Contact Pressure Conditions Research Articles

Effect of Vehicle Speed on Contact Pressure and Current Collecting Quality

In the subway movement the stability of current collection is extremely important. Using experiment system of the pantograph current collection to simulate the vehicle running in different speed can be used to analyze the condition of contact pressure, the current collection quality, the disconnection frequency under varies speed conditions and bring up the method to reduce the disconnection occurred. The results of the study have the positive significance in researching the characteristics of pantograph-catenary disconnection parameters when the vehicle running, and have certain reference value in analyzing mechanism of pantograph-catenary disconnection.

Simple evaluation method for temperature drop at contact interface between rough surfaces under low contact pressure conditions

For heat removal from systems such as electronic equipment, satellite thermal control systems, and nuclear reactors, reduction of thermal contact resistance (TCR) is the most crucial issue to be addressed. Several studies have attempted to propose evaluation equations for predicting TCR for flat rough surfaces. However, as is well known, there are still wide discrepancies among measured results, even for similar materials. In this study, based on the conventional unit cell model for flat surfaces with roughness and the newly proposed contact surface model for wavy surfaces with roughness, thermal contact resistance under a low contact pressure of 0.I-I.0 MPa is investigated theoretically and experimentally. Comparison of the measured and calculated results shows that the measured temperature drop at the interface (that is, the thermal contact resistance) between flat surfaces with roughness lies between the values evaluated by the unit cell model for the cases with and without the heat flow constriction. Furthermore, when the rough surface has waviness, the introduction of macroscopic constriction resistance is shown to be important for evaluating the temperature drop at the interface.

Influence of Surface Roughness on the Tribological Behavior of Gear Oils in Steel–Steel Contacts: Part II—Mixed Friction Properties

Hypoid gears are known to be commonly used in rear-wheel-drive automobiles and they typically operate under high sliding and high contact pressure conditions. Providing efficient lubrication and necessary surface finish to such gear contacts is important in order to achieve a significant gain in energy and torque efficiencies. This requires knowledge of the behavior of gear oils under different operating conditions, especially their abilities to work under high contact pressure and sliding conditions. In light of this and in view of optimizing friction in transmission systems, this article explores the influence of surface roughness on friction in a mixed lubrication regime. In addition to friction–speed measurements and Stribeck curves described in a companion article (Vengudusamy, et al. (1)), this article explores the friction response of tribofilm-generated surfaces with base oil and highlights the significance of such experiments.

J0420305 接触界面における分調波発生現象の数値解析([J042-03]超音波計測・解析法の新展開(3),機械材料・材料加工部門)

Subharmonic wave generation at double contact surfaces is analyzed with one-dimensional finite - difference time - domain scheme in which contacting surfaces are represented by separable spring model. Increasing incident amplitude, subharmonic component suddenly appeared and then chaotic low frequency vibration was observed, which qualitatively agree well with our previous experimental results. Intensity maps of subharmonic component were obtained and showed that subharmonic wave generates under a limited condition of incident amplitude, interfacial stiffness and contact pressure

From uni- to multi-axial fretting-fatigue crack nucleation: Development of a stress-gradient-dependent critical distance approach

Fretting fatigue is characterized by combined high stress gradients induced by contact loading and more homogeneous stress gradients induced by bulk fatigue stressing. The stress gradients computed at the “hot-spot” located on the surface at the trailing contact border are very high, usually above 10GPa/mm. For such uncommon stressing conditions, prediction of cracking risk becomes very complex and non-local fatigue approaches must be adopted. The purpose of the present study was to investigate how non-local strategies, such as “critical distance”, developed for medium stress gradient conditions such as “notch” configurations, were transposed to predict fretting cracking risk. Elastic crack nucleation conditions of a 35 Ni Cr Mo 16 low alloyed steel at 10E6 cycles have been identified for various cylinder pad radius, contact pressure and fatigue stress conditions. The experimental crack nucleation conditions were then compared to predictions from analytical simulations coupling uni-axial and Crossland’s multiaxial fatigue descriptions. The local “hot-spot” analysis systematically overestimated cracking risk and induced more than 30% error with respect to the experimental values. The non-local “critical distance method” based on a constant length scale value still displayed more than 10% dispersion suggesting that a non-constant “critical distance” approach must be considered. By expressing the critical distance evolution as a function of the hydrostatic stress gradient operating next to the stress hot-spot, dispersion was reduced below 5%. Established for the Crossland’s stress invariant formulation, this tendency is confirmed by comparing McDiarmid and MWCM critical plane fatigue approaches.

