Contact Pressure Conditions Research Articles

A Novel Contact Stiffness Model for Grinding Joint Surface Based on the Generalized Ubiquitiformal Sierpinski Carpet Theory

A novel analytical model based on the generalized ubiquitiformal Sierpinski carpet is proposed which can more accurately obtain the normal contact stiffness of the grinding joint surface. Firstly, the profile and the distribution of asperities on the grinding surface are characterized. Then, based on the generalized ubiquitiformal Sierpinski carpet, the contact characterization of the grinding joint surface is realized. Secondly, a contact mechanics analysis of the asperities on the grinding surface is carried out. The analytical expressions for contact stiffness in various deformation stages are derived, culminating in the establishment of a comprehensive analytical model for the grinding joint surface. Subsequently, a comparative analysis is conducted between the outcomes of the presented model, the KE model, and experimental data. The findings reveal that, under identical contact pressure conditions, the results obtained from the presented model exhibit a closer alignment with experimental observations compared to the KE model. With an increase in contact pressure, the relative error of the presented model shows a trend of first increasing and then decreasing, while the KE model has a trend of increasing. For the relative error values of the four surfaces under different contact pressures, the maximum relative error of the presented model is 5.44%, while the KE model is 22.99%. The presented model can lay a solid theoretical foundation for the optimization design of high-precision machine tools and provide a scientific theoretical basis for the performance analysis of machine tool systems.

Experimental Study of Thermal Contacts for the Enhancement of Interfacial Heat Transfer

Abstract The thermal management in high-performance electronic devices demands the enhanced rate of heat dissipation for controlling operational temperatures and achieving optimal functioning. There are many interfaces in the heat dissipation circuit where thermal interface materials are applied to enhance heat transfer rate. An experimental investigation is presented on metallic contacts to study the interfacial heat transfer with and without a thermal interface material. Thermal contact conductance is known to be an important parameter estimated for the analysis of interfacial heat transfer across the thermal contacts. Therefore, the thermal contact conductance has been evaluated to identify an effective thermal interface material suitable for the present range of contact pressure and heat flux conditions. Silicone grease is a widely used thermal interface material in electronic industry. Thus, commercially available Silicone grease is evaluated in different boundary line thicknesses for a range of contact pressure and mean interface temperatures. Further, a novel composite thermal paste has been prepared by mixing cupric oxide nanopowder and Silicone grease in three different mass concentrations. Eventually, the results for the new thermal paste showed improved thermal contact conductance and lower interfacial temperature drops as compared to Silicone grease for similar test conditions with few limitations.

Wear and Friction Behaviour of Additive Manufactured PEEK under Non-conformal Contact

Tribological properties of laser sintered polyether-ether-ketone (EOS PEEK HP3) were investigated using a rolling-sliding test rig. This investigation aimed to study the wear and friction failure mechanism of EOS PEEK HP3. The main objectives included to conduct wear and friction tests under non-conformal contact, to monitor surface temperature, to carry out surface characterization with microscopy. With this rolling-sliding test rig, tests were carried out on an EOS PEEK HP3 specimen running against a steel disc unlubricated, with various slip-ratios under a contact pressure of 56 MPa, 48 MPa and 39 MPa respectively. Both wear and friction were measured. The results have shown that both friction and wear were increased with an increase of either slip-ratios or the contact pressures, exacerbated by high surface temperatures. It has also been observed that both friction and wear failures were associated with the degradation of the non-conformal contact surfaces due to crystallinity changes that correlated well with working conditions. Using microscopy it was found that such failures as pitting, fatigue and surface cracking were affected by the surfaces in contact, including the degree of melting of the surface. Based on the observation on the contact surfaces, the failure mechanisms of EOS PEEK HP3 include surface melting and contact fatigue failures with the high slip-ratio and the high contact pressure conditions. The findings of this investigation have the potential to help to design & develop additive manufacturing PEEK products. Typically, these results can be used in a design process for a more effective polymeric gear system.

