Increase In Contact Temperature Research Articles

Equivalent Heat Source Model of Thermal Relay Contact Based on Surface Roughness of Silver-Magnesium-Nickel Contact.

In a sealed electromagnetic relay, the change in the surface roughness mainly depends on the collision wear between the contact and the moving reed and the ablation effect of the arc on the contact surface based on the strong correlation between the contact resistance and the surface roughness of the Ag-Mg-Ni contact. With a change in contact resistance, the contact temperature increase in a hermetically sealed electromagnetic relay (HSER) is greatly affected. Under extreme overload conditions, the contact surface is severely ablated by the arc, and the roughness increases rapidly with the number of cycles, which greatly affects the contact resistance of the contact surface and the reliability of the relay. A thermal model of a relay contact system based on the surface roughness of Ag-Mg-Ni contacts was established in this paper by analyzing the effect of an arc on the surface roughness of Ag-Mg-Ni contacts under heavy overload conditions. The arc image of the Ag-Mg-Ni contact was recorded using a double-axis arc photographing platform, and the moving track of the arc center under overload conditions was drawn. This paper explored the patterns of arc center movement on the contact surface and the effects of the arc on the surface roughness of the contacts by analyzing the probabilities of the arc center appearing in various locations. A mathematical model correlating the number of contact cycles with contact resistance was established. Subsequently, a finite element simulation model for the equivalent heat source of the contact was developed. The theoretical model error was less than 10%. The accuracy of the equivalent heat source model was verified by comparing the measured data with the simulation results.

A contrastive characterization of pure Mg and AZ91D alloy based on the testing of mechanical, corrosion, wear, and erosion properties

Abstract Magnesium alloy of grade AZ91D is utilized for a variety of applications in aircraft design and frames, as well as vehicle engine radiators, bumpers, and suspension components to reduce the weight of automobiles. This research compared the mechanical, corrosion, wear, and erosion resistance of pure Mg to that of AZ91 alloy. The corrosion media was NaCl, NaOH, and MgSO4, and the weight loss method was utilised to evaluate corrosion. The pin-on-disc configuration was utilized to assess the dry sliding wear mechanism of the Pure Mg and AZ91D alloy. Pure monolithic Mg and AZ91D magnesium alloy have a low resistance to wear as a result of an increase in contact temperature brought about by a shift of operational conditions. Erosive wear is caused when solid particles in a liquid or air jet strike a surface. Significantly influencing the erosive wear are particle velocity, impact angle, and erodent particle size. In this work, the erosive wear of AZ91D was studied using an Air jet erosion tester. SiO2 was used as the eroding material, and the flow rate of the eroding material and air was 5 gm min−1. The erosive factor experiments are designed using Taguchi orthogonal array (L16). The erosive factor response is erosion rate and primarily regulated by three factors as angle (30°, 45°, 60°, and 90°), time (5 and 10 min) and, contact pressure (1 and 2 bar). The results of the experiments showed that the rate of wear increased with increasing pressure, and that the angle of impact of the jet at 60° caused the most wear of any of the tested angles. Analysis of variance (ANOVA) shows that time is the most important factor in determining erosive rate for AZ91D. SEM is used to investigate the structure and morphology of worn-out materials, and its findings are then confirmed.

Investigation on Wear Characteristics of AZ91D/Nanoalumina Composites

This paper discusses the wear and friction with the 2 W% Al2O3 nanocomposite content of pure Mg and AZ91D Mg alloys. Sliding speeds of 0.5 and 1.5 m/s in cast materials with normal stress conditions have been used in sliding distances up to 2000 m/s (0.5, 1.0, and 1 MPa). In order to evaluate the work hardness of the materials measured on temperature similar to the contact surface, we used hardness patterns and hot‐compression flow curves. Mg and AZ91D magnesium alloy pure monolithic Mg are low wear resistant due to an increase in contact temperature due to the adjustment of working conditions, but the wear rate was significantly lower in composite materials, mainly because of nanoparticle strength improvements. Although wear generally contributes to grain refining, increased wear capacity, and greater durability, wear resilience due to dislocation resistance and nanoparticles is seen as the primary wear mechanism in the existing nanocomposites.

