Dynamic Friction Coefficient Research Articles

Preparation of a Ni-P-nanoPTFE Composite Coating on the Surface of GCr15 Steel for Spinning Rings via a Defoamer and Transition Layer and Its Wear and Corrosion Resistance.

In this study, a method of preparing a Ni-P-nanoPTFE composite coating on the surface of GCr15 steel for spinning rings is proposed. The method incorporates a defoamer into the plating solution to inhibit the agglomeration of nano-PTFE particles and pre-deposits a Ni-P transition layer to reduce the possibility of leakage coating. Meanwhile, the effect of varying the PTFE emulsion content in the bath on the micromorphology, hardness, deposition rate, crystal structure, and PTFE content of the composite coatings was investigated. The wear and corrosion resistances of the GCr15 substrate, Ni-P coating, and Ni-P-nanoPTFE composite coating are compared. The results show that the composite coating prepared at a PTFE emulsion concentration of 8 mL/L has the highest concentration of PTFE particles (up to 2.16 wt%). Additionally, its wear resistance and corrosion resistance are improved compared with Ni-P coating. The friction and wear study shows that the nano-PTFE particles with low dynamic friction coefficient are mixed in the grinding chip, which gives the composite coating self-lubricating characteristics, and the friction coefficient decreases to 0.3 compared with 0.4 of Ni-P coating. The corrosion study shows that the corrosion potential of the composite coating has increased by 7.6% compared with that of the Ni-P coating, which shifts from -456 mV to a more positive value of -421 mV. The corrosion current reduces from 6.71 μA to 1.54 μA, which is a 77% reduction. Meanwhile, the impedance increased from 5504 Ω·cm2 to 36,440 Ω·cm2, which is an increase of 562%.

Numerical simulation study on the spontaneous rupture process and its influencing factors of the 2001 MS 8.1 Kunlun earthquake in China

On November 14, 2001, the MS 8.1 Kunlun earthquake occurred in the west of Kunlun Mountain pass in the East Kunlun fault zone of the Qinghai-Tibet Plateau, China. The field investigation and the results of kinematic inversion indicate that it is a strike-slip earthquake with a complex rupture process. The study of the spontaneous rupture process of this earthquake and its influencing factors is of great significance for understanding the occurrence mechanism of continental large earthquakes. First, based on the results of geological survey and kinematic inversion, a three-dimensional non-planar fault model is established. Then, using the curved-grid finite difference method (CG-FDM), the dynamic rupture process of the 2001 MS 8.1 Kunlun earthquake is numerically reproduced by adjusting the parameters for numerical simulation experiments. On this basis, the influence of background stress field, fault geometry and friction coefficient on the surface slip distribution, seismic moment rate function and rupture velocity are discussed respectively. The results show that the important reasons for the super-long rupture scale and super-shear rupture velocity of this earthquake may be the clockwise rotation of the maximum horizontal principal compressive stress along the NNE ∼ NE direction and the low friction coefficient distribution on the whole fault surface. The difference between the dynamic and static friction coefficients along the fault strike may be non-uniform, and it may be larger on the main fault than that on the secondary fault. This will result in a higher level of stress drop on the main fault, leading to the occurrence of super-shear rupture and the slip distribution with the Kusai Lake as the macroseismic epicenter. The large local geometric variation along the strike of the main fault may also have some influence on the distribution of co-seismic slip and the location of the super-shear rupture. In addition, the numerical simulation results in this paper confirm the conclusion that the East Kunlun fault zone has low friction coefficient.

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.

Justification of the soil dem-model parameters for predicting the plow body resistance forces during plowing

The discrete element method has recently become a popular tool for developing soil models to be used for modelling the tillage process, which involves using working tools. The research aims to evaluate the parameters of the contact model particles when modelling tillage with large–sized working tools using the discrete element method. The paper presents the results of calibration of the physico-mechanical parameters of the particles of the soil environment model described using the discrete element method. The model is used for modelling the tillage process using moldboard plow. The parameters of the simulated particles to be studied are the Poisson's ratio, coefficients of static and dynamic friction of particles, Young's modulus, surface energy, particles' diameter, coefficients of static and dynamic metal friction of particles. Calibration was carried out according to the horizontal, vertical and transverse components of the traction resistance of the plow body. The obtained dependences of the components of the plow body traction resistance on soil moisture and surface energy help select parameters for the Hertz-Mindlin contact model while modelling the behavior of the soil environment when interacting with the working tools of tillage and sowing machines.

