High Static Friction Research Articles

Majority of Ruptures in Large Continental Strike-Slip Earthquakes Are Unilateral: Permissive Evidence for Hybrid Brittle-to-Dynamic Ruptures

Abstract Finite-element models of neotectonics require transform faults to rupture seismically even where preseismic shear stresses are low, presumably by dynamic-weakening mechanisms. A long-standing objection is that, if a rupture initiated at an asperity with high static friction stresses, which then transitioned to low dynamic-weakening stresses, local stress drop would be near total and on the order of 80 MPa, which is 4×–40× greater than observed. But the 5 Mw ≥ 7.8 transform earthquakes since 2000 initially ruptured on the branch faults of small net slip (Stein and Bird, 2024). If the slip initiates on a branch fault with different slip physics and no dynamic weakening, this solves the stress-drop problem. We propose that most large shallow earthquakes are hybrid ruptures, which begin on branch faults of small slip with high shear stresses, and then continue propagating on a connected dynamically weakened fault of large slip, even where shear stresses are low. One prediction of this model is that most large shallow ruptures should be unilateral. We test this prediction against the 100 largest (m ≥ 6.49) shallow continental strike-slip earthquakes 1977–2022, using information from the Global Centroid Moment Tensor and International Seismological Centre catalogs. The differences in time and location between the epicenter and the epicentroid define a horizontal “migration” velocity vector for the evolving centroid of each rupture. Early aftershock locations are summarized by a five-parameter elliptical model. Using the geometric relations between these (and mapped traces of active faults) and guided by a symmetrical decision table, we classified 55 ruptures as apparently unilateral, 30 as bilateral, and 15 as ambiguous. Our finding that a majority (55%–70%) of these ruptures are unilateral permits the interpretation that a majority of ruptures are hybrids, both in terms of geometry (branch fault to transform) and in terms of the physics of their fault slip.

Tribological properties of titanium alloy with micro-nano multiscale texturing against bone under simulated implant contact conditions

The stability of a titanium alloy screw implant in a spinal internal fixation system is primarily influenced by its tribological properties. We integrated laser texturing and anodic oxidation technology to fabricate surface micro/nanostructures on titanium alloys. The tribological properties of titanium alloys against bone were investigated by mimicking the progress of screw implantation. The results demonstrated that surface structure reduced the dynamic friction of the titanium alloy under dry conditions and increased the static friction under wet conditions. The low sliding friction in the dry state facilitated the initial implantation of the titanium alloy screws. Conversely, the high static friction in the wet state prevents post-implantation loosening of the titanium alloy screw and enhances its stability within bone tissue.

Static friction measurement methodology for the assessment of performance of industrial valves at high temperatures: Case study for a nickel-based alloy coating

High static friction between functional surfaces poses a serious challenge for industrial valves, particularly for those used in the advanced ultra-supercritical power generation industry that requires raising the steam temperature to 760 °C. In this context, we established the static friction measurement methodology by evaluating the effects of temperature, loading time, and number of static cycles on the evolution of the static coefficient of friction up to 800 °C. This methodology was applied on a nickel-based solid lubricant coating that appears an attractive candidate to withstand very harsh environments. The tribological behavior is explained in terms of a competition of three mechanisms governing the static friction processes: micro-welding or sintering of asperities, creep of asperities, and formation of lubricious oxides.

Fractional Maxwell viscoelastic model to explain dynamic magneto-viscoelastic properties of an isotropic magnetorheological elastomer containing flake-shaped magnetic particles

ABSTRACT A modified fractional Maxwell viscoelastic model was developed for the dynamic magneto-viscoelastic behavior of an isotropic magnetorheological elastomer (MRE) having flake-shaped iron particles. This model can capture the low-frequency and high magnetic field static friction contribution with frequency, both in storage and loss modulus. The magnetic dipole-dipole interaction model is used to find the influence of the external magnetic field on viscoelastic behavior. The variation of field-induced modulus with the magnetic field is well described using the Langevin function. The predicted and experimental measured storage and loss modulus agree with the present model with an accuracy of ≥99%. The present model is compared with the results of spherical particle-based MRE.

Friction between human skin and incontinence pads in the presence of barrier protection products.

