Thermal Friction Research Articles

Thermal Cracking and Friction Performance of Two Kinds of Compacted Graphite Iron Brake Discs under Intensive Braking Conditions

The limited thermal conductivity of compacted graphite iron constrains its application in brake discs. The matrix plays a crucial role in balancing the thermal conductivity and mechanical performance of compacted graphite iron. Therefore, two kinds of compacted graphite brake discs with different ferrite proportions were utilized to investigate their thermal cracking and friction performance under intensive braking conditions based on inertia friction tests. The variations in peak temperature, pressure load and friction coefficient stability were also analyzed. The brake disc with a higher ferrite proportion exhibited a lower peak temperature, attributed to increased thermal conductivity. Moreover, the elevated content of soft ferrite resulted in a greater furrow height on the worn surface, contributing to an increase in friction force and stability. As a result, both the input pressure and mechanical stress decreased. It was observed that the compacted graphite iron brake disc with a higher ferrite proportion exhibited fewer thermal cracks without compromising wear resistance. Furthermore, the results suggest that lowering the disc temperature to 210 °C–250 °C can mitigate fatigue wear and matrix oxidation, hindering the propagation of thermal cracks.

Fabrication of high thermal conductivity and wear resistance graphite/copper composites by microwave hot press sintering

Graphite/copper composites have great potential for tribological applications because of their high thermal and abrasion resistance. In this study, we successfully manufactured graphite/copper composites that demonstrated superior thermal conductivity and wear resistance by employing microwave hot press sintering (MHPS). The results demonstrated an enhancement in the density and hardness of the composites as the graphite particle size increased, owing to the influence of MHPS. Meanwhile, the graphite/copper composite with a graphite particle size of 300 µm has excellent thermal conductivity and friction properties, with a thermal conductivity of up to 679.5 W/mK and a wear rate of only 3.019 10−6 cm3/(N·m). The work is expected to provide a new route for the developing highly thermally conductive and abrasion-resistant materials.

Criterion for ultra-fast bubble walls: the impact of hydrodynamic obstruction

The Bödeker-Moore thermal friction [1] is usually used to determine whether or not a bubble wall can run away. However, the friction on the wall is not necessarily a monotonous function of the wall velocity and could have a maximum before it reaches the Bödeker-Moore limit. In this paper, we compare the maximal hydrodynamic obstruction, a frictional force that exists in local thermal equilibrium, and the Bödeker-Moore thermal friction. We study the former in a fully analytical way, clarifying its physical origin and providing a simple expression for its corresponding critical phase transition strength above which the driving force cannot be balanced out by the maximal hydrodynamic obstruction. We find that for large parameter space, the maximal hydrodynamic obstruction is larger than the Bödeker-Moore thermal friction, indicating that the conventional criterion for the runaway behavior of the bubble wall may have to be modified. We also explain how to apply efficiently the modified criterion to particle physics models and discuss possible limitations of the analysis carried out in this paper.

Optimization of responses in single and multi-point machining processes using Dragon-fly algorithm coupled with TOPSIS and VIKOR decision-making approaches