Combined Analysis of Results on Single and Multiple Contacts: Potting Soil, Sand and Clay Transfers to Cloth for the Estimate of Soil Adherence to Human Skin

Humans can be exposed to contaminated soil and household dust via contact with environmental surfaces. A mechanical device was used to measure the transfer of soils from one surface to the other to provide estimates of adherence factors (mg/cm 2 ) used in estimates of human exposure to contaminants found in soils/household dust. This paper presents the analysis and comparison for thetransfer of clay, potting soil, and sand from aluminum to cloth samples for single and multiple contacts under varying environmental and contact time and pressure conditions. Adherence for clay was over 73 times that of sand and over 114 times that of potting soil. Clay particles with their softer texture and finer composition compared to potting soil and sand, are more likely to compress and adhere to surfaces producing higher transfers. Contact time and temperature had no effect, however: contact pressure, soil loading on the aluminum surface, and environmental humidity did have an effect on soil transfer.

English

Introduction The aim of this article was to critically review the literature about lubricin and its involvement in normal and pathological joint tissue. In particular, our research focused on new therapeutic approaches for the treatment of osteoarthritis related to lubricin. We reviewed the literature regarding lubricin expression. We examined the current literature by searching on PubMed and Scopus using appropriate keywords related to lubricin and joint tissue. Main research articles were then selected for review. Discussion Cartilage is the tissue that covers the ends of the bones where the bones meet to form a joint. The cartilage allows the bones to glide over one another with limited friction and wear. It contains proteoglycans such as aggrecan and lubricating fluidcontaining glycosaminoglycans such as hyaluronic acid. Osteoarthritis is the most common form of arthritis, a degenerative joint disease that mostly affects the cartilage. Lubricin, also commonly referred to as the superficial zone protein, is a glycoprotein specifically synthesised by chondrocytes located at the surface of articular cartilage. It has been shown that lubricin is critical to normal joint function, providing boundary lubrication of congruent articular surfaces under conditions of high contact pressure and nearzero sliding speed. Recent studies have demonstrated that administration of recombinant lubricin in the joint cavity would be effective in the prevention of cartilage degeneration in animal osteoarthritis models. It is a promising treatment for cartilage diseases, but further studies are necessary to shed light on its therapeutic value. Conclusion This critical review reported recent findings about the possible distribution of lubricin in some normal and pathological tissues and further provided new insights for future approaches in the treatment of osteoarthritis.

Effects of surface texturing on the performance of biocompatible UHMWPE as a bearing material during in vitro lubricated sliding/rolling motion

The effect of surface texturing on the performance of biocompatible ultra-high molecular weight polyethylene (UHMWPE) as a bearing material has been investigated using the kinematic range of motions reported for a knee-joint replacement. An experimental apparatus consisting of a ball and a disk rotating independently from each other was used to compare the performance of UHMWPE textured versus plain surfaces, under different combinations of sliding and rolling motion, better known as sliding-to-rolling ratio (SRR). Performance was evaluated through the coefficient of traction of a tribosystem comprising a steel ball on a flat UHMWPE disk and distilled water at 36°C, acting as lubricant. A square array of cavities with diameter D=0.397mm and center-to-center spacing of 1.5D was machined on UHMWPE disks. The experimental design considered two levels for cavity depth, D and D/2, and two for the applied load, 17 and 25N. The SRR was varied from 1 to 11% and the mean speed range was set from 5 to 55mm/s, covering the kinematics and contact pressure conditions of a sauntering cycle on a knee-joint replacement. Stribeck curves of the plain and textured surfaces were obtained and compared against one another. The results demonstrate that the proposed surface pattern reduces the coefficient of traction of the tribological system for the 17N load in the entire kinematic range explored, while for the 25N load the effects were more noticeable at low mean speed and SRR, corresponding to the beginning of motion.