Spatial Separation of Enantiomers by Field-Modulated Surface Scattering

A new optomechanical chiral resolution scheme for molecules possessing a permanent dipole moment is proposed. The approach involves the following molecular manipulation sequence: (i) a molecular alignment electromagnetic pulse, (ii) a time-delayed dipole orienting static electric field, and (iii) scattering from a frictional surface. The method offers various control parameters including pulse duration and intensity, static field strength, delay time, surface dynamic friction coefficient, and incident molecular velocity that can be tuned to optimize spatial enantioseparation. The scheme is demonstrated for the prototypical HSOH chiral molecule, predicting an enantiomeric excess as high as 50%.

Numerical calculation of barrel chamber mechanical wear based on the principle of dynamic pressure lubrication

Thermal-chemical erosion and mechanical wear are the main factors restricting the service life of barrel weapons. Considering the lack of systematic research on the mechanical wear of the barrel weapons, this paper gives the display expression of the dynamic pressure lubrication friction coefficient in projectile-barrel clearance based on the principle of dynamic pressure lubrication. The trend of friction coefficient is basically consistent with the friction experiment data. In the framework of dynamic pressure lubrication friction, the mechanical wear model of artillery barrel is derived, and the mechanical wear model in the whole life cycle is calculated by using the ALE mesh adaptive technology. The results show that the derived mechanical wear model can accurately describe the material degradation of the barrel chamber. The mechanical wear is mainly concentrated at the beginning of the rifling and the muzzle. After 500 shots, the mechanical wear of the beginning of the rifling and the muzzle are generally 0.3mm and 0.4mm.

Bending mechanics test and parameters calibration of ramie stalks

Research and development of ramie harvesting equipment is a key link to revitalize ramie industry, problems such as the tendency of stalks to tangle and clog the machine are very problematic, seriously affect the quality and fluency of the harvester. The structure of ramie stalk is complex, and the mechanical properties of each component vary greatly, collision between stalk and machine creates complex stress relationship. By building a finite element model, it is possible to analyze the stress state of the stalk during bending from a microscopic perspective, and to analyze the complex stress–strain situation within the stalk. The purpose of this paper is to establish a standard ramie stalk bending finite element model to provide a theoretical basis for the subsequent kinematics and dynamics. Firstly, material experiments were carried out on ramie straw. The structural and mechanical parameters of the straw components were obtained through measurement and calculation tests, and the force–deformation curves for straw bending were obtained. Bending finite element simulations were carried out on the basis of mechanical tests, and the parameters such as dynamic friction coefficient, wood Poisson's ratio and bast Poisson's ratio were determined by the central combination design. Then established an accurate bending finite element simulation model of ramie stalk, the accuracy of the model was verified at the end. In this paper, the key parameters of the ramie stalk model were calibrated through a combination of material tests and simulations. All parameters of the ramie stalk model were finally obtained, and the bending mechanical properties of the ramie stalk were analysed by applying finite element analysis. This bending mechanics simulation model can be used for kinematic and dynamics simulation analysis of conveying and baling to provide a theoretical basis for the structural design of the harvester. The methods explored here can be applied to other slender straw crops.

Highly Durable Bidirectional Rotary Triboelectric Nanogenerator with a Self-Lubricating Texture and Self-Adapting Contact Synergy for Wearable Applications.

