Frictional Heat Generation Research Articles

Determination of Load-Speed Modes for Fluoroplastic Seals of Rotary Shaft by Temperature Limitation

Unsteady temperature field in the lip seal of rotary shaft is determined by solving axisymmetric problem of thermal conductivity. Finite element method is used to compare mathematical models of thermal process with various assumptions. At the same time, function of frictional heat generation is modeled by set of concentrated heat sources. To seal filled fluoroplast-4, the validity of assumption of removal of almost all the heat released by friction into steel shaft is shown. Calculations show that for seals operating in low temperature conditions, it is necessary to consider dependence of thermophysical properties of seal material on temperature. To determine coefficient of convective heat transfer, known formulas, that consider its dependence on the sliding speed of the shaft, are used. Method for determining the load-speed regimes of polymer seals of rotary shaft according to temperature limiting, considering dependence of thermal properties on temperature and heat transfer coefficients on the sliding speed, is proposed.

The influences of bump foil structure parameters on the static and dynamic characteristics of bump-type gas foil bearings

Bump-type gas foil bearing is a special type of sliding bearing, especially suitable for supporting rotors with light loads and high speeds. In this paper, a deformation model of bump foil is established by using elastic mechanics theory. A fluid-structure interaction algorithm is proposed according to Reynolds equation of compressible gas. On this basis, a method for calculating the static and dynamic characteristics of the bump-type gas foil bearing is established considering the structure parameters of the bump foil. The presented model is validated using the data reported in the existing research. The gas film pressure distribution, gas film thickness distribution of the bearing, and the influences of bump foil structure parameters on the static and dynamic characteristics of the bearing are studied with an example. Results show that, decreasing the bump foil thickness tB or increasing the bump pitch s will increase the limiting load-carrying capacity W and decrease the attitude angle β. And increasing tB or decreasing s will decrease the friction torque Tr and increase the side leakage flow of gas Qz, resulting in less friction heat generation and faster heat dissipation. Increasing tB or decreasing s will increase the absolute values of [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of the gas film, leading to higher equivalent stiffness of the gas film [Formula: see text].

Friction behaviors of staple carbon fiber composites

This study aims to examine the frictional behavior of staple carbon fiber composites (sCFCs). The staple carbon fiber reinforced polycarbonate (PC) composites were prepared by film stacking for two different impregnation levels. Mechanical properties such as tensile and flexural strengths and moduli and static/dynamic friction coefficient (COF) were determined. The COF and temperature as a function of wearing cycles for sCFCs subjected to different applied pressures were also determined by a disk-on-disk sliding wear test machine. The less impregnated sample exhibited superior tribological performance owing to its rough surface and low frictional heat generation.

Transient thermoelastic analysis of carbon/carbon composite multidisc brake using finite element method

In the current paper, a generalization of the results of Zhao et al. (2008) on a new design of C/C composite multidisc brake system is presented. The purpose of this paper is to study the effect of thermal sensitivity of Carbon/Carbon (C/C) composite material on the temperature distributions, deformation, and stress during braking. In this regard, a transient temperature–displacement coupled analysis for C/C composite brake discs with frictional heat generation under simulated operating conditions is performed. An axisymmetric model for brake system is used for the finite element analysis according to the theory of energy transformation and transportation. The transient temperature distributions on the friction surfaces, deformation, and stress are obtained. To check the validity, the results are corroborated with other solutions available in the literature, wherever possible. The current study could be used as a guide in the initial design of a high performance multidisc brake system.

Temperature-variation effect of piston-driven synthetic jet and its influence on definition of heat transfer coefficient

This study focuses on the temperature-variation effects in the piston-driven synthetic jet impingement and its influence on the definition of heat transfer coefficient. For this purpose, three test runs are conducted, including temperature variation test in the free synthetic jet, temperature variation test in the presence of an impinging target, and heat transfer test. Five operational frequencies (ranging from f = 5 Hz to f = 25 Hz) and seven dimensionless jet-to-surface distances (ranging from H/d = 2 to H/d = 14) are considered in the current tests. Due to the friction heat generation from the actuator itself and the warm air suction from the ‘synthesized’ formation, the temperature of synthetic jet experiences apparent variation during its working process. At the worst, the temperature rise could reach up to 20 °C with respect to the ambient temperature. As a consequence, the selection of the reference temperature shows a significant influence on the Nusselt number definition for the synthetic jet impingement, especially under small jet-to-surface distances and high operational frequencies. At the worst, the Nusselt number defined in the jet temperature or the adiabatic wall temperature maybe twice times of that defined in the ambient temperature. As the jet temperature and the adiabatic wall temperature are affected by too many process parameters, therefore, the accurate determination of them is really a challenging problem in the applications, which remains further identifications.

