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The ice surface is known for presenting a very small kinetic friction coefficient, but the origin of this property remains highly controversial to date. In this work, we revisit recent computer simulations of ice sliding on atomically smooth substrates, using newly calculated bulk viscosities for the TIP4P/ice water model. The results show that spontaneously formed premelting films in static conditions exhibit an effective viscosity that is about twice the bulk viscosity. However, upon approaching sliding speeds in the order of m/s, the shear rate becomes very large, and the viscosities decrease by several orders of magnitude. This shows that premelting films can act as an efficient lubrication layer despite their small thickness and illustrates an interesting interplay between confinement enhanced viscosities and shear thinning. Our results suggest that the strongly thinned viscosities that operate under the high speed skating regime could largely reduce the amount of frictional heating. [ABSTRACT FROM AUTHOR]

We use molecular dynamics simulations to study the frictional response of monolayers of the anionic surfactant sodium dodecyl sulfate and hemicylindrical aggregates physisorbed on gold. Our simulations of a sliding spherical asperity reveal the following two friction regimes: at low loads, the films show Amonton's friction with a friction force that rises linearly with normal load, and at high loads, the friction force is independent of the load as long as no direct solid–solid contact occurs. The transition between these two regimes happens when a single molecular layer is confined in the gap between the sliding bodies. The friction force at high loads on a monolayer rises monotonically with film density and drops slightly with the transition to hemicylindrical aggregates. This monotonous increase of friction force is compatible with a traditional plowing model of sliding friction. At low loads, the friction coefficient reaches a minimum at the intermediate surface concentrations. We attribute this behavior to a competition between adhesive forces, repulsion of the compressed film, and the onset of plowing. [ABSTRACT FROM AUTHOR]

We discuss the origin of the breakloose (or static) friction force when an ice block is slid on a hard randomly rough substrate surface. If the substrate has roughness with small enough amplitude (of order a 1 nm or less), the breakloose force may be due to interfacial slip and is determined by the elastic energy per unit area, Uel/A0, stored at the interface after the block has been displaced a short distance from its original position. The theory assumes complete contact between the solids at the interface and that there is no elastic deformation energy at the interface in the original state before the application of the tangential force. The breakloose force depends on the surface roughness power spectrum of the substrate and is found to be in good agreement with experimental observations. We show that as the temperature decreases, there is a transition from interfacial sliding (mode II crack propagation, where the crack propagation energy GII = Uel/A0) to opening crack propagation (mode I crack propagation with GI the energy per unit area to break the ice–substrate bonds in the normal direction). [ABSTRACT FROM AUTHOR]

We study the friction when rectangular blocks made from rubber, polyethylene, and silica glass are sliding on ice surfaces at different temperatures ranging from −40 to 0 °C, and sliding speeds ranging from 3 μm/s to 1 cm s−1. We consider a winter tire rubber compound both in the form of a compact block and as a foam with ∼ 10 % void volume. We find that both rubber compounds exhibit a similar friction on ice for all studied temperatures. As in a previous study at low temperatures and low sliding speeds, we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface. At temperatures around 0 °C (or for high enough sliding speeds), a thin pre-melted water film will occur at the rubber–ice interface, and the contribution to the friction from shearing the area of real contact is small. In this case, the dominant contribution to the friction force is due to viscoelastic deformations of the rubber by the ice asperities. The sliding friction for polyethylene (PE) and silica glass (SG) blocks on ice differs strongly from that of rubber. The friction coefficient for PE is ∼ 0.04 − 0.15 and is relatively weakly velocity dependent except close to the ice melting temperature where the friction coefficient increases toward low sliding speeds. Silica glass exhibits a similarly low friction as PE for T > −10 °C but very large friction coefficients (of order unity) at low temperatures. For both PE and SG, unless the ice track is very smooth, the friction force depends on the position x along the sliding track. This is due to bumps on the ice surface, which are sheared off by the elastically stiff PE and SG blocks, resulting in a plowing-type of contribution to the friction force. This results in friction coefficients, which locally can be very large ∼ 1 , and visual inspection of the ice surface after the sliding acts show ice wear particles (white powder) in regions where ice bumps occur. Similar effects can be expected for rubber blocks below the rubber glass transition temperature, and the rubber is in the (elastically stiff) glassy state. [ABSTRACT FROM AUTHOR]