Sliding-freestanding triboelectric nanogenerators (SF-TENGs) are desirable for application in wearable power sources; however, improving their durability is the primary challenge. Meanwhile, few studies focus on enhancing the service life of tribo-materials, especially from an anti-friction perspective during dry operation. Herein, for the first time, a surface-textured film with self-lubricating property is introduced into the SF-TENG as a tribo-material, which is obtained by the self-assembly of hollow SiO2 microspheres (HSMs) close to a polydimethylsiloxane (PDMS) surface under vacuum conditions. The PDMS/HSMs film with micro-bump topography simultaneously reduces the dynamic coefficient of friction from 1.403 to 0.195 and increases the electrical output of SF-TENG by an order of magnitude. Subsequently, a textured film and self-adapting contact synergized bidirectional rotary TENG (TAB-TENG) is developed, and the superiorities of the soft flat rotator with bidirectional reciprocating rotation are systematically investigated. The obtained TAB-TENG exhibits a remarkable output stability and an outstanding mechanical durability over 350 000 cycles. Furthermore, a smart foot system for stepping energy harvesting and wireless walking states monitoring is realized. This study proposes a pioneering strategy for extending the lifetime of SF-TENGs and advances it toward practical wearable applications.

Model of Friction with Plastic Contact Nudging: Amontons-Coulomb Laws, Aging of Static Friction, and Nonmonotonic Stribeck Curves with Finite Quasistatic Limit.

We introduce a model of friction between two contacting (stationary or cosliding) rough surfaces, each comprising a random ensemble of polydisperse hemispherical bumps. In the simplest version of the model, the bumps experience on contact with each other only pairwise elastic repulsion and dissipative drag. These minimal ingredients are sufficient to capture a static state of jammed, interlocking contacting bumps, below a critical frictional force that is proportional to the normal load and independent of the apparent contact area, consistent with the Amontons-Coulomb laws of friction. However, they fail to capture two widespread observations: (i)that the dynamic friction coefficient (ratio of frictional to normal force in steady sliding) is a roughly constant or slightly weakening function of the sliding velocity U, at low U, with a nonzero quasistatic limit as U→0 and (ii)that the static friction coefficient (ratio of frictional to normal force needed to initiate sliding) increases ("ages") as a function of the time that surfaces are pressed together in stationary contact, before sliding commences. To remedy these shortcomings, we incorporate a single additional model ingredient: that contacting bumps plastically nudge one another slightly sideways, above a critical contact-contact load. With this additional insight, the model also captures observations (i) and (ii).

A novel dynamic dry friction model for applications in mechanical dynamical systems

This work presents a novel continuously differentiable, dynamic dry friction model, with dependence on normal contact force, slip velocity, and static and dynamic coefficients of friction. The state-of-the-art, Brown and McPhee friction model depends on transitional velocity, which is an empirical parameter. A limitation with this model is that there is no generic approach to select the optimal value for the transitional velocity for a certain application. The simulation results presented in this work highlight the sensitivity of friction force with transitional velocity in Brown and McPhee’s model to obtain smooth solutions, which are supportive in control system applications. It is because control systems require jitter-free signals in order to save costs on low-pass filters. The proposed model overcomes such empirical dependence on transition velocity through a combination of an iterative methodology and an empirical parameterization. In this article, a comprehensive analysis of the proposed friction model and the contributing parameters is carried out. The algorithm to implement the proposed friction model is elaborated. The proposed friction model is then simulated and compared against Brown and McPhee’s model. using a stick-slip benchmark problem. Furthermore, the proposed force model is applied to two spatial multibody systems formulated using index 0 tangent space differential-algebraic equations. The results demonstrate how the proposed friction model can be employed in dynamical mechanical systems. The independence on transitional velocity in the proposed friction model is observed to be effective for obtaining smooth solutions that make it suitable for control system applications.

Laboratory evaluation of microwave heating and skid resistance of pavement friction surfacing using calcined bauxite and magnetite aggregates