This novel experimental work aims to bring further knowledge of frictional performance of common barrier products used in the treatment of incontinence-associated dermatitis and determine how the skin-pad interface changes when a treatment is applied to the skin. Key data is reported and there is an in-depth analysis into friction profiles which reveals great differences between how different skin-pad tribosystems operate when exposed to commercially available barrier treatments. In a wet-pad state Barrier cream A (3M™ Cavilon™ Barrier cream) reduced friction and had much lower dynamic and static coefficients of friction than the other barrier treatments (Barrier cream B (Sorbaderm Barrier cream) and the Barrier spray C (Sorbaderm Barrier spray)). Barrier cream A provided stable friction coefficients in reciprocating sliding, whereas the other treatments, and untreated skin, did not display this unique characteristic. The barrier spray gave rise to high static friction coefficients and exhibited the most stick-slip. All three candidate barrier protection products were found to reduce directional differences in the static coefficient of friction: indicative of reduced shear loading. Knowledge of the desirable frictional properties would drive innovation in product development, and benefit companies, clinicians and users.

Frictional Response of Reinforced Polymers under Quasistatic and Fast-Transient Dry Contact Conditions

Reinforced polymers have recently gained interest because of their high stiffness associated with the classical features and cost-effectiveness of polymers. A further characteristic, suitable for several applications, is the possibility to provide high frictional and wear resistance. The frictional response of commercially available reinforced materials was here investigated in a wide range of contact boundary conditions. Experimental tests were performed on different test benches, to investigate the material frictional response under either quasistatic or fast-dynamic contact solicitations. While carbon-fiber-reinforced material exhibits a stable but low friction coefficient, the glass-fiber-reinforced material leads to the suitable combination of high friction and low wear. The PPS material, 40% (wt) glass-reinforced polymer, sliding against the Ti6Al4V titanium alloy, provided high static friction coefficients (>0.4). The same material pair was then tested in endurance under fast-dynamic contact solicitations, highlighting their resistance to wear.

Influence of Material Characteristics of Hoppers on Particle Flow Behavior

In the previous study, different structures of hoppers were proposed. And the dust suppression performance of hoppers were evaluated. In this paper, different materials of hoppers were selected.And influence of different material on particle behaviors were studied based on the discrete element method (DEM). Results shows that the wall material with low collision recovery coefficient for the hopper has positive effect on suppressing dust diffusion.and the wall material with high static friction coefficient showed little effect on the particle flow state through the hopper.

Dynamics of Droplets Impacting on Aerogel, Liquid Infused, and Liquid-Like Solid Surfaces.

Droplets impacting superhydrophobic surfaces have been extensively studied due to their compelling scientific insights and important industrial applications. In these cases, the commonly reported impact regime was that of complete rebound. This impact regime strongly depends on the nature of the superhydrophobic surface. Here, we report the dynamics of droplets impacting three hydrophobic slippery surfaces, which have fundamental differences in normal liquid adhesion and lateral static and kinetic liquid friction. For an air cushion-like (super)hydrophobic solid surface (Aerogel) with low adhesion and low static and low kinetic friction, complete rebound can start at a very low Weber (We) number (∼1). For slippery liquid-infused porous (SLIP) surfaces with high adhesion and low static and low kinetic friction, complete rebound only occurs at a much higher We number (>5). For a slippery omniphobic covalently attached liquid-like (SOCAL) solid surface, with high adhesion and low static friction similar to SLIPS but higher kinetic friction, complete rebound was not observed, even for a We as high as 200. Furthermore, the droplet ejection volume after impacting the Aerogel surface is 100% across the whole range of We numbers tested compared to other surfaces. In contrast, droplet ejection for SLIPs was only observed consistently when the We was above 5-10. For SOCAL, 100% (or near 100%) ejection volume was not observed even at the highest We number tested here (∼200). This suggests that droplets impacting our (super)hydrophobic Aerogel and SLIPS lose less kinetic energy. These insights into the differences between normal adhesion and lateral friction properties can be used to inform the selection of surface properties to achieve the most desirable droplet impact characteristics to fulfill a wide range of applications, such as deicing, inkjet printing, and microelectronics.

A Novel Process for Manufacturing High-Friction Rings with a Closely Defined Coefficient of Static Friction (Relative Standard Deviation 3.5%) for Application in Ship Engine Components.