Specific Electrical Contact Resistance of Copper in Resistance Welding

The electrical contact resistance (ECR) of copper (Cu‐ETP R200, soft) contacts for resistance welding (RW) is characterized. ECR plays a major role in the RW process and provides local heat generation between the parts. A special determination method is used on different testing variants to observe the influence of contact pressure (two levels: 68, 155 MPa), contact temperature (20–550 °C), and surface parameters, like roughness or oxide layer thickness, on the specific electrical contact resistance (SECR). For each surface parameter, three different levels are investigated. The study shows decreasing SECR with higher mechanical load on the contact and a more complex behavior for increase in contact temperature. SECR shows a characteristic behavior for contact states near the temperature‐dependent tensile strength of the base material for rough and clean surfaces, where SECR approaches toward zero. The variation of oxide layer thickness and surface roughness has a strong influence on the resulting SECR and both surface parameters show a strong coupling regarding their effects.

Abrasive Wear Behavior of CNT-Filled Unidirectional Kenaf–Epoxy Composites

Kenaf (Hibiscus Cannabinus) fibers have received significant attention for replacing the usage of synthetic fibers, especially glass fiber, in the fabrication of fiber-reinforced polymer (FRP) composites. The aim of this research was to study the change in wear behavior of kenaf-epoxy fiber composites by filling them with multiwall carbon nanotubes (MWCNT). In particular, the effect of untreated MWCNT (PMWCNT), acid-treated MWCNT (AMWCNT), and silane-treated MWCNT (SMWCNT) was studied, using three different MWCNT loadings, i.e., 0.5, 0.75, and 1 wt.%. The abrasive wear test was conducted to measure the wear properties of the composites. A thermal infrared camera was also used to measure the punctual contact temperature during the abrasive wear test, while the abraded surfaces were analyzed using the stereomicroscope. Starting from the considerable reduction of wear rate with the introduction of kenaf fibers, it was observed that PMWCNT provided some further, yet modest, reduction of wear rate only at the higher loadings. In contrast, the inclusion of AMWCNT proved to increase the specific wear rate of the epoxy-kenaf composites, an effect worsened at higher loadings. This may be due to the weakened interfacial bonding between the AMWCNT and epoxy. On the other hand, the presence of SMWCNT improved the interfacial bonding between CNT and epoxy, as shown by an increase in contact temperature. However, the increase in bonding strength was stipulated to have caused the rougher worn debris, thus inducing a three-body abrasive wear effect.

Fully-coupled thermomechanical analysis for sliding contact between textured slipper and swashplate in axial piston pump

A fully coupled thermo-mechanical model is developed to investigate the transient sliding contact between textured slipper and swashplate considering the frictional heating. The model is capable of predicting the friction stress, contact temperature distribution and friction coefficient of the textured slipper pair. The effects of the sliding rate on the friction stress and contact temperature are studied. In addition, the effects of material stiffness and friction coefficient on contact temperature are further discussed. Based on the thermo-mechanical model, a parametric study is conducted to evaluate the friction coefficient and flash temperature. It is found that the greater the slip rates, the higher the contact temperature, and thus, the more the friction reduction. The shear bearing capacity of the interface material decreases with the increase of contact temperature, and finally results in the friction stress reduction. Due to the effect of friction force, contact temperature increases with the increase of friction coefficient. The change of material stiffness have little effect on temperature rise. The effective parameters combination of the textured slipper pair can be selected to achieve minimum coefficient. For selected texture parameters, the flash temperature between textured slipper and swashplate becomes higher due to the increase of slip rate and external load, but the friction coefficient decreases.

Tribological behavior of glass fiber reinforced-PA66 in contact with carbon steel under high contact pressure, sliding and grease lubricated conditions

Polyamide 66 is widely used for sliding parts, such as resin worm gear. Glass fibers are usually added to increase its strength. In this study, the tribological behavior of glass fiber reinforced-polyamide 66 composite in contact with carbon steel under high contact pressure, sliding, and grease lubricated conditions is studied. Measurement of mechanical properties and SEM observations of composite sliding surfaces after different sliding cycle numbers indicate that sliding induces characteristic damage of the surface (peeled off fibers and scratching of polyamide) and a degradation in mechanical properties. These lead to an increase in friction and creep of the composite. The wear effect increases with the increase in sliding cycles, and the initial orientation of the fibers in the composite sliding surface has significant effects on the wear of the steel counterpart. The contribution of each phenomenon to the tribological behavior is discussed. The damage to the composite surface and the increase in contact temperature due to sliding have great effects on the tribological properties compared to the presence of wear debris in grease and wear on the steel. The effects of the hardness of the steel on the tribological properties are investigated, and it is found that wear of the composite is reduced by using softer steels.

