It is now commonly accepted that real contact area rises linearly with increasing normal load for the contact of rough solids. However, the coefficient of proportionality is distinct in various ...models and simulations. This study advances a general method to determine the area-load proportionality based on the incremental contact concept. A pair of loose bounds on the coefficient of proportionality for general Gaussian random rough surfaces and a tight one working in the thermodynamic limit are derived. The resultant predictions are in accord with numerical results presented in literature. The current study might offer some deep insight into the role of surface morphologies in contact of rough elastic solids.
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•An incremental contact model is proposed for the contact of rough elastic solids.•The role of asperity shape in contact deformation is studied.•Bounds on the proportionality between contact area and normal load are derived for various rough surfaces.•The applicability of the current model is verified by comparisons with simulation results in literature.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
Friction behavior is crucial for metal deformation and failure analysis. Tests on contact between specimens and rigid mold (S-S) and rubber (S-R) were conducted. Results show that S-S friction ...coefficient decreases with normal pressure, while S-R static friction coefficient increases and kinetic remains low. Friction coefficient is influenced by real contact area changes due to softer surface deformation. S-S friction depends on specimen strength, and S-R friction on rubber properties. A proposed friction model based on contact area variation accurately predicts friction changes with normal pressure and workpiece properties. Integrated with finite element simulation, the model improves efficiency and accuracy compared to classical Coulomb friction model.
•Friction coefficient depends on the normal pressure and the properties of the softer surface in the two contact surfaces.•The relationship between true contact area and normal pressure follows an exponential function.•Friction coefficient decreases with normal load for workpiece-rigid die contact.•The use of variable friction coefficients can effectively improve simulation accuracy and efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
The impact of non-Gaussian height distribution on the real contact area evolution of elastic, frictionless and non-adhesive contact is studied. The Weibull probability function is used to model the ...height distribution, as it can capture surfaces of practical relevance. The set of variables needed to parametrise the problem is discussed, including the shape parameter of the height distribution, the topography’s wavelength ratio and the Hurst exponent. As the topographies become more non-Gaussian, a significant deviation from the Gaussian case is observed. Moreover, the spectral properties show a distinct effect on different non-Gaussian surfaces and the dependency on Nayak’s parameter is not inherited. A power-law evolution of the real contact area is found to fit the numerical results obtained with the boundary element method precisely. Finally, two semi-analytical asperity-based models are compared with numerical results, using the statistics of artificially generated topographies. The qualitative behaviour predicted with the numerical simulations is captured.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Capillary adhesion contributes to friction of sliding multi-asperity contact in humid environment by increasing the solid-solid contact area; whereas the increased adhesion from capillary meniscus is ...hard to measure due to elastic recovery of contacting asperities. Here, we report the first direct measurement of increased interfacial adhesion from mesoscopic menisci in a macroscale multi-asperity contact comprising soft elastomer and glass surfaces with a diminishing water film. Results also found capillary adhesion and its contribution to a high transient friction coefficient decrease with increased interfacial roughness, which is consistent with prior literature hypotheses.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
The contact characteristics of the blade-disk structure are difficult to predict due to complex working conditions. This paper presented an improved model to predict its real contact area. Firstly, ...the deformation state and load of the asperities with different radii on the deterministic rough surface are determined based on improved truncation theory. Subsequently, the real contact area of the blade-disk structure is obtained by combined with the finite element method at a lower computational cost. Finally, the application of the proposed method in the wear prediction of dovetail blade-disk structures is demonstrated, which proves that considering roughness is significant for wear prediction. The proposed method has great potential in predicting the wear characteristics of complex systems under real working conditions.
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•The proposed model based on truncation theory has high computational accuracy.•Real contact area of complex systems can be calculated at low computational cost.•Real wear volume of the blade-disk structure can be predicted at low cost.•Friction coefficient and roughness affect real contact area of blade-disk structure.•The prediction of wear volume may be significantly larger if roughness is neglected.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
Real contact area is a challenging phenomenon in tribology, where despite established theoretical models, detailed experimental studies are still lacking. This work is focused on the evolution of the ...real contact area of multi-asperity steel contacts during sliding, by using sub-micron characterisation of entire multi-asperity contact area and simultaneous measurement of the friction force. Steel-sapphire contact was monitored by using an in-situ optical system in real time during 5 mm of unidirectional sliding in surface roughness range Ra = 0.1–1.0 µm and normal loads up to the nominal contact pressure equal to steel yield strength (Y). The results showed that the initial real contact area caused by static loading increased during sliding. At low nominal contact pressure of 0.3Y, the increase in real contact area was the largest: for Ra = 0.1 µm it went from 9.5% of the nominal area under static conditions to 15.0% after sliding, a 56% relative increase, and for Ra = 1.0 µm it went from 5.0% to 11.5% after sliding, a 106% increase. The increase in real contact area was smaller at higher nominal contact pressures of 0.6Y and 1.0Y. At 1.0Y for Ra = 0.1 µm the real contact area went from 18.0% to 21.8% after sliding and for Ra = 1.0 µm it went from 9.4% to 12.9% after sliding. The coefficient of friction increased with roughness at the lowest nominal contact pressure 0.3Y (for Ra = 0.1 µm it was 0.24 and for Ra = 1.0 µm it was 0.29) but became independent of roughness at higher contact pressures (on average 0.18).
