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1
Han, Yujin, Pierre-Marie Thebault, Corentin Audes, Xuelin Wang, Haiwoong Park, Jian-Zhong Jiang e Arnaud Caron. "Temperature and chemical effects on the interfacial energy between a Ga–In–Sn eutectic liquid alloy and nanoscopic asperities". Beilstein Journal of Nanotechnology 13 (23 agosto 2022): 817–27. http://dx.doi.org/10.3762/bjnano.13.72.
Testo completoAbstract (sommario):
The interfacial energies between a eutectic Ga–In–Sn liquid alloy and single nanoscopic asperities of SiOx, Au, and PtSi have been determined in the temperature range between room temperature and 90 °C by atomic force spectroscopy. For all asperities used here, we find that the interfacial tension of the eutectic Ga–In–Sn liquid alloy is smaller than its free surface energy by a factor of two (for SiOx) to eight (for PtSi). Any significant oxide growth upon heating studied was not detected here, and the measured interfacial energies strongly depend on the chemistry of the asperities. We also observe a weak increase of the interfacial energy as a function of the temperature, which can be explained by the reactivity between SiOx and Ga and the occurrence of chemical segregation at the liquid alloy surface.
2
Wiertlewski, Michaël, Rebecca Fenton Friesen e J. Edward Colgate. "Partial squeeze film levitation modulates fingertip friction". Proceedings of the National Academy of Sciences 113, n. 33 (1 agosto 2016): 9210–15. http://dx.doi.org/10.1073/pnas.1603908113.
Testo completoAbstract (sommario):
When touched, a glass plate excited with ultrasonic transverse waves feels notably more slippery than it does at rest. To study this phenomenon, we use frustrated total internal reflection to image the asperities of the skin that are in intimate contact with a glass plate. We observed that the load at the interface is shared between the elastic compression of the asperities of the skin and a squeeze film of air. Stroboscopic investigation reveals that the time evolution of the interfacial gap is partially out of phase with the plate vibration. Taken together, these results suggest that the skin bounces against the vibrating plate but that the bounces are cushioned by a squeeze film of air that does not have time to escape the interfacial separation. This behavior results in dynamic levitation, in which the average number of asperities in intimate contact is reduced, thereby reducing friction. This improved understanding of the physics of friction reduction provides key guidelines for designing interfaces that can dynamically modulate friction with soft materials and biological tissues, such as human fingertips.
3
Wu, Chu Han, Liang Chi Zhang, Shan Qing Li, Zheng Lian Jiang e Pei Lei Qu. "Effect of Asperity Plastic Deformation on the Interface Friction in Metal Forming". Key Engineering Materials 626 (agosto 2014): 222–27. http://dx.doi.org/10.4028/www.scientific.net/kem.626.222.
Testo completoAbstract (sommario):
This paper investigates the effect of the plastic deformation of surface asperities on the interface friction in metal forming involving multi-scale deformation with random surface topography. The equivalent interfacial layer (EIL) introduced by the authors previously was used to integrate the Reynolds equation with the plastic deformation of the randomly distributed surface asperities. The contributions of solid-lubricant interaction, lubricant viscosity and microscopic deformation were therefore included efficiently in a conventional macroscopic finite element analysis. The merit of the method was demonstrated by an investigation into the metal strip rolling, whose friction, lubrication and pressure distribution are otherwise hard to be characterized accurately.
4
Komvopoulos, K., e D. H. Choi. "Elastic Finite Element Analysis of Multi-Asperity Contacts". Journal of Tribology 114, n. 4 (1 ottobre 1992): 823–31. http://dx.doi.org/10.1115/1.2920955.
Testo completoAbstract (sommario):
The plane-strain contact problem of an elastic half-space indented by a nominally flat rigid surface having a finite number of regularly spaced cylindrical asperities is investigated using the finite element method to gain an understanding of the interactions in multi-asperity contacts. The significance of the number and spacing of asperities on the contact behavior at the center and edges of the interfacial region is examined. Subsurface stress fields of multi-asperity contacts are presented for various asperity distributions and indentation depths. Asperity interaction effects are quantified in terms of representative parameters, such as the maximum contact pressure, normal load, and maximum von Mises equivalent stress, normalized with similar quantities of the single-asperity contact problem. These nondimensional parameters are principally affected by the spacing and radius of asperities and secondarily by the indentation depth. Significant deviations from the single-asperity Hertzian solution may be encountered, especially in the neighborhood of asperity contacts, because of the unloading and superposition mechanisms which depend on the distance and radius of asperities and indentation depth. The finite element results are in fair qualitative agreement with the phenomenological behavior and analytical predictions.
5
Komvopoulos, K., N. Saka e N. P. Suh. "The Mechanism of Friction in Boundary Lubrication". Journal of Tribology 107, n. 4 (1 ottobre 1985): 452–62. http://dx.doi.org/10.1115/1.3261108.
Testo completoAbstract (sommario):
The primary friction mechanism between boundary-lubricated sliding surfaces was investigated. Experiments were performed on well-polished aluminum, copper, and chromium using mineral oil lubricant. It was found that the prevailing boundary lubrication model, which is based on the adhesion between asperities and shearing of the lubricant film, cannot account for the formation of plowing grooves on polished surfaces. Scanning electron micrographs of the worn surfaces and surface profiles have shown that plowing is the dominant mechanism of friction in boundary lubrication. Theoretical analysis has shown that the coefficient of friction depends on the sharpness and the size of the entrapped wear debris or the surface asperities, and the interfacial “frictional” conditions. Reasonable agreement was obtained between theoretical and experimental friction coefficients.
6
Komvopoulos, K., e W. Yan. "Three-Dimensional Elastic-Plastic Fractal Analysis of Surface Adhesion in Microelectromechanical Systems". Journal of Tribology 120, n. 4 (1 ottobre 1998): 808–13. http://dx.doi.org/10.1115/1.2833783.
Testo completoAbstract (sommario):
High adhesion is often encountered at contact interfaces of miniaturized devices, known as microelectromechanical systems, due to the development of capillary, electrostatic, and van der Waals attractive forces. In addition, deformation of contacting asperities on opposing surfaces produces a repulsive interfacial force. Permanent surface adhesion (referred to as stiction) occurs when the total interfacial force is attractive and exceeds the micromachine restoring force. In the present study, a three-dimensional fractal topography description is incorporated into an elastic-plastic contact mechanics analysis of asperity deformation. Simulation results revealing the contribution of capillary, electrostatic, van der Waals, and asperity deformation forces to the total interfacial force are presented for silicon/silicon and aluminum/aluminum material systems and different mean surface separation distances. Results demonstrate a pronounced effect of surface roughness on the micromachine critical stiffness required to overcome interfacial adhesion.
7
Komvopoulos, K., N. Saka e N. P. Suh. "Plowing Friction in Dry and Lubricated Metal Sliding". Journal of Tribology 108, n. 3 (1 luglio 1986): 301–12. http://dx.doi.org/10.1115/1.3261181.
Testo completoAbstract (sommario):
Experimental evidence for plowing under dry and lubricated sliding conditions is presented and analytical expressions for the coefficient of friction due to plowing are obtained. The theoretical friction coefficient was found to be a function of the sharpness of the hard asperities, the interfacial “friction” conditions and the shape of the plastic zone. The agreement between theoretical and experimental friction coefficients from lubricated sliding and cutting experiments was remarkably good. The discrepancy between theory and experiment in the case of dry sliding between like metals was shown to be due to plastic deformation of the asperities. Consequently, a different model for plowing was proposed for the case of dry sliding between like metals which produced estimates for the coefficient of friction in fair agreement with the experimental results.