This paper compares various angle-tracking algorithms to balance the performance and noise for a steering-by-wire (SBW) system. Direct and quiet steering experiences can improve drivers' acceptance of the SBW system. Linear quadratic regulator (LQR) control, robust control, and conventional cascade proportional–integral (PI) control have been developed and compared both theoretically and experimentally. To avoid the risky and time-consuming parameter-tuning process, a high-fidelity steering resistance model, which comprises a linear two-degree-of-freedom vehicle model and a dynamic LuGre friction model is established. Step and sine wave tests are simulated in a Matlab/Simulink environment to determine the reasonable parameter region for various methods. Then, the three types of algorithms are implemented on a prototype SBW vehicle and compared under the same scenarios. Finally, the simulated and experimental results are illustrated in detail. According to the indicators of control bandwidths, steady-state errors, cockpit sounds, and current waveforms, it is clear that LQR and robust control can achieve faster response and more acceptable noise, with uncertain and relatively larger tracking errors. Cascade PI control, in comparison, can realize smaller steady-state errors and gentler current waveforms, with slight noise and slower response. [ABSTRACT FROM AUTHOR]

The sliding process and characteristics of earthquake-induced landslides are complex, and many factors affect landslide movement. The damage caused by landslides is often closely related to their movement characteristics. Therefore, establishing an efficient and quick analysis model for earthquake-induced landslide movement is very important in considering multiple control factors in the sliding process. Based on the typical characteristics of earthquake-induced landslide movement, considering the influences of earthquake action, friction characteristics of sliding surfaces, topographic relief, and morphological changes in landslide masses, a widely applicable quick analysis model for earthquake-induced landslide movement (ELQA) is constructed based on energy conservation. Compared with the existing landslide movement models, this model can consider multiple control factors and significantly improve the applicability of the model. Through comparisons with theoretical analysis, model tests, and actual landslide (Kolka glacial detrital flow), the movement distance of the landslide front edge obtained by the ELQA model matches well with the comparison results, indicating that the ELQA model can reproduce earthquake-induced landslide movement more accurately and quickly. Based on the ELQA model, the influences of control parameters (terrain sampling point density, time step, calculated point number) and calculation parameters (internal friction angle, slip mass volume, terrain concavity, and convexity characteristics) on the calculation results are studied. The results show that control parameters such as terrain sampling point density, time step, and calculated point number have limited influence on the movement characteristics; as long as appropriate values are selected, the error rate can be controlled within 5%. The calculation parameters have a significant influence on the movement characteristics. For example, the influence of the internal friction angle on the coverage area reaches up to 83.75%. The slip mass volume has an insignificant influence on the maximum movement speed, but it on the coverage area reaches approximately 20%. The influence of the terrain concavity and convexity characteristics on the results is less than 10%. The ELQA model is suitable for in-situ estimation and can provide effective suggestions for disaster prevention and reduction in earthquake-prone areas. [ABSTRACT FROM AUTHOR]

The rockmass in the practical engineering is often prone to compression; therefore, how to establish a fracture criterion to reflect the rockmass compression failure is vital. Take the rockmass with one inclined crack for instance, the mechanical behavior of the inclined crack face closure and friction sliding in uniaxial compression is firstly analyzed, and then the Kolosov–Muskhelishvili stress function of the cracked rockmass in uniaxial compression is established based on the complex stress functions. Next, the calculation methods of the stress intensity factor (SIF) K and three T‐stress components at or near the crack tip considering three kinds of crack parameters (e.g., geometry parameter, friction strength parameter and deformation parameter) are obtained. Thirdly, the improved maximum tangential stress (MTS) criterion is obtained considering T‐stress and three kinds of crack parameters. Finally, the test results of the wing‐crack initiation angle in uniaxial compression obtained by other researchers are adopted to verify the improved MTS criterion. Meanwhile, the effect of γ, the crack normal stiffness kn and shear stiffness ks, and the crack friction coefficient f on the wing‐crack initiation angle are discussed with the parametric sensitivity analysis. Highlights: An improved maximum tangential stress (MTS) criterion is proposed.The SIF and T‐stress at or near the crack tip in compression are analytical solved.The crack deformation parameters are not seen as constant in the improved MTS criterion. [ABSTRACT FROM AUTHOR]