•In-situ measurement of real contact area evolution during 5 mm of sliding.•Whole multi-asperity steel contacts observed using optical method.•Real contact area increased due to sliding from the initial static conditions.•The largest increase from static to sliding conditions was at the lowest load.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZRSKP
Determining the very nature of an interface within a sliding contact is a central question in tribology. Contacts between asperities, normal and shear stresses and resulting real contact area are ...important characteristics governing friction losses but also wear. Despite the fundamental nature of these quantities, being able to experimentally and in-situ measure them is still a real challenge. This is even truer as far as extreme contact conditions are concerned, i.e. operating under high temperatures and/or contact pressures and/or sliding velocities.
This work presents the development of a method for in-operando contact monitoring of a sliding contact. Based on an ultrasonic array of 32 elements, this approach uses wave propagation to assess the contact area and wear between two metallic materials. Each element of the probe is individually pulsed with a given sequence to construct a picture of the contact zone based on the reflected signals. A numerical model is first developed to study the propagation of the ultrasonic waves through a friction pin and its interaction with the contact interface. The influence of contact stresses and contact size on the ultrasonic signals is investigated in order to establish a method for online estimating the contact area.
The experimental set-up is then described with the integration of an ultrasonic array on an open tribometer. A multi-channel pulser receiver is employed to control the probe while a dedicated software is used for processing the signals and monitoring in real time the data. Finally, an experimental campaign is performed with a cemented carbide pin sliding on a AISI 1045 steel to validate the methodology.
•This campaign has explored ultrasonic reflectometry results as well as time of flight analysis WCCo rubbing against AISI1045.•The systems showed a different reaction between the two sliding conditions while giving a good repeatability.•In the case of dry sliding contact, the US signal is mostly sensitive to the geometrical modification of the rubbing pin end.•The heat flow has a secondary effect and give information of the thermal properties during sliding.•An thermal diffusion appears in the pins when it is leaving the contact and can be monitored with TOF analysis.•This paper also shown a deep correlation between geometry and thermal loads which is hard to decorelate.•This technology showed that the US technology is capable of monitoring the wear on metallic materials on a scale of 0–60 μm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We investigate the measurement of real contact area, denoted by Ar, between various floor materials and rubber. Observation of Ar plays an important role for better understanding of frictional force. ...The Ar between them, however, has yet to be observed over regions wider than what an optical microscope can cover. Current optical microscopy techniques are limited by the measurement time required to observe the whole apparent contact area. Further, it is difficult to reproduce actual contact situations between the rubber and the floor materials because at least one of the contacting specimens must be transparent. Usually, glass plates much harder than rubber are used as counter specimens. In this study, we observed the Ar between a transparent silicone rubber and the various floor materials by using a laser microscope with a wide field of view, allowing us to observe the whole apparent contact area of 9 mm × 7 mm for a very short time. By using transparent rubber, we were able to reproduce the actual contact situations of the rubber-floor specimens, which is impossible with glass plates. The measurement of Ar when the apparent contact area was too small suffered from large fluctuations in measurement values due to waviness of the floor specimen. We investigated the apparent contact area required to accurately understand the relationship between frictional force and Ar and clarified the influence of waviness of the floor materials on the distribution of Ar.
•We measure real contact area, Ar, between various floor materials and rubber.•We use an ultra-transparent silicone rubber instead of a glass plate.•Measurement values of Ar in small regions show large fluctuation.•Wide field of view microscope leads to less variation in measurement values of Ar.•Effect of grooves in floor specimen on the distribution of Ar is clearly demonstrated.
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Contact surfaces do not make contact perfectly because such surfaces have a lot of asperities. The real contact area is much smaller than the nominal contact area, and the real contact areas has a ...non-uniform distribution because of the waviness in the contact surface. The contact stiffness is influenced not only by the deformation of the asperities, but also by the distribution of the real contact areas. In general, a contact surface with a uniform distribution of the real contact areas has greater contact stiffness. However, this requires a grinding finish and costs more than the cutting finish. In this study, a method for uniformly distributing the real contact areas easily, is proposed to improve the contact stiffness of a contact surface finished by cutting. The method is called the cutter mark cross (CMC) method. The allowable waviness in the CMC method is shown. In addition, the effect of the CMC method is investigated by experimentation. The results show that the real contact areas can be distributed uniformly using the CMC method. The horizontal and vertical contact stiffness can also be improved.
•Cutter mark cross method (CMC method) is proposed.•The distribution of real contact area can be controlled by CMC method.•The contact stiffness is improved by CMC method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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