Fretting behavior of a rubber coating: Friction characteristics of rubber debris

This paper presents friction characteristics of a rubber coating undergoing fretting-like, oscillatory motion. Results are presented for rubber coated stainless steel as well as uncoated stainless steel experiencing fretting motion. Friction coefficients are experimentally investigated before and after the rubber coating is fully worn out. The effect of load, velocity and displacement amplitude on the friction coefficients of both uncoated and coated stainless steel is discussed.     

Tribological behavior of reciprocating friction drive system under lubricated contact

The dynamic friction and wear behaviors are investigated in reciprocating friction drive system using a 0.45% carbon steel pair. The effects of various operating parameters on the traction force, stick and slip time, and friction modes are examined under the lubricated contacts. Moreover, the critical operating conditions in classifying three friction modes are also established. Results show that the fluid friction induced by the shearing of lubricant dominates the variation of traction force and produces the positive slope γ at the first period of slip in the traction force–relative sliding velocity curve. The γ value decreases at higher driver speed during stick-slip motion due to the thicker fluid film and shear thinning effect. The γ value increases due to the asperity interactions as the friction region is transferred from stick-slip to sticking with normal load from 196 to 980 N. Furthermore, it is also found that the static friction force is independent of stick time for the tangential loading rate ranged from 1.12 to 16.8 s⁻¹. The transition region produces the severest wear under the different driver speeds, but the wear is insensitive to the friction regions and the severe wear only occurs at higher normal load due to the action of Hertzian contact.     

Effect of rubber on tribological behaviors of polyamide 66 under dry and water lubricated sliding

The friction and wear behaviors of polyamide 66 (PA 66) and rubber-filled PA 66 (PA 66/SEBS-g-MA) composites were investigated on a block-on-wheel model friction and wear tester under dry sliding and water lubricating conditions. In order to further understand the wear mechanisms, the worn surfaces and scraps of samples were analyzed by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The experimental results indicated that the wear mass loss and the friction coefficient of PA 66 decreased with the addition of rubber particles. The friction coefficients of PA 66 and PA 66/SEBS-g-MA composites under water lubricating condition are lower than those under dry sliding condition, but the wear mass losses are higher than those under dry sliding condition. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing. Whereas the main wear mechanisms under water lubricating condition are the mechanical microploughing and abrasive wear.     

金属橡胶成型工艺研究及其应用

主要研究了金属橡胶的成型工艺,介绍了金属橡胶材料在工业中的应用.     

金属橡胶成型工艺研究及其应用

金属橡胶是一种具有广阔应用前景的新型材料,这里主要对金属橡胶的成型工艺进行了研究,并介绍了金属橡胶材料在工业中的应用。     

Tribological behavior and phase transformation of single-crystal silicon in air

The tribological behaviors and phase transformations of single-crystal silicon against Si₃N₄ with different sliding velocities and durations under low contact stress at room temperature were investigated. SEM and Raman analysis indicate that phase transformation was involved and characterized by plastically deformed area which consists of Si-III, Si-XII, and a-Si, especially in the early stage at the low sliding velocity. The plastically deformed layer was wiped off at high-velocity or long sliding duration. TEM analysis indicated that the wear debris consists of amorphous silicon.     

Rolling contact between a rubber ring and rigid cylinders: Mechanics of rubber belts

We revisit the classical creep theory for a belt drive system as a rolling contact problem between a rubber ring and rigid cylinders to evaluate the effects of linear viscoelasticity and large strain of the belt on the system in a steady state. We first construct the general theory of belt mechanics for a multi-pulley system by dimensional reduction from 3D extensible, unshearable rod. We then develop the belt mechanics for a linear viscoelastic belt and show that the effect of retardation time can be involved in the effective friction coefficient: the classical Euler's belt formula can be recovered. Next, we assume that the belt is a neo-Hookean material and examine the effect of large strain of the belt on the contact pressure distribution. We compare the theory with the results by finite element analysis and show that the theory provides good quality.     

Tribological behavior of scar skin and prosthetic skin in vivo

The interfacial rub phenomena between scar skin and other external surfaces are a prevalent problem in everyday life. Literature on the tribological behavior of scar skin is scarce to date. In this study, the tribological behavior and comfort sensations of residual limb scar skin, prosthetic wearing skin and healthy limb skin were investigated in vivo by using UMT-II multi-specimen Micro-Tribometer under the simulated rubbing conditions between the residual limb skin and prosthetic socket. The results showed that the tribological behavior and comfort sensations differ remarkably among the three kinds of skin. Due to the changes of skin histological structure and surface roughness, higher the friction coefficient with higher fluctuation has been obtained for the scar skin during testing. The friction coefficients of the prosthetic wearing skin are close to those of the healthy skin, but have a slight fluctuation compared to those of the healthy skin. The scar and healthy skins are sensitive to the comfortless sensations induced by rubbing. The prosthetic wearing skin is tolerant to the comfortless sensations.     