An experimental method for characterizing friction properties of sheet metal under high contact pressure

Contact friction is present on interacting surfaces of steel thin-walled structural members under axial folding during vehicle crash, and often occurs under relatively high contact pressure (∼100MPa) and sliding velocity (∼6m/s). The contact friction could affect structural deformation mode and kinetic energy absorption capacity, and yet has not received sufficient attention in the area of automotive crashworthiness. The lack of knowledge on contact friction behavior and friction data of sheet metal has long affected the reliability and predictability of vehicle crash simulations. The objective of this study is to develop an appropriate experimental method for friction measurement on self-paired sheet metal under high contact pressure conditions. A fixture is designed for applying clamping pressure of 1–100MPa on contact interfaces, under which sliding friction is generated by additional loading devices. Using a standard material test machine and a drop tower, two experimental configurations are set up for measuring the friction properties of steel sheet couples under the pressures of 1–100MPa and the sliding velocities of 0–6m/s. The test method is proved to be valid and viable in friction tests on a typical high-strength steel sheet. The results show distinct friction behaviors of the high steel under different loading conditions, which has also been discussed.

Rolling Contact Fatigue Performance of Vibro-Mechanical Textured Surfaces

The rolling contact fatigue (RCF) performance of vibro-mechanical textured surfaces in a point elastohydrodynamic lubrication (EHL) condition is investigated. Two dimple designs, small (100 μ m × 100 μ m) and large (240 μ m × 100 μ m), are compared with a nontextured sample. Experimental RCF tests show that the textured surfaces exhibit a significantly reduced number of cycles to failure compared with the nontextured sample for the high load, pure rolling conditions evaluated. In order to understand these results, numerical models are used to calculate the lubrication and contact pressure conditions and the subsurface stress distribution. The fatigue failure trends observed experimentally are compared with the simulation results with good agreement. It is determined that RCF performance is related to the presence and size of the generated dimple.

Sliding velocity dependency of the friction coefficient of Si-containing diamond-like carbon film under oil lubricated condition

In this study we investigated the sliding velocity dependency of the coefficient of friction for a Si-containing diamond-like carbon (DLC-Si) film in an automatic transmission fluid (ATF) under a wide range of contact pressures. The DLC-Si film and a nitrided steel with a surface roughness, Rz JIS, of around 3.0 μm were used as disk specimens. A high-carbon chromium steel (JIS-SUJ2) bearing ball was used as a ball specimen. Friction tests were conducted using a ball-on-disk friction apparatus under a wide range of sliding velocites (0.1–2.0 m/s) and contact pressures ( P max: 0.42–3.61 GPa) in ATF. The friction coefficients for the nitrided steel had a tendency to decrease with an increase in sliding veloicity under all the contact pressure conditions; however, the friction coefficients for the DLC-Si film were stable with respect to sliding velocities under all the contatct pressures. These results indicate that the DLC-Si film suppresses the stick-slip motion during sliding againt steel in ATF, which is a desired frictional characteristic for the electromagnetic clutch disks used under lubrication. Furthermore, the DLC-Si film showed a higher wear resistance and lower aggression on the steel ball specimen than the nitrided steel. There were less hydrodynamic effects on the friction coefficient for the DLC-Si film possibly due to maintenance of the initial surface roughness and its poorer wettability with the fluid. X-ray photoelectron spectroscopy (XPS) analysis of the sliding surfaces revealed that the adsorption film derived from the succinimide on the sliding surfaces of the DLC-Si film and the mating steel ball also contributed to the sufficient and less sliding-velocity-dependant friction coefficients.

FEM numerical simulation of the warm and hot upsetting sliding test

For bulk forming applications involving friction, the classical Coulomb-Amonton and Tresca-constant friction laws are not representative of the actual phenomenon when large changes in the contact pressure conditions occur. In order to address these issues, alternative friction laws has been proposed in the last decade. The present paper deals with the analysis of the stress distributions during the Warm and Hot Upsetting Sliding Test for further identification of friction parameters. A first part of the paper is devoted to the description of the mechanical and thermal device used at LAMIH for a sliding test at hot temperature with a polished contactor ironing a steel workpiece. Then, the experimental data are compared to numerical results obtained from 3D simulations of the thermo-mechanical ironing test with the finite element method. The last part of the paper presents some comparisons between numerical data obtained by different 3D finite element models on the first hand, and results of the 2D simulations (under plane stress, plane strain and generalised plane strain) and with slip line theory calculus on the second hand.

