Effect Of Counterface Roughness Research Articles

Effect of counterface roughness on the friction of bionic wall-shaped microstructures for gecko-like attachments

Hairy adhesive systems involved in gecko locomotion have drawn the interest of many researchers regarding the development of bionic solutions for fast and reversible adhesive technologies. To date, despite extensive efforts to design gecko-inspired adhesive surfaces, adhesion and friction capacities are often evaluated using smooth and rigid counterfaces, in general glass, whereas most natural and artificial surfaces inevitably have a certain level of roughness. For that reason, in this study experiments tested the effects of the substrate roughness on the friction of bionic wale-shaped microstructures for gecko-like attachments. To this end, 12 substrates with different isotropic roughness were prepared using the same Epoxy material. Friction force was measured under various normal loads. It was concluded that classical roughness parameters, considered separately, are not appropriate to explain roughness-related variations in friction force. This has led us to develop a new integrative roughness parameter that combines characteristics of the surface. The parameter is capable of classifying the obtained experimental results in a readable way. An analytical model based on the experimental results has been developed to predict the variation of the friction force as a function of counterface roughness and applied normal load.

The Effect of Counter-face Roughness on the Tribological Behavior of Filled and Unfilled PTFE

The Effect of Counter-face Roughness on the Tribological Behavior of Filled and Unfilled PTFE

Effect of counterface roughness on adhesion of mushroom-shaped microstructure

In this study, the effect of the substrate roughness on adhesion of mushroom-shaped microstructure was experimentally investigated. To do so, 12 substrates having different isotropic roughness were prepared from the same material by replicating topography of different surfaces. The pull-off forces generated by mushroom-shaped microstructure in contact with the tested substrates were measured and compared with the pull-off forces generated by a smooth reference. It was found that classical roughness parameters, such as average roughness (Ra) and others, cannot be used to explain topography-related variation in pull-off force. This has led us to the development of an integrated roughness parameter capable of explaining results of pull-off measurements. Using this parameter, we have also found that there is a critical roughness, above which neither smooth nor microstructured surface could generate any attachment force, which may have important implications on design of both adhesive and anti-adhesive surfaces.

Wear of crosslinked polyethylene under different tribological conditions

Ultra high molecular weight polyethylene (UHMWPE) wear debris has been shown to be a major cause of long term failure of total joint replacements. Recently, crosslinking has been extensively introduced to reduce the wear of UHMWPE. In this study the wear of non-crosslinked and crosslinked UHMWPE were compared under a range of conditions. The materials examined were UHMWPE GUR 1050, non-crosslinked, moderately crosslinked--5MRad, and highly crosslinked--10MRad. The wear was examined on a multidirectional pin on plate rig. The effect of counterface roughness on wear under different kinematics was examined. The results from the different counterface conditions showed that highly crosslinked UHMWPE had significantly lower wear against both smooth and scratched counterfaces. However the reduction in wear for crosslinked polyethylene was less for scratched counterfaces. The second part of the study showed that all the UHMWPE's produced lower wear rates under lower multidirectionality because of reduced cross shear frictional forces and work. These findings are relevant to the consideration of the use of crosslinked polyethylene in the knee, where the kinematics have lower levels of cross shear and in the hip and knee against roughened metallic counterfaces.

The effect of counterface roughness on the wear of UHMWPE for rectangular wear paths

Ultra-high molecular weight polyethylene (UHMWPE) is used worldwide as a bearing material in total joint replacement prostheses. Multi-directional motion has been identified as a major factor affecting the wear rate of UHMWPE in total hip replacement prostheses. The trajectory of relative motion between a femoral head and an acetabular cup takes a general quasi-elliptical or rectangular shape during the patient's gait cycle. Differences in motion pattern can affect the in vivo wear rates of UHMWPE cups in patients when all other factors are equal. In a previous study that utilized smooth Co–Cr counterfaces, we compared wear factors, k, for UHMWPE articulated in a series of rectangular wear paths (width = A, length = B) with systematically increasing aspect ratios ( B/ A) and linear tracking ( A = 0), all with identical path lengths per cycle. The results showed that the wear factor significantly decreased in the rectangular wear path with the highest aspect ratio and in linear tracking. The goal of our current study was to quantify the effect of a roughened counterface on the cross-path wear of UHMWPE. UHMWPE pins were articulated against both smooth and rough Co–Cr disks in diluted calf serum using a multi-directional wear tester under physiological loading conditions. Five different rectangular wear path geometries and linear tracking, all with identical path lengths per cycle, were employed for each wear test. Gravimetric weight loss was converted into volumetric wear rates and wear factors, k. The results showed that roughened counterfaces produced a larger increase in the wear factor in rectangular wear paths with higher aspect ratios. The ratio of k rough/ k smooth decreased monotonically as a function of increasing width of rectangles, normalized by total path length, or A/( A + B).

