Influence Of Contact Pressure Research Articles

TRIBOLOGICAL PROPERTIES OF THERMOPLASTIC ELASTOMER USED IN 3D PRINTING TECHNOLOGY

The use of thermoplastic elastomers (TPE) in 3D printing technology enables the use of this technology to produce prototype seals with an unusual shape or design solution. Tribological tests were carried out on a pin-on-disc test stand. The influence of contact pressure and sliding velocity on the friction coefficient of the TPE-steel friction pair under mixed lubrication conditions was analyzed. Based on the obtained tribological test results, it was found that the coefficient of friction of the thermoplastic TPE elastomer on steel in the presence of hydraulic oil (mixed lubrication) at a sliding velocity below 1 m/s does not exceed μ = 0.25. The obtained friction coefficient values are comparable to the results for other elastomeric materials used for technical seals. It was found that the influence of contact pressure on the value of the friction coefficient in the tested friction pairs is varied and depends, for example, on the sliding velocity. It was recommended to carry out research on the assessment of durability (wear intensity) and structure (porosity) of the material in elements manufactured using 3D printing to obtain full knowledge of the possibility of using these materials in the area of technical aircraft seals.

Influence of Contact Pressure and Flow Rate on the Performance of Anion Exchange Membrane Electrolysis

Hydrogen production by electrolysis is a key aspect of a climate-neutral economy. However, there are still weak points in the established low-temperature technologies such as high material costs in case of PEM electrolysis and poor dynamic operations in case of alkaline electrolysis. The emerging electrolysis technology, the anion exchange membrane (AEM) electrolysis, addresses these weaknesses and combines their advantages. Due to the solid polymer electrolyte and the alkaline environment, AEM water electrolysis is featured by a compact zero-gap cell design and inexpensive materials like non-noble metal catalysts. Hence, it offers the potential to a cost-effective and efficient electrolysis technology.To enable the breakthrough of this technology, we contribute by conducting performance evaluations of membrane electrode assemblies (MEAs) under application-oriented conditions. One focus is on non-noble metal MEAs with an active area of 25 cm2 operated with pure water and low concentrated potassium hydroxide solution.To ensure comparability of different MEAs, it is crucial to compare them at their performance optimum. This is achieved by determining the optimal set-up parameters like contact pressure and operation parameters like flow rate for each MEA type. Otherwise, deviation from the optimal operating point by up to 50 % may occur.The influence of the parameters contact pressure and flow rate on the MEA performance is discussed in this presentation. To investigate their impact, we analysed the MEAs in an electrolyser test station using polarisation curves, electrochemical impedance spectroscopy and load tests at constant current and constant voltage.Some of the results presented are obtained within the project “REVAL – reversible anion exchange membrane electrolysis” (funding code 03ZZ0732D) funded by the German Federal Ministry of Education and Research (BMBF).

Influence of contact pressure and velocity on the brake behaviour and particulate matter emissions

In this work, the braking performance and the emission behavior of airborne wear particles of a low-metallic and NAO friction material have been investigated using a reduced-scale dynamometer, adapted for emission measurements. A specific braking cycle has been developed to assess the influence of velocity and pressure on the tribological performance of friction materials sliding against a cast iron disc. The adopted brake cycle consists of a factorial design of blocks of repeated brake stops, where each block was intercalated with a so-called reference block, meant to recover the initial characteristics of the sliding surfaces. A progressive stabilization of the tribological parameters was observed during the blocks featuring a higher initial velocity. The relevant values of these parameters would depend on the extension of the secondary plateaus in the friction layer. At high pressure and velocity, the low-metallic friction material exhibited a higher wear rate and lower friction coefficient than the NAO material, although the NAO material displayed a weaker recovery behavior regarding the friction coefficient. The emissions of the NAO material were found to be lower and more stable than the low-metallic material. In general, the emissions were found to be correlated with the initial brake velocity mainly, through a cubic relationship, whereas the emissions did not show a clear dependence on contact pressure.