The influence of cross shear and contact pressure on the wear of UHMWPE-on-PEEK-OPTIMA™ for use in total knee replacement

PEEK-OPTIMA™ polymer is being considered as an alternative material to cobalt chrome in the femoral component of total knee arthroplasty to give a metal-free knee replacement system. Simple geometry pin-on-plate wear simulation can be used to systematically investigate and understand the wear of materials under many different conditions. The aim of this study was to investigate the wear of UHMWPE-on-PEEK-OPTIMA™ under a range of contact pressure (2.1–80 MPa) and cross-shear ratio (0–0.18) conditions.With increasing contact pressure, there was a trend of decreasing UHMWPE wear factor with a significant difference (p<0.001) in the wear factor of UHMWPE under the different contact pressure conditions of interest. Under uniaxial motion (cross-shear ratio = 0), the wear of UHMWPE was low, introducing multi-axial motion increased the wear of the UHMWPE. There was a significant difference (p<0.01) in the wear factor at different cross-shear ratios however, post hoc analysis showed only the study carried out under unidirectional motion to be significantly different from the other conditions.With varying contact pressure and cross-shear ratio, the wear of UHMWPE against PEEK-OPTIMA™ polymer showed similar trends to previous studies of UHMWPE-on-cobalt chrome.

Influence of TiN Coating on the Drawing Force and Friction Coefficient in the Deep Drawing Process of AlMg4.5Mn0.7 Thin Sheets.

The influence of various process parameters on the deep drawing process is a current research topic in sheet metal forming technology. Starting from the application of the previously constructed original testing device, an original tribological model was developed based on the process of sheet metal strip sliding between flat contact surfaces under variable pressures. A complex experiment was executed using an Al alloy sheet, tool contact surfaces of different roughness, two types of lubricants and variable contact pressures. The procedure included analytically pre-defined contact pressure functions based on which, for each of the mentioned conditions, the dependencies of the drawing forces and friction coefficients were obtained. The pressure in function P1 constantly decreased from a high initial value until the minimum, while in function P3 the pressure increased until the minimum value at the halfway point of the stroke, after which it increased up to the initial value. On the other hand, the pressure in function P2 constantly increased from the initial minimum value until the maximum value, while in function P4 the pressure increased until reaching the maximum value at the halfway point of the stroke, after which it decreased to the minimum value. This enabled the determination of the influence of tribological factors on the process parameters of intensity of traction (deformation force) and coefficient of friction. The pressure functions starting with decreasing trends produced higher values for the traction forces and the friction coefficient. In addition, it was established that the roughness of the contact surfaces of the tool, especially those with titanium nitride coating, has a significant influence on the process parameters. For surfaces of lower roughness (polished), a tendency of the Al thin sheet to form a glued-on layer was noticed. This was especially prominent for lubrication with MoS2-based grease under conditions of high contact pressure (functions P1 and P4 at the beginning of the contact).

Influences of probe shape and surface roughness on tack properties measured by the probe tack test and characterization of crosslinked polyacrylic pressure‐sensitive adhesives

AbstractFor a probe tack test for a pressure‐sensitive adhesive (PSA) under the conditions of light contact pressure and short contact time, probes with shapes and surface roughnesses suitable to achieve better wettability were investigated. A smooth, polished probe that became slightly convex at its center was found to be superior to flat‐ended. High surface roughness decreased tack. Debonding observations showed that fibrillation started from the probe edge and extended to the center. The fibril grew, without peeling, until the peak of the force–displacement curve was reached. After the peak, the fibril growth and peeling advanced simultaneously. The fibrillation was important to tack development. The test conditions necessary to observe the deformation behavior of PSA tape with sufficient interfacial adhesion were investigated. The system was preheated at 60°C for 1 h after the probe and PSA tape contacted each other, and was then cooled. The PSA performance of crosslinked random copolymers poly(n‐butyl acrylate‐acrylic acid) (A) and poly(2‐ethylhexyl acrylate‐acrylic acid) (B) were compared. A shoulder formed by fibrillation after the peak in the force–displacement curve was observed only for B. Copolymer B exhibited better interfacial adhesion and deformability. The preheating method was found to be useful for characterizing PSAs.