8
Takahashi, Yasuo, Terumi Nakamura, Yoshihiro Asakura e Masakatsu Maeda. "Influence of surface asperities on interfacial extension during solid state pressure welding". IOP Conference Series: Materials Science and Engineering 61 (1 agosto 2014): 012001. http://dx.doi.org/10.1088/1757-899x/61/1/012001.
Testo completo
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Maciejewski, Jan, Sebastian Bąk e Paweł Ciężkowski. "Modelling of Rock Joints Interface under Cyclic Loading". Studia Geotechnica et Mechanica 42, n. 1 (19 marzo 2020): 36–47. http://dx.doi.org/10.2478/sgem-2019-0030.
Testo completoAbstract (sommario):
AbstractThe problem of numerical simulation of the material interface response under monotonic and cyclic loading is of fundamental scientific and engineering importance. In fact, such interfaces occur in most engineering and geotechnical structures. The present work is devoted to the deformational response analysis of contact interfaces under monotonic and cyclic loads. The class of materials includes rock and structural joints, soil structure interfaces, masonry and cementitious joints, localized shear bands and so on.The aim of the proposed model is to simulate the cyclic shear test under constant normal load. The associated dilatancy effect is associated with the configurational effects of asperity interaction or dilatancy of wear debris layer. The large primary asperities are assumed as responsible for interfacial dilation and small size asperities as governing frictional sliding and hysteresis response. The elliptic loading yield function is assumed to translate and rotate during progressive or reverse loading events. The model formulation is discussed and confronted with experimental data.
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De Meyere, Robin M. G., Kay Song, Louise Gale, Stephen Harris, Ian M. Edmonds, Thomas J. Marrow, Eduardo Saiz, Finn Giuliani, David E. J. Armstrong e Oriol Gavaldà-Diaz. "A novel trench fibre push-out method to evaluate interfacial failure in long fibre composites". Journal of Materials Research 36, n. 11 (23 marzo 2021): 2305–14. http://dx.doi.org/10.1557/s43578-021-00153-1.
Testo completoAbstract (sommario):
AbstractTraditional fibre push-outs for the evaluation of interfacial properties in long fibre ceramic matrix composites present their limitations—solutions for which are addressed in this work by introducing the novel trench push-out test. The trench push-out makes use of a FIB milling system and an SEM in-situ nanoindenter to probe a fibre pushed into a trench underneath, allowing in-situ observations to be directly correlated with micromechanical events. SiCf/BN/SiC composites—candidate material for turbine engines—were used as model materials in this work. Different fibre types (Hi-Nicalon and Tyranno type SA3) were coated with BN interphases, presenting mean interfacial shear stresses of 14 ± 7 MPa and 20 ± 2 MPa, respectively, during fibre sliding. The micromechanical technique enabled visualisation of how defects in the interphase (voids, inclusions & milled notches) or in the fibre (surface asperities, non-uniform coatings) affected the variability of interfacial property measurement. Graphic abstract
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Khosravizadeh, Negar, Duowei Lu, Yichen Liao, Baoqiang Liao e Pedram Fatehi. "Simulation and Experimental Analysis of Microalgae and Membrane Surface Interaction". Colloids and Interfaces 7, n. 1 (20 marzo 2023): 24. http://dx.doi.org/10.3390/colloids7010024.
Testo completoAbstract (sommario):
The microalgae-induced membrane system applied in wastewater treatment has attracted attention due to microalgae’s outstanding nutrient fixation capacity and biomass harvesting. However, the fundamental understanding of the interaction of microalgae and membrane surfaces is still limited. This study presents experimental and numerical methods to analyze the attachment of microalgae to the membrane. An atomic force microscope (AFM) analysis confirmed that a polydimethylsiloxane (PDMS) sensor, as a simulated membrane surface, exhibited a rougher surface morphology than a polyurethane (PU) sensor did. The contact angle and adsorption analysis using a quartz crystal microbalance confirmed that the PDMS surface, representing the membrane surface, provided a better attachment affinity than the PU surface for microalgae because of the lower surface tension and stronger hydrophobicity of PDMS. The simulation studies of this work involved the construction of roughly circular-shaped particles to represent microalgae, rough flat surfaces to represent membrane surfaces, and the interaction energy between particles and surfaces based on XDLVO theory. The modeling results of the microalgae adsorption trend are consistent and verified with the experimental results. It was observed that the interfacial energy increased with increasing the size of particles and asperity width of the membrane surface. Contrarily, the predicted interaction energy dropped with elevating the number of asperities and asperity height of the microalgae and membrane. The most influential parameter for controlling interfacial interaction between the simulated microalgae and membrane surface was the asperity height of the membrane; changing the height from 50 nm to 250 nm led to alteration in the primary minimum from −18 kT to −3 kT. Overall, this study predicted that the microalgae attachment depends on the size of the asperities to a great extent and on the number of asperities to a lesser extent. These results provide an insight into the interaction of microalgae and membrane surface, which would provide information on how the performance of microalgae-based membrane systems can be improved.
12
Takahashi, Y., e M. Tanimoto. "Experimental Study of Interfacial Contacting Process Controlled by Power Law Creep". Journal of Engineering Materials and Technology 117, n. 3 (1 luglio 1995): 336–40. http://dx.doi.org/10.1115/1.2804548.
Testo completoAbstract (sommario):
Interfacial contacting processes under a high temperature and a high bonding pressure (T = 973 K, P = 30 MPa) are experimentally studied, using oxygen free copper. The faying surfaces were machined by lathe, resulting in controlled regular surface asperities. The asperity angle of surface ridges was changed from 10 to 60 deg. The change in the interfacial deformation mode with the asperity angle has been investigated. Results show the interfacial contact process is strongly influenced by the asperity angle (shape of surface ridge). The bonding tests were carried out in high vacuum atmosphere (10−4 Pa) so that the surface oxide film need not be considered. Experimental results are in good agreement with the results calculated by a finite element model, in which the interfacial contact is assumed to be produced by power law creep alone. It was thus suggested that void coalescence is governed by power law creep under the present test conditions (T = 973 K and P = 30 MPa) except for the final stage of bonding. Experimental results also suggest that the elementary rate process of interfacial contact due to power law creep is classified into two types; surface folding and interfacial expansion. Here, the surface folding is the phenomenon that two faying surfaces are overlapped to each other and the interfacial expansion means that the bonded interface area is extended along the bond-interface.
13
Danyluk, Steven, e Sum Huan Ng. "Mechanical Mechanisms of Chemical Mechanical Polishing". Advanced Materials Research 47-50 (giugno 2008): 1486–89. http://dx.doi.org/10.4028/www.scientific.net/amr.47-50.1486.
Testo completoAbstract (sommario):
This paper describes a mechanical mechanism of chemical mechanical polishing (CMP) and the model is applied to the polishing of silicon substrates by polyurethane pads and slurries containing fumed silica as is typically done in the manufacture of integrated circuits. The model utilizes the concept that the polishing pad surface contains asperities that support the normal load on the wafer, and that friction and hydrodynamic forces influence wear. The interfacial fluid pressure can significantly influence the normal pressures on the wafers and its effects modify the wear rate predictions.
14
Weber, B., T. Suhina, A. M. Brouwer e D. Bonn. "Frictional weakening of slip interfaces". Science Advances 5, n. 4 (aprile 2019): eaav7603. http://dx.doi.org/10.1126/sciadv.aav7603.