Platooning is an effective way to reduce air resistance and fuel consumption in vehicular transportation. However, stochastically generated disturbances can significantly impact the string stability of platoons. This article proposes a novel control law, based on sliding mode control and leader‐predecessor communications, designed to improve the exponential mean‐square string stability of platoons with Ito‐type stochastic disturbances that consider friction force. Specifically, our approach employs a third‐order nonlinear dynamic model to capture the relevant spatiotemporal correlations present in vehicle platoons. The proposed longitudinal control strategy effectively stabilizes the platoons with time delay and was verified through simulation experimentation. In this study, the stability of sliding mode motion is thoroughly investigated by means of sub‐reachable and practical stability analysis with sliding mode control. The findings of this study provide a theoretical foundation for further research on vehicle platoons with increasingly complicated interference and time delays. Overall, our results demonstrate that our approach can achieve significant improvements in both fuel economy and exhaust emissions while maintaining high levels of string stability, further contributing to the development of efficient and sustainable transportation systems. [ABSTRACT FROM AUTHOR]

The reduction of friction-induced noise is a crucial research area for enhancing vehicle comfort, and this paper proposes a method based on circular pit texture to achieve this goal. We conducted a long-term sliding friction test using a pin-on-disc friction and a wear test bench to verify the validity of this method. To compare the friction noise of different surfaces, texture units with varying line densities were machined on the surface of friction disk samples. The resulting friction-wear and noise characteristics of the samples were analyzed in conjunction with the microscopic morphology of the worn surfaces. The results indicate that surfaces with textures can delay the onset of squeal noise, and the pattern of its development differs from that of smooth surfaces. The noise reduction effect is most evident due to the proper distribution of textures that can form furrow-like wear marks at the wear interface. The finite element results demonstrate that this morphology can improve pressure distribution at the leading point and reduce the tendency of system instability. [ABSTRACT FROM AUTHOR]

Polyimide (PI) is a special engineering plastic, widely involved in mechanical components, instruments, and petrochemicals. However, single PI material is inevitably subject to wear and tear in practice, which leads to weakened material properties. In this work, Ti3C2Tx@SiO2 was prepared to enhance the wear resistance and lubrication properties of PI by intercalating SiO2 into the interlayer of Ti3C2Tx sheets. Ti3C2Tx@SiO2/PI composites were fabricated in two steps to test the tribological performances. SiO2 particles change the form of interfacial friction from sliding to rolling, thus relieving direct friction between material and steel ball. So, the composites have a minimum COF (COF = 0.33) when the content of Ti3C2Tx@SiO2 is 0.80 wt%. Moreover, the average value of wear rate was 0.24 × 10−5 mm3/(N·m) when Ti3C2Tx@SiO2 content was 1.60 wt%, which was 91.0% lower compared to the PI matrix. During the friction process, the abrasive chips of the material migrate to the surface of the steel ball to form a transfer film, which protects the material and thus reduces the wear rate. Therefore, the hybrids Ti3C2Tx@SiO2 are effective and important wear‐resistant agents and solid lubricants to improve the wear resistance and lubricity of PI or other polymer materials. Highlights: SiO2 insert Ti3C2Tx is a key factor in changing sliding friction into rolling friction, effectively reducing the COF.The average wear rate was 91.0% lower than that of the polyimide matrix when Ti3C2Tx@SiO2 content was 1.60 wt%.The minimum COF of Ti3C2Tx@SiO2/PI composites reached 0.33 when the content of Ti3C2Tx@SiO2 was 0.80 wt%.The transfer film effectively reduces further wear of the material during friction. [ABSTRACT FROM AUTHOR]