Due to complex production practices, it is becoming crucial to provide greater thermal management and friction reduction in manufacturing processes. Lubricants play a crucial role by effectively reducing friction, minimizing wear and tear thereby extending the lifespan of the tool. It is observed that there is a shortage of studies associated with the machining of hard materials like Ti-6Al-4V. The present work has therefore focused on the machining of high-grade Titanium alloy under dry and Neem oil aerosol-mist spray wet conditions. The machining is performed on two kinds of machining processes, such as plain facing with single point tool and co-axial turn-mill facing with multi-point cutting tools on computer numerical controlled Turn-mill machine tool. Furthermore, there are very few articles reported on usage of Neem oil (AzadirachtaIndicaL.) as a lubricant. This has motivated the authors to use Neem oil in a mist condition to minimize the quantity of coolant, without compromising on the tool temperature, surface quality, and tool-wear. The responses obtained are subjected to regression analysis to evolve the fitness functions. Multi-objective optimization of these functions is than adopted using Dragon-fly algorithm (MODA) under the constraints of the machining parameters. A set of pareto optimal solutions for each of the machining cases are obtained and are further evaluated using TOPSIS and VIKOR decision-making approaches to achieve the optimal values of the cutting parameters. The optimum parameters for single point cutting under wet conditions were observed as speed (592 rpm), feed (0.058 mm rev−1) and depth of cut (1.00 mm).The corresponding values of responses were tool temperature (37.05 °C), surface roughness (0.128 μm) and tool wear (155.19 μm). The equivalent values for multi-point cutting were determined as 510 rpm, 0.086 mm rev−1 and 0.25 mm. The responses for these optimal conditions are 32.17 °C, 0.725 μm and 45.72 μm in that order.

Innovative twist design for solar water heaters: Experimental findings and implications

More effective use of solar energy in hot water systems is made possible by optimising heat transfer and flow resistance. In light of this, Research has been conducted to enhance convective heat transfer while analysing flow friction characteristics for best performance, resulting in the design of novel inserts known as customised twists, which increase the efficiency of the solar hot water system. A conventional, plain tube heater is used as a baseline for the study on thermal characteristics, heat transportation and flow friction attributes. A thorough analysis and comparison of the thermal behaviour of the system with customised twist inserts that have been modified using rods and spacers of different lengths is performed. As a result of the induced disturbance in the fluid particle flow pattern throughout the length of risers, a significant improvement in the coefficient of convective heat transfer is observed. The study validated the correlations for the convective heat transfer coefficient and the resistance coefficient against previous research findings. The findings indicated that the thermal efficiency of the full-length twist-inserted system is almost three times greater than that of a plain collector while doubling its pressure drop. The findings of this research could be useful in designing low-cost, compact solar water heaters.

Effect of ECAP process on deformability, microstructure and conductivity of AA5083 under thermal effect

An alternate method of alloying is to use extreme plastic deformation on commercially available AA5083 to generate an ultrafinegrained microstructure. The objective of this approach is to improve mechanical characteristics without sacrificing corrosion resistance and biocompatibility. Anisotropy in mechanical properties is introduced by plastic deformation leading to the production of a distinct texture. This is a crucial concept to understand in order to build and model structural devices and components from a perspective based approach. The ultrafine-grained structure of AA5083, which was obtained by equal channel angular pressing, is examined in this work. Ex-situ and indirect in-situ thermal studies are used to supplement this investigation while the material is heat treated at different annealing temperatures. The results show that the elastic properties undergo very small change during the annealing process, in contrast to other parameters as thermal expansion, internal friction, or hardness. The strong relationship between the elastic anisotropy and texture highlights the importance and possibilities of using texture into the design and customization of mechanical characteristics. Pure deforms plastically in order to improve mechanical qualities while maintaining biocompatibility and corrosion resistance. Analysis of the materials elastic inhomogeneity and crunchiness in detail. In comparison to other characteristics like as inner conflict thermal enlargement or hardness, the results demonstrate that elastic properties barely marginally change during annealing. The microstructure fragmentation had no influence on the conductivity of the AA5083, which oscillated at 18 MS/m after the ECAP procedure. According to the findings, all deformed specimens strain hardening exponent and capacity were lower than they were in their as-received state. Investigated was the effect of size of grains on the strain hardening comportment of the ECAPed AA5083.