Testo completoAbstract (sommario):
When two objects are in contact, the force necessary to overcome friction is larger than the force necessary to keep sliding motion going. This difference between static and dynamic friction is usually attributed to the growth of the area of real contact between rough surfaces in time when the system is at rest. We directly measure the area of real contact and show that it actually increases during macroscopic slip, despite the fact that dynamic friction is smaller than static friction. This signals a decrease in the interfacial shear strength, the friction per unit contact area, which is due to a mechanical weakening of the asperities. This provides a novel explanation for stick-slip phenomena in, e.g., earthquakes.
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Levert, Joseph A., Steven Danyluk e John Tichy. "Mechanism for Subambient Interfacial Pressures While Polishing With Liquids". Journal of Tribology 122, n. 2 (24 agosto 1999): 450–57. http://dx.doi.org/10.1115/1.555381.
Testo completoAbstract (sommario):
This paper reports the results of a model for predicting the development of subambient pressures during the polishing of flat hard substrates by sliding against a compliant pad in the presence of a slurry (liquid). This work is an extension of our prior experimental work on the polishing of single crystal silicon wafers with polyurethane pads and high pH slurries containing silica particles. Subambient pressures have important implications in the polishing rate and uniformity of silicon and, therefore, in the manufacture of large-scale integrated circuits. The subambient pressure is the result of pad asperity compression at the wafer leading edge followed by elastic reexpansion beneath the wafer due to the nonuniform wafer/pad contact stress. Liquid is expelled from interasperity voids where high leading edge contact stress causes asperities to be compressed. Lower contact stress behind the leading edge causes asperity reexpansion leading to recreation of interasperity voids and subambient liquid pressures. A Poiseuille like in-flow of liquid from the sides of the wafer limits the value of the subambient pressure. Numerical simulations predict subambient pressures as a function of liquid viscosity and relative velocity of the pad and wafer and the pad and wafer mechanics which follow the same trend as the experimental data. [S0742-4787(00)01702-1]
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Roberts, A. D. "A Guide to Estimating the Friction of Rubber". Rubber Chemistry and Technology 65, n. 3 (1 luglio 1992): 673–86. http://dx.doi.org/10.5254/1.3538633.
Testo completoAbstract (sommario):
Abstract Vulcanized rubber, as a material, can exhibit extremes in friction level when utilized in all manner of mechanical devices. There is no single value of friction coefficient for a particular vulcanizate. Guidelines for estimating the friction of a rubber component can be based on the idea that the friction force will depend upon the real area of contact that the component makes with its counter-surface. That depends upon such factors as vulcanizate hardness, viscoelastic response, shape, and surface finish. The latter can influence hysteresis losses, as can asperities on the counter-surface. The friction will also depend upon the interfacial shear strength. This is related to the nature of the contact materials and is reduced in the presence of any lubricants or contaminants.
17
Suh, Allison Y., Sung-Chang Lee e Andreas A. Polycarpou. "Design Optimization of Ultra-Low Flying Head-Disk Interfaces Using an Improved Elastic-Plastic Rough Surface Model". Journal of Tribology 128, n. 4 (9 giugno 2006): 801–10. http://dx.doi.org/10.1115/1.2345399.
Testo completoAbstract (sommario):
Sub-5nm flying head-disk interfaces (HDIs) designed to attain extremely high areal recording densities of the order of Tbit∕in2 are susceptible to strong adhesive forces, which can lead to subsequent contact, bouncing vibration, and high friction. Accurate prediction of the relevant interfacial forces can help ensure successful implementation of ultra-low flying HDIs. In this study, an improved rough surface model is developed to estimate the adhesive, contact, and friction forces as well as the mean contact pressure relevant to sub-5nm HDIs. The improved model was applied to four different HDIs of varying roughness and contact conditions, and was compared to the sub-boundary lubrication rough surface model. It was found that the interfacial forces in HDIs undergoing primarily elastic-plastic and plastic contact are more accurately predicted with the improved model, while under predominantly elastic contact conditions, the two models give similar results. The improved model was then used to systematically investigate the effect of roughness parameters on the interfacial forces and mean contact pressure (response). The trends in the responses were investigated via a series of regression models using a full 33 factorial design. It was found that the adhesive and net normal interfacial forces increase with increasing mean radius R of asperities when the mean separation is small (≈0.5nm), i.e., pseudo-contacting interface, but it increases primarily with increasing root-mean-square (rms) surface height roughness between 2 and 4nm, i.e., pseudo-flying interface. Also, increasing rms roughness and decreasing R, increases the contact force and mean contact pressure, while the same design decreases the friction force. As the directions of optimization for minimizing the individual interfacial forces are not the same, simultaneous optimization is required for a successful ultra-low flying HDI design.
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Balokhonov, Ruslan, Varvara Romanova, Eugen Schwab, Aleksandr Zemlianov e Eugene Evtushenko. "COMPUTATIONAL MICROSTRUCTURE-BASED ANALYSIS OF RESIDUAL STRESS EVOLUTION IN METAL-MATRIX COMPOSITE MATERIALS DURING THERMOMECHANICAL LOADING". Facta Universitatis, Series: Mechanical Engineering 19, n. 2 (11 luglio 2021): 241. http://dx.doi.org/10.22190/fume201228011b.
Testo completoAbstract (sommario):
A technique for computer simulation of three-dimensional structures of materials with reinforcing particles of complex irregular shapes observed in the experiments is proposed, which assumes scale invariance of the natural mechanical fragmentation. Two-phase structures of metal-matrix composites and coatings of different spatial scales are created, with the particles randomly distributed over the matrix and coating computational domains. Using the titanium carbide reinforcing particle embedded into the aluminum as an example, plastic strain localization and residual stress formation along the matrix-particle interface are numerically investigated during cooling followed by compression or tension of the composite. A detailed analysis is performed to evaluate the residual stress concentration in local regions of bulk tension formed under all-round and uniaxial compression of the composite due to the concave and convex interfacial asperities.
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Soós, Eniko, e Tibor Goda. "Numerical Analysis of Sliding Friction Behaviour of Rubber". Materials Science Forum 537-538 (febbraio 2007): 615–22. http://dx.doi.org/10.4028/www.scientific.net/msf.537-538.615.
Testo completoAbstract (sommario):
A study has been made of asperity interaction of unlubricated steel/rubber sliding pair. The aim is to study the effect of the internal friction (hysteresis) of rubber on the friction force. In the two-dimensional finite element analysis, asperities are modeled by cylinders and both the interfacial adhesion and the friction at steel-rubber interface are neglected. Rate-dependent material behavior of rubber is described, as a first approximation, by a three-parameter Zener-model. It is found that the viscoelastic properties of rubber have a strong influence on the hysteresis component of friction. Distribution of energy loss generated over a cycle of contact in the rubber asperity is also studied. It is concluded that the energy dissipation is most intensive at a certain depth below the rubber surface.
20
Bidulsky, Robert, Jana Bidulská, Tibor Kvačkaj e Marco Actis Grande. "Case study of advanced processed OFHC copper by dry sliding wear test". Acta Metallurgica Slovaca 29, n. 1 (23 marzo 2023): 34–38. http://dx.doi.org/10.36547/ams.29.1.1734.
Testo completoAbstract (sommario):
The wear behaviour of copper material processed by ECAP (Equal Channel Angular Pressing) and orbital forging (OF) is presented in this study. Dry sliding wear tests were carried out for the wear behaviour of the investigated system. Oxygen-free high thermal conductivity (OFHC) copper was used for testing. The new combination of metal forming processes was used because of ease of fabrication. Additionally, wear rate, friction coefficient and wears mechanisms were observed. The friction resistance is caused by the destruction of the adhesion between surface asperities in metal friction. Moreover, increased asperity interactions connected with wear particle entrapment gradually increase the friction coefficient. These results show the metal forming process's positive influence in reducing interfacial adhesion and asperity deformation. Finally, the combinations of newly used advanced processing demonstrated excellent wear characteristics of copper.