Dieless friction stir lap joining of AA 5050-H32 with AA 6061-T6 at varying pre-drilled hole diameters

The role of hole diameter on mechanical behavior and joint formation of dieless friction stir lap joints in dissimilar alloy grades of aluminum is investigated in the present article. Concurrent occurrence of mechanical interlocking along with metallurgical bonding reinforce the fabricated joints. Keyhole defect and hook defect of conventional friction stir spot welding are apparently suppressed. Hole diameter range from 3 to 3.5 mm is found to be favorable, while considering the macrostructure analysis, joint morphology analysis and load performance analysis. Appreciable fracture load up to 7 kN is obtained in lap shear test throughout the hole diameters employed. Zones present in the joint are identified, in addition the effect of size of the hole on mechanical interlocking is exposed through macrostructure analysis. The extent of recrystallization induced by frictional heat generation along with plastic deformation has affected the grain structure of the joint. Critical zones resulting in the failure of the joints are stir spot circumference and neck of the pin. A tool diameter to hole diameter ratio for successful DFSL joint fabrication is also established through the present work.

Uncovering Technological and Environmental Potentials of Aluminum Alloy Scraps Recycling Through Friction Stir Consolidation

Conventional metal chips recycling processes are energy-intensive with low efficiency and permanent material losses during re-melting. Solid state recycling allows direct recycling of metal scraps into semi-finished products. It is expected that this process category would lower the environmental performance of metals recycling. Friction Stir Consolidation is a new solid-state technique taking advantage of friction heat generation and severe plastic deformation to consolidate chips into billets. In this research, the feasibility of Friction Stir Consolidation as aluminum chips recycling process is analyzed. Specifically, an experimental campaign has been carried out with varying main process parameters. Three main aspects have been evaluated in order to highlight products quality and environmental impact of the process: (i) metallurgical and mechanical properties of the consolidated products; (ii) primary energy demand, as compared to conventional processes; (iii) forgeability of the consolidated products, as compared to parent material. Results revealed that a proper process parameters selection results in fully consolidated aluminum disk with satisfactory mechanical properties. Also, the new recycling strategy allows substantial energy savings with respect the conventional (remelting based) route.

DCTF Flow Distribution Design in Clutch Packs of wet DCTs

Wet clutch pads require temperature control on contact surface because increased frictional heat abruptly decreases friction coefficient, and eventually, the desired torque transfer becomes difficult to control. Generation of frictional heat is inevitable during clutch engagement, but the frictional heat should be cooled by the convective flow of DCTF for the stable torque transfer capacity in the wet clutch pack. Two-phase DCTF flow behavior was investigated inside the entire cavity space of a wet clutch pack, and detailed flow patterns were computed using CFD analysis. Particularly, outer clutch pack of the DCT, which has severe thermal duty, was studied with respect to DCTF flow rate distribution through the gaps of the clutch pads. Hydrodynamic pressures, velocity fields of DCTF flow, and volume fractions of the DCTF fluid in the wet clutch pack were computed, and evenly distributed flows through the gaps of outer clutch pads to combat unbalanced thermal durability among the clutch pads were achieved by optimizing the design of hub shell outlets. Using computational results, DCTF velocity fields and the volume of fluid (VOF) were compared and they will lead to the well-distributed flow design against the abnormal local frictional temperature rises without unnecessary additional oil pump power.