Heterogeneity in tribologically transformed structure (TTS) of Ti–6Al–4V under fretting

Fretting wear is a surface degradation process caused by oscillatory motion and contact slipping. During gross slip, high local stresses and plastic deformation in the surface and subsurface can lead to the creation of a nanosized grained structure called Tribologically Transformed Structure (TTS). The current paper studies the formation of TTS in an alpha-beta Ti–6Al–4V alloy under fretting loading while changing the contact pressure and the number of fretting cycles.Cross-sections of wear scars are observed after polishing and chemical etching. Above a threshold pressure of 300 MPa, TTS appears early in the contact (before 1000 cycles) along with two other structures: a Third Body Layer (TBL) made of compacted debris and a General Deformed Layer (GDL) which is the plastic zone under the TTS. TTS first appears as islands and merges in the middle of the contact after enough cycles. Below 200 MPa, only TBL and GDL are formed. At 200 MPa, only small, localized TTS is found. All structures have the same chemical compositions as the initial bulk material except for the nitrided TBL. TTS has a very high hardness compared to the bulk. TTS was carefully extracted using a Focused Ion Beam (FIB) and its microstructure was observed with a Transmission Electron Microscope (TEM). It shows extreme grain refinement and is composed of two alternated zones. The first zone I is composed of α grains with a size of 20–50 nm with crystallographic texture. Zone II comprises nanosized equiaxed grains whose sizes range from 5 to 20 nm without texture. The results made it possible to establish a scenario of the appearance of the TTS according to the conditions of contact pressure and number of fretting cycles.

H2 Production by Methane Oxy-Reforming: Effect of Catalyst Pretreatment on the Properties and Activity of Rh-Ce0.5Zr0.5O2 Synthetized by Microemulsion

Green hydrogen introduction in hard-to-abate processes is held back by the cost of substituting steam reforming plants with electrolyzers. However, green hydrogen can be integrated in properly modified reforming processes. The process proposed here involves the substitution of steam reforming with oxy-reforming, which is the coupling of the former with catalytic partial oxidation (CPO), exploiting the pure oxygen coproduced during electrolysis to feed CPO, which allows for better heat exchange thanks to its exothermic nature. With the aim of developing tailored catalysts for the oxy-reforming process, Ce0.5Zr0.5O2 was synthetized by microemulsion and impregnated with Rh. The Ce-based supports were calcined at different temperatures (750 and 900 °C) and the catalysts were reduced at 750 °C or 500 °C. Tuning the calcination temperature allowed for an increase in the support surface area, resulting in well-dispersed Rh species that provided a high reducibility for both the metal active phase and the Ce-based support. This allowed for an increase in methane conversion under different conditions of contact time and pressure and the outperformance of the other catalysts. The higher activity was related to well-dispersed Rh species interacting with the support that provided a high concentration of surface OH* on the Ce-based support and increased methane dissociation. This anticipated the occurrence and the extent of steam reforming over the catalytic bed, producing a smoother thermal profile.

Experimental and numerical investigation on multiscale hysteresis friction on artificial printed surfaces

In order to investigate hysteresis friction separately from other friction contributions (mainly adhesive friction), linear friction tests are performed with cut out tread specimens from passenger car tires on 3D-printed sinusoidal surfaces under dry and wet conditions. In this work, a multiscale approach based on the finite element method (FEM) is used to reproduce the hysteresis friction features obtained in the laboratory. On each scale, finite element simulations at block level are evaluated at different contact pressure, sliding velocity and temperature conditions, which are homogenized with respect to time, to build up a friction characterization for the next coarser scale. The height difference correlation function is applied to consider microscopic asperities, which originate from the printing process. Using the Williams-Landel-Ferry equation, the thermal influence on the viscoelastic rubber material is taken into account. By comparing the output of the friction tests against the results of the multiscale simulations, an analysis of contact temperature as well as friction contribution of each length scale is enabled.