21
Jeng, Yeau-Ren, e Pay-Yau Huang. "A Material Removal Rate Model Considering Interfacial Micro-Contact Wear Behavior for Chemical Mechanical Polishing". Journal of Tribology 127, n. 1 (1 gennaio 2005): 190–97. http://dx.doi.org/10.1115/1.1828068.
Testo completoAbstract (sommario):
Chemical Mechanical Polishing (CMP) is a highly effective technique for planarizing wafer surfaces. Consequently, considerable research has been conducted into its associated material removal mechanisms. The present study proposes a CMP material removal rate model based upon a micro-contact model which considers the effects of the abrasive particles located between the polishing interfaces, thereby the down force applied on the wafer is carried both by the deformation of the polishing pad asperities and by the penetration of the abrasive particles. It is shown that the current theoretical results are in good agreement with the experimental data published previously. In addition to such operational parameters as the applied down force, the present study also considers consumable parameters rarely investigated by previous models based on the Preston equation, including wafer surface hardness, slurry particle size, and slurry concentration. This study also provides physical insights into the interfacial phenomena not discussed by previous models, which ignored the effects of abrasive particles between the polishing interfaces during force balancing.
22
Zhang, Yi, Wei Wang, Kun Liu, Baohong Tong, Zhaowen Hu e Ruhong Song. "Thermomechanical analysis on the frictional contact behavior of a high-strength steel 22MnB5–die steel H13 tribopair at 800 °C by experiment and finite-element simulation". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 235, n. 9 (6 gennaio 2021): 1958–73. http://dx.doi.org/10.1177/1350650120980868.
Testo completoAbstract (sommario):
High-strength boron steels are widely used in manufacturing the auto bodies and parts of light-weight vehicles, but the high rates of surface scratches and die wear have consistently occurred during hot stamping for these steels. For an in-depth understanding of the tribological characteristics at this interface, the frictional contact behavior and thermomechanical mechanisms of boron steel 22MnB5 against die steel H13 at 800 °C were studied through experiments and finite-element simulations. The coefficient of friction and worn surface topography were investigated by pin-on-disk sliding tests. A three-dimensional thermomechanical finite-element model of a friction pair was established to explore the interfacial dynamic variations. Experimental and simulation results show that severe elastic–plastic deformation occurred on the worn surface of the boron steel, whereas an increase in the load decreased the coefficient of friction within a certain range because the growth rate of shear force was slower than that of the normal force. When the finite-element model was changed from the gradual loading stage to the initial sliding stage, the tangential friction force further increased the plastic deformation on the surface of boron steel. The scratches and furrows were mainly caused by the compression and shear from asperities of the rough surface, as confirmed by the high-frictional-stress regions concentrated on the peaks and flanks of asperities. During the high-temperature and high-pressure experiments, the plasticized and softened surface materials of the boron steel adhered to the die surface readily, resulting in peeling and delamination.
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Zhu, Shengguang, e Liyong Ni. "Calculation and AFM Experimental Research on Slip Friction for Unlubricated Spherical Contact with Roughness Effect". Micromachines 12, n. 11 (21 novembre 2021): 1428. http://dx.doi.org/10.3390/mi12111428.
Testo completoAbstract (sommario):
Previous research on friction calculation models has mainly focused on static friction, whereas sliding friction calculation models are rarely reported. In this paper, a novel sliding friction model for realizing a dry spherical flat contact with a roughness effect at the micro/nano scale is proposed. This model yields the sliding friction by the change in the periodic substrate potential, adopts the basic assumptions of the Greenwood–Williamson random contact model about asperities, and assumes that the contact area between a rigid sphere and a nominal rough flat satisfies the condition of interfacial friction. It subsequently employs a statistical method to determine the total sliding friction force, and finally, the feasibility of this model presented is verified by atomic force microscopy friction experiments. The comparison results show that the deviations of the sliding friction force and coefficient between the theoretical calculated values and the experimental values are in a relatively acceptable range for the samples with a small plasticity index (Ψ≤1).
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Cochard, A., L. Bureau e T. Baumberger. "Stabilization of Frictional Sliding by Normal Load Modulation". Journal of Applied Mechanics 70, n. 2 (1 marzo 2003): 220–26. http://dx.doi.org/10.1115/1.1546241.
Testo completoAbstract (sommario):
This paper presents the stability analysis of a system sliding at low velocities (<100 μm⋅s−1) under a periodically modulated normal load, preserving interfacial contact. Experiments clearly evidence that normal vibrations generally stabilize the system against stick-slip oscillations, at least for a modulation frequency much larger than the stick-slip one. The mechanical model of L. Bureau, T. Baumberger, and C. Caroli validated on the steady-state response of the system, is used to map its stability diagram. The model takes explicitly into account the finite shear stiffness of the load-bearing asperities, in addition to a classical state and rate-dependent friction force. The numerical results are in excellent quantitative agreement with the experimental data obtained from a multicontact frictional system between glassy polymer materials. Simulations at larger amplitude of modulation (typically 20 percent of the mean normal load) suggest that the nonlinear coupling between normal and sliding motion could have a destabilizing effect in restricted regions of the parameter space.
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Wang, R. Z., Z. Suo, A. G. Evans, N. Yao e I. A. Aksay. "Deformation mechanisms in nacre". Journal of Materials Research 16, n. 9 (settembre 2001): 2485–93. http://dx.doi.org/10.1557/jmr.2001.0340.
Testo completoAbstract (sommario):
Nacre (mother-of-pearl) from mollusc shells is a biologically formed lamellar ceramic. The inelastic deformation of this material has been experimentally examined, with a focus on understanding the underlying mechanisms. Slip along the lamellae tablet interface has been ascertained by testing in compression with the boundaries oriented at 45° to the loading axis. The steady-state shear resistance τss has been determined and inelastic strain shown to be as high as 8%. The inelastic deformation was realized by massive interlamellae shearing. Testing in tension parallel to the tablets indicates inelastic strain of about 1%, occurring at a steady-state stress, σsss ≈ 110 MPa. The strain was associated with the formation of multiple dilatation bands at the intertablet boundaries accompanied by interlamellae sliding. Nano-asperities on the aragonite tablets and their interposing topology provide the resistance to interfacial sliding and establish the level of the stress needed to attain the inelastic strain. Detailed mechanisms and their significance for the design of robust ceramics are discussed.
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Patitsas, A. J. "Squeal vibrations, glass sounds, and the stick-slip effect". Canadian Journal of Physics 88, n. 11 (novembre 2010): 863–76. http://dx.doi.org/10.1139/p10-077.
Testo completoAbstract (sommario):
The origin of the squeal acoustic emissions when a chalk is rubbed on a blackboard or better on a ceramic plate, and those when a wet finger is rubbed on a smooth surface, such as a glass surface, is sought in the stick-slip effect between the rubbing surfaces. In the case of the squealing chalk, the stick-slip effect is anchored by shear modes of vibration in about a 0.3 mm thick chalk powder band at the rubbing interface, while in the case of the wet finger on glass, by such modes in a band comprising the finger skin. Furthermore, there are the interfacial bands at the contact areas that result in the decrease of the friction coefficient with relative velocity of slide, i.e., the condition for the stick-slip effect to occur. Such bands are basically composed of the asperities on the surface of the chalk band and of the epidermis ridges and the water layer, respectively.