Tribological Properties of Friction Pair between 316L Stainless Steel and CF/PEEK with Nonsmooth Surface under Seawater Lubrication

This work improves the tribological behavior via innovative surface designs for slipper pairs in seawater axial piston pumps. 316L stainless steel and carbon fiber/polyether ether ketone (CF/PEEK) were selected as friction pair matching materials due to their good corrosion resistance, self-lubrication, and wear resistance. One type of smooth surface and five different types of pit nonsmooth surfaces were created on CF/PEEK specimens. Rotational sliding tests were performed on a friction and wear tester at a load of 200 N at five different sliding speeds (0.79, 1.18, 1.57, 1.96, and 2.36 m/s) under seawater lubrication. The experimental results indicate that the friction process of the smooth surface friction pair is mainly based on abrasive wear and adhesive wear. The friction coefficient range is 0.05–0.08, the specimen contact temperature is 38–75 °C, and the wear rates of 316L and CF/PEEK are 2.3 × 10−5 to 1.2 × 10−4 mm3/(MPa·m) and 5.6 × 10−4 to 7.6 × 10−3 mm3/(MPa·m), respectively. Pits on the specimen surface produce a hydrodynamic effect and store wear debris. The friction process of the nonsmooth surface friction pair is mainly controlled by a ploughing mechanism with only a slight amount of adhesive wear. The friction coefficient range is decreased to 0.03–0.07, the specimen contact temperature is decreased to 28–54 °C, and the wear rates of 316L and CF/PEEK are decreased to 1.2 × 10−5 to 9.1 × 10−5 mm3/(MPa·m) and 2.6 × 10−3 to 7.1 × 10−3 mm3/(MPa·m), respectively. The geometrical arrangement of the elliptical and tri-prism pits increases the convergence gap range and produces a higher bearing capacity. As the sliding speed increases, the friction coefficient first decreases and subsequently slightly increases, the specimen contact temperature increases, and the wear rate decreases.

The Effect of Cable Section on the Variation of Power Automotive Connector Temperature

Electric car requires more electric power. However, the automotive connector that is used to connect two electrical systems should resist the high electric power or electric current. The increase in electric current can lead to an increase in contact temperature by the Joule effect and can cause more damage to an improperly designed connector. The objective of this work is to study experimentally and numerically the influence of cable section on the connector capacity to pass high current. Thus, to study this phenomenon, a finite-element model of power automotive connector with cables and crimping zones was developed to calculate contact resistance and contact temperature. The comparison between the experimental and numerical results shows a good agreement for all tested electric currents. The obtained results lead us to use only the developed numerical model to estimate the value of contact resistance and contact temperature for different cable sections. Moreover, the developed model is beneficial financially. Finally, results have illustrated that the effect of the cable section on the decrease in contact temperature and contact resistance is not negligible.

An experimental study on thermal contact conductance across the SS316L/CuCrZr interface

A vacuum apparatus to measure thermal contact conductance (TCC) was introduced. A TCC test method and procedure was presented. By monitoring the temperature distribution on the test specimen, the heat flux and temperature drop of the contact interface were calculated, and then the TCC was obtained. The experimental research was conducted with pressed pairs SS316L/CuCrZr contacts in a range of 100∼300°C and 1∼10MP. The experimental data analysis results show that the TCC increases with the increase of contact temperature and the TCC also grows with the growth of contact pressure. The TCC appears as a linear relationship with the change trend of pressure at a given temperature. By uncertainty analysis, the measurement error of TCC decreases with the increase of contact pressure at a given temperature. And the variation rate of measurement error increases with the rise in contact temperature.

The effect of specimen temperature on the fretting wear behaviour of a non-nitrided against nitrided high strength alloy steel contact pair

The fretting wear performance of the heterogeneous non-nitrided against nitrided contact pair of the high strength alloy steel, SCMV was investigated in the gross slip regime at ambient and elevated temperatures (120 and 150 °C). The tests were performed with displacement amplitudes of 25 and 100 μm at an applied normal load of 250 N using a cylinder-on-flat configuration. As the fretting contact temperature increases, the energy dissipation and total wear volume decreases for the same applied normal load irrespective of the displacement amplitude. The energy dissipation increases with increase in displacement amplitude for the same applied normal load. During fretting at ambient temperature, a substantial loss of material as wear debris was observed in the contact, whereas the overall loss of material from the contact significantly reduces with an increase in temperature. The variation in the tangential force coefficient and the total wear volume at elevated temperatures may be attributed to the sintering of oxide particles in the contact to form a protective debris bed. The worn surface morphology of the fretted specimen investigated using a scanning electron microscope shows the presence of wear debris in the wear track, oxide patches, delamination cracks, delamination cavities and discontinuities, scale like topography and plate-like wear debris. The abrasive action of the particles in the contact interface promoted wear at ambient temperature whereas at elevated temperatures, the compaction of the oxide particles reduced the wear.