Black-box modeling to estimate tissue temperature during radiofrequency catheter cardiac ablation: feasibility study on an agar phantom model

The aim of this work was to study linear deterministic models to predict tissue temperature during radiofrequency cardiac ablation (RFCA) by measuring magnitudes such as electrode temperature, power and impedance between active and dispersive electrodes. The concept involves autoregressive models with exogenous input (ARX), which is a particular case of the autoregressive moving average model with exogenous input (ARMAX). The values of the mode parameters were determined from a least-squares fit of experimental data. The data were obtained from radiofrequency ablations conducted on agar models with different contact pressure conditions between electrode and agar (0 and 20 g) and different flow rates around the electrode (1, 1.5 and 2 L min−1). Half of all the ablations were chosen randomly to be used for identification (i.e. determination of model parameters) and the other half were used for model validation. The results suggest that (1) a linear model can be developed to predict tissue temperature at a depth of 4.5 mm during RF cardiac ablation by using the variables applied power, impedance and electrode temperature; (2) the best model provides a reasonably accurate estimate of tissue temperature with a 60% probability of achieving average errors better than 5 °C; (3) substantial errors (larger than 15 °C) were found only in 6.6% of cases and were associated with abnormal experiments (e.g. those involving the displacement of the ablation electrode) and (4) the impact of measuring impedance on the overall estimate is negligible (around 1 °C).

Lubricin: a novel potential biotherapeutic approaches for the treatment of osteoarthritis

Osteoarthritis (OA) is a multi-factor disorder of sinovial joints, which characterized by escalated degeneration and loss of articular cartilage. Treatment of OA is a critical unmet need in medicine for regeneration of damaged articular cartilage in elderly. On the other hand, lubricin, a glycoprotein specifically synthesized by chondrocytes located at the surface of articular cartilage, has been shown to provide boundary lubrication of congruent articular surfaces under conditions of high contact pressure and near zero sliding speed. Lubrication of these surfaces is critical to normal joint function, while different gene expressions of lubricin had been found in the synovium of rheumatoid arthritis (RA) and OA. Moreover, mutations or lacking of lubricin gene have been shown to link to the joint disease such as camptodactyly-arthropathy-coxa vara-pericarditis syndrome (CACP), synovial hyperplasia and failure of joint function, suggesting an important role of lubricin in the pathogenesis of these joint disease. Recent studies demonstrate that administration with recombinant lubricin in the joint cavity would be effective in the prevention of cartilage degeneration in animal OA models. Therefore, a treatment with lubricin which would protect cartilage in vivo would be desirable. This article reviews recent findings with regard to the possible role of lubricin in the progression of OA, and further discusses lubricin as a novel potential biotherapeutic approaches for the treatment of OA.

Experimental and finite element simulations of cold pressure welding of aluminium by divergent extrusion

In the present investigation, the aptness of the divergent extrusion process in simulating cold pressure welding (CPW) is further documented and explored. As a starting point, the situation existing both prior to and after cold bonding is adequately reproduced using finite element (FE) modelling. Combined extrusion and joining experiments are then carried out to unravel the conditions under which cold bonding takes place in commercial purity aluminium. Based on three-point bend testing and fracture surface investigations in the scanning electron microscope (SEM), it is observed that bond initiation occurs gradually during the course of the extrusion process. Full metallic bonding is achieved when the surface exposure, as determined by the x-component of the strain acting in the extrusion direction, reaches a value of 0.97. This surface exposure is comparable to that reported for bond formation using conventional CPW and cold roll bonding (CRB) in the presence of oxide and lubricant films at the mating interfaces under similar contact pressure conditions.

Rolling contact fatigue mechanism of a plasma‐sprayed and laser‐remelted Ni alloy coating

ABSTRACTThe rolling contact fatigue behaviour of the plasma‐sprayed and laser‐remelted Ni‐Cr‐B‐Si alloy coatings under two different tribological conditions of contact pressure was investigated. Two sets of fatigue‐life data of coatings were characterized by Weibull distributions. The failure mode of the coatings was identified on the basis of worn morphologies as observed at the surfaces of the failed coatings. The tribological mechanism leading to the formation of the fatigue spall was discussed on the basis of the subsurface morphologies observed in the failed coating. Experimental results showed that, the mean life and characteristic life of the coating decreased with increasing the contact pressure. The failure of the coatings can be termed as spalling‐type failure. A refined ‘ring‐crack model' was proposed to explain the formation of the fatigue spall. In the refined model, it was postulated that the joining of the ring‐type cracks and subsurface branched cracks was directly responsible for the spall formation.