This paper investigates the sliding friction and erosion resistance of untreated and heat-treated electroless Ni–B coatings, reinforced with ZrO 2 and (3 mol%) YSZ nanoparticles. A ball-on-flat system was used for the sliding friction wear test, and an air jet carries solid particles for the erosion wear test. The wear scars were studied with a 3D profilometer. Further, a scanning electron microscope (SEM) for morphological and energy-dispersive spectroscopy (EDS) was used to examine the chemical properties of the worn surfaces. These scars correlate with properties of hardness, Young's modulus, and fracture toughness has been studied with microhardness and nanoindentation tests. X-ray diffraction (XRD) analyzed the coating phase structure and synthesis. The wear tests revealed that Ni–B–ZrO 2 and Ni–B-YSZ coatings had lower friction coefficients at heat-treated conditions (with an average value of μ = 0.3) than Ni–B, HT, which had a 14 % higher coefficient. Consequently, the Ni–B-YSZ demonstrates the lowest specific wear rates (2.4 x10−6 mm3/N-m) and erosion resistance which is more promising for use in indented gun barrel applications. [ABSTRACT FROM AUTHOR]

As part of this research, the shear process during asphalt paving with the paver screed was investigated in the laboratory. An extensive international literature search revealed that the influence of the shear process on the compaction success during asphalt paving has not been investigated to date. In addition, only limited data on the coefficient of friction between the asphalt mix and the screed plate exist from in-situ measurements. The investigations in the laboratory were carried out with a customized frame shear device of the Institute of Geotechnics at the Technical University of Darmstadt. The asphalt mix types AC 11 DS, SMA 11 DS and AC 16 BS (according to the German guideline TL Asphalt-StB) were used for this purpose. In addition, the influence of temperature changes and grading curve changes was investigated using the AC 11 DS asphalt mix. On the basis of the results, it was possible to prove for the first time that a significant increase in density takes place as a result of the shear process under constant normal stress. Where the influence on the compaction success depends on the asphalt composition. In addition, in-situ measurements could be validated based on determined sliding friction coefficients. The friction coefficients showed a material and temperature-dependent behavior. [ABSTRACT FROM AUTHOR]

The accidental initiation of explosives under mechanical loads has caused numerous catastrophic events. Therefore, the dynamic damage behavior of confined polymer-bonded explosives (PBXs) must be assessed to improve their practical applicability. In this study, polymer-bonded sugar (PBS) materials were prepared using a novel agglomerate to develop a PBX substitute material with enhanced experimental safety. The mechanical properties of the PBS shell were evaluated using a dynamic compression test, which revealed that the compression response of the shell was affected by the strain rate. A low-velocity impact experiment was performed to investigate the dynamic damage and load transfer characteristics of the PBX substitute. A constitutive model was developed to characterize the mechanical response of PBS subjected to high strain rates, and implementing this model in ABAQUS ensured successful prediction of the damage evolution process associated with PBS. Simulation results indicated that the PBS specimen was primarily damaged around its center while sliding friction was dominant near the center during pressure application. Notably, different stress states result in distinct crack growth velocity histories along the axial direction, with the damage ratio progressively decreasing toward regions closer to the impact surface. [ABSTRACT FROM AUTHOR]

This article by William H. Bassichis explores two different approaches to teaching introductory physics to engineering students. One approach is the traditional mechanics-based approach, while the other is a newer thermodynamics-based approach. The article discusses the role of free-body diagrams (FBD) in both approaches and highlights the differences in how forces are considered in each. It also compares the use of work and energy in problem-solving and discusses the challenges and benefits of each approach. The author, a highly respected professor, provides valuable insights into the topic. [Extracted from the article]

Here, the prediction of friction characteristics for pipe jacking drives during soil traversing has been explored. This work is done in the context of no great understanding of how drivers negotiate highly weathered rock formations. Based on a series of jacking force prediction models, including the Staheli model, Pellet-Beaucour and Kastner models (PK-O models) and proposed modified Pellet-Beaucour and Kastner models (PK-M models), direct shear tests are performed on initial-contacted specimens to obtain the friction coefficient μavg using back-analysis. The evaluation of the reliability of the parameter μavg and the modified vertical pressure σv is carried out through a three-dimensional finite element in ADINA in combination with the "wished-in place" method (WPM). The shear stress of the pipe–rock interface and the compressive stress of the end area are obtained by numerical analysis and in good agreement with the measured jacking force predicted by the proposed PK-M-1 model, indicating the correctness and necessity of considering the degree of the arching effect when modeling strong weathering rock masses. According to these results, the friction coefficient μavg of back-analysis can be used as a reliable input parameter for the finite-element modeling of pipe-jacking force in highly weathered geological formations. Highlights: The modified Pellet-Beaucour and Kastner models (PK-M models) have been established. A modified simulation method for rock pipe jacking in highly weathered rocks has been studied in ADINA. The correctness and superiority of the PK-M models have been discussed and verified. [ABSTRACT FROM AUTHOR]