Influence of Contact Pressure on the Specific Electrical Contact Resistance of Copper

The specific electrical contact resistance (SECR) [<inline-formula> <tex-math notation="LaTeX">$\Omega \text{m}^{2}$ </tex-math></inline-formula>] of Cu-ETP (CW004A) contacts is characterized in dependence of contact pressure up to high pressures close to the tensile strength of the base material. Two different material states are considered, R200 (soft) and R300. Static four-wire measurements are carried out on a special experimental setup, which favors homogeneous contact states during mechanical loading. A finite-element simulation is utilized for interpretation and evaluation of the measurements, including the deformation of the samples during the test. The results show that the SECR of the harder material state R300 is higher than that of the softer material R200. The developed data show a decrease of SECR with increasing contact pressure. For contact pressures up to 0.5 of the tensile strength <inline-formula> <tex-math notation="LaTeX">$\sigma _{t}$ </tex-math></inline-formula> of the base material, the SECR decreases according to a power law. For contact pressures above <inline-formula> <tex-math notation="LaTeX">$0.6~\sigma _{t}$ </tex-math></inline-formula>, the decrease shifts toward a linear behavior. In addition, the measurements show that the SECR vanishes at contact pressures in region of the tensile strength of the base material.

Investigations on the interfacial heat transfer coefficient during hot stamping of ultra-high strength steel with Al-Si coating

The ultimate mechanical properties and microstructures of hot-stamped components are highly related with the interfacial heat transfer coefficient (IHTC) between blank and tool. In this paper, an advanced temperature acquisition system was established to measure the temperature of boron steel Usibor 1500P with Al-Si coating during the hot stamping process, and an inverse algorithm was developed to calculate the IHTC. Moreover, the influences of contact pressure and tool roughness on IHTC were discussed. The results show that the IHTC only increases with pressure when it is less than 1MPa, while remains almost unchanged under higher pressure. Meanwhile, little effects on the IHTC are generated by tool surface roughness. Those phenomena are quite different from the commonly studied uncoated blanks. Further exploration demonstrates that the effect of high pressure and tool surface roughness on IHTC is not significant due to the oxidation resistance and the spalling of the Al-Si coating respectively.

Influence of contact pressure on the thermal contact conductance of layered metallic sheets

For the optimisation of the annealing process of aluminium coils, simulation of the process is often performed. To simulate the process with higher accuracy, reliable input parameters are required, and thermal conductivity (thermal contact conductance) is one of them. In the present study, a method to measure the thermal conductivity and thermal contact conductance of metallic sheets were developed based on the steady-state comparative longitudinal heat flow. The apparatus was built with a compression test machine, and thus it allows to control the pressure to the sample and carry out the measurements at different contact pressure. An equipped heater allows to heat the sample to 573 K. To evaluate the thermal conductance at the interface, a thermal resistance network model was applied. The measurements were carried out with an aluminium alloy (AA3003 sheets). In addition to the thermal contact conductance measurements, the surface roughness of the sheets was also investigated. The semi-empirical equation for the relationship between thermal contact conductance and contact pressure was obtained based on the measurement results.

A Novel Reciprocating Tribometer for Friction and Wear Measurements with High Contact Pressure and Large Area Contact Configurations

There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines.

Influence of Stress Ratio and Contact Pressure on Fretting Fatigue Behavior of Modified 9Cr-1Mo Steel

Influence of contact pressure and maximum cyclic stress (σmax) on the fretting fatigue behavior of modified 9Cr-1Mo steel has been studied using contact pads made of the same steel. The contact pressure was varied from 50 to 200 MPa using σmax of 400 and 500 MPa at a stress ratio (R) of 0.1. The fatigue life was observed to decrease in the presence of fretting action. For a given σmax the fretting fatigue life of the steel decreased with an increase in contact pressure up to 100 MPa beyond which saturation was observed. The ratio of slip to stick area increased with the contact pressure. This is in agreement with the increased depth of the fretting-induced debris and roughness.