Tribological behaviour of Cu based materials produced by mechanical milling/alloying and spark plasma sintering

Aim of the work is to investigate the tribological behaviour of Cu based materials produced by mechanical milling (MM), mechanical alloying (MA) and finally sintered by Spark Plasma Sintering (SPS). MM causes a significant strain hardening of Cu, while MA by 0.5wt%TiB2 adds a further dispersion hardening contribution. During dry sliding contact against high speed steel a close relation has been found between friction coefficient and contact temperature highlighting two regimes. The first one, occurring at an early stage of the process, is characterized by a high friction coefficient (~1), typical of the strong adhesion of Cu–Cu contact. The second one is characterized by a lower steady-state friction (~0.7) related to the change of wear mechanism from adhesive metallic into triboxidative. By increasing the load the friction coefficient decreases, the transition time from the adhesive to triboxidative friction regime decreases and the contact temperature increases. Under abrasive wear conditions the penetration depth of the indenter is progressively reduced by increasing hardness, highlighting the benefits of MM and, even more, of MA. The Cu+0.5wt.%TiB2 composite alloyed for 240min shows the best wear resistance under both wear conditions. The good wear resistance combined to high thermal conductivity represent very attractive properties for many applications.

Wear behavior of high chromium sintered steel under dynamic impact-sliding: Effect of temperature

The present research was carried out to study the combined aspects of impact and sliding failure mechanisms of high chromium sintered steel at different contact temperatures. The tribological behavior (mainly mass loss) was investigated both under reciprocating motion and with a dynamic impact-sliding loading. In case of reciprocating motion, the measured friction coefficient decreases as the contact temperature increases. The presence of oxides seems to be the key factor of this evolution. When for the combined impact with sliding, wear rate and damage mechanisms vary strongly with temperatures. Scanning electron microscopy observations coupled with EDX analysis were performed inside and outside of the wear track in order to understand the surface accommodation with temperatures.

The role of frictional power dissipation (as a function of frequency) and test temperature on contact temperature and the subsequent wear behaviour in a stainless steel contact in fretting

Temperature is known to affect the fretting wear behaviour of metals; generally, a critical temperature is observed, above which there are substantial reductions in wear rate, with these being associated with the development of protective oxide beds in the fretting contact. This work has examined the gross-sliding fretting behaviour of a stainless steel as a function of bulk temperature and fretting frequency (with changes in the fretting frequency altering the frictional power dissipated in the contact amongst other things). An analytical model has been developed which has suggested that at 200Hz, an increase in the contact temperature of more than 70°C can be expected, associated with the high frictional power dissipation at this frequency (compared to that dissipated at a fretting frequency of 20Hz). With the bulk temperature at either room temperature or 275°C, the increase in contact temperature does not result in a transition across the critical temperature (and thus fretting behaviour at these temperatures is relatively insensitive to fretting frequency). However, with a bulk temperature of 150°C, the increase in temperature associated with the increased frictional power dissipation at the higher frequency results in the critical temperature being exceeded, and in significant differences in fretting behaviour.

Surface imprinted core‐shell nanorod with ultrathin water‐compatible polymer brushes for specific recognition and adsorption of sulfamethazine in water medium

ABSTRACTA surface imprinted core‐shell nanorod with water‐compatible property was first prepared, using a two‐step “living” polymerization technique, with magnetic attapulgite (MATP) as core, and it was applicable in the enhanced selective removal of sulfamethazine residue from pure water environments. MATP was synthesized by an impregnation and pyrolysis method, and polymerable group was subsequently attached onto the surface. The imprinted polymer nanoshell (13 nm) with the “living” fragments was formed via a reverse atom transfer radical precipitation polymerization, avoiding the tedious graft of initiator and providing the easy‐accessible imprinted sites. Ultrathin hydrophilic polymer brushes (2.0 nm) were surface‐grafted to improve their water‐compatibility. The nanoadsorbent exhibited good thermal stability, magnetism, and hydrophilicity through characterization. The nanoadsorbent showed large adsorption capacity toward sulfamethazine from water, which increased with the increase of contact temperature. Langmuir isotherm fitted the equilibrium data better, and the kinetic data (within 45 min) were well‐analyzed by the pseudo‐second‐order kinetic model. Also, the specific adsorption property of the nanoadsorbent was greatly improved through the surface‐grafting, which exhibited excellent selectivity to sulfamethazine compared with other reference antibiotics. Efficient magnetic separation and good reuse of the nanoadsorbent provided the potential possibility for selective recognition and fast removal of antibiotic pollutions from water environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40854.