An experiment is described where a metal nut was allowed to slide from the top to the bottom of a vertical wire loop. An interesting feature is that the normal reaction force on the nut decreases to zero and reverses direction before the nut reaches the bottom of the loop. [ABSTRACT FROM AUTHOR]

Exploring the mechanical response of rock joint subjected to dynamic shear load is essential for revealing the mechanism of dynamic disasters in jointed rock masses. Using an impact-induced direct-shear method, a series of dynamic shear experiments were conducted on artificial granite joints with regularly undulating interface. The dynamic friction coefficient of joint was first obtained from planar jointed granite specimens before the dynamic shear strength and shear displacement of the regularly undulating joints were tested. During the test, the effects of normal stress and shear rate were both considered. The results show that when the shear velocity ranges from 1 to 9 m/s, the dynamic friction coefficient of the planar joint is negatively correlated with shear velocity, and decreases by at least 50% compared with that under quasi-static condition. The rate dependence of shear strength appears opposite for granite joints with undulating angles of 11.3° and 26.6°, respectively. A shear strength model for rock joint with an undulating angle of 11.3° is then suggested based on the test results. During impact shear sliding, the maximum shear displacement of the joint is linearly negatively related to the initial normal stress. While, non-driven sliding may occur under low normal stress and high impact velocity, which leads to a large magnitude of shear slip. Highlights: The shear strength and shear displacement of rock joints are tested with shear rate ranging from 1 to 9 m/s. The rate dependence of shear strength appears opposite for rock joints with sharp and gentle undulation and a shear strength model is suggested. Besides impact-driven sliding, the non-driven sliding may also occur in the joint under low normal stress and high impact velocity. [ABSTRACT FROM AUTHOR]

This study established a novel vehicle–track coupled dynamics model (VTCDM) considering the disc brake system of a high-speed train (HST). The structure parameters of each friction block are applied to compute the non-linear friction forces and torques. This more elaborate model enables detailed investigations on the coupled mechanical system excited by the brake sliding friction, wheel-rail rolling friction and track irregularity. Further, it is validated by comparing with the experimental results from the aspects of time domain, frequency domain, Poincaré map and phase plane. Results indicate that the brake system substantially influences the vehicle–track system (VTS) and causes strong non-linear characteristics. Furthermore, this model can be used for tribological and dynamics-related assessment, like braking squeal and friction-induced vibration. [ABSTRACT FROM AUTHOR]

In this work, we introduce a collision model specifically tailored for the simulation of inextensible textiles. The model considers friction, contacts, and inextensibility constraints all at the same time without any decoupling. Self-collisions are modeled in a natural way that allows considering the thickness of cloth without introducing unwanted oscillations. The discretization of the equations of motion leads naturally to a sequence of quadratic problems with inequality and equality constraints. In order to solve these problems efficiently, we develop a novel active-set algorithm that takes into account past active constraints to accelerate the resolution of unresolved contacts. We put to a test the developed collision procedure with diverse scenarios involving static and dynamic friction, sharp objects, and complex-topology folding sequences. Finally, we perform an experimental validation of the collision model by comparing simulations with recordings of real textiles as given by a Motion Capture System. The results are very accurate, having errors around 1 cm for DIN A2 textiles (42 x 59.4 cm) even in difficult scenarios involving fast and strong hits with a rigid object. In this work, we present a novel collision model for inextensible textiles and validate it experimentally through a comparison with real textiles as recorded by a Motion Capture System. In the figure we can see four frames comparing the recorded hitting with a stick of a DIN A2 (42 x 59.4 cm) polyester sheet (left) with its inextensible simulation (right); its average error being 1.44 cm. The recordings are obtained by attaching 20 reflective markers of diameter 3 mm and weight of 0.013 g to the real textile and following their trajectory. On the bottom, we show a full plot of the mean absolute error of the position of each marker with respect to its simulation and with yellow lines we highlight the moments in which the object is in contact with the cloth. Notice that the biggest errors appear not during the hits but just after because of aerodynamic effects. The above simulations, with a 7 × 9 mesh, are two times faster than real-time. Our custom active-set solver is three times faster than a standard interior-point method using the same mesh resolution. • We develop a cloth collision model which results in a coupled resolution of friction, inextensibility, and contact forces. • Self-collisions are modeled in a way that allows considering cloth's thickness without introducing unwanted oscillations. • An active-set solver for the system's integration is developed, which can start from any non-necessarily feasible point. • An empirical validation is performed, with scenarios involving high-friction surfaces and strong hits with a stick. [ABSTRACT FROM AUTHOR]

