is due to the fact that the iron content of more than 30 vol.% results in the change of the frame structure of the material to the matrix one having a sintering temperature higher than the temperature used in the paper for friction material sintering. It was found that for the BrO6-based friction material there are both rounded and elongated inclusions in the copper phase up to 2.5 μm in size with the iron content of 30–50 %. In the BrO12-based material there are more iron inclusions in the copper phase and their size are much larger, the length of inclusions reaches 20 μm, and the iron content in them is 49–73 %.

Study of tribo-mechanical properties of laser clad Al2O3-TiB2-TiN-BN‖Ti-6Al-4 V alloy

Low wear resistance and high coefficient of friction of the Ti-6Al-4 V alloy surface limits its application in situations requiring tribological participation of the alloy. In the present study, a laser clad layer, formed by laser melting of a preplaced powder mixture (Al, TiO2, TiB2, TiN, and h-BN), had been applied on the Ti-6Al-4 V alloy substrate surface to improve its mechanical and tribological properties. The microstructure, phase composition, hardness, wear properties, and scratch-resistance of the coatings were analyzed using a scanning electron microscope (SEM), X-ray diffraction (XRD), Vickers micro-hardness test, ball-on-disk wear test, and scratch indentation test, respectively. A multi-objective optimization technique was implemented to solve a multi-objective optimization problem for the determination of preferred powder composition and optimum process parameters. The optimization result showed that higher values of coating thickness and higher degree of uniformity in microstructure were obtained in the case of laser cladding carried out at a higher value of laser power-to-scan speed ratio. The formation of ceramic phases such as TiB2 and TiN reinforced with Al2O3 particles helped increase the hardness and wear resistance by four fold and two fold, respectively. The presence of partially reacted h-BN particles in the Ti-rich coating matrix helped reduce the friction coefficient by a factor of two-third. Hence, the composite ceramic coating of Al2O3-TiB2-TiN-BN on Ti-6Al-4 V alloy may be considered suitable for tribo-mechanical applications.

Calculation model for ventilation friction resistance coefficient by surrounding rock roughness distribution characteristics of mine tunnel

Real-time mine ventilation network solution is the core way to realize the actual intelligent ventilation, and ventilation friction resistance coefficient is a significant parameter of network solution. With the help of fractal theory to characterize the three-dimensional roughness characteristics of tunnel surrounding rock. A method to describe the roughness by fractal dimension and fractal intercept. We put the fractal dimension and fractal intercept into Matlab to randomly generate three-dimensional laser scanning data of tunnels. The fusion of the two fractal parameters made the three-dimensional roughness surface information more comprehensive. It has been applied to field practice accurately. Compared to the simulation results show that the relative error of the new prediction results is 3%. Comprehensive evaluation analysis shows that the new friction wind resistance formula can fully reflect the influence of three-dimensional rough surfaces on airflow friction resistance. With the help of three-dimensional laser scanning technology, we can calculate the airflow friction resistance of the tunnel quickly and accurately, which provides a reference for the development of key technology and the theory of intelligent ventilation parameter measurement.

Research of the Brittleness and Crack Resistance of Samples Made of Highly Hardened Silicon Carbide Ceramics

The paper presents a quantitative assessment of the brittleness of highly hardened silicon carbide ceramics. This characteristic is important for predicting the strength characteristics of the material. The analysis of existing methods for determining the brittleness of the material is carried out. During the research, it was assumed that the production of composite materials in the SiC-Al2O3 and SiC-Al2O3-AlN systems would combine high chemical resistance, wear resistance, and low coefficient of friction. These properties inherent in aluminum oxide and nitride, along with high thermal conductivity and strength, are characteristic of silicon carbide. Materials in the SiC-Al2O3 system containing 20, 50 and 80 percent of aluminum oxide – Al2O3 were selected as objects of research. Their advantages and disadvantages are shown. The results of an experimental study of samples made of highly hardened silicon carbide ceramics are presented. Based on experimental studies, analytical and graphical dependences are proposed that allow determining the crack resistance of ceramics from the crack length at the corners of the Vickers pyramid. It is shown that these dependences change exponentially, which makes it possible to predict the appearance of cracks at various stages of mechanical processing of products made of highly hardened ceramic materials.