In recent years, there has been an increased uptake for surface functionalization through the means of laser surface processing. The constant evolution of low-cost, easily automatable, and highly repeatable nanosecond fibre lasers has significantly aided this. In this paper, we present a laser surface-texturing technique to manufacture a surface with a tailored high static friction coefficient for application within driveshafts of large marine engines. The requirement in this application is not only a high friction coefficient, but a friction coefficient kept within a narrow range. This is obtained by using nanosecond-pulsed fibre lasers to generate a hexagonal pattern of craters on the surface. To provide a suitable friction coefficient, after laser processing the surface was hardened using a chromium-based hardening process, so that the textured surface would embed into its counterpart when the normal force was applied in the engine application. Using the combination of the laser texturing and surface hardening, it is possible to tailor the surface properties to achieve a static friction coefficient of ≥0.7 with ~3–4% relative standard deviation. The laser-textured and hardened parts were installed in driveshafts for ship testing. After successfully performing in 1500 h of operation, it is planned to adopt the solution into production.

The Design and Analysis of a Novel Passive Quasi-Zero Stiffness Vibration Isolator

This project aims to design a novel passive quasi-zero stiffness vibration isolator (QZS-VI) and analyze the static and dynamic mechanical properties of the QZS-VI. First, a novel combination of V-shaped lever, plate spring and cross-shaped structure (VL-PS-CS) vibration isolation platform is designed, and a nonlinear QZS-VI is built by parallel connecting VL-PS-CS and coil spring. Second, the static and dynamic modeling of QZS-VI are derived considering the geometrical nonlinearity of V-shaped lever and the large deflection of plate spring, and the average method is applied to obtain the displacement transmissibility. Third, the effects of different structural parameters (e.g., the lengths of long arm and short arm of V-shaped lever, the assembly angle between two arms, the thickness of plate spring) on the static mechanical and equivalent nonlinear friction properties of QZS-VI are thoroughly investigated. Finally, the vibration isolation performance of the designed QZS-VI is compared with another QZS-VI of buckled beam mechanism and traditional linear vibration isolator. The QZS-VI with VL-PS-CS fully explores the nonlinear advantages of plate spring and V-shaped lever and can achieve excellent high static and low dynamic stiffness and nonlinear friction properties. The superior static mechanical properties and nonlinear friction of QZS-VI can be tuned with different structural parameters. The designed QZS-VI exhibits much smaller resonant frequency, lower peak value and more stability property at the peak frequency than other isolators due to its special nonlinear friction and stiffness properties. The designed QZS-VI is practical, novel and suitable for low-frequency vibration isolation. The innovative structure provides novel insights into the design of passive vibration isolators and has great potential for application in engineering practice.

Experimental Study on Micro Forming of Structured Surfaces for High Static Friction Connection Elements

Bolt connections are the most prevalent technical solution to join several devices. To meet high requirements on lightweight constructions and safety-relevant technologies bolt connections require additional security elements or surface modifications to increase static friction without damaging the workpiece surface significantly. One possible solution is the micro structuring of the connection element surface within the conventional forming process chain. For the manufacturing of micro structured connection elements a micro structured forming tool is needed. Therefore, the forming tool has to feature a negative geometry of the connection element surface micro geometry. Requirements on forming tool materials are high hardness in combination with high wear resistance and good toughness. Suitable technologies to manufacture such micro structured metal dies are laser beam machining (LBM), electrochemical machining (ECM) and electrical discharge machining (EDM), respectively. In this study the micro forming process of high static friction connection elements is investigated. The manufactured connection element surfaces are analyzed after the forming experiments and the results are associated with the surfaces of the metal dies. Therefore the surfaces of the utilized metals dies are compared with each other and with a grinded reference surface and characteristic parameters are analyzed. The comparison is based on the resulting surface roughness parameters and surface conditions before and after lubricated forming experiments. At least wear of the metal dies after multiple forming operations is analyzed. As one result, ECM manufactured metal dies have shown a high degree of replication in combination with high wear resistance.