• Proposing and establishing a dynamic model for the combined rotor that accounts for rub-impact. • Increasing the stiffness of the stator advances the speed at which the system enters the quasi-periodic period. • The Stribeck friction model reduces the speed range of the system's period three motion compared to Coulomb friction. • The magnitude and phase angle of the imbalance significantly alters the state of motion of the system. • Analyzing the basic mechanism that governs the variation of friction and its impact on the stability of the system. This paper aims to analyze the dynamic behavior of the rod-fastening combined rotor(RFCR) system in a rub-impact state and proposes a rod-fastening rotor dynamics model based on the Stribeck friction model. This model offers advantages such as generating frictional forces based on relative velocities and considering the coupling effects of rub-impact under complex excitations, providing greater flexibility in studying rotor systems. The Lagrange equation is utilized to deduce the RFCR formula, and the balance equation of the combined rotor is presented under friction, oil-film, and unbalanced conditions. This paper investigates the dynamic response of the RFCR system under rub-impact using the 4th-order Runge–Kutta method. The effects of parameter variations on the nonlinear dynamics of the combined rotor are systematically analyzed by means of bifurcation diagrams, motion trajectory, time domain waveform, frequency spectrum, and Poincaré maps. The results show that the dynamic characteristics of the rotor system show a regular variation with the variation of the system parameters. Different forms of periodic motions, namely Periodic 1 motion (P1), Periodic 2 motion (P2), and Periodic 3 motion (P3) motions, along with quasi-periodic motions, are observed in response to varying system parameters. The results show that the higher the stator stiffness, the earlier the rotor enters the quasi-periodic speed. The velocity effect of friction reduces the speed range of the P3 motion of the rotor system and enhances the nonlinearity of the system. The magnitude and phase of the unbalance force change the frequency component of the system, which has a more substantial effect on the rotor system. These findings can help engineers and researchers in comprehending system behavior and designing more dependable and effective gas turbine rotor systems. [ABSTRACT FROM AUTHOR]

It is generally accepted that ice is slippery due to an interfacial water film wetting the ice surface. Despite the current progress in research, the mechanism of low ice friction is not clear, and especially little is known about the behavior of this surface water film under shear and how the sheared interfacial water film influences ice friction. In our work, we investigated the ordering and diffusion coefficient of the interfacial water film and the friction of ice sliding on an atomically smooth solid substrate at the atomic level using molecular dynamics simulations. There are two layers of water molecules at the ice-solid interface that exhibit properties very different from bulk ice. The ice-adjacent water layer is ice-like, and the solid-adjacent water layer is liquid-like. This liquid-like layer behaves in the manner of "confined water," with high viscosity while maintaining fluidity, leading to the slipperiness of the ice. Furthermore, we found that the interfacial water exhibits shear thinning behavior, which connects the structure of the interfacial water film to the coefficient of friction of the ice surface. We propose a new ice friction mechanism based on shear thinning that is applicable to this interfacial water film structure. [ABSTRACT FROM AUTHOR]

Currently, mechanical gears with cycloid engagement are increasingly used in mechