Interfacial Temperature Rise Research Articles

Thermo-mechanical contact between a rigid sphere and an elastic–plastic sphere

The mechanical and thermal response of a rigid sphere sliding over an elastic–plastic sphere with radius larger than that of the rigid sphere, namely, plowing contact model, are investigated using a finite element method. Dimensionless solutions for the maximum values of contact force, friction force, contact area, residual interference, and interfacial temperature rise are obtained as a function of dimensionless contact time. A detailed comparison is performed with the results between the plowing contact model and the flattening contact model in which an elastic–plastic sphere flattened by a rigid sphere with radius larger than that of the elastic–plastic sphere.

Microscale Friction Behaviour of Single Crystal Si (111) When Rubbed with Diamond Spherical and Conical Styli

An experimental study is described of the friction behaviour of samples of single crystal Si (111) when they were rubbed with diamond spherical (radius of 0.18 mm) and conical styli of included angles of 120° and 136°. Several techniques were used including (1) a reciprocating friction machine, (2) Raman spectroscopy and (3) environmental scanning electron microscopy. Friction force was measured for a constant relative speed of 0.22 mm s−1 between the rubbing stylus and the substrate. The normal load on the stylus was varied in the range 100–500 mN. In the case of the spherical stylus, the coefficient of friction was in the range 0.03–0.08, whereas for the conical styli, it was up to ten times higher, but it varied with the number of friction cycles. Raman spectroscopy revealed that in all cases, structural phase transitions of the silicon had occurred in the friction tracks and both amorphous silicon and Si-III phases were found. Environmental scanning electron microscope showed no debris in the friction tracks produced by the spherical stylus, whereas a considerable amount of debris was found within the friction tracks produced by the conical styli. This debris has been shown to be responsible for the gradual decrease in the coefficient of friction with increasing number of friction cycles. Calculations of the frictional heating between the spherical stylus and the Si (111) substrate have shown that only a negligible interfacial temperature rise would occur. It has been suggested that, in the absence of ploughing, the coefficient of friction between the spherical stylus and the Si (111) substrate is controlled by the adhesion between the two surfaces, whereas the very initial coefficient of friction between the conical styli and the Si (111) substrate is controlled by the ploughing process.

Experimental Study on Tool Wear when Machining Super Titanium Alloys: Ti6Al4V and Ti-555

To understand the effect of the workpiece microstructure on the tool wear behavior, anexperimental investigation was conducted on machining two different microstructures of supertitanium alloys: Ti-6Al-4V and Ti-555. The analysis of tool-chip interface parameters such asfriction, heat flux and temperature rise and the evolution of the workpiece microstructure underdifferent cutting conditions have been discussed. As cutting speed and feed rate increase, the meancutting forces and temperature show different progressions depending on the consideredmicrostructure. Results show that wear modes for cutting tools used in machining the Ti-555 alloyshow contrast from those exhibited by tools used in machining the Ti6AI4V alloy. In fact, onlyabrasion wear was observed for cutting tools in the case of machining the near-β titanium Ti-555alloy. The last alloy is characterized by a fine-sized microstructure (order of 1 μm). For the usualTi6Al4V alloy, adhesion and diffusion modes followed by coating delamination process on the toolsubstrate have been clearly identified. Moreover, a deformed layer was observed under secondaryelectron microscope (SEM) from the sub-surface of the chip with β-grains orientation along thechip flow direction. The analysis of the microstructure confirms the intense deformation of themachined surface and shows a texture modification, without phase transformation. For the Ti-555β-alloy, β grains experiences more plastic deformation and increases the microhardness of theworkpiece inducing then an abrasion wear process for cemented carbide tools. For the Ti6Al4Vmicrostructure, the temperature rise induces a thermal softening process of the workpiece andgenerates adhesive wear modes for cutting tools. The observed worn tool surfaces confirm theeffect of the microstructure on tool wear under different cutting conditions for the two studiedtitanium alloys.