Estimation of heat transfer coefficient and friction factor with showering of aluminum nitride and alumina water based hybrid nanofluid in a tube with twisted tape insert

Twisted tape is one of the active thermal proficiency boosting technology which has been deeply examined because to consistent efficiency findings and easy implementations. Thermo-hydraulic effectiveness of tubes fitted with twisted tapes is becoming highly significant. Although twisted tapes can cause swirls and disturb boundary layers, this is the most widely used method for improving convection. In the present attempt, to enhance the heat transfer twisted tape is inserted in tube. In the current modern research, the effect of twisted tape, on the enhancement of thermal transport, Nusselt number and friction factor performance of AIN–Al2O3/water hybrid nanofluid is evaluating utilizing CFD and ANSYS-FLUENT software. the consequence of twisted pitch 44 mm, 66 mm, 88 mm, 100 mm and Reynolds numbers 800, 1200, 1600 and 2000 on Nusselt number, heat transfer coefficient and friction coefficient have been computed numerically with 0.01 to 0.04 volume friction of nanopowders. The commercial ANSYS-FLUENT code was used in this analysis utilizing the SIMPLE method for pressure–velocity coupling. The K-ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K - \\omega$$\\end{document} model and Navier Stokes equations are integrating utilizing finite volume method in ANSYS-FLUENT. It was observed that inserting the twisted tape in tube significantly improves the thermal conductivity as well as friction factor compared with the simple tube without turbulator.

Mechanism Study of Symmetric Mechanism-Rolling Bearing Dynamic System Considering the Influence of Temperature Factor

Due to the symmetry of their structure and the way they rotate, rolling bearings are often used at high temperatures and high speeds. When the temperature changes, the material properties of the rolling bearing change, which in turn causes the dynamic model equation of the rolling bearing to change. Given the problem in that the conventional dynamic model equation does not consider temperature changes, but because temperature changes cause changes in material performance parameters resulting in differences between the dynamic simulation signals and the actual signals, this paper fully considers three factors, namely, the thermal expansion coefficient, the hardness value, and the friction coefficient. With the influence of temperature changes, a study on the mechanism of the symmetric mechanism-rolling bearing dynamic system considering the influence of temperature factors is proposed. First, combined with the material properties of the rolling bearing, the changes in thermal expansion coefficient, hardness value, and friction coefficient caused by temperature changes were analyzed. Second, the functional relationship expressions obtained above were substituted into the existing conventional dynamic model. Finally, the comprehensive functional relationship formula was substituted into the conventional dynamic model to obtain the rolling bearing dynamic model under temperature difference changes. By studying the mechanism of the symmetric mechanism-rolling bearing dynamic system that considers the influence of temperature factors, this method can undertake a more comprehensive consideration of the dynamic analysis research into rolling bearing fault diagnosis, thereby verifying the effectiveness of the method.

High thermal conductivity and ultralow friction of two-dimensional ice by molecular dynamics simulations

Two-dimensional ice (2D ice) is a relatively new family member of ice polymorphs. While the phase transitions and growth kinetics of 2D ice have aroused intensive investigation, its thermal and mechanical properties are seldom studied. The unique 2D structure of this polymorph suggests that it may possess distinct physical characteristics compared to its bulk counterparts. In this work, the thermal conductivities and friction of 2D ice were systematically studied by molecular dynamics (MD) simulations. It was found that the thermal conductivities of 2D ice show a strong dependence on their length and the extrapolated value of the infinite system can achieve ∼4.7 W/(m∙K), which is notably higher than that of bulk phase of ice Ih ∼1.5 W/(m∙K). Decreasing temperature or applying mechanical strains can both increase the thermal conductivity of 2D ice, which can be explained by structure or phonon analyses. 2D ice also exhibits an ultralow friction of ∼0.24 nN when sliding upon a graphene substrate, lower than that of ice Ih ∼0.70 nN at the same sliding conditions. With the decrease in temperature or the increase in normal load, the friction coefficient of 2D ice exhibits a downward trend, and it could be as low as ∼0.005, indicating superlubricity. The analysis on structural lubricity suggests that ordered but mismatched crystal-crystal contacts have lower friction than disordered case. The results on high thermal conductivity and ultralow friction would guide the potential application of 2D ice in efficient thermal management or design of nanofluidic devices.