An investigation on girth friction welding of duplex stainless steel pipes

Girth friction welding is a novel technique to join co-axial linepipes with an external ring (girth) in solid state and without melting of materials. The ring or the girth is rotated between two pipes under an axial force resulting in frictional heat generation and plastic deformation along the pipe-girth interfaces. The rotation of the girth is stopped after a preset displacement of the pipes while the force is maintained to consolidate the deformed material and form the joint along the girth-pipe interfaces. Since the girth is only rotated and the pipeline sections remain stationary, the process simplifies the in situ assembly operations and enables the joining of complex configurations. As the melting of pipes and girth is avoided, the formation of harmful intermetallic compounds and deterioration of toughness in the heat affected zone are minimized. A comprehensive numerical model is reported in the present work to analyse the influence of key process variables on the rate of heat generation, resulting temperature field and thermal cycles, and the nature of material flow along the pipe-girth interfaces in girth friction welding of duplex stainless steel pipes. The computed results of thermal cycles and joint shapes are validated with the corresponding experimentally measured results. The results showed a favorable balance of the ferrite and austenite phases, and very little presence of the harmful sigma phases in the recrystallized weld-zone, which is difficult in fusion welding processes of similar materials.

Prediction of thermally induced postbuckling of clutch disks using the finite element method

Buckling and postbuckling of automotive clutch disks can be excited by the temperature fields caused by frictional heat generation during engagement of clutch systems. Linear and nonlinear buckling finite element analyses are performed to evaluate the thermal postbuckling of clutch metal disks. The dominant buckling modes are first obtained through performing linear buckling finite element analysis (FEA) analyses. The scaled displacement fields obtained from the linear buckling FEA analyses are added to the original geometries to generate the perturbed meshes. The postbuckling is then investigated by performing nonlinear buckling FEA analyses. The commercial FEA software ABAQUS is used in the current study. The effects of the temperature-dependent material properties are studied. It is concluded that the temperature dependence of material properties affects the postbuckling behaviors significantly.

The Calculation of Friction Heat and Thermal Analysis of Spur Gears Based on Thermal Elastohydrodynamic Lubrication Theory

In order to predict the temperature distribution of gears more accurately, the influence of oil film on frictional heat generation should be taken into account in computational model. In this paper, based on the theory of thermal elastohydrodynamic lubrication, the calculation of frictional heat flux in the meshing process and the steady thermal analysis of spur gears is completed. The reliability of the model is verified by comparing the calculated results with the value of empirical formulas and experimental data. This paper provides an effective analysis method for gluing prediction, failure analysis and lubrication state analysis of aero-engine transmission gears.

Theoretical study on ignition of titanium alloy under high temperature friction condition

Combustion of titanium alloy is a typical catastrophic failure of modern aeroengine. The abnormal friction between compressor rotor and stator is the main ignition source. A thermal theory model with friction heat source of titanium alloy is established based on the theory of heterogeneous ignition. The corresponding equation of critical temperature and ignition delay time are derived. The difference between the frictional ignition model and the classic model is discussed. The concept of critical heat generation temperature is proposed. The difference from the heterogeneous ignition model, and the effects of friction coefficient, oxygen concentration, flow velocity, contact radius and flame retardant layer thickness on the ignition parameters are analyzed. The research result shows that when the instantaneous temperature of the contact surface is lower than the critical heat temperature, the heat generation process is dominated by frictional heat, and when the temperature is higher than the critical heat temperature, the heat generation process is dominated by chemical reaction heat, that reducing the coefficient of friction can dramatically increase the critical temperature, but the change of friction coefficient has very little effect on the ignition delay time which can be ignored, that the critical temperature decreases significantly with the increase of oxygen concentration and the decrease of flow velocity. When the oxygen concentration increases from 21% to 42% and the flow velocity decreases from 310 m/s to 50 m/s, the critical temperature decreases by about 213 K and 197 K, respectively. The relative error between the experimental result and the theoretical result is 8.3%, which verifies the reliability of the model. The contact area has an effect on friction heat generation, reaction heat generation, and surface heat dissipation, and has a great influence on the critical temperature. The critical temperature decreases exponentially with contact radius increasing. When the contact radius increases to 0.007 m, the ignition temperature of the titanium alloy and its flame retardant layer are 899 K and 988 K, respectively. The increase of the thickness of flame retardant layer can effectively improve the critical temperature and ignition delay time. The critical temperature of titanium alloy with flame retardant layer is increased by about 172 K, and the ignition delay time is increased by about 3 s.