27
Arroyave, M., W. Perez, J. Quintero, S. Casanova e A. Devia. "Mechanical Measurements of Multilayer Thin Films Obtained by a PAPVD System". Microscopy and Microanalysis 11, S03 (dicembre 2005): 138–41. http://dx.doi.org/10.1017/s1431927605051081.
Testo completoAbstract (sommario):
The need of techniques for determining the mechanical properties of thin films, e.g. hardness coatings on ion beam treated surfaces has prompted a study of the microindentation hardness technique. The present interest is driven to a good understanding of the adhesion, friction, wear, and indentation processes. In most of the solid-solid interfaces of technological relevance, it occurs contact in many asperities, and this is why the study of fundamental properties of micro-mechanic and tribology of surfaces and interfaces is very important. The recent developments of different microscopic techniques based on tips and force surface devices (i.e. AFM, FM, LFM) allowed investigations of interfacial problems with high resolution and have led to the nanoscale regime the mechanical properties study for a wide spectrum of materials. In this work a method for Young's modulus determination of hard coatings multilayers of TiN/ZrN is evaluated. This method is based on AFM and spectroscopy-force modes [1-2].
28
Suk, M. "The Effect of Disk Roughness on the Wear of Contact Recording Heads". Journal of Tribology 118, n. 4 (1 ottobre 1996): 794–99. http://dx.doi.org/10.1115/1.2831610.
Testo completoAbstract (sommario):
In conventional disk files, the slider is supported by an air-bearing when the disk is rotating at its designed speed. With the continued reduction of magnetic spacing in order to increase the areal density, a natural extension of the traditional recording system is contact recording. We investigate the wear of the contact recording head designed for such a class of rigid magnetic disk files where the read/write element carrying slider is intended to remain in continuous contact during every phase of the disk drive operation. In particular, we study the effect of disk roughness and load on the wear rate of the recording head. It is observed that the wear rate is proportional to initial interfacial load, however the observation cannot be extrapolated beyond the loads studied in the paper. The experimental observations agree well with expectations for a system where an abrasive wear model applies. We also show that the wear rate is predominantly governed by the existence of isolated asperities that lie well outside of three standard deviations of the disk surface roughness.
29
Bernardin, John D., e Issam Mudawar. "A Leidenfrost Point Model for Impinging Droplets and Sprays". Journal of Heat Transfer 126, n. 2 (1 aprile 2004): 272–78. http://dx.doi.org/10.1115/1.1652045.
Testo completoAbstract (sommario):
This study presents, for impinging droplets and sprays, a model of the Leidenfrost point (LFP); the minimum liquid/solid interface temperature required to support film boiling on a smooth surface. The present model is an extension of a previously developed sessile drop model, based on bubble nucleation, growth, and merging criteria, as well as surface cavity size characterization [3]. The basic concept of the model is that for liquid/solid interface temperatures at and above the LFP, a sufficient number of cavities are activated and the bubble growth rates are sufficiently fast that a continuous vapor layer is established nearly instantaneously between the liquid and the solid. For impinging droplets, the influence of the rise in interfacial pressure created by the impact of the droplet with the surface, must be accounted for in determining fluid properties at the liquid-solid interface. The effect of droplet impact velocity on the LFP predicted by the model is verified for single impinging droplets, streams of droplets, as well as sprays. While the model was developed for smooth surfaces on which the roughness asperities are of the same magnitude as the cavity radii (0.1–1.0 μm), it is capable of predicting the boundary or limiting Leidenfrost temperature for rougher surfaces with good accuracy.
30
Song, H., V. S. Deshpande e E. Van der Giessen. "Discrete dislocation plasticity analysis of loading rate-dependent static friction". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, n. 2192 (agosto 2016): 20150877. http://dx.doi.org/10.1098/rspa.2015.0877.
Testo completoAbstract (sommario):
From a microscopic point of view, the frictional force associated with the relative sliding of rough surfaces originates from deformation of the material in contact, by adhesion in the contact interface or both. We know that plastic deformation at the size scale of micrometres is not only dependent on the size of the contact, but also on the rate of deformation. Moreover, depending on its physical origin, adhesion can also be size and rate dependent, albeit different from plasticity. We present a two-dimensional model that incorporates both discrete dislocation plasticity inside a face-centred cubic crystal and adhesion in the interface to understand the rate dependence of friction caused by micrometre-size asperities. The friction strength is the outcome of the competition between adhesion and discrete dislocation plasticity. As a function of contact size, the friction strength contains two plateaus: at small contact length ( ≲ 0.6 μ m ) , the onset of sliding is fully controlled by adhesion while for large contact length ( ≳ 10 μ m ) , the friction strength approaches the size-independent plastic shear yield strength. The transition regime at intermediate contact size is a result of partial de-cohesion and size-dependent dislocation plasticity, and is determined by dislocation properties, interfacial properties as well as by the loading rate.
31
Sammonds, Peter R., Daniel C. Hatton e Daniel L. Feltham. "Micromechanics of sea ice frictional slip from test basin scale experiments". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n. 2086 (13 febbraio 2017): 20150354. http://dx.doi.org/10.1098/rsta.2015.0354.
Testo completoAbstract (sommario):
We have conducted a series of high-resolution friction experiments on large floating saline ice floes in an environmental test basin. In these experiments, a central ice floe was pushed between two other floes, sliding along two interfacial faults. The frictional motion was predominantly stick–slip. Shear stresses, normal stresses, local strains and slip displacement were measured along the sliding faults, and acoustic emissions were monitored. High-resolution measurements during a single stick–slip cycle at several positions along the fault allowed us to identify two phases of frictional slip: a nucleation phase, where a nucleation zone begins to slip before the rest of the fault, and a propagation phase when the entire fault is slipping. This is slip-weakening behaviour. We have therefore characterized what we consider to be a key deformation mechanism in Arctic Ocean dynamics. In order to understand the micromechanics of sea ice friction, we have employed a theoretical constitutive relation (i.e. an equation for shear stress in terms of temperature, normal load, acceleration, velocity and slip displacement) derived from the physics of asperity–asperity contact and sliding (Hatton et al. 2009 Phil. Mag. 89 , 2771–2799 ( doi:10.1080/14786430903113769 )). We find that our experimental data conform reasonably with this frictional law once slip weakening is introduced. We find that the constitutive relation follows Archard's law rather than Amontons' law, with (where τ is the shear stress and σ n is the normal stress) and n = 26/27, with a fractal asperity distribution, where the frictional shear stress, τ = f fractal T ml w s , where f fractal is the fractal asperity height distribution, T ml is the shear strength for frictional melting and lubrication and w s is the slip weakening. We can therefore deduce that the interfacial faults failed in shear for these experimental conditions through processes of brittle failure of asperities in shear, and, at higher velocities, through frictional heating, localized surface melting and hydrodynamic lubrication. This article is part of the themed issue ‘Microdynamics of ice’.
32
McHale, Glen, Michael I. Newton, Neil J. Shirtcliffe e Nicasio R. Geraldi. "Capillary origami: superhydrophobic ribbon surfaces and liquid marbles". Beilstein Journal of Nanotechnology 2 (10 marzo 2011): 145–51. http://dx.doi.org/10.3762/bjnano.2.18.