Characterization of the Transient Contact Heat Transfer between C276 Superalloy and 5CrMnMo

The thermal contact conductance (TCC) between billet and tool is a key parameter to determine the contact heat transfer in the thermal processing of alloys and metals. In this work, a self-developed transient contact heat transfer detective equipment was applied to determine the TCC between C276 superalloy and die steel. The temperature variations in specified regions of specimens during transient heat transfer process were measured and the temperatures at contacted interface were programed based on the reverse heat transfer algorithm. Then the values of TCC between C276 superalloy and die steel were calculated. The TCC shows high dependency on the interface temperature, contact pressure, lubricant, and surface oxidation conditions. The increasing interface temperature difference and contact pressure enhanced the thermal contact conductance, while the surface oxidation alleviated the heat transfer capability. In addition, the addition of lubricant was also found to enhance the thermal contact conductance. The determined values are supposed to be of significant importance for processing optimization and numerical simulation.

Measurements of viscosity profile in elastohydrodynamic lubrication film using fluorescence method under various contact pressure conditions

This paper describes rheological properties of hydrodynamic and elastohydrodynamic lubrication (EHL) film under various contact pressure conditions using the fluorescence measurement method. In this measurement method, the viscosity and the information about the state of the lubricant (liquid or solid) can be obtained via the analysis of fluorescence spectrum of a pyrene excimer emission. Previous research revealed that the intensity of excimer emission decreased with increasing of viscosity. In addition, the intensity ratio between the excimer peak and lubricant 5P4E fluorescence peak was introduced for the analysis, and the ratio decreased with increasing viscosity of lubricant. In this study, the viscosity profile obtained from the relationship between the intensity ratio and viscosity showed that the state of lubricant in the lubrication film corresponded almost exactly to the lubrication regime proposed in previous researches. It is concluded that the viscosity measurement technique proposed in this study is useful method for practical uses in hydrodynamic and elastohydrodynamic conditions, while in the high viscosity range, the measured viscosity varies widely due to the variation of intensity ratio.

An experimental study of the transition in the wear regime of brake friction materials

AbstractBrake friction materials (BFMs) are designed to have low wear rate under different conditions of contact pressure, temperature, and sliding velocity. The conditions to ensure a low wear rate (i.e., a moderate wear regime) between the disc and the BFM are not well established. The present article aims to enhance the comprehension about the wear regimes for BFMs. For this purpose, a commercial BFM was slid against a gray cast iron rotor (disc). Tests were performed under different sliding velocities and with both increasing and decreasing steps of pressure levels. Tribofilm formed on the disc's surface and BFM's wear were monitored during the tests. It was possible to conclude that the previous condition of the surface of the disc, with respect to the presence or absence of tribofilm, affects the required conditions for the transition in the wear regime. The removal of tribofilm on the surface of the disc was affected by high contact pressures and high sliding velocities. Those conditions led to a severe wear regime with a destruction of contact plateaus and an increase in friction and BFM's wear.

Investigation of heat transfer between 22MnB5 and KDAHP1 hot work tool steel

The IHTC (Interfacial-Heat-Transfer-Coefficient) between 22MnB5 and KDAHP1 hot work tool steel during the hot stamping process is an important thermal parameter to reflect the heat transfer efficiency. The instantaneous heat transfer law for 22MnB5 blank is based on the cylindrical-die model, and the experiment is contained different contact pressure and gap conditions. The average IHTC value is calculated by the heat balance method (HBM) and finite element optimisation method (FEOM). There is a power function relationship between the average IHTC and both the contact pressure and the one-side gap. From the results of the one-side and bilateral gap condition, 0.2 mm can be considered as the ‘critical gap’ where the heat exchange between the blank and dies starts or ends.