The Mutual Influence of Thermal Contact Conductivity and Convective Cooling on the Temperature Field in a Tribosystem with a Functionally Graded Strip.

An analytical model to find the temperature field that has been developed for friction systems consists of a strip and semi-space. The strip is made of a two-component functionally graded material (FGM) with an exponentially changing coefficient of thermal conductivity. In contrast, the material of the semi-space is homogeneous. An appropriate boundary-value problem of heat conduction with constant specific friction power was formulated and solved using the Laplace integral transform method. The model takes into consideration the imperfect thermal friction contact between the strip and the semi-space, and also the convective cooling on the exposed surface of the strip. The appropriate asymptotic solutions to this problem for low and high values of Fourier number were obtained. It is shown how the determined exact solution can be generalized using Duhamel's formula for the case of a linearly reduction in time-specific friction power (a braking process with constant deceleration). Numerical analysis for selected materials of the friction pair was carried out in terms of examining the mutual impact on the temperature of the two Biot numbers, characterizing the intensity of the thermal contact conductivity and convective heat exchange on the exposed surface of the strip. The obtained results can be used to predict the temperature of friction systems containing elements made of FGM. In particular, such systems include modern disc braking systems.

Numerical Simulation and Application of a Channel Heat Sink with Diamond Ribs

This paper presents a channel radiator with ribbed ribs and primarily investigates the fluid flow and heat-transfer characteristics of the channel radiator. A three-dimensional numerical simulation of the radiator’s pressure-drop and heat-transfer process was conducted using the finite volume method. A comparison between the experimental data and the simulation results demonstrates that the simulation in this paper is accurate, with a maximum error not exceeding 5%. Furthermore, the radiator was further subjected to geometric parameter studies, principally including the height ratio between the fins and the channel, the fin angle, and the spacing between the fins. The thermal resistance, Nusselt number, friction factor, and heat-transfer enhancement factor were calculated. The results indicate that if the geometric parameters are selected appropriately, the heat sink will enhance heat-transfer performance within an acceptable pressure drop. When the Reynolds number is greater than 507.5, the height ratio of 25%, the rib angle of 135°, and the rib spacing of 2.5 mm can be given priority. This heat sink is used in PCR devices, and experimental results show that the novel channel heat sink can meet the heat dissipation requirements of the TEC during the PCR process.

Triboxidation and softening induced by dry sliding of copper coupling with steel at 3.36 m s−1 speeds

In this paper, the copper coupled with steel under dry sliding are comparatively sdudied at 0.56 m s−1 and 3.36 m s−1 condition from the morphology, structure and composition of tribolayer of the copper. It is found that the wear rate of Cu at 3.36 m s−1 is twice that at 0.56 m s−1, and the temperature of Cu block at 3.36 m s−1 (240 °C) is much higher than that at 0.56 m s−1 (75 °C). The results show that when the grinding speed is 0.56 m s−1, the grain distortion occurs in the top area of the subsurface layer of Cu block. When the grinding speed is 3.36 m s−1, the grain refinement zone appears below the subsurface layer of Cu block wear. The study further proves that the softening caused by friction heat occurs in the grain refinement zone, and a large number of softened metal copper tends to transfer to the opposite side. At the same time, the friction heat changes the mechanical and thermal deformation, material transfer and friction oxidation of the contact surface, which has a great influence on the dry sliding behavior of Cu.

Exact solutions for permeable wall laminar jet with velocity slip: Momentum and thermal profiles

This study presents exact analytical solutions for the two-dimensional laminar jet flow and heat transport of Casson fluid under velocity slip condition. The laminar wall jet of classical Glauert type is extended to the Casson fluid model considering the flow to be along a flat permeable surface. The roles of velocity slip, wall temperature, and mass transfer on the fluid flow and rate of thermal exchange are investigated. The outcomes for momentum and thermal fields, skin friction and heat transfer gradient are obtained analytically with numerical solutions of the suction-far stream velocity expression. It is noted that mass transfer and velocity slip have significant effects on the flow of fluid and heat transfer. Thermal profile varies significantly for increasing Prandtl values with small suction.