Testo completoAbstract (sommario):
In the wetting of a solid by a liquid it is often assumed that the substrate is rigid. However, for an elastic substrate the rigidity depends on the cube of its thickness and so reduces rapidly as the substrate becomes thinner as it approaches becoming a thin sheet. In such circumstances, it has been shown that the capillary forces caused by a contacting droplet of a liquid can shape the solid rather than the solid shaping the liquid. A substrate can be bent and folded as a (pinned) droplet evaporates or even instantaneously and spontaneously wrapped on contact with a droplet. When this effect is used to create three dimensional shapes from initially flat sheets, the effect is called capillary origami or droplet wrapping. In this work, we consider how the conditions for the spontaneous, capillary induced, folding of a thin ribbon substrate might be altered by a rigid surface structure that, for a rigid substrate, would be expected to create Cassie–Baxter and Wenzel effects. For smooth thin substrates, droplet wrapping can occur for all liquids, including those for which the Young’s law contact angle (defined by the interfacial tensions) is greater than 90° and which would therefore normally be considered relatively hydrophobic. However, consideration of the balance between bending and interfacial energies suggests that the tendency for droplet wrapping can be suppressed for some liquids by providing the flexible solid surface with a rigid topographic structure. In general, it is known that when a liquid interacts with such a structure it can either fully penetrate the structure (the Wenzel case) or it can bridge between the asperities of the structure (the Cassie–Baxter case). In this report, we show theoretically that droplet wrapping should occur with both types of solid–liquid contact. We also derive a condition for the transition between the Cassie–Baxter and Wenzel type droplet wrapping and relate it to the same transition condition known to apply to superhydrophobic surfaces. The results are given for both droplets being wrapped by thin ribbons and for solid grains encapsulating droplets to form liquid marbles.
33
Wang, S., e K. Komvopoulos. "A Fractal Theory of the Temperature Distribution at Elastic Contacts of Fast Sliding Surfaces". Journal of Tribology 117, n. 2 (1 aprile 1995): 203–14. http://dx.doi.org/10.1115/1.2831227.
Testo completoAbstract (sommario):
The statistical temperature distribution at fast sliding interfaces is studied by characterizing the surfaces as fractals and considering elastic deformation of the asperities. The fractions of the real contact area in the slow, transitional, and fast sliding regimes are determined based on the microcontact size distribution. For a smooth surface in contact with a rough surface, the temperature rises at the real contact area are determined under the assumption that most of the frictional heat is transferred to one of the surfaces. The interfacial temperature rises are bounded by the maximum temperature rise at the largest microcontact when the fractal dimension is 1.5 or less, and are unbounded when it is greater than 1.5. Higher temperature rises occur at larger microcontacts when the fractal dimension is less than 1.5, and at smaller microcontacts when it is greater than 1.5. For a fractal dimension of 1.5, the maximum temperature rise at a microcontact is independent of its size. The maximum temperature rise at the largest microcontact is expressed as a function of the friction coefficient, sliding speed, elastic and thermal properties, real and apparent contact areas, and fractal parameters. The closed-form solutions for the distribution density function of the temperature rise can be used to calculate the fraction of the real contact area of fast sliding surfaces subjected to temperature rises in any given range. The present theory is applied to boundary-lubricated and dry sliding contacts to determine the fractions of the real contact area where lubricant degradation and thermal surface failure may occur.
34
Spinu, Sergiu. ""THERMOELASTIC DISPLACEMENT AND TEMPERATURE RISE IN A HALF-SPACE DUE TO A STEADY-STATE HEAT FLUX "". International Journal of Modern Manufacturing Technologies 14, n. 3 (20 dicembre 2022): 326–32. http://dx.doi.org/10.54684/ijmmt.2022.14.3.326.
Testo completoAbstract (sommario):
Due to model complexity, classical contact mechanics theory assumes isothermal contact processes, involving bodies with uniform temperatures and no heat transmitted or generated through or near the contact interface. This paper addresses the problem of frictional heating in non-conforming or rough contacts by investigating the thermoelastic behaviour of asperities. The heat generated in a sliding contact by interfacial friction leads to thermoelastic distortion of the contact surface, further modifying contact parameters such as pressure, gap or temperature. The thermal expansion of the contacting bodies must therefore be accounted for when solving the contact problem. The thermoelastic displacement is computed with the aid of the half-space theory and of fundamental solutions for point sources of heat located at the free surface, derived in the literature of heat conduction in solids. The linearity of conduction equations encourages the use of superposition principle in the same way as for the elastic displacement. As the thermoelastic displacement is expressed mathematically as a convolution product, methods derived in contact mechanics for elastic displacement calculation are adapted to the heat conduction equations. The influence coefficients needed to efficiently compute the convolution products are derived, and the Discrete Convolution Fast Fourier Transform technique is applied to improve the algorithm computational efficiency. A similar method is then advanced for the temperature rise on the contact interface due to arbitrary heat input. The predictions of the newly advanced computer programs are tested against existing closed-form solutions for uniform circular or ring heat sources, and a good agreement is found.
35
Moose, C. A., D. A. Koss e J. R. Hellmann. "Interfacial Shear Behavior of Sapphire-Reinforced NiAi Composites". MRS Proceedings 194 (1990). http://dx.doi.org/10.1557/proc-194-293.
Testo completoAbstract (sommario):
AbstractThe interfacial shear behavior in near-equiatomic NiA1 reinforced by sapphire filaments has been examined at room temperature using a fiber pushout test technique. The loaddisplacement data indicate a large variability in the initial interface failure stress, although reverse push behavior indicates a comparatively constant interfacial sliding friction stress. The observed behavior suggests that the presence of asperities on the fiber surfaces and nonuniformities in fiber diameter require constrained plastic flow within the NiAl matrix in order for interfacial shear to occur. The location, shape, severity, and distribution of fiber asperities as well as the uniformity of fiber diameter are critical to the interfacial shear process.
36
Gao, Zhiqiang, Weiping Fu, Wen Wang, Leiting Lou e Jiebei Wu. "Normal Damping Model of Mechanical Joints Interfaces Considering Asperities in Lateral Contact". Journal of Tribology 140, n. 2 (9 ottobre 2017). http://dx.doi.org/10.1115/1.4037954.
Testo completoAbstract (sommario):
A mechanical interface behaves as the stiffness and damping when the interface is bearing a static normal force and a sine normal exciting force. For the interfacial normal damping, a calculating model was proposed. This proposed model studied the lateral contact (shoulder–shoulder contact) between upper and lower asperities in the elastic and elastic-perfectly plastic stages, which is neglected by other classical models. The normal force can be divided into a normal component and a tangential component when two asperities are contacting in dislocation. The relation between the loading–unloading normal component forces and deformation can be calculated, and then the strain energy dissipation between asperities can be gotten by integral. The friction energy dissipation also can be calculated based on the relation between loading–unloading tangential component forces and the slippage. Furthermore, the total interfacial energy dissipation can be obtained according to the statistical theory. Finally, the equivalent viscous damping is estimated using the vibration theory. The proposed model and classical models are compared by simulation and experiment, and it was found that the interfacial damping of the proposed model is more than the damping of the classical models. Moreover, the proposed model is consistent with the experimental results.
37
Shan, Lei, Steven Danyluk e Joseph Levert. "Interfacial Pressure Measurements at Chemical Mechanical Polishing Interfaces". MRS Proceedings 566 (1999). http://dx.doi.org/10.1557/proc-566-187.
Testo completoAbstract (sommario):
We have found that the entrainment of a slurry between a silicon surface and a polyurethane pad will cause the generation of subambient pressure at that interface. These pressures cause the silicon to be further impressed into the pad. We have measured these pressures and this paper reports on the pressure distribution maps over an area beneath a 100mm diameter silicon wafer. The pressures are generally not uniform. The leading 2/3 of the wafer has subambient pressures of the order of 50kPa and the trailing 1/3 of the wafer has positive pressures of approximately 10kPa. The reasons for the subambient pressures is related to the dynamics of the compression of pad asperities, the boundary effects of the silicon edge, the rebound of the asperities, and re-infiltration of the slurry.