High-temperature tribological behavior of Ti containing diamond-like carbon coatings with emphasis on running-in coefficient of friction

Diamond-like carbon (DLC) coatings show a low coefficient of friction (COF) and high wear resistance against aluminum at elevated temperatures, yet they exhibit a high running-in COF (μ R ) prior to reaching a low and stable steady-state COF (μ s ). This study shows that incorporating titanium (Ti) atoms into the DLC structure would reduce the μ R . During pin-on-disk tests conducted on Ti incorporating hydrogenated-DLC (Ti-H-DLC) with 6.2 at.% Ti subjected to dry sliding against 319 Al (Al-6.5% Si), μ s values decreased from 0.27 at 25 °C to 0.11 at 200 °C. The specific wear rate of Ti-H-DLC decreased from 2.44 × 10 −5 mm 3 /Nm at 25 °C to 0.71 × 10 −5 m 3 /Nm at 200 °C. A typical DLC with 40 at.% H (H-DLC) tested at 200 °C showed a low μ s of 0.08 and a wear rate of 1.11 × 10 −5 mm 3 /Nm. However, at 200 °C, Ti-H-DLC showed a lower μ R of 0.16 compared to μ R = 0.78 of H-DLC, and the duration of the running-in period for Ti-H-DLC, t R = 3 revolutions, was shorter than H-DLC with t R of 200 revolutions. Comparisons made with other DLCs, including, NH-DLC, W-DLC, ta-C, and Si-O-H-DLC, in addition to H-DLC, all tested using the same method, revealed that, in the temperature range of 100–250 °C, Ti-H-DLC showed a better running-in behavior making Ti-H-DLC a suitable tool coating for manufacturing processes where high-temperature running-in sliding friction is important, including warm forming and (single-point) turning of aluminum alloys . • High-temperature tribological behavior of Ti-H-DLC against 319 Al was studied. • Low running-in COF and short running-in duration were recorded at 100 and 200 °C. • Compared to other DLC coatings, the lowest μ R and t R were obtained using Ti-H-DLC. • Ti-H-DLC tool coatings are useful for Al warm forming, machining operations ~200 °C.

Sliding wear and friction behaviour of WC‐stainless steel and WC–Co composites

AbstractThe sliding wear and friction behaviour of new developed WC‐stainless steel composites without and with carbon addition were evaluated using a linearly reciprocating sliding tribometer under ball‐on‐flat configuration, sliding against an alumina ball under unlubricated conditions. The wear of both, discs and ball were measured for different applied loads, sliding distances and frequencies. Worn surfaces were investigated by using microscopy and topography techniques. Comparative experiments were performed using flat samples of a conventional WC–Co composite. It was found that the WC–Co grade displayed an undoubtedly better sliding wear resistance and lower coefficient of friction if compared with the newly produced WC‐SS composites.

Aerodynamics and Complicated Heat Transfer with the Mixed Motion of Air in the Flat Duct of a High-Temperature Heat Exchanger

The purpose of the research is to study the aerodynamics and heat transfer in the duct of a high-temperature recuperation system. The object of the research is a flat duct with a thickness-to-height ratio a:b = 1:10, length c = 400·a with one-sided heat input to the duct surface, complicated heat transfer and mixed air movement in the duct. The objectives of the research are to determine: (a) average temperatures on the duct surfaces; (b) air temperature distribution along the length of the duct; (c) local and average integral temperature values along the length of the duct; (d) local and average integral heat flow densities on the duct surfaces; (e) local and average integral heat exchange coefficients and Nusselt numbers on the duct surfaces; and (f) pressure distribution along the length and total pressure drop in the duct. The research method is based on conducting a mathematical numerical experiment in a stationary three-dimensional Cartesian formulation and physical modeling of processes on a prototype. It is established that the dominant heat transfer between the duct walls and the air is a complicated convective heat transfer, in which forced convection is affected by free convection. There is a 1.5–2.0-fold difference in the values of the heat flow density on the hot and non-heated surfaces of the duct. Generalizing dependences of Nusselt numbers, temperature pressures and friction resistance coefficients as functions of a dimensionless coordinate are obtained.

Influence of ultrasonic agitation on the abrasive wear characteristics of Al-Cu/ 2 vol% Grp composite

In the present study, the abrasive wear behavior of Al–4.4 wt% Cu composite reinforced with 2 vol% graphite particle (Grp) has been investigated. In the preparation of composite, Ultrasonic Treatment (UT) is provided in the composite melt for the uniform distribution of reinforcement particles. Two bond abrasive wear tests are conducted for composites treated with ultrasound and without UT and base alloy. The results of abrasive wear studies indicate that at 5 and 10 Newton (N) loads, the composite with UT has a higher coefficient of friction (COF) and wear resistance than that of the base alloy (Al–4.4 wt% Cu). Whereas, at 15 and 20 N load, the value of COF and wear resistance is lower for the composite. Two abrasive wear mechanisms micro-plowing and micro-cutting have been observed during the wear tests of base alloy and composites. The analysis of worn-out sample surfaces at higher load reveals that softened material layer due to localized elevation in temperature between two contact surfaces during wearing acts as a tribolayer in base alloy while in composites both softened material layer and graphite layer have worked together as tribolayer.