Numerical Modeling, Experimental Investigation, and Optimization of a Micro Hot Embossing Process

Abstract This paper describes the development of a finite element simulation model and a self-made low-cost experimental setup for the micro hot embossing process. The simulation model incorporates stress relaxation behavior through the utilization of the generalized Maxwell model. It also considers thermal expansion and contact friction effects, enabling accurate prediction of the deformed pattern of polymethyl methacrylate (PMMA). Simulations and experiments were performed for various pressure and temperature combinations, and the resulting pattern profile depths were found to be in good agreement, between the simulation and experimental results. In addition, the simulation model was used to generate response surfaces through face-centered central composite design (CCD) to identify the ideal combination of process parameters of the micro hot embossing process for creating a patterned SMD (surface mount device) LED chip panel.

On the Temperature-Dependence of Deformation-Induced Martensite Formation in AISI 304L Type Steel

In this study, the deformation-induced α-martensite formation in AISI 304L steel was investigated in the temperature range between 75 °C and − 196 °C in the light of the temperature-dependence of hydrogen embrittlement phenomena. For this purpose, tensile tests with in-situ and ex-situ magnetic measurement of the α-martensite volume content as a function of plastic strain were carried out. In addition, a theoretical assessment of the temperature-dependence of the austenite stability was undertaken, evaluating chemical and non-chemical driving force contributions to the martensitic γ → α transformation as proposed by Ghosh and Olson. The experimental results clearly show an increase in the α-martensite volume content and a shifting of the phase transformation to lower strain levels upon reducing the temperature to − 75 °C. A further reduction of the temperature to − 196 °C revealed to have no significant impact on the α-martensite formation. The theoretical assessments indicate a similar temperature-dependence of the austenite stability as observed experimentally and suggest contributions of the thermal friction work at the fcc/bcc interface to be responsible for a constant austenite stability in low-temperature regimes. Additional investigations of deformed microstructures showed that element segregation effects on the local austenite stability are pronounced around room temperature, but become less relevant at low temperatures.

Simultaneously improved modulus, thermal expansion coefficient and wear resistance of a Mg–6Zn–1Gd–0.3Ca matrix composite by adding high volume fraction SiC particles

In this paper, three sizes (5, 20 and 50 μm) SiC particles (SiCp) were selected, and the SiCp/Mg–6Zn–1Gd-0.3Ca (SiCp/ZG61X) composites with ∼50 vol.% were successfully prepared by squeeze casting. The effect of particle size on the properties of the composites was studied, while the wear resistance and the wear mechanism of composites were investigated. The results showed that compared with the matrix alloy, the addition of SiCp can significantly improve the properties of the composites, in which the strength increased from 175.2 to 326.5 MPa and the modulus increased from 45.0 to 159.6 GPa. At the same time, the coefficient of thermal expansion and friction were significantly reduced. In addition, the smaller the particle size, the higher the strength and modulus of the composite. However, for the coefficient of friction and thermal expansion, the larger particle size was conducive to the reduction of the two coefficients. The analysis of friction and wear behavior showed that the wear mechanism of the matrix alloy was mainly abrasive wear and adhesive wear, while the wear mechanism of the composites was abrasive wear and layered wear.