Ambient and Nitrogen Environment Friction Data for Various Materials &amp; Surface Treatments for Space Applications

A multivariate tribological evaluation of candidate materials, surface treatments and dry film lubricants is needed for design of moving mechanical components that function reliably in extreme conditions, including for long-duration space missions. In this study, linear reciprocating or unidirectional sliding friction data was collected using ball-on-flat tests. The balls were hardened 440C stainless steel (either uncoated or sputtered with MoS2) and flat surfaces were 440C stainless steel, Nitronic 60 stainless steel or Ti6Al4V titanium alloy with various surface treatments and/or dry film lubricants. Surface treatments included anodizing, nitriding and electrical discharge machining. The dry film lubricants included Microseal 200-1, sputtered MoS2 and a nano-composite coating i-Kote. The data contains applied normal load, measured friction force, calculated coefficient of friction, ball position, ambient temperature and relative humidity during testing. Tests were performed at different peak Hertzian contact pressure conditions ranging from 300 to 2000 MPa. Data is also available for flat surfaces that were vacuum baked at 150 °C after surface treatment and dry film coating as well as samples tested in inert gas (nitrogen) environment. This data can be used both to fundamentally understand the tribological properties of different material systems as well as to enable design of components for specific applications, conditions and duty cycles.Graphical Abstract

Experimental Analysis of Frictional Characteristics of the Interface between Gantry Crane Wheels and Rails under Submerged Rail Conditions

The purpose of this paper is to clarify the influence of rail submergence that occurs at the quay on the frictional characteristics of the interface between gantry crane wheels and rails. The characteristics serve as a basis for the dynamic simulation analysis of cranes that run away due to wind and crane designs. An experimental analysis system developed uniquely by the authors was used to carry out this research. Wheel was pressed to submerged rail, then the rail was slid. The friction force generated between the wheel and the rail was measured. This experimental analysis was conducted for contact pressure conditions that the ratios of the maximum Hertzian contact pressure to the yield stress of the material of the rail are approximately 1.76, 2.12 and 2.39. Under these various contact pressures, the ratio of the maximum static friction force under submergence conditions to the same friction force under dry conditions increased slightly. In contrast, when contact pressure conditions were nearly identical, the dynamic friction force under submergence and dry conditions was about same. Finally, the ratio of the dynamic friction coefficient to the static friction coefficient as a reference for designing cranes was shown and discussed.

Исследование эксплуатационных свойств стальных пар трения с антифрикционными покрытиями из медных сплавов, полученных методом электроискрового легирования

Improving the reliability, durability and safety of operation of heavily loaded friction units is an urgent problem in physics, chemistry and surface mechanics. The tribotechnical characteristics of coatings made of bronzes BrAZhMts10-3-1.5 and BrMtsF3-6, applied by electrospark alloying on bushings made of structural steel 30KhGSN2A for operation under conditions of high contact pressure under friction without lubrication, have been investigated. Modes of coating deposition from the standpoint of tribology (the value of the electric discharge current in a pulse, the value of the longitudinal electrode feed per one rotation of the part, the rotation speed of the workpiece, the number of passes during processing, finishing of the coating) have been developed. It was found that when applying bronze BrMtsF3-6 to obtain a high-quality coating, the process must be performed in a protective atmosphere of argon to prevent phosphorus burnout. The tribotechnical efficiency of coatings when working under dry friction conditions is shown. For the steady-state wear mode, the friction coefficient is 0.10 – 0.13 at a pressure of 200 – 250 MPa, the wear resistance of coated steel is doubled. Steel with a bronze coating BrAZhMts10-3-1.5 has a higher bearing capacity, with BrMtsF3-6 coating — a higher antifriction. The ways of increasing the service life of steel-coated steel friction pair are analyzed.