Effect of counterface roughness on abrasive wear of hydroxyapatite

The present study was undertaken to evaluate the effect of surface roughness of glass-infiltrated alumina on the abrasive wear of hydroxyapatite using a pin-on-disk tribometer. Hydroxyapatite was used as a model material to simulate tooth enamel. The wear tests were conducted in distilled water at room temperature using a constant sliding speed and three loads to model the normal occlusal contact conditions. The wear volume of polished hydroxyapatite pins increased by more than 20-fold as the average roughness of the alumina disks increased from 14 to 649 nm Ra. No measurable wear was detected on the alumina specimens. The wear surfaces were viewed in a scanning electron microscope (SEM) and were analyzed with X-ray dispersion spectroscopy to determine the extent of surface damage and the wear mechanisms. It is suggested that polished ceramic restorations will cause relatively low enamel wear, while increased roughness could severely abrade and damage the tooth enamel.

Effect of counterface roughness on the wear of conventional and crosslinked ultrahigh molecular weight polyethylene studied with a multi-directional motion pin-on-disk device.

The effect of counterface roughness on the wear of conventional gamma-sterilized, and electron-beam-crosslinked ultrahigh molecular weight polyethylene was studied with a circularly translating pin-on-disk device. The counterfaces, CoCr disks, were either polished, or roughened so that they represented the type of roughening and the range of surface roughness values (R(a) = 0.014-0.24 microm) observed in explanted femoral heads of total hip prostheses. The lubricant was diluted calf serum, and the test length 3 million cycles. A total of 24 tests were done. With both types of polyethylene, there was a strong correlation between R(a) and wear factor k. The power equations were k = 5.87 x 10(-5)(R(a))(0.91) for conventional polyethylene (R(2) = 0.94), and k = 7.87 x 10(-5)(R(a))(2.49) for crosslinked polyethylene (R(2) = 0.82). Crosslinking improved wear resistance significantly. The wear of crosslinked polyethylene against the roughest counterfaces was lower than the wear of conventional polyethylene against the polished counterfaces. Against rough counterfaces, the wear of crosslinked polyethylene was an order of magnitude lower than that of conventional polyethylene. On the crosslinked polyethylene pins that were tested against polished counterfaces, remains of original machining marks were still visible after the test. The average size of wear particles produced by both types of polyethylene against rough counterfaces was similar, 0.4 microm, whereas that produced by conventional and crosslinked polyethylene against polished counterfaces was significantly smaller, 0.2 and 0.1 microm, respectively.

The development of transfer layers and their role in polymer tribology

When polymers slide against metal counterfaces, transfer films are formed. This is also the case when sliding occurs between a polymer and another polymer. In the latter case, the transfer of material has been documented by infrared studies which show that material transfer occurs from a polymer of low cohesive energy density to one of higher cohesive energy density. The transfer film formed on a non-polymer counterface is governed by the counterface material and roughness, and of course the sliding conditions. The growth of transfer film with the number of passes is presented and the effect of counterface roughness is examined. The mechanism of wear is discussed with respect to the transfer film. It is shown that when polymers are modified, such as by the addition of fillers, the transfer film affects the tribological behavior. Some fillers affect the development of transfer film and enhance its adhesion to the counterface. Such fillers reduce the wear rate of polymer, often drastically. On the other hand, there are many fillers which have no such effect on the transfer film and wear in these cases is increased. The results of friction and wear behavior for both types of fillers are discussed in view of the transfer film characteristics. The analyses of transfer films as performed by XPS for a few cases are also presented.

Effect of testing conditions on friction and wear of a polyetheretherketone‐based composite

AbstractFriction and wear characteristics of a type of polyetheretherketone (PEEK)‐ based composite were evaluated under two different loading pressures and sliding speeds (P = 1.0 MPa, V = 1.0 m/s and P=2.0 Mpa, V=3.3 m/s). The material was in contact with steel surfaces of two different roughnesses (Ra=0.15 μm and Ra=0.33 μm). Interface temperature, coefficient offriction, depth wear rate, and specific wear rate of the polymer composite changed considerably with the PV value and the counterface roughness. The interface temperature increased with increasing PV value, whereas the friction coefficient decreased. The depth wear rate at the higher PV value was much higher than that at lower PV. In addition, the rougher counterface resulted in a higher friction coefficient, depth wear rate, and specific wear rate, when the PV value was fixed. The effect of counterface roughness on the specific wear rate at the higher PV value was smaller than that at the lower PV. Further variations in friction and wear with testing conditions are discussed along with the corresponding microscopic observations of the worn polymer surfaces and the polymer transferred counterfaces.

The lubrication of plastics by perfluoropolyether fluids

AbstractThe work reported here demonstrates that very small quantities of perfluoropolyether fluids will provide effective boundary lubrication for a number of plastics materials. This includes plastics which are known to benefit from trace quantities of lubricants, as well as high‐temperature plastics, where a reduction of two orders of magnitude in wear rate can be achieved at temperatures up to 200°C. Direct application of fluid to the plastics surfaces appears to give better results than impregnation into a porous plastic. The effect of counterface roughness and bearing pressure on wear performance is also discussed.

The friction and wear behaviour of amorphous selenium under lightly loaded contact conditions

This paper describes an experimental friction and wear investigation carried out on amorphous selenium under conditions of light loading. Tribological similarities are found to exist with organic polymers, namely the effect of counterface roughness and transfer film behaviour below the glass transition. Three stages of selenium wear can be identified, all broadly based on plastic interactive effects as dictated by counterface roughness. As a consequence, true contact area is an important parameter characterizing selenium friction and wear. In addition to the optimum frictional and wear conditions found to exist, a maximum load for a minimum wear condition has also been identified.