Numerical analysis of interfacial deformation and temperature rise during ultrasonic Al ribbon bonding

The plastic deformation, thermal behaviour and interfacial state during ultrasonic bonding of Al ribbon with substrate were analyzed based on numerical simulations. The numerical simulations were carried out by finite difference and element methods. The change of bond interface temperature with the bonding time t was simulated. It is suggested that the interfacial frictional behaviour between ribbon and substrate does not only affect the temperature rising behaviour but also the stress situation and plastic deformation behaviour, i.e., the ribbon deformation and the frictional slip behaviours influence each other. It is also found that partial constraint (frictional slip) at the bond-interface increases interfacial shear stress drastically and controls the frictional heat input and temperature rise of the Al ribbon.

Contact and temperature rise of thermal flying height control sliders in hard disk drives

Contact and interfacial temperature rise upon slider-disk contact in hard disk drives is investigated using thermal flying height control (TFC) sliders. To achieve contact, the heater element of the TFC slider is energized with constant and square wave voltage input profiles with increasing bias. The temperature rise during slider-disk contact is estimated from the resistance change at the read element using auxiliary calibration measurements. Laser Doppler vibrometer measurements show that vertical gimbal vibrations occur if the power input to the heater exceeds a critical level, seemingly related to slider-disk contact. During contact, the same frequencies occur in the spectrum of the resistance of the read element and the vertical gimbal velocity. Furthermore, it is found that the gimbal is excited at additional frequencies for a square wave heater input profile compared to a constant heater input profile.

On estimations of maximum and average interfacial temperature rise in sliding elliptical contacts

This study considers the approaches of Blok and Jaeger for the estimation of maximum and average temperatures in sliding elliptical contacts with both uniform and semi-ellipsoidal (Hertzian) heat distributions. The accuracy of each of these methods, which are based on single-point temperature matching between contacting bodies, is assessed relative to a numerical solution of the heat partition problem developed in a previous work, which imposed temperature matching at all nodal points. Comparisons are made for a wide range of Peclet numbers, as well as for moderate ranges of thermal conductivity ratio and elliptical ratio. It is found that the application of Blok's hypothesis yields remarkably accurate predictions of the maximum interfacial temperature, with typical errors less than 3%, whereas the hypothesis of Jaeger leads to predictions of the average interfacial temperature that have typical errors of around 6%. The authors also assess the accuracy of approximate formula developed by Tian and Kennedy to predict the maximum temperature at the interface for the case of sliding circular contacts and find the error to be no more than 2.6% for the full range of Peclet number. Further, the authors of the current study use fundamental heat source solutions developed by Tian and Kennedy to arrive at formulae for average temperature rise for circular contacts that are analogous to the Tian and Kennedy maximum temperature rise formulae. It is found that the formulae for computing the average interfacial temperature rise are also quite accurate, but have slightly more error than the maximum temperature rise formulae. Finally, in the present work, extensions are suggested to the maximum and average temperature rise formulae of Tian and Kennedy to include the effects of elliptical contact geometry. It is found that these formulae are at least 91% accurate for elliptical ratios between 0.4 and 5.0.

Effect of Operating Conditions on Tribological Response of Al–Al Sliding Electrical Interface

Aluminum is widely used in electrical contacts due to its electrical properties and inexpensiveness when compared to copper. In this study, we investigate the influence of operating conditions like contact load (pressure), sliding speed, current, and surface roughness on the electrical and tribological behavior of the interface. The tests are conducted on a linear, pin-on-flat tribo-simulator specially designed to investigate electrical contacts under high contact pressures and high current densities. Control parameters include sliding speed, load, current, and surface roughness. The response of the interface is evaluated in the light of coefficient of friction, contact resistance, contact voltage, mass loss of pins, and interfacial temperature rise. As compared to sliding speed, load, and roughness, current is found to have the greatest influence on the various measured parameters. Under certain test conditions, the interface operates in a “voltage saturation” regime, wherein increase in current do not result in any increase in contact voltage. Within the voltage saturation regime the coefficient of friction tends to be lower, a result that is attributed to the higher temperatures associated with the higher voltage (and resulting material softening). Higher interfacial temperatures also appear to be responsible for the higher wear rates observed at higher current levels as well as lower coefficients of friction for smoother surfaces in the presence of current.