Effect of liquid high positive friction (HPF) modifier on wheel-rail contact and rail corrugation

This paper presents an experimental study on the influence of HPF friction modifier on rail corrugation. The tests were carried out on a curve section of a commuter line, where corrugation appeared in the inner rail of the curves. The influence of HPF on wheel-rail contact forces has been studied based on acceleration measurements on the rail. These measurements were carried out with and without corrugation on the rail.Also, in order to compare the corrugation levels developed with and without the HPF, the evolution of corrugation was analyzed for this particular curve. The corrugation amplitudes and wavelengths were studied. It was found that the application of HPF substantially reduces the acceleration levels on the rail in vertical and lateral directions and delays the corrugation growth.     

Tribological behavior and topography of friction surfaces of diamond-like coatings in contact with steel,silicon nitride,and quartz glass

The paper presents the study results of the tribological behavior and surface topography formed at friction of diamond-like coatings against indenters made of silicon nitride, quartz glass, and steel. It is shown that the tribological behavior depends on the nature and hardness of the counterbody material whose wear causes changes in the surface topography of the diamond-like coating at the nanometer level. At friction of the diamond-like coating against the silicon nitride indenter surface asperities are deformed plastically and the deformation rate is governed by the coating structure.     

Experimental and numerical investigation of the sliding behaviour in a fretting contact between poly (methylmethacrylate) and a glass counterface

The fretting conditions in a contact between poly (methylmethacrylate) and a rigid counterface have been investigated using both experiments and finite elements computations. The computation of the microdisplacements in the contact area during a tangential loading allowed the determination of the critical displacement for transition from partial sliding to gross sliding conditions. These conditions were mapped in friction maps as a function of the contact loading parameters (i.e., normal load and displacement amplitude) and the friction coefficient. This analysis was performed assuming that the polymer behaved elastically and that the friction obeyed Coulomb's law. Experimental results were found to be in accordance with the numerical predictions, despite the fact that some plastic deformation of the polymer surface occurred during tangential loading.     

Electric contact resistance between finely polished nickel plates with PFPE coating and its relation to friction

The electric contact resistance between mechanically polished nickel plates, with one side dip-coated in perfluoropolyether (PFPE), was evaluated under statically loaded and sliding conditions to investigate the isolation property of the PFPE coating, which may have an important role in thin-film lubrication on relatively large, minutely rough, plane surfaces. The nickel plate surfaces had a roughness of 1–3 nm and the PFPE coating had a thickness of 4–6 nm. Two types of relationship between load and contact resistance were observed. One was estimated to be for a uniform coating of the oil film, the other for a patchy one. Friction tests revealed that a uniform coating of oil film would be preferable to a patchy one to prevent solid–solid contact, if the nominal thicknesses of the oil films were similar.     

Tribological Sensitivity of PTFE/Alumina Nanocomposites to a Range of Traditional Surface Finishes

Wear tests were performed with polytetrafluoroethylene (PTFE) + Al ₂ O ₃ nanocomposites on various manufactured surfaces to determine whether or not the wear resistance of these nanocomposites is a strong function of surface preparation. Four different surface finishes of grade 304 stainless steel counterfaces were used: electropolished (R _q = 88 nm), lapped (R _q = 161 nm), wet-sanded (R _q = 390 nm), and dry-sanded (R _q = 578 nm). PTFE + Al ₂ O ₃ nanocomposites made from powders of roughly 2-20 μm PTFE (matrix) and ～44 nm Al ₂ O ₃ (filler) were prepared at filler weight percentages of 0, 1, 5, and 10% and tested on each surface finish. Additionally, 5 wt% 44-nm nanocomposites were compared to identically prepared 5 wt% 80- and 500-nm Al ₂ O ₃ filled PTFE composites on each surface. Friction coefficients were between 0.12 and 0.19 and wear rates decreased from K = 810 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 500-nm alumina-filled PTFE on the dry-sanded surface to K = 0.8 × 10^{? 6} mm ³ /(Nm) for the 5 wt% 80-nm filled composite on the lapped surface. It was found that the minimum wear rate occurred on the lapped counterface for every composite, and the wear rate is a strong function of the transfer film thickness and morphology.     

Tribological Effects on the Wear Life of a Coating-Protected OPC Drum with Regard to Temperature,Load, and Rotation Speed

Greatly improved technology in laser printers requires that companies innovate to provide consumers with high-quality printed images, durable equipment, and low costs. The toner cartridge of a laser printer is where the organic photoconductor drum, also known as the OPC drum, is located, which is the central feature of the printer responsible for reproducing what has been created accurately on paper. However, with continuous printing, constant contact between the OPC drum and the paper, toner, and doctor blade causes wear and thus the quality of the image deteriorates and eventually will cause the equipment to fail, which then costs the consumer for repairs. In this study, we conducted a friction/wear test on the OPC drum to determine the relationships between temperature, load input, and rotational speed in the deterioration of an OPC drum, causing the end of its service life. Test results showed that load input with respect to increasing rotational speed increased the temperature in the OPC drum's surface during operation. With the increase in temperature, the average amount of wear on the surface of the drum increases. However, toner dispersion greatly influences the temperature increase in the OPC surface.     