38
Carmona, Eric A., e Paul Albertus. "Modeling How Interface Geometry and Mechanical Stress Affect Li Metal / Solid Electrolyte Current Distributions". Journal of The Electrochemical Society, 3 febbraio 2023. http://dx.doi.org/10.1149/1945-7111/acb8e3.
Testo completoAbstract (sommario):
Abstract We develop a coupled electrochemical-mechanical model to assess the current distributions at Li/single-ion conducting solid ceramic electrolyte interfaces containing a parameterized interfacial geometric asperity, and carefully distinguish between the thermodynamic and kinetic effects of interfacial mechanics on the current distribution. We find that with an elastic-perfectly plastic model for Li metal, and experimentally relevant mechanical initial and boundary conditions, the stress variations along the interface for experimentally relevant stack pressures and interfacial geometries are small (e.g., <1 MPa), resulting in a small or negligible influence of the interfacial mechanical state on the interfacial current distribution for both plating and stripping. However, we find that the current distribution is sensitive to interface geometry, with sharper (i.e., smaller tip radius of curvature) asperities experiencing greater current focusing. In addition, the effect on the current distribution of an identically sized lithium peak vs. valley geometry is not the same. These interfacial geometry effects may lead to void formation on both stripping and plating and at both Li peaks and valleys. The presence of high-curvature interface geometry asperities provides an additional perspective on the superior cycling performance of flat, film-based separators (e.g., sputtered LiPON) versus particle-based separators (e.g., polycrystalline LLZO) in some conditions.
39
Shi, Xi, Yunwu Zou e Huibo Fang. "Numerical Investigation of the Three-Dimensional Elastic–Plastic Sloped Contact Between Two Hemispheric Asperities". Journal of Applied Mechanics 83, n. 10 (1 agosto 2016). http://dx.doi.org/10.1115/1.4034121.
Testo completoAbstract (sommario):
For real engineering surfaces contact, most asperities come into contact in a configuration of shoulder-to-shoulder instead of aligned head-on. In this work, a three-dimensional (3D) model of two identical elastic–plastic spherical asperities in contact was developed which characterizes the initial contact offset with polar angle α and azimuthal angle β. The simulations with finite-element method (FEM) show that the adhesive coefficient of friction (COF) is only influenced by large initial azimuthal angle thus mainly depends on interfacial shear strength. The plowing COF is determined, however, by effective contact interference, which reflects the combined effects of α and β. Moreover, a detailed parametric study shows that the load ratio is significantly dependent on Young's modulus and interfacial shear strength, while the maximum elastic rebound force during the unloading phase is mainly dependent on polar angle.
40
Marks, L. D., e K. P. Olson. "Flexoelectricity, Triboelectricity, and Free Interfacial Charges". Small, 25 agosto 2024. http://dx.doi.org/10.1002/smll.202310546.
Testo completoAbstract (sommario):
AbstractTriboelectricity has been a topic of some confusion for many years, probably because it is very diverse and some of the fundamental science has not been clear. This is now starting to change. A few years ago, the importance of flexoelectricity at asperities is pointed out. That paper exploited the established physics of compensation of bound surface or interfacial charges without going into detail. The purpose of this paper is to expand further on this, mapping from the established physics of electrostatics with contact potentials and Maxwell's displacement field to the underlying fundamentals of charge transfer in triboelectricity. Examples from the published literature are used to illustrate this. In the discussion, some of the open questions and challenges to the community are mentioned.
41
Dini, D., e D. A. Hills. "Frictional Energy Dissipation in a Rough Hertzian Contact". Journal of Tribology 131, n. 2 (3 marzo 2009). http://dx.doi.org/10.1115/1.3063697.
Testo completoAbstract (sommario):
The interfacial contact pressure and shear traction distributions are found for a sphere pressed onto an elastically similar half-space whose surface is populated by a uniform array of spherical asperities, when the normal load is constant and an oscillatory shear, less than that needed to cause sliding, is imposed. Details of the load history suffered by asperities in an outer sliding annulus and an inner disk, where they experience partial slip, are found, together with the effects of the roughness on the overall tangential compliance and the frictional energy losses. It is shown that for the example combination of parameters chosen, under light shear loads, the rough contact absorbs less energy than a smooth one subject to the same loading history, but that for larger shearing forces the reverse is true.
42
Huang, Gancai, Chao Liu, Wenzhen Xie e Dongxiang Jiang. "Normal contact stiffness model for fractal surfaces considering scale dependence and friction behavior". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, 16 novembre 2022, 135065012211389. http://dx.doi.org/10.1177/13506501221138995.
Testo completoAbstract (sommario):
The normal contact stiffness on rough surfaces has a significant impact on the interfacial dynamic characteristics of mechanical joints. Based on the fractal geometry theory, this work improves the contact stiffness modeling by considering the complete contact characteristics of multiple asperities and frictional factor. First, to include the property that the critical contact areas of asperities are scale-dependent, the model for the contact stiffness is formed on each scale and the relationship between total stiffness and load on rough surfaces is obtained by the summation of all length scale asperities. Second, friction factor is taken into account in the revised normal contact stiffness model, where a contact friction coefficient is introduced into the equation to incorporate the effects of friction force. Moreover, the influences of fractal dimension D and fractal roughness G on normal contact stiffness and friction coefficient are investigated. Through the comparison of numerical and experimental results, the revised model is shown to be more reasonable and presents higher consistency of the stiffness versus load curve than the original model. It is therefore concluded that a complete and more accurate model for normal contact stiffness is proposed in this work with precise modeling of scale-dependent contact characteristics and friction behavior taken into account, which is critical for exact estimation of rigidity of contact surfaces in industrial applications.
43
Jeng, Yeau-Ren, e Shin-Rung Peng. "Static Friction Model of Elastic-Plastic Contact Behavior of Surface With Elliptical Asperities". Journal of Tribology 131, n. 2 (5 marzo 2009). http://dx.doi.org/10.1115/1.3075857.
Testo completoAbstract (sommario):
The friction coefficient (μ) of a contact surface with elliptical asperities is examined at various values of the plasticity index (ψ), the effective radius ratio (γ), the shear-strength-pressure proportionality constant (c), and the dimensionless limiting interfacial shear strength (τ¯m). The results demonstrate that the friction coefficient of the contact system increases with an increasing value of γ but decreases with an increasing value of ψ. Furthermore, it is shown that Amonton’s law is applicable for contact systems with either a low ψ and a high τ¯m or a high ψ and a low τ¯m. Analyzing the ratio of the nonelastic contact area, it is found that the asperities of a surface characterized by a large γ generally deform elastically at all values of the plasticity index, while those of a surface with a larger c deform plastically, particularly for surfaces with higher values of τ¯m and ψ. Finally, an inspection of the critical dimensionless real contact area shows that the contact mode of the surface is determined primarily by the value of the effective radius ratio.
44
Jin, Fan, Qiang Wan e Xu Guo. "Plane Contact and Partial Slip Behaviors of Elastic Layers With Randomly Rough Surfaces". Journal of Applied Mechanics 82, n. 9 (1 settembre 2015). http://dx.doi.org/10.1115/1.4030742.