Low-Temperature, Shear-Induced Tribofilm Formation from Dimethyl Disulfide on Copper

The frictional properties of a sliding copper-copper interface exposed to dimethyl disulfide (DMDS) are measured in UHV under conditions at which the interfacial temperature rise is <1 K. A significant reduction in friction is found from the clean-surface values and sulfur is found on the surface and below the surface in the wear scar region by Auger spectroscopy. Because the interfacial temperature rise under the experimental conditions used to measure friction is very small, tribofilm formation is not thermally induced. The novel, low-temperature tribofilm formation observed here is ascribed to a shear-induced intermixing of the surface layer(s) with the subsurface region as suggested using previous molecular dynamics simulations. Although the tribofilm contains predominantly sulfur, a small amount of carbon is also found in the film.

Interface Temperature Measurement and Experimental Studies of Super-High Speed Polishing of CVD Diamond Films

Super-high speed polishing of diamond film is a newly proposed method due to its outstanding features such as low cost and simple apparatus. The interface temperature rise is due to the friction force and the relative sliding velocity between the CVD diamond film and the polishing metal plate surface. In this paper, the interface temperature rise in super-high speed polishing of CVD diamond film was investigated by using the single-point temperature measurement method. Additionally, the influence of polishing plate material on the characteristics of super-high speed polishing has been studied. The results showed that cast iron is not suitable for super-high polishing, while both 0Cr18Ni9 stainless steel and pure titanium can be used for the super-high polishing of CVD diamond film. The quality and efficiency of polishing with 0Cr18Ni9 stainless steel plate is much higher than those of pure titanium, and the material removal rate could reach to 36-51 m/h when the polishing speed and pressure are 100 m/s and 0.17-0.31 MPa, respectively.

Infrared Thermography Investigation of an Evaporating Sessile Water Droplet on Heated Substrates

The present study is an experimental investigation of the thermal evolution of millimeter-sized sessile water droplets deposited on heated substrates. Infrared thermography is used to record temperature profiles on the droplet interface in time as evaporation takes place. The local measurements of the interface temperature allowed us to deduce the local evaporation rate and its evolution in time. To our knowledge, this is the first time that such measurements have been performed. The deduced evaporation rate using thermography data has been validated with optical measurements. Temperature evolution is used to reveal the contact line location and transient temperature fields. Temperature differences between the apex of the droplet and the contact line are shown to decrease in time. The rate of local temperature increase at the interface is found to behave linearly with time. The slope of this linear increase turns out to be more pronounced as the substrate temperature is increased. A generalized linear trend, using dimensionless properties for the interface temperature rise, is deduced from the measurements.

Energy dissipation mechanism of phononic friction

Focusing on the interfacial friction, the energy accumulation and dissipation mechanisms are analyzed in the present paper. Based on the lattice thermokinetics theory, the potential difference of interfacial atom during the jumping process is calculated, then the formula of interfacial temperature rise is deduced successfully. The analysis indicates that the interfacial temperature depends on the contact status and material properties of the friction system, and the interfacial interactive potential is an important factor. In the initial stage of slipping process, as the interfacial atoms are in the non-equilibrium thermal state, new phonon are excited to enable the friction energy dissipation, which finally makes the non-thermal equilibrium transit to equilibrium state. Based on the quantum mechanics and the thermodynamics, the energy dissipation mechanism of interfacial friction is studied. The results show that the elastic potential energy stored during the sticking process dissipates more quickly with higher vibration frequency, and the dissipation time is much shorter than the slip time in one cycle.