Low-friction nanojoint prototype

High surface energy of individual nanostructures leads to high adhesion and static friction that can completely hinder the operation of nanoscale systems with movable parts. For instance, silver or gold nanowires cannot be moved on silicon substrate without plastic deformation. In this paper, we experimentally demonstrate an operational prototype of a low-friction nanojoint. The movable part of the prototype is made either from a gold or silver nano-pin produced by laser-induced partial melting of silver and gold nanowires resulting in the formation of rounded bulbs on their ends. The nano-pin is then manipulated into the inverted pyramid (i-pyramids) specially etched in a Si wafer. Due to the small contact area, the nano-pin can be repeatedly tilted inside an i-pyramid as a rigid object without noticeable deformation. At the same time in the absence of external force the nanojoint is stable and preserves its position and tilt angle. Experiments are performed inside a scanning electron microscope and are supported by finite element method simulations.

Slip of a Two-degree-of-freedom Spring-slider Model in the Presence of Slip-dependent Friction and Viscosity

In this study, we study the slip of a two-degree-of-freedom spring-slider model, consisting of two sliders, in the presence of slip-dependent friction and viscosity. Simulation results show that the coupling between the sliders is weak when the stiffness ratio, s , of the model is smaller than 5 and/or either U c1 or U c2 , which are the characteristic displacements of slip-dependent friction law at the two sliders, is smaller than 0.5. The patterns of motions of two sliders yielded by large U c1 and small U c2 are opposite to those by small U c1 and large U c2 . The ratio of static friction force at slider 2 to that at slider 1 is a factor in influencing the motions of two sliders. A higher static friction force at slider 2 leads to a longer delay time to trigger its motion. Slider 2 cannot move when the static friction force at it is higher than a critical value which will depend on other model parameters. The presence of viscosity between the slider and moving plate results in increases in duration times and predominant periods of motions of sliders and depresses the generation of nonlinear behavior. Viscosity results in small amplitudes and low velocities of motions of sliders.

Heating, weakening and shear localization in earthquake rupture.

Field and borehole observations of active earthquake fault zones show that shear is often localized to principal deforming zones of order 0.1-10 mm width. This paper addresses how frictional heating in rapid slip weakens faults dramatically, relative to their static frictional strength, and promotes such intense localization. Pronounced weakening occurs even on dry rock-on-rock surfaces, due to flash heating effects, at slip rates above approximately 0.1 m s-1 (earthquake slip rates are typically of the order of 1 m s-1). But weakening in rapid shear is also predicted theoretically in thick fault gouge in the presence of fluids (whether native ground fluids or volatiles such as H2O or CO2 released by thermal decomposition reactions), and the predicted localizations are compatible with such narrow shear zones as have been observed. The underlying concepts show how fault zone materials with high static friction coefficients, approximately 0.6-0.8, can undergo strongly localized shear at effective dynamic friction coefficients of the order of 0.1, thus fitting observational constraints, e.g. of earthquakes producing negligible surface heat outflow and, for shallow events, only rarely creating extensive melt. The results to be summarized include those of collaborative research published with Nicolas Brantut (University College London), Eric Dunham (Stanford University), Nadia Lapusta (Caltech), Hiroyuki Noda (JAMSTEC, Japan), John D. Platt (Carnegie Institution for Science, now at *gramLabs), Alan Rempel (Oregon State University) and John W. Rudnicki (Northwestern University).This article is part of the themed issue 'Faulting, friction and weakening: from slow to fast motion'.

Temperature- and time dependency on high friction poly(styrene-co-butyl methacrylate) coated paper

For several industrial applications, high friction surfaces with low adhesion are essential. Here, a poly(styrene-co-butyl methacrylate) polymer latex is coated on paper to achieve a high static friction at the interface between a coating and e.g. a wood pallet. At this interface, the adhesion should be low enough for easy removal of objects placed on the coated paper. The static friction is measured with a custom designed and constructed frictometer and is investigated as a function of temperature from 25 to 55°C and the resting time. Furthermore, the static friction is investigated with varying coating thicknesses and coatings containing calcium based fillers. Results show that the static friction is increasing non-linearly with both temperature and resting time. Furthermore, an amount of 10wt% filler increases static friction. In conclusion, the static friction coefficient between coated paper and wood are up to 700% of uncoated paper depending on temperature and resting time.