Friction behavior of quenched and tempered steel in partial and gross slip conditions in fretting point contact

Tangential traction caused by friction in contacting surfaces is a major factor in fretting fatigue that increases stress levels and leads to a reduction in fatigue life. Friction in fretting contact was studied in partial, mixed and gross slip conditions on quenched and tempered steel. Measurements were made with sphere-on-plane contact geometry for polished and ground surfaces. Friction was evaluated from on-line energy ratio and, after the tests, from wear marks. A maximum friction coefficient of over 1.0 was measured at mixed slip zone with polished surfaces, whereas ground surfaces promote lower values in similar operating conditions. The friction coefficient dependence on load cycles and loading frequency is also presented and briefly discussed. The friction data and understanding thus gained is to be used for evaluation of crack initiation with the numerical fretting fatigue model.     

Surface Texture Effect on Friction of a Microtextured Poly(dimethylsiloxane) (PDMS)

The effect of surface textures on the friction of a poly(dimethylsiloxane) (PDMS) elastomer has been investigated at both macro and microscales using a nanoindentation-scratching system. Friction tests were conducted by a stainless-steel bearing ball with a diameter of 1.6 mm (macroscale tests) and a Rockwell diamond tip with a radius of curvature of 25 μm (microscale tests) under normal loads of 5, 10, and 25 mN and with a sliding speed of 1 μm/s. Coefficient of friction (COF) on the pillar-textured surface was found to be much lower than that on the smooth surface of the same material, and it was reduced by about 59% at the macroscale tests and 38% at the microscale tests. The reduction of COF can be attributed to the reduced contact areas. The use of the JKR model revealed that the adhesion force has less effect on contacts under higher normal loads. COFs in different sliding directions on the groove-textured surfaces were compared, and a friction anisotropic behavior was identified and analyzed.     

Analysis of the friction and wear behavior of hot work tool scale: application to the hot rolling process

In hot forming processes, the interface tool/product is important for the quality of the finished product. In hot rolling, the scale formed on the roll material plays an essential role. As soon as the contact oxide–oxide is established between the roll and the slab, friction allows the process to start. However, the oxide scale will continue to grow under the cyclic action of hot contacts and water cooling and will be subjected to thermo-mechanical stresses. Beyond a certain critical thickness, the oxidized surface layer of the cylinders has not sufficient mechanical strength to withstand the shear stresses.

The wear and friction behavior of the oxides appearing on the surface of the hot working rolls is not well known. The influence of these oxides on the friction and, consequently, the quality of the products of finishing mills, seems very significant. So, in this study, we investigate the evolution of the friction coefficient and the wear, according to the growth, the nature and the thickness of the formed scale. We use a high temperature pin on disc tribometer. The pin consists of material “rolls” while the disc consists of the slab. The pin is instrumented with thermocouples in order to couple the friction coefficient measurements with the thermal gradient in the pin and the surface temperature and the formed oxides. Then, the characterization of the surfaces is done by scanning electronic microscopy (SEM) and EDS analyses. We use the method of sin² Ψ to evaluate residual stresses of oxide and correlate these data with shear stress behavior.     

Simulation of friction and wear in the contact between the valve bridge and rocker arm pad in a cam mechanism

In this paper the surface velocities obtained from a rigid body model are used to simulate friction and wear in the contact between the rocker arm pad and valve bridge in the cam mechanism of a diesel engine. The friction is simulated with two different friction models, a 3D brush model capable of handling transient conditions such as an varying normal load and varying surface velocities and a Coulombian friction model. The wear simulations are based on a generalised form of Archard's wear model.The results presented here show that both the maximum wear depths and the wear distributions are influenced significantly by the combination of wear pad radius and the position of the wear pad radius centre relative to the rocker arm bearing centre. A combination with wear pad radius of 20 mm and centre position of 5 mm is found to give the least wear depths on both the wear pad and the valve bridge. It is also seen that the contact between the wear pad and the valve bridge is mainly a sliding contact and that the transitions from sliding in one direction to the opposite are very rapid. The change of the surface shapes due to wear has a negative effect on the contact situation causing very high contact pressures.     

Tribological behavior of uncoated and DLC-coated CoCr and Ti-alloys in contact with UHMWPE and PEEK counterbodies

There are very few studies of PEEK wearing against DLC. In this study, DLC and Zr-DLC coatings were deposited by magnetron sputtering onto Ti alloy substrates. Coated and un-coated Ti alloy samples were tribologically tested in multidirectional pin-on-disk equipment against UHMWPE and PEEK. CoCr alloy was also tested as control. Each of the materials was tested for 2 million cycles (Mc) in bovine serum lubricant (37 °C). Gravimetrical weight loss and changes in surface profile were similar when tested against UHMWPE. However, Zr-DLC samples delaminated after 1.2 Mc. When tested against PEEK, both coated samples delaminated, despite that the coatings maintained their structural integrity. The synergetic effect of stress-induced corrosion through biological fluid and high cyclic shear stress may have caused interface fatigue and subsequent delamination of both coatings.