Effective usage of 2D MXene nanosheets as solid lubricant – Influence of contact pressure and relative humidity

Newly emerging Ti3C2Tx–nanosheets (MXenes) have attracted considerable attention in energy storage, catalysis and, more recently, tribology. MXene nanosheets are characterized by a weakly-bonded multi-layered structure with self-lubricating ability, making them a suitable candidate for solid lubrication. This contribution aims at addressing for the first time their application in higher loaded steel/steel dry sliding contacts by investigating the influence of contact pressure and relative humidity on friction and wear performance. Compared to the uncoated reference, a 2.3-fold friction reduction and a 2.7-fold reduction of the wear volume were verified for MXene-coated specimens for moderate contact pressures and low relative humidity. This was due to the in-situ formation of a compacted tribo-film consisting of densified Ti3C2Tx–nanosheets. In contrast, too high pressures induced a partial rupture of the wear-protecting tribo-layer, thus reducing its beneficial effects. Additionally, no beneficial effects regarding friction and/or wear were found at higher relative humidities, which was correlated with the expansion of the basal spacings. Therefore, this study summarizes favorable operating conditions for MXene nanosheets when used as solid lubricant to improve friction and/or wear thus making them excellent candidates for advanced, next-generation solid lubricants.

Influence of Contact Pressure on the Thermal Contact Conductance of Layered AA3003 Aluminium

For the optimization of the annealing process of aluminium coils, simulation of the process is often performed. To simulate the process with higher accuracy, reliable input parameters are required and the thermal conductivity (thermal contact conductance) is one of them. In the present study, the thermal conductivity and thermal contact conductance of AA3003 alloy sheets were measured by a steady state comparative longitudinal heat flow method at different contact pressure. To evaluate the thermal conductance at the interface, thermal resistance network model' was applied. In addition, the surface roughness of the sheets was also investigated. Based on the measurement results, the semi-empirical equation for the relationship between thermal contact conductance and contact pressure was obtained

Temperature Rise in Sliding Solids: Influence of Contact Pressure and Temperature on Thermal Conduction

Accurate estimation of temperature rise for sliding solids is still challenging. Part of the challenge is accounting for the actual thermal behavior of the solids while sliding (i.e., the nonlinear effects taking place because of sliding conditions and their evolutionary path). Conventionally, only temperature-induced influence on transport properties has been considered. However, thermal properties of the solids also depend on contact stress, the rate of strain, and the rate of heat generation. The contact stress within the mechanically affected zone, even considering the hardness of the softest of the sliding pair, can reach several thousand times the value of atmospheric pressure. Under such a condition, thermal conductivity of many materials show a different behavior than that manifested under standard conditions. This work considers such an influence and its effect on the evolution of temperature. The results show that conventional estimates can considerably under-estimate the actual temperature rise. It is also shown that initial loading, may result in the contacting materials behaving as a layered structure, with each layer having a different capacity of thermal load dissipation. Depending on the distribution of that capacity, dissipation of friction heat may be constrained which may accelerate wear.

Calibration of thermal contact conductance for precision forming

In cold precision forming the heat caused by deformation has a significant influence on the temperature distribution, which might affect the geometry accuracy of the part and tooling life. Well definition of the thermal contact conductance (TCC) between the contact pairs could be helpful to characterize the heat influences. In the present research, an experimental setup was developed to measure the TCC between the tool and specimen. The influence of contact pressure, temperature and surface roughness have been considered. On this basis, a novel model for the prediction of TCC was proposed, and expanded to the large plastic deformation, by involving the effect of contact stress and contact temperature. Correlated sheet metal extrusion experiments and corresponding simulations are applied to verify the model. It is found that the dynamic update of the TCC parameters can improve the prediction accuracy of temperature distribution.