Film−Penetration Model for Nonisothermal Physical Gas Absorption

A two-parameter model, which utilizes the hybrid film−penetration concept, is developed for describing exothermic physical absorption of a gas into a liquid. The model is applied to the absorption of dry saturated water vapor into aqueous lithium bromide solution, which system is used in absorption cooling. The conventional film and penetration models predict constant values of 0.55 and 6.59 K for the interfacial temperature rise, respectively, and also suggest that the rate of absorption at the gas−liquid interface will be depressed by 3 (film model) and 40% (penetration model) compared to assumed isothermal absorption at the bulk liquid temperature. The holistic film−penetration model resolves this large discrepancy between the film and penetration models, which are fragmentary perspectives of the absorption process.

Tribo-electrification mechanisms for dissimilar metal pairs in dry severe wear process: Part I. Effect of speed

The effect of reciprocating speed on the tribo-electrification mechanism is investigated for the sliding of five soft metals (Pb, Ag, Cu, Zn and Al) on iron under dry severe wear condition. In general the main sources of tribo-electrification are from material transfer, residual heat, and frictional heating with the latter two commonly referred to as the Seebeck potential and is linearly proportional to the reciprocating speed. In contrast, the tribo-electrification caused by material transfer is almost independent of reciprocating speed at higher reciprocating speeds although it is significant at lower speeds. Results from this series of tests showed that material transfer from the soft metals to the iron component formed a very thin layer for the incompatible pairs, resulting in smaller friction coefficient and seemingly stable variations of the tribo-electrification voltage. On the other hand, the compatible or partially compatible pairs induced large soft material transfer to the iron component in the form of large flake-like debris. As a result, the corresponding friction coefficient was larger and the tribo-electrification variation was unstable. It was also shown that tribo-electrification resulted mainly from the Seebeck effect at an average sliding velocity higher than 200 mm/s, but the average interface temperature rise estimated by tribo-electrification had to be calibrated by the effect of material transfer, especially at lower speeds.

Another method of using dynamic tribo-electrification mechanisms for measuring gas flowrate

Another method of applying the dynamic tribo-electrification mechanisms in a gas flow sensor was studied experimentally in this paper. The gas used was nitrogen (N2) and the tribo-electrification mechanisms were from the incompatible pair (Pb/Fe) and the partially compatible pair (Cu/Fe) in dry severe wear condition. Generally, flow sensors using the dynamic tribo-electrification mechanisms will be sensitive for material pairs with high thermal eletromotive force, low specific heat, and thermal conductivity. For the incompatible pairs, results from this study revealed that the method was adequate for measuring small flowrate and only a small amount of masses was transferred from the soft metals to the iron, forming a very thin layer with a friction coefficient of less than 0.3. Moreover, variations of the tribo-electrification and friction coefficient with sliding time appeared to be very stable, indicate that the effect of N2 flowrate on tribo-electrification was significant. This effect of N2 flowrate and the average interface temperature rise were particularly pronounced at a N2 flowrate of less than 1001/min. Finally, a model to represent the tribo-electrification mechanisms of various soft metals sliding on iron in N2 gas flow was proposed.

Polishing of polycrystalline diamond by the technique of dynamic friction, part 1: Prediction of the interface temperature rise

This paper investigates the interface temperature rise in polishing a polycrystalline diamond (PCD) surface. First, the Greenwood–Williamson's statistical asperity model is applied to characterise the surface roughness of a PCD specimen. The result is then used to estimate the contact area and total number of contact asperities under an applied polishing load. The heat generated is taken as the product of the friction force and the relative sliding velocity between the PCD asperities and the metal disk surface. The Jaeger's moving heat source analysis is then applied to determine the fractions of heat flux flowing into the PCD asperities and their counterpart in contact sliding and to give rise to the average temperature rise. A comparison with the observations made in the authors' experiments and those reported in the literature showed that the model predicts very well the temperature rise at the polishing interface.