A high friction surface treatment (HFST) with magnetite (MT) aggregates instead of conventional calcined bauxite (CB) aggregates as microwave absorbers were prepared in this paper. The deicing properties by microwave heating and long-term skid resistance of HFST with different proportions of CB and MT aggregate were evaluated. The deicing properties by microwave heating of HFST were determined by electromagnetic characteristics, heating surface temperature, and microwave deicing time (MDT) tests. The long-term skid resistance of the HFST was characterized by conducting dynamic friction coefficient and mean profile depth (MPD) tests after long-term polishing using a three-wheel polishing device. The results showed that the electromagnetic characteristics of HFST were enhanced greatly by the addition of MT. The microwave heating efficiency of HFST was enhanced by the increase of MT substitution rate, which further enhanced its microwave deicing efficiency. The microwave deicing efficiency of HFST with MT substitution rate of 25% was 1.4 times that of HFST with MT substitution rate of 0%. Long-term skid resistance of HFST was reduced by the addition of MT, however, HFST with MT substitution rate of 25% also maintained a terminal μ40 and μ60 above 0.7, which can provide higher friction comparable with other high friction aggregate such as taconite, basalt, emery and flint. To improve the deicing properties by microwave heating and maintain high skid resistance, 25% MT replacement rate in HFST is recommended.

Microstructural features, physicο-mechanical properties, and wear behavior of dental translucent polychromic multilayer zirconia of hybrid composition prepared by milling technology.

The present study determined the mechanical properties and the wear behavior, as results of the micro(nano)structure, of the enamel, transition, and dentine layers, which comprise the polychromic multilayer zirconia materials of hybrid composition fabricated by milling technology. Prismatic blocks were fabricated from two commercial pre-sintered dental polychromic multilayer zirconia materials of hybrid composition, IPS e.max ZirCAD Prime (medium and high translucency, from the dentine to the incisal layer) and 3D Pro ML (translucency gradient, from the dentine to the incisal layer) by milling technique, and then, cut into 3 distinct parts to separate the enamel, transition, and dentine layers. The samples were sintered, thermally treated (similarly to the glazing procedure), and polished for characterization. Their microstructure, mechanical properties (determined by nanoindentation and microhardness), and wear behavior (evaluated by scratch test), were examined. The produced materials had a homogeneous and dense nanostructure, where the grain size decreased from the enamel to dentine layer. The mechanical properties decreased from the dentine to enamel layer. However, the three layers manifested similar dynamic friction coefficient. The differences in the above properties in the three layers negligibly influenced the wear behavior of the entire multilayer zirconia material. The properties of dental restorations produced from polychromic multilayer zirconia of hybrid composition by milling technology (i.e., strong, non-fragile, and esthetic materials), anticipate good performance in oral cavity.

Comparative Research on Corrosion Resistant Non-Skid Al and Al-3%Ti Coating Fabricated by Twin Wire arc Spraying

To ensure the lifetime of marine constructions and the safety of workers and pedestrians, corrosion protective non-skid coating is an effective solution. However, the conventional polymer-based coating has some limitations. In this study, newly-suggested Al and Al-3%Ti coatings were deposited on high strength low alloyed steel substrate using twin wire arc spraying (TWAS). The static and dynamic friction coefficients of the Al-based coatings under dry and wet conditions were measured using portable friction testers. To evaluate the corrosion behavior under sea water conditions, a cyclic potentiodynamic polarization test (CPDP) and salt solution immersion test (SSIT) were performed with a 3.5% NaCl solution. To confirm the coating degradation, mechanical properties (Vickers hardness and adhesion strength) were compared before and after SSIT. The results showed that the TWAS Al-based coatings were well fabricated on HSLA steel and had the general microstructure of a thermal spray. The coatings provided excellent corrosion protection for the steel substrate and greatly increased the friction coefficient of the surface. The Vickers hardness slightly increased and adhesion strength decreased after SSIT. The microstructure observation revealed that the TWAS coatings had a bimodal structure induced by non-uniform droplet generation at the TWAS tips. After SSIT, some oxides formed on the surface and porous regions of the coatings. This indicated that the TWAS coating successfully provided corrosion protection and non-skid properties.

Study on Friction and Wear Properties of 3D Braided Carbon Fiber

In this paper, the friction and wear properties of 3D braided carbon fiber wet friction material at 2550r/min, 3800r/min and 5100r/min were studied with MM3000 friction and wear tester, and the wear mechanism was studied with SEM. The results show that the average static friction coefficient of friction materials is 0.153; With the increase of rotating speed, the dynamic friction coefficient decreases from 0.095 to 0.087; The volume wear rate decreased from 9.46*10−8cm3/J to 2.58*10−8cm3/J; The friction torque curves at three different speeds are relatively stable, showing the material has good braking stability. 3D braided carbon fiber friction material has fiber fracture and crack on the raised surface of the material after 1500 times of jointing at three different speeds. The mechanism of friction and wear is abrasive wear and fatigue wear.