Covalently grafting of self-assembled functionalized graphene oxide multilayer films on Si substrate for solid film lubrication

Graphene-based polymer brush containing multilayer film has been fabricated on silicon wafer (SW) via self-assembled multistep approach based on covalent insertion of 3-aminopropyltrimethoxysilane as a chemical linker on graphene oxide (GO) followed by covalently anchored with polyethyleneimine (PEI). A multilayer polymer brush film was then constructed by electrostatic layer-by-layer (LBL) self-assembly technique between positively charged outer layer PEI grafted GO and anionic polyelectrolyte, poly (sodium 4-styrenesulfonate) (PSS). The LBL formation and microstructure of as prepared films were characterized by Raman spectroscopy, atomic force microscopy, field emission scanning electron microscopy and elemental electron dispersive spectroscopy analysis. The changes in wettability of films during grafting of chemical components on silicon substrate were determined by water contact angle measurement. Microtribological performances of the films were investigated using ball-on-disc contact geometry in ambient condition. The influence of contact pressure and sliding velocity were also studied under reciprocating tribo contact to evaluate the load bearing ability of the films. The multilayer films exhibited low (~0.15–0.17) and steady coefficient of friction (COF) at 1 N load (contact pressure ~ 0.54 GPa) compared to bare SW (~0.6) with remarkable wear-resistivity. With increasing contact pressure (4 N, ~0.86 GPa), the multilayer films provided minimal COF and low wear depth with improved sliding durability among the films. The improved friction and wear resistivity of the multi-layer films are attributed to densely packed polymeric graphene lamella contributing low-resistance to shear during sliding and the presence of sulphur on PSS might assists in superior adhesion of delaminated film to steel counterface ball during shearing, which was investigated by microscopic and Raman spectral analysis.

Simulations on Current Distribution in Railgun Under Imperfect Contact Conditions

In the process of electromagnetic launch, the initial contact pressure distribution of armature/rail (A/R) contacts interface is uneven, and the actual contact area is obviously different from the perfect contact. The uneven contact pressure leads to uneven contact resistance distribution, affecting the magnetic diffusion process and changing the A/R interface current distribution. Therefore, it is necessary to consider the influence of contact pressure on the current distribution. In the past, the simulation studies usually considered the contact between rails and armature as the perfect contact, and the result obtained may be different from the actual situation. This paper uses the finite element software COMSOL to perform coupling simulation analysis on the electromagnetic module and solid mechanics module in the initial stage of electromagnetic launch. At the initial stage of electromagnetic launch, the contact pressure is mainly provided by the prepressure generated by the interference fit. In this paper, the influence of contact pressure on current distribution and the influence of magnitude of interference on contact position, contact pressure, and current distribution are analyzed.

Effect of contact pressure on torsional fretting fatigue damage evolution of a 7075 aluminum alloy

Abstract Contact pressure is a crucial factor which can affect fretting fatigue (FF) life significantly. In this research, the influence of contact pressure on torsional fretting fatigue (TFF) damage of a 7075 aluminum alloy is investigated. According to the experiment results, below 72.5 N⋅m torque as the contact pressure increases, the TFF life decreases firstly and then it reaches to the lowest point at 300 N, while afterward the TFF life increases. The P-N curve shows a C shape. The damage analysis results show that with increasing the contact pressure, the damage becomes severer. The oxidative products are mainly Al2O3 and Al(OH)3, and the loading side is found to be more oxidized than the center position and fixed side.

Bolt preload measurement based on the acoustoelastic effect using smart piezoelectric bolt

Precise measurement of bolt preload force is particularly important in the assembly process of aviation equipment, which is directly related to the normal working performance and indicators of the equipment. According to the acoustoelastic effect, a model considering theoretical error and measurement error is proposed. The relationship between the change of time-of-flight (CTOF) and the bolt preload is established by the model. With the increase of the preload, the CTOF approximately increases linearly. Therefore, a smart piezoelectric bolt was developed. Piezoceramic transducer is embedded in the bolt head at pre-determined spatial locations. Experimental results show that the relative error of the smart bolt is about 1%. In addition, the influence of contact pressure and contact phase is discussed. The results show that the characteristic of smart piezoelectric bolt eliminates the effect of the couplant and makes the measurement more precise than the measurement performed using the ultrasonic probe. This method provides a promising way to measure the bolt preload.