The Numerical Simulation of Temperature Field in Friction Stir Welding of 7075 Aluminium Alloy

Considering friction heat generation between rotating tool and workpiece and plastic deformation heat generation of material, a numerical simulation model of friction stir welding of 7075 aluminium alloy sheet was established. In this study, the temperature field of the welding process was analysed, and the effects of different stirring speeds and welding speeds on the temperature field were compared. The results show that the high temperature region is located below the shoulder and diffuses outward in a ring shape. After the welding is completed, the workpiece center temperature is high and the ambient temperature is low. The stirring speed of the tool has a large effect on the peak temperature during the welding process. The effect of the welding speed on the peak temperature is less than the stirring speed. The comparison shows that the welding temperature is about 478°C at a stirring speed of 800r/min and a welding speed of 120mm/min, which is a suitable welding parameter.

Study the performance of solid lubricants during hard turning of AISI 4340 steel

Hard turning process is widely used in manufacturing industries. The main problem associated with hard turning is the high frictional heat generation. Traditionally cutting fluids are used to control the heat generation. However, the major drawback related with the use of cutting fluids is the environmental pollutions. The use of solid lubricants during machining is another alternative technique to control the heat generation. It is environmental as well operator friendly. Therefore, in this research work, an experimental study has been conducted to investigate the performance of solid lubricants assisted hard turning. The hexagonal boron nitride (h-BN) and zinc sulfide (ZnS) were taken as a solid lubricating medium. The cutting speed, feed rate, workpiece hardness and tool nose radius were selected as process parameters. The cutting force and chip tool interface temperature were taken as performance indicators. The experiments were performed by using central composite design. The significance of process parameters was analyzed by performing analysis of variance (ANOVA). The second order mathematical models of cutting force and chip tool interface temperature were formulated. The optimal value of the process parameters which provides minimum cutting force and chip tool interface temperature was suggested. The experimental results were compared with dry and wet conditions of machining. The results indicate that solid lubricants have shown better machining performance when compared to dry and wet conditions.

Influence of boron nitride nano additives in cutting fluid for improving surface roughness with MRR

Surface quality is the essential requirement of industrial sector which depends on the certain machining parameters such as surface roughness, material removal rate and indirectly on frictional resistance and heat transfer characteristics during machining. Selection of cutting fluids enables the reduction of frictional resistance and heat generation between tool and work. At present, quality and machining characteristics of cutting fluids attain better focus to improve the surface finish using blends and additives, obviously nano additives are assumed to be a possible solution in betterment of machining outcome. Present work discusses the preparation of nano cutting fluids using boron nitride, characteristics and influence on machining parameters such as material removal rate, tool life particularly surface quality in surface grinding operation. The output results revealed that addition of boron nitride particles is providing greater surface finish when compared to the conventional cutting fluids.

Time-varying stiffness characteristics of roller bearing influenced by thermal behavior due to surface frictions and different lubricant oil temperatures

In this paper, the time-varying stiffness of the cylindrical roller bearing due to the thermal behavior, i.e. warm-up process and different lubricant oil temperatures are experimentally investigated. Firstly, a special test rig that can measure the bearing stiffness is built. Then, a bearing stiffness identification method is proposed, which can avoid the influence of the clearance and deformation on measurement results. Finally, a series of measurements are carried out at different operational conditions. Results reveal that the bearing stiffness shows strong nonlinearity and time-varying characteristics due to the variation of structure and oil performance. In startup (quasi-isothermal condition) and thermal balance states (combined with the frictional heat generation), the influence of the rotational speed on stiffness is opposite.

Computational investigation of welding heat transfer characteristics and parameters effectiveness in mild steel linear friction welding

Numerical simulation of heat transfer represented an efficient tool for the prediction of the effectiveness of the selected welding parameters in industrial application of the linear friction welding (LFW). A fully coupled model was established to study the effect of welding parameters on the welding heat transfer characteristics in LFW of mild steel. The interfacial temperature increased quickly owing to friction heat generation, and stress distribution showed dynamic variations owing to the periodic motion. The energy ratio of friction work and plastic deformation work increased with increasing friction pressure, oscillation frequency, and amplitude, thus indicating the significance of heat generation by plastic deformation. The heat transfer characteristics were found to be highly dependent on the welding parameters. A practical mathematical equation correlating the average friction power with welding parameters was proposed and used to select the suitable welding parameters for a sound LFW joint. The simulated results indicated excellent agreement with the experimental measurements. Finally, microstructures of the experimental welded joint were investigated by consideration of the thermal process. It was hoped that the greater understanding of heat transfer behavior could improve the efficient of process optimization when joining steel as well as other metal materials.