Scale effects in dry and wet friction, wear, and interface temperature

Scale effects in tribology at the macroscale to nanoscale are considered. The coefficient ofdry friction depends on the real area of contact and the shear strength due toadhesion and two- and three-body deformation. The real area of contact dependson the surface topography and elastic modulus for elastic contact, and on thehardness for plastic contact. The surface topography is scale dependent, on thebasis of a fractal model or an empirical rule. The hardness is scale dependent onthe basis of the strain gradient plasticity. The adhesional shear strength is scaledependent on the basis of a dislocation-assisted sliding model. The two-bodydeformation component of the coefficient of friction is scale dependent due to the scaledependence of the average asperity slope. The real area of three-body contact is scaledependent due to the scale dependence of the probability for a particle to betrapped at the interface and shear strength. In the presence of a liquid film themeasured value of the coefficient of friction is different from the coefficient of dryfriction due to the meniscus contribution. The meniscus force is scale dependent,since it depends on the number of contacts and summit radius of the asperities,which are scale dependent, on the basis of the surface topography. The scaledependence of other parameters of tribological importance, such as the wear coefficient,which depends on the scale dependent hardness, and the interface temperaturerise, which depends on the scale dependent mean contact size, is also considered.

Introduction to Tribology

Introduction to Tribology

On the size of hot spots in the dry sliding of metals

This paper investigates the influence of the interfacial temperature rise, in the dry sliding of metals, on the size of hot spots. An area expansion coefficient that corrects for such thermally induced changes is introduced. It is shown that the discrepancy between theoretical and experimental estimates of the area ratio, reported by some authors, may be avoided by taking into consideration the effects of temperature elevation on the properties of the sliding pair: namely, material softening and thermal expansion.

Non-isothermal gas absorption with reversible chemical reaction

A fundamental description of non-isothermal mass transfer accompanied by a single reversible chemical reaction has been presented. The description is based on the Higbie penetration theory. Arrhenius type dependence of solubility, reaction rates and diffusivities on temperature has been assumed. Special emphasis has been paid to bimolecular irreversible reactions where depletion of the liquid phase reactant occurs. In addition, the mass transfer behavior in the infinite enhancement regime has also been presented. It has been shown that the Shah criterion fails under conditions where depletion of the liquid phase reactant occurs. In the infinite enhancement regime, the non-isothermal enhancement factor is dependent on the ratio of the diffusivities of the reactants, the ratio of the initial stoichiometric reactant concentrations and the activation energies of solubility and reactant diffusivity. These characteristics of the infinite non-isothermal enhancement factor have been reported earlier by Asai et al. (1985, A.I.Ch.E. J.31, 1304–1312). Additionally, it has been shown that, for bimolecular irreversible reactions, the use of correlations for interfacial temperature rise that assume all heat to be released at the interface is not valid for systems with low Lewis numbers but also not for systems where depletion of the liquid phase reactant occurs. Further, the model has been used to study the effect of reversibility on bimolecular reactions. The effect of temperature dependence of the solubility of the gaseous component and diffusivities of the various species on the overall enhancement has been presented. Since the non-isothermal enhancement factor of bimolecular reversible reactions is dependent on various parameters, it is not possible to determine its value by analytical or via approximate techniques. One is forced to use numerical methods for this purpose instead.

Determination of interfacial temperatures under extreme pressure conditions

Interfacial temperatures attained in a pin and v-block apparatus under extreme pressure (EP) conditions were measured using pins made from either copper or an aluminum alloy from the asymptotes in the curve of removal rate versus applied load since these have been shown to correspond to the temperatures at which the interfacial material melts. The interfacial temperature rise was proportional to the applied load, where the proportionality constant α = Aμ where μ is the interfacial friction coefficient and A a geometrical constant which has been previously measured for steel pins and v-blocks lubricated by chlorinated hydrocarbons dissolved in a poly α-olefin as 2.3 ± 0.3 K/N. Values of A measured when using the aluminum alloy (2.4 ± 0.1) and for copper (2.1 ± 0.2) were in good agreement with this measurement and indicated that interfacial temperatures in excess of 1000 K can be attained during EP lubrication. Finally, the rate of material removal in the pin and v-block apparatus can be related to the metallurgical properties of the pins.