Numerical Study on Thermo-Hydraulic Performance of Enhanced Tube With Crossed Helical Dimples

Abstract A numerical investigation was performed to study the thermo-hydraulic performance in an enhanced tube with crossed helical dimples. The simulations were carried out in the Reynolds number range of 5000–30,000 in crossed helical dimple tube of a period length with a constant wall temperature of 350 K. The thermal enhancement, friction factor, and performance evaluation criteria (PEC) were the primary focus of the present work. Moreover, geometric parameters such as spiral pitch, transverse length, and dimple depth were investigated for their effects on thermo-hydraulic performance. The results revealed that the shape of crossed helical dimple exerts positive effects on the heat transfer enhancement. This unique shape generated intensive transverse flow and induced a higher transverse velocity, leading to heat transfer enhancement. Therefore, the synthesized heat transfer performance was increased by 150–225% over that of the smooth tube. Furthermore, the heat transfer enhancement and friction factors increased with increasing dimple depth and declining spiral pitch and transverse length. Within the scope of this study, the maximum PEC = 2.25 was observed for Re = 30,000, P = 30 mm, L = 11.064 mm, and H = 3 mm.

The effect of tool wear on the damaged layer thickness and tool wear rate in ultra-precision turning of quartz glass

Quartz glasses have been extensively used for many fields, such as semiconductor technology, optical instruments, inertial navigation and others. Ultra-precision turning with diamond tools can achieve high surface accuracy when processing non-ferrous materials. In recent years, ultra-precision turning has also been tried to be applied to process brittle materials, but there are constraints including small removal amount and tool wear. When diamond tools are used to cut quartz glass, tool wear occurs under the combined action of thermal effect and mechanical friction, which will affect the damaged layer thickness of the processed quartz glass. In this paper, the tool wear factor is led into the calculation of the extrusion volume, and the damaged layer thickness is calculated by the extrusion volume. Combined with the results of quartz glass turning experiments and the calculated results by simulation, the effect of tool wear factor on the damaged layer thickness and the tool wear rate is analyzed. The analysis shows that tool wear will lead to chip fracture thickness decrease and extrusion volume increase. Combined action of these two aspects, the damage layer thickness keeps unchanged at first and then rises with the increase of tool wear. In addition, the experimental results show that the tool wear rate rises with the increase of tool wear.

Experimental Study and Computer Modelling of Thermal Friction Treatment Process of the HARDOX 450 Steel

Experimental Study and Computer Modelling of Thermal Friction Treatment Process of the HARDOX 450 Steel

Stability Analysis of Dual Solutions of Convective Flow of Casson Nanofluid past a Shrinking/Stretching Slippery Sheet with Thermophoresis and Brownian Motion in Porous Media

This article considered the steady two-dimensional boundary layer flow of incompressible viscous Casson nanofluids over a permeable, convectively heated, shrinking/stretching slippery sheet surface. The achievements of this work are extremely relevant, both theoretically with respect to the mathematical modeling of non-Newtonian nanofluid flow with heat transfer in engineering systems and with respect to engineering cooling applications. The combined impacts of suction/injection, viscous dissipation, convective heating, and chemical reactions were considered. The governing modeled partial differential equations with boundary conditions are transformed into nonlinear ordinary differential equations using similarity transformations and finally converted to the first-order initial value problem. Then, the technique of the fourth-fifth order Runge–Kutta–Fehlberg with the shooting method is used to obtain numerical solutions. Moreover, the effects of different involving parameters on the dimensionless temperature, velocity, and concentration, as well as, from an engineering viewpoint, local Nusselt number, the skin friction, and local Sherwood number are illustrated and presented in graphs and tabular forms. For critical shrinking parameter λ c , the existence of a dual solution within the interval λ c < λ < 0 is revealed, and this range escalates with the suction and slipperiness parameters; hence, both control the flow stability. The increment in the values of the porous media, Casson, Forchheimer, slipperiness, and convective heating parameters reduces the local skin friction and intensifies the rates of mass and heat transfer. For the Newtonian flow (that is, as the Casson parameter β gets to infinity ∞ ), the thermal boundary layer thickness, temperature profile, and skin friction diminish, whereas the concentration profile, mass, and heat transfer rates increase compared to the non-Newtonian Casson nanofluid. These results excellently agree with the existing ones.