Comparison and validation of thermal contact resistance models at solid–liquid interface taking into account the wettability parameters

Two analytical models for thermal constriction resistance prediction at solid–liquid interface have been compared in this study. The wettability parameters (surface tensions and contact angle) have been taken into account in the models. These models have been used in conjunction with a thermal interstitial resistance to improve the prediction of the bulk thermal contact resistance (TCR) at the solid/liquid interface. A relatively good agreement between the predictions and the experimental data has been obtained and the capability of the models to predict the TCR is shown. Therefore, the models have been used to investigate the effect of the contact temperature on the constriction and interstitial resistance. The evolution of the equivalent entrapped air layer thickness with the temperature has been estimated. The results have shown that the TCR and the equivalent air layer thickness decrease when contact temperature increases.

The Effect of Electrical Switch Structure to the Contact Voltage-Drop and Temperature Variations

Due to the continuing renovation of the modern technology and the demand for the better consumer products, electricity has become one of the important factors that affect people’s life. The electrical switch is an important element of the electrical device and has been used intensively in industry and transportation devices, such as electrical bicycle, electrical motorcycle, winch etc. As the increasing usage of the electrical switch, the switch quality requirement increases as well. The important factors are contact point mass transferring loss, electric arc energy and contact point resistance and loss. Once the contact point fails to function, the whole electrical device ceases to function. However, regarding the electrical efficiency, in addition to the effect of the contact point materials, the structure is an important factor. In this study the structure of the electrical switch is studied and the effects of spring stiffness, guiding pin and ring to the switch lifespan are discussed. Taguchi method was used to design the experiment. L9(34) Orthogonal Array table was used to perform and discuss the effect of four factors to the desired characteristics; that is to minimize both the contact voltage-drop and the contact temperature increase. Four factors chosen are guiding pin material, compression spring, contact spring and buckle. Test results show that contact spring has the most effectiveness to the contact voltage-drop and temperature increase and is followed by compression spring. Guiding pin and ring type have minimum influence.

CAGEDYN: A Contribution to Roller Bearing Dynamic Calculations Part I: Basic Tribology Concepts

Basic relationships and physical concepts used for the development of a bearing dynamic tool (called CAGEDYN) are explained. Emphasis is put on some key physical concepts affecting the calculated cage impact forces: the appropriate roller-cage contact stiffness (derived herein using a novel equivalent stiffness), the tangential hydrodynamic rolling and pressure forces, the hydrodynamic effect on the roller normal load (for which a new relationship is given for calculating a load, even when there is no interference between the roller surface and counter race or cage bridge surface), and the appropriate traction force calculated using a nonlinear viscous model and contact temperature increases.

A study of contact temperature and tribological behaviour of magnetized sliding brass—steel couple in different gas environments

The wear tests of the sliding magnetized brass—steel couple are investigated on a pin—disc configuration under three various gas environments: in ambient air, under oxygen at 105 Pa, and in vacuum at 1.5 × 10−6 torr. The tribological behaviour of the couple strongly depends on the environment gas and a little effect of the magnetic field intensity. The results obtained show that the magnetic field decreases the wear rate and the friction coefficient in both air and oxygen atmosphere, respectively. However, in vacuum, the magnetic field has a negligible effect. The wear mode follows a transition from abrasive wear to adhesive wear after some cycles at the beginning of sliding contact. The temperature increment is very large in vacuum and it is almost stationary in both ambient air and oxygen. On the other hand, the application of magnetic field induces a little increase in contact temperature of average value about 5–8 °C in each gas environment. The temperature rise is correlated directly to interface properties, namely the hardness, the real contact area, and the roughness of the steel counterface.

Tribological Properties of a Hot-Pressed Ba-Doped S-Phase Sialon Ceramic

In this study, we report the tribological properties of hot-pressed S-sialon ceramics. In our experiments, the tribological properties have been studied against bearing grade steel, alumina, and sialon using a ball-on-flat fretting tribometer under dry unlubricated conditions. While the steady-state coefficient of friction (COF) remains the same (0.63) irrespective of the counterbody, the wear rate varies in the range of 10−5–10−6 mm3/N·m, depending on the counterbody. Tribochemical wear as well as adhesion and abrasion are found to be the underlying mechanisms for material removal. The possible influence of Hertzian contact stress and the contact temperature increase on the possible damage mechanisms/tribological interaction has been analyzed.