Work Hardening and Change in Contact Condition of Rolling Contact Surface with Plastic Deformation

Machine designers are sometimes confronted with high contact pressure conditions which generate plastic deformation. However there is no clear design method for such severe condition. We investigate the contact condition in the high contact pressure by using a ball-on-glass disc type test. According to the test results, the following conclusions were obtained. 1) The ratio of calculating contact pressure and the hardness in consideration of working hardness, the number of the ratio is settled about 0.4 for any loading condition. 2) In the condition of high contact pressure generating plastic deformation, the contact pressure converges with constant value according to the work hardening behavior of material.

摩擦型継手のフレッティング疲労強度に及ぼす面圧の影響

In friction-type joints where vibratory load is carried only by friction, the effect of contact pressure on fretting fatigue strength differs from that observed in conventional pad-type load-carrying tests. In this study, in order to clarify the effect and the mechanism of contact pressure in friction-type tests, we performed fatigue tests measuring changes in strain distribution with repetition and finite element (FE) analyses focusing on the shifting of actual contact edges. It was found that fatigue limits decreased as contact pressure decreased, and the minimum limits were observed at certain contact pressure. We clarified that the reduction in fatigue strength that occurred with decreasing contact pressure was caused by increasing stress concentration due to shifting of the actual contact edge, and decreasing compressive mean stress. The actual contact edges were confirmed to be positioned inside the contact surface under low contact-pressure conditions, and to move inwardly from the initial edge with the repetition of cycles under high relative-slip-range conditions. We also showed that fatigue limits can be explained well considering the shifting of the actual contact edge using the local reference stresses (mean stress and principal stress amplitude) specially defined in this study.

Comparison of Lesion Sizes Produced by Cryoablation and Open Irrigation Radiofrequency Ablation Catheters

The relative lesion sizes created by large electrode cryoablation catheter and irrigated radiofrequency (RF) ablation are not known. The purpose of this study was to directly compare lesion sizes created by cryoablation and irrigated RF under controlled conditions. Ablation lesions were created in freshly harvested porcine left ventricular myocardium in a blood-filled tissue bath using an 8-mm-tip cryoablation catheter and a 3.5-mm-tip open-irrigated RF ablation catheter. Lesions were created under all permutations of the following conditions: electrode orientation vertical (perpendicular) or horizontal (parallel) to the tissue, electrode contact pressure at 6 or 20 g, and blood flow at 0.2 or 0.4 m/s over the electrode-tissue interface. The largest lesion volumes created with cryoablation were 961 +/- 103 mm(3), compared with the largest lesions volumes created with RF of 680 +/- 48 mm(3) (P < 0.001). The 3-way interactions among electrode orientation, contact pressure, and superfusate blood velocity accounted for the variation in lesion volumes for both catheters (both r(2)= 0.97, both P < 0.0001). The greater contact pressure increased lesion size for both cryoablation and RF. For cryoablation, lesion sizes were increased by the horizontal orientation and by the lower blood flow velocity. For open-irrigated RF, lesion sizes were significantly reduced by the horizontal orientation, however. Depending on conditions of electrode orientation, contact pressure, and blood velocity, either 8-mm-tip cryoablation or open-irrigated RF may produce the larger lesion volumes. Open-irrigated RF lesion sizes are reduced in the horizontal catheter orientation.

Enhanced tribological properties of PECVD DLC coated thermally sprayed coatings

This research investigates the enhancement of the tribological properties of various thermally-sprayed coatings (APS Ni–50Cr, APS Al 2O 3–13%TiO 2 and HVOF WC–17Co) on steel substrate, achieved through the deposition of a thin DLC-based film. Higher adhesive strength between thin films and thermally-sprayed coatings compared to the simple thin film/carbon steel system was found by scratch testing. Dry sliding ball-on-disk tests performed under lower contact pressure conditions (5 N normal load, 6 mm diameter alumina ball) indicated a significant decrease in wear rates and friction coefficients of thermally-sprayed coatings when the thin DLC-based film is employed; little differences exist between the tribological behaviour of the various thin film/thermal spray coating systems and that of DLC-based film on carbon steel. Under higher contact pressure conditions (10 N normal load, 3 mm diameter alumina ball), the thin film/WC–Co system exhibited the best wear performance. These results indicate the superior tribological performance of DLC/thermal spray coating systems, especially under severe contact conditions.