Dynamical friction due to fuzzy dark matter on satellites described by axisymmetric logarithmic potentials

A plausible dark matter candidate is an ultralight bosonic particle referred to as fuzzy dark matter. The equivalent mass-energy of the fuzzy dark matter boson is ∼ 10-22 eV and has a corresponding de Broglie wavelength of kiloparsec scale, thus exhibiting wave behaviour in scales comparable to a galactic core, which could not appear in conventional cold dark matter models. The presence of fuzzy dark matter in galactic clusters will impact the motion of their members through dynamical friction. In this work, we present simulations of the dynamical friction on satellites traversing an initially uniform fuzzy dark matter halo. We focus on the satellites whose shapes are beyond spherical symmetry described by ellipsoidal and logarithmic potentials. We find that the wakes created on the fuzzy dark matter halo due to the passage of such satellites are qualitatively different from those generated by spherically symmetric ones. Furthermore, we quantify the dynamical friction coefficient for such systems, finding that the same satellite may experience a drag differing by a factor of 5 depending on its ellipticity and the direction of motion. Finally, we find that the dynamical friction time-scale is close to Hubble time, assuming a satellite of 1011 M ⊙ traversing at 103 km/s a FDM halo whose mean density is ∼ 106 M ⊙ kpc-3.

Study on the shear-slip process and characteristics of fracture in shale

To clarify the shear-slip process and characteristics of fault, we conducted triaxial shear tests driven by displacement on shale samples with prefabricated sawcut and natural fractures, and the acoustic emission (AE) technology was used to monitor the shear-slip process in real-time. According to the test results, the shear-slip process and mechanical characteristics of sawcut and natural fractures were analyzed. The test results indicate that the shear-slip process of fractures can be divided into four stages, improving the confining pressure will cause more serious plastic failure in the shear-slip process, and the increase of roughness will make the phenomenon of “stress drop” more obvious, which is closely related to the earthquake occurrence. Confining pressure and roughness all have implications for the stress thresholds of each stage. With the transition of shear-slip stages, the effects of confining pressure and roughness on the shear-slip of fractures are more drastic. The maximum static friction coefficient μ0 increases with initial roughness increasing and is independent of confining pressure. Due to the strain-strengthening effect of fracture slip, the average value of dynamic friction coefficient μd under simple shear deformation is greater than the maximum static friction coefficient μ0. Based on AE response characteristics, microcracks development, and rupture scale during the shear-slip process were also explored. AE events are mainly distributed along the inclined fracture. The AE response in different shear-slip stages displays pronounced differences, and the AE evolution and macro mechanical characteristics of fractures show significant time-synchronization. The variation of peak frequency can reflect the rupture scale transformation and the influence of confining pressure and roughness. Additionally, the differences in the morphological evolution of sawcut and natural fractures are mainly reflected in the wear pattern, degree and the rock debris attach amount. Finally, we also discussed the micro-deformation mechanism of asperities during the shear-slip process. This work may provide a reference for the research of fault activation and slip in shale reservoirs.

Mixed reality-integrated soft wearable biosensing glove for manipulating objects

Recent advances in flexible sensors and wireless electronics have driven the development of lightweight and ergonomic wearable sensing gloves. Such gloves can be employed in mixed reality (MR) environments to give haptic capabilities during interactions with various objects. However, no prior study shows a quantitative measurement of physical user interactions of object manipulation in MR. Here, we report an MR-integrated soft bioelectronic system on a glove for quantifying the changes in the user's pinching tasks. We use nanomanufacturing techniques to fabricate flexible sensors, wireless circuits, and stretchable interconnectors seamlessly integrated with a wearable glove. The wearable biosensing glove with an integrated capacitive pressure sensor evaluates how users interact directly and indirectly interact with objects. The direct mode describes a user's direct touching and manipulating objects in MR. In contrast, in the indirect mode, objects are located far away and touched via a narrow light beam. The virtual object measurement parameters include mass, movement latency, dynamic friction coefficient, angular drag coefficient, and linear drag coefficient. The experimental results with human subjects show positive, linear relationships between pinching force and dynamic friction coefficient and mass parameters during the direct manipulation mode. Collectively, the MR-enabled wearable biosensing glove system offers unique advantages in detecting physical interactions and sensory feedback for various rehabilitation applications and MR human-machine interfaces.