Tribological Behavior of Tool Steel Substrate and Solid Films against 304 BA Austenitic Stainless Steel under Dry Sliding

The objective of this work is to study the tribological behavior of the contacting surfaces of SKD11 grade hardened cold work tool steel against grade SUS304BA austenitic stainless steel. DLC, CrN, TiN, and TiCN films were coated on the surface of the tool material to test the tribological performance. Simulation testing with a pin-on-disk was used in this study. The study was done under dry conditions with sliding velocities at 50, 100, and 150 mm/s and contact pressures of 807, 1095, and 1280 MPa. The results show that the main problem is the adhesion of the workpiece material on the tool surface. The severity of the adhesion from the workpiece material is proportional to the sliding velocity and the contact pressure between the contacting surfaces. The coefficient of friction between the contacting surfaces has a positive relationship with the adhesion occurring on the tool surface. The hardness of the film coating is useful for preventing wear of the tool material, especially under high pressure between the contacting surfaces. However, it does not prevent the adhesion of workpiece material of low sliding velocity and low contact pressure conditions. Noncoated SKD11 tool steel has better effectiveness of adhesion performance than CrN, TiN, and TiCN film coatings.

Optimization of spinning parameters of 20/316L bimetal composite tube based on orthogonal test

Abstract The spin forming parameters of bimetallic composite pipe were optimized by FEM and experiment, and the torque and the residual contact pressure were analyzed during forming process. Adoption of The orthogonal test of four factors and five levels to gain the optimal spinning parameters (δ = 0.16mm, Ψ = 0.4mm, β = 3.0∘, f = 0.5) and the effects of factors on analysis indicators under the condition of maximum residual contact pressure and small torque. The simulation results showed that the residual contact pressure was nearly 1MPa higher and the torque was lower about 160N·m than unoptimized results. It proved that the orthogonal test method was effective for the optimization of spinning parameters of bimetal composite tube. The accuracy of numerical simulation value was verified by the drawing experiment of the composite tube.

Noise, vibration and harshness during dry clutch engagement oscillations

Determining the root causes of various noise, vibration and harshness phenomena in modern automotive drivetrains is a critical task for industry, since noise, vibration and harshness issues often result in worsened driving experience. The aim of the current research is to investigate the dynamics during dry clutch engagement and the associated – often problematic – oscillations. This paper reports the development and partial validation of numerical models to study dry clutch behaviour. The models are used to investigate the influence of clutch and throttle actuation on the occurrence of unwanted clutch oscillations. The dynamic coefficient of friction between the clutch interacting surfaces was measured using a pin-on-disc rig under different slip speeds and contact pressure conditions, which are representative of a typical clutch engagement manoeuvre. The paper highlights the occurrence of instability issues in clutch dynamics (disc radial mode) as potential generators of aggressive noise, vibration and harshness, particularly during two different clutch pedal actuations. Such analysis has not hitherto been reported in the open literature.

An evaluation of ultrasonic arrays for the static and dynamic measurement of wheel–rail contact pressure and area

The interfacial contact conditions between a railway vehicle wheel and the rail are paramount to the lifespan, safety and smooth operation of any rail network. The wheel–rail interface contact pressure and area conditions have been estimated, calculated and simulated by industry and academia for many years, but a method of accurately measuring dynamic contact conditions has yet to be realised. Methods using pressure-sensitive films and controlled air flow have been employed, but both are limited. Ultrasonic reflectometry is the term given to active ultrasonics in which an ultrasonic transducer is mounted on the outer surface of a component and a sound wave is generated. This ultrasonic wave packet propagates through the host medium and reflects off the contacting interface of interest. The reflected waveform is then detected and contact area and interfacial stiffness information can be extracted from the signal using the quasi-static spring model. Stiffness can be related to contact pressure by performing a simple calibration procedure. Previous contact pressure measurement work has relied on using a focusing transducer and a two-dimensional scanning arrangement which results in a high-resolution image of the wheel–rail contact, but is limited to static loading of a specimen cut from a wheel and rail. The work described in this paper has assessed the feasibility of measuring a dynamic wheel–rail contact patch using an array of 64 ultrasonic elements mounted in the rail. Each element is individually pulsed in sequence to build up a linear cross-sectional pressure profile measurement of the interface. These cross-sectional, line measurements are then processed and collated resulting in a two-dimensional contact pressure profile. Measurements have been taken at different speeds and loads.