Testo completoAbstract (sommario):
A plane contact and partial slip model of an elastic layer with randomly rough surface were established by combining the Greenwood–Williamson (GW) rough contact model and the Cattaneo–Mindlin partial slip model. The rough surface of the elastic layer bonded to a rigid base is modeled as an ensemble of noninteracting asperities with identical radius of curvature and Gaussian-distributed heights. By employing the Hertzian solution and the Cattaneo–Mindlin solution to each individual asperity of the rough surface, we derive the total normal force, the real contact area, and the total tangential force for the rough surface, respectively, and then examine the normal contact and partial slip behaviors of the layer. An effective Coulomb coefficient is defined to account for interfacial friction properties. Furthermore, a typical stick–slip transition for the rough surface was also captured by distinguishing the stick and slip contacting asperities according to their respective indentation depths. Our analysis results show that an increasing layer thickness may result in a larger real contact area, a lower mean contact pressure, and a higher effective Coulomb coefficient.
45
Jiang, Jishen, Bingqian Xu, Weizhe Wang, Richard Amankwa Adjei, Xiaofeng Zhao e Yingzheng Liu. "Finite Element Analysis of the Effects of Thermally Grown Oxide Thickness and Interface Asperity on the Cracking Behavior Between the Thermally Grown Oxide and the Bond Coat". Journal of Engineering for Gas Turbines and Power 139, n. 2 (13 settembre 2016). http://dx.doi.org/10.1115/1.4034259.
Testo completoAbstract (sommario):
Finite element simulations based on an interface cohesive zone model (CZM) have been developed to mimic the interfacial cracking behavior between the α−Al2O3 thermally grown oxide (TGO) and the aluminum-rich Pt–Al metallic bond coat (BC) during cooling from high temperature to ambient temperature. A two-dimensional half-periodic sinusoidal geometry corresponding to interface undulation is modeled. The effects of TGO thickness and interface asperity on the stress distribution and the cracking behavior are examined by parametric studies. The simulation results show that cracking behavior due to residual stress and interface asperity during cooling process leads to stress redistribution around the rough interface. The TGO thickness has strong influence on the maximum tensile stress of TGO and the interfacial crack development. For the sinusoidal asperities, there exists a critical amplitude above which the interfacial cracking is energetically favored. For any specific TGO thickness, crack initiation is dominated by the amplitude while crack propagation is restricted to the combine actions of the wavelength and the amplitude of the sinusoidal asperity.
46
Luo, Xiangcheng, e D. D. L. Chung. "Tribology of Material Contacts under Dynamic Loading, Studied by Electrical Resistance Measurement". MRS Proceedings 697 (gennaio 2001). http://dx.doi.org/10.1557/proc-697-p8.11.
Testo completoAbstract (sommario):
AbstractThe tribology of material contacts under cyclic compression in the direction perpendicular to the plane of the contact was studied by measurement of the contact electrical resistivity of the contact during the dynamic loading. The real-time monitoring allowed observation of both reversible and irreversible effects. The material contacts studied were those involving steel, carbon fiber polymer-matrix composite, cement mortar and graphite, due to their relevance to fastening, concrete structures, electric brushes and electrical pressure contacts. Correlation was made between the contact resistivity and the occurrence of elastic/plastic deformation at asperities. The interfacial structure was found to depend on the stress and the loading history.
47
Hu, Mengsu, e Jonny Rutqvist. "Multi-scale Coupled Processes Modeling of Fractures as Porous, Interfacial and Granular Systems from Rock Images with the Numerical Manifold Method". Rock Mechanics and Rock Engineering, 9 aprile 2021. http://dx.doi.org/10.1007/s00603-021-02455-6.
Testo completoAbstract (sommario):
AbstractThe greatest challenges of rigorously modeling coupled hydro-mechanical processes in fractured rocks at different scales are associated with computational geometry. In addition, selections of continuous or discontinuous models, physical laws, and coupling priorities at different scales based on different geometric features determine the applicability of a numerical model for a certain type of problem. In this study, we present our multi-scale modeling capabilities that have been developed based on the numerical manifold method for analyzing coupled hydro-mechanical processes in fractured rocks. Based on their geometric features, the fractures are modeled as continua—finite-thickness porous zones, and discontinua—discontinuous interfaces and microscale asperities and granular systems. Different governing equations, physical laws, coupling priorities, and approaches for addressing fracture intersections and shearing are then applied to describe these. We applied these models to simulate coupled processes in fractured rocks using realistic geometry obtained from rock images at different scales. We first calculated shearing of a single fracture with different models and demonstrated the impacts of asperities on shearing. We then applied the continuous and discontinuous models to simulate a network of rough fractures, demonstrating that contact dynamics contribute significantly to the geometric, multi-physical evolution of systems where rough fractures are not mineral filled. For a discrete fracture network, our coupled processes modeling demonstrates that shearing of the discrete fractures can have a major impact on stress and pore pressure distribution. Lastly, we applied the discontinuous granular model to simulate evolution of a complex granular system with a deformation band, demonstrating that the deformation band can dominate contact dynamics, the structural and the stress evolution of the granular system.
48
Baker, William, e James L. Rutledge. "Analytical Solution for Transient Thermal Behavior of Two Semisolids with Contact Resistance and Interfacial Heat Generation". ASME Journal of Heat and Mass Transfer, 10 giugno 2024, 1–22. http://dx.doi.org/10.1115/1.4065692.
Testo completoAbstract (sommario):
Abstract The problem of two dissimilar semi-infinite solids at different initial temperatures brought into contact has a well-known simple analytical solution. In the present work, this problem is re-examined with the additional simultaneous complications of both contact resistance and surface heat generation. While contact resistance is always present to some degree due to surface asperities or oxidation layers, heat generation at the contact interface can also occur in certain situations. These situations can occur in applications such as ultrasonic welding or arise in situations involving electromagnetic radiation passing through an optically transparent medium, but dissipating as heat at an interface with an opaque material that is in contact with the transparent material. In this paper, an analytical solution to the unsteady conduction problem is developed that accounts for both contact resistance and interfacial heat generation. The solution confirms that the initially warmer object rapidly decreases in temperature in the vicinity of the interface as heat flows into the cooler object and the heat generated at the interface preferentially flows to the cooler material. After a short time, however, the temperatures of both materials at the interface increase in temperature above even the initial temperature of the initially hotter material. An experiment was performed that verified the analytical solution.
49
Sohail, Tanvir, Rebekah Sweat, Hongbing Lu, Ray Baughman e Samit Roy. "Prediction of interfacial shear strength of CNT overwrapped carbon fibers using molecular dynamics and Fourier series decomposition of surface asperities". Composite Interfaces, 23 febbraio 2023, 1–24. http://dx.doi.org/10.1080/09276440.2023.2180842.
Testo completo
50
Chen, W. Wayne, e Q. Jane Wang. "A Numerical Static Friction Model for Spherical Contacts of Rough Surfaces, Influence of Load, Material, and Roughness". Journal of Tribology 131, n. 2 (3 marzo 2009). http://dx.doi.org/10.1115/1.3063814.
Testo completoAbstract (sommario):
The relative motion between two surfaces under a normal load is impeded by friction. Interfacial junctions are formed between surfaces of asperities, and sliding inception occurs when shear tractions in the entire contact area reach the shear strength of the weaker material and junctions are about to be separated. Such a process is known as a static friction mechanism. The numerical contact model of dissimilar materials developed by the authors is extended to evaluate the maximum tangential force (in terms of the static friction coefficient) that can be sustained by a rough surface contact. This model is based on the Boussinesq–Cerruti integral equations, which relate surface tractions to displacements. The materials are assumed to respond elastic perfectly plastically for simplicity, and the localized hardness and shear strength are set as the upper limits of contact pressure and shear traction, respectively. Comparisons of the numerical analysis results with published experimental data provide a validation of this model. Static friction coefficients are predicted for various material pairs in contact first, and then the behaviors of static friction involving rough surfaces are extensively investigated.