Performance evaluation of friction dampers considering different metal pairs and loading rates

Metal friction dampers are widely applied for structural energy dissipation and shock absorption, and their dynamic performance needs further study. Cyclic loading tests were conducted on 30 specimens to evaluate the effects of loading sequence and rate under high speed (20 mm/s ∼ 60 mm/s) and low speed (0.2 mm/s ∼ 3 mm/s). The friction pairs included five types: brass-hot rolled steel with untreated surfaces (B-HS), brass-hot rolled steel with polished surfaces (B-PHS), brass-stainless steel (B-SS), stainless steel-hot rolled steel with untreated surfaces (SS-HS), and stainless steel-hot rolled steel with polished surfaces (SS-PHS). The test results showed that all specimens exhibited plump rigid-plastic hysteresis behavior under different loading rates, and the mechanical indices of the specimens met the discreteness requirements of FEMA-356. The loading rates obviously influenced the normal force loss and friction coefficient of the friction interfaces. The static friction coefficients for the five metal friction pairs were recommended, and analytical models of the dynamic friction coefficient concerning loading rate were established. It was suggested that the B-HS, B-PHS, SS-HS, and SS-PHS friction pairs should be pre-friction within the travel range before use, and the friction coefficient of the B-SS and SS-HS friction pairs should be calibrated after the first loading.

Effect of dynamic friction and static friction in finite element analysis of carbon fiber preform

AbstractThis paper aims to improve the accuracy of the finite element analysis for the preform shape transformation according to the difference in the type of carbon fiber and friction force. The carbon fiber type (Toray T700, Zoltek), the fiber direction (0°/90°, ± 45°), and the frictional force were measured, which occurred between the fiber and the mold and between the fiber and the fiber. A comparative experiment was conducted through actual preform production by designating it as a variable for element analysis. The analysis was conducted according to the difference between the static friction coefficient and the dynamic friction coefficient in the molding analysis. Within the range of the Coulomb equation, the shear angle changing was compared with the actual preform shape to show similar results.

A prediction model of the friction coefficient of asphalt pavement considering traffic volume and road surface characteristics

ABSTRACT In order to build an appropriate prediction model of pavement friction coefficient attenuation, the effects of aggregate texture, on a basis of texture scanning and pavement testing of the dynamic friction coefficient, traffic volume, and rock characteristics on pavement slide decay resistance were studied, and the accuracy of the developed prediction model of friction coefficient was thereafter compared and analysed. First, based on the tire-pavement dynamic friction analyzer independently developed by the research group, accelerated loading tests under different traffic conditions were conducted by the orthogonal test method, and the dynamic friction coefficient of pavement during the abrasion process was recorded. At the same time, the non-contact laser profile measurement system was used to collect three-dimensional micro-texture data of coarse aggregate surface at different abrasion stages, and characteristic parameters such as height, wavelength, and shape were calculated. Second, the factors such as traffic volume and rock characteristics were incorporated, and the algorithms such as multiple linear stepwise regression, feedforward neural network, and random forest regression were adopted to develop estimation models of pavement friction. The results showed that the model constructed based on only texture feature parameters poorly represented pavement skid resistance. After introducing the two indicators of total traffic volume and rock type, the correlation coefficients of the model significantly improved, reaching 0.63, 0.58, and 0.82 respectively, indicating that the latter two factors have significant effects on the anti-skid attenuation of pavement. Moreover, the above three models can achieve satisfactory prediction results. In addition, when a large sample size can be obtained, a random forest algorithm is recommended to acquire higher prediction accuracy of pavement friction coefficient attenuation.