Laser surface texturing for high friction contacts

A pulsed, nanosecond fibre laser with wavelength of 1064nm was used to texture grade 316 stainless steel and ‘low alloy’ carbon steel in order to generate contacts with high static friction coefficients. High friction contacts have applications in reducing the tightening force required in joints or to easily secure precision fittings, particularly for larger components where standard methods are difficult and expensive. Friction tests performed at normal pressures of 100MPa and 50MPa have shown that very high static friction coefficients greater than 1.25, an increase of 346% over untextured samples at 100MPa, can be easily achieved by single pass laser texturing of both contacting surfaces with the use of low pulse separations. The high static friction coefficients, obtained at 100MPa normal pressure with textures with up to 62.5μm pulse separation (processing speed ∼0.67cm2/s), were found to be associated with a significant amount of plastic deformation caused by the high normal pressures. As a result, higher normal pressures were found to result in higher friction coefficients.

GA-Optimized Fuzzy-Feedforward-Bias Control of Motion by a Rugged Electrohydraulic System

An electrohydraulic system with a proportional valve and industry-grade cylinder has been used to target the servoclass tracking performance. Such systems have a wide range of heavy-duty applications, where the environment could be quite dirty along with the demands becoming faster and more precise every day. High static friction in the cylinder and large deadband of the valve in the system pose control challenges that are more severe than in a system with a servovalve and a low-friction cylinder. A fuzzy-feedforward-bias controller has been developed and a genetic algorithm has been used to optimize the controller parameters. The real-time control experiments revealed excellent tracking throughout the cycle for sinusoidal displacements beyond 1.5 Hz.

Physical principles of fluid-mediated insect attachment - Shouldn’t insects slip?

Insects use either hairy or smooth adhesive pads to safely adhere to various kinds of surfaces. Although the two types of adhesive pads are morphologically different, they both form contact with the substrate via a thin layer of adhesive fluid. To model adhesion and friction forces generated by insect footpads often a simple “wet adhesion” model is used, in which two flat undeformable substrates are separated by a continuous layer of fluid. This review summarizes the key physical and tribological principles that determine the adhesion and friction in such a model. Interestingly, such a simple wet-adhesion model falls short in explaining several features of insect adhesion. For example, it cannot predict the observed high static friction forces of the insects, which enable them to cling to vertical smooth substrates without sliding. When taking a closer look at the “classic” attachment model, one can see that it is based on several simplifications, such as rigid surfaces or continuous layers of Newtonian fluids. Recent experiments show that these assumptions are not valid in many cases of insect adhesion. Future tribological models for insect adhesion thus need to incorporate deformable adhesive pads, non-Newtonian properties of the adhesive fluid and/or partially “dry” or solid-like contact between the pad and the substrate.

Nanosecond laser texturing for high friction applications

A nanosecond pulsed Nd:YAG fibre laser with wavelength of 1064nm was used to texture several different steels, including grade 304 stainless steel, grade 316 stainless steel, Cr–Mo–Al ‘nitriding’ steel and low alloy carbon steel, in order to generate surfaces with a high static friction coefficient. Such surfaces have applications, for example, in large engines to reduce the tightening forces required for a joint or to secure precision fittings easily. For the generation of high friction textures, a hexagonal arrangement of laser pulses was used with various pulse overlaps and pulse energies. Friction testing of the samples suggests that the pulse energy should be high (around 0.8mJ) and the laser pulse overlap should be higher than 50% in order to achieve a static friction coefficient of more than 0.5. It was also noted that laser processing increases the surface hardness of samples which appears to correlate with the increase in friction. Energy-Dispersive X-ray spectroscopy (EDX) measurements indicate that this hardness is caused by the formation of hard metal-oxides at the material surface.

High-vacuum adhesion and friction properties of sliding contact-mode micromachines

The evolution of adhesion and friction in contact-mode micromachines operated in high vacuum was studied by tracking changes in the adhesive pressure, interfacial shear strength, and static coefficient of friction with accumulating sliding cycles. Low adhesion and high static friction observed during the initial stage of sliding were followed by monotonically intensifying adhesion and decreasing friction until reaching an equilibrium stage at steady-state sliding. This trend revealed the existence of two friction regimes in which asperity deformation and adhesion were the dominant friction mechanisms. Scanning electron microscopy and atomic force microscopy observations indicated that sliding resulted in physical and chemical surface changes. The evolution of the adhesion and friction properties with sliding cycles is attributed to the increase of both the real contact area and the work of adhesion due to nanoscale surface smoothening and the removal of contaminant adsorbents, respectively.