Study on the Influence of Lubrication Cooling State on Sliding Shoe and Guiding Plate of Fracturing Pump

During the operation of the fracturing pump, the friction between the sliding shoe and the guiding plate generates heat, which can rise the temperature of the friction surface, causing the fracturing pump to fail. Generally, relying only on worker experience to adjust the gap between the guiding plate and the sliding shoe and determine the oil supply flow lacks scientific basis and theoretical guidance, which may result in sliding shoe and guiding plate wear, and the increasing probability of burning tile. It seriously shortens the service life of the fracturing pump and affects the safe production of fracturing operations. Therefore, this paper studies the frictional heat generation and heat dissipation mechanism of the sliding shoe and guiding plate. After deriving the formula, a model for the influence of the gap of the sliding shoe and the guiding plate and the oil supply flow rate on the temperature rising of lubricating oil is established. And the test validation was carried out on the experimental platform of 6000 HP fracturing pump. The results showed that the change of temperature rise of the lubricating oil is more obvious as the gap decreases. When the gap between the sliding shoe and the guiding plate is less than 0.2 mm, the temperature of the lubricating oil reaches 360 K, which has exceeded the allowable working temperature of the selected lubricating oil. An increase in the flow rate of the lubricating oil can lower the temperature of the lubricating oil; however, when the flow rate of the lubricating oil exceeds 2 L/min, the effect on the temperature rise of the lubricating oil is not significant. In this study, a lubrication cooling state model for fracturing pump calibration was proposed. It provides a theoretical basis and design reference for reasonable selection of lubricating oil supply flow and the gap.

Examining the influence of shoulder to pin diameter ratio on corrosion behavior of friction stir LM25 aluminum alloy with 10% silicon carbide particles

Friction stir processing (FSP) is a unique method that facilitates the generation of frictional heat between the tool and the workpiece. Stir casted LM 25 aluminum alloy-10% SiCp Metal Matrix Composites (MMC) consists of large aggregated strengthened particles and cast item dendrites. In FSP, a non-consumable instrument made of harder material plays a crucial part in changing the substrate material's surface. In the present study, an attempt has been made to analyze the impact of different ratio of shoulder diameters to pin diameter (D/d) on the immersion corrosion conduct of the LM25AA processed friction stir – 10% SiCp MMCs. The size and dispersion of SiC particles in friction stir processed (FSPed) MMC were studied. The microhardness and tensile characteristics of the FSPed material were assessed and associated with the micro and macro structures. The influence of D/d ratio on the microstructure, micro-hardness, and corrosion rate was analyzed and observed that the hardness and rate of corrosion increase with the decrease in grain size of the matrix and SiC particles.

Shear Punching of Amorphous Alloys under High-Frequency Vibrations

Although amorphous alloys possess many excellent properties, their practical application is limited due to the difficulty of plastic forming. In this work, an effective shear punching of amorphous alloys under high-frequency vibrations was proposed. Under the high-frequency vibration of the punch, the plastic powder was melted into a flexible punch due to the frictional heat generation effect and the viscoelastic heat effect and continued to flow downward under the extrusion of the ultrasonic head to plastically deform the amorphous alloy ribbon. The disordered structure of the amorphous alloys helps them get soft in a localized region during high-frequency vibrations, which can result in low-stress deformations that are different from amorphous alloys in the conventional state. We manufactured various shapes with area of 5 mm2 using high-frequency vibrations and a molten plastic viscous medium. The molds were shaped into the letters “B”, “M”, and “G” and the Chinese characters “工” and “大”. The shapes were made from Fe-based, Al-based, La-based, and Cu-based amorphous alloys. Our results show that shear punching of amorphous alloys under high-frequency vibrations is an effective and low-cost production method of amorphous alloy, which also provides a basis for the wide application of amorphous alloy.