Identification of friction coefficients when drilling titanium TiAl6V4

This paper investigates the friction behaviour around a carbide drill when drilling titanium with an oil mist lubrication. It questions whether friction is constant along the cutting edge and along the margins. The application of specially designed tribometer reveals that tribological conditions on margins are fully different that the ones on rake and flank faces. Friction coefficients are quantified for both tribological conditions (open and closed tribosystem). The influence of contact pressure and of an AlCrN coating are also investigated. It is shown that friction varies a lot between both tribosystems, and that a closed tribosystem (i.e. margins) leads to much higher friction, adhesion and wear rate than an open tribosystem (i.e. flank faces).

On Stress-Induced Tribochemical Reaction Rates

A number of recent experiments have demonstrated that normal and shear stresses are able to accelerate the rates of chemical reactions of adsorbates on surfaces, yielding an approximately exponential increase in reaction rate with force. It seems that such mechanochemical reactions play a central role in tribochemistry and the consequent formation of anti-wear or friction-reducing films from lubricant additives. It is thus appropriate to summarize the theories that can be used to analyse such tribochemical data. The models have a strong parallel with those used to analyse sliding friction, the Prandtl/Tomlinson model. It is found that the force-dependent activation barrier for chemical reactions varies as $$E_{\text{act}} (F) = E_{\text{act}} + AF + BF^{2}$$ . The linear variation in activation barrier with force, the so-called Bell equation, and the quadratic dependence, the so-called Hammond effect, are analysed using model reaction energy profiles, which reveal a dependence of the parameters A and B on the shape of the energy profile. The influence of contact pressure and sliding velocity is also discussed. The above models assume that the normal and shear stresses are coplanar with the thermal reaction coordinate for the tribochemical processes, and the effects of this not being the case are also discussed. Finally, the existing results of tribochemical reactions of oxygen-functionalized graphene and zinc dialkyl dithiophosphates are also analysed using these models.

Calculation of the Thermal State of the Graphite Moderator of the RBMK Reactor

This work is devoted to study the temperature field of the graphite stack of the RBMK reactor. In work was analyzed the influence of contact pressure between the components of the masonry on the temperature of the graphite moderator.

Influence of contact pressure, cross-shear and counterface material on the wear of PEEK and CFR-PEEK for orthopaedic applications

Total joint replacement is a successful surgical intervention for the treatment of the degeneration of many joints, particularly the hip and knee. As the demand for joint replacement grows, and the life expectancy of the population increases, the performance requirements of these implants also changes. New materials, to improve longevity and enhance performance have been explored including PEEK and CFR-PEEK.This study investigated whether CFR-PEEK and PEEK were appropriate materials for total joint replacement by examining wear performance in simple configuration studies articulating against cobalt chrome under a range of cross-shear and contact pressure conditions. Simple geometry pin on plate studies were conducted for one million cycles for each test condition, with the contact pressure and cross-shear conditions representing a range in which the material may need to operate in-vivo.The wear factor for PEEK was significantly higher than CFR-PEEK and conventional polyethylene under all test conditions. Both PEEK and CFR-PEEK wear were influenced by contact pressure, with the highest wear factors for both materials measured at the highest pressure conditions. PEEK appeared to have a cross-shear dependent wear response, but this was not observed for the CFR-PEEK material.This study has further characterised the wear performance of two materials that are gaining interest for total joint replacement. The wear performance of the PEEK material showed poorer wear performance compared to polyethylene when articulating with a metal counterface, but the performance of the CFR-PEEK material suggested it may provide a suitable alternative to polyethylene in some applications. The wear performance of CFR-PEEK was poorer than polyethylene when it was used as the plate, when there was translation of the contact zone over the surface of the CFR-PEEK plate. This has implications for applications in low conforming contacts, such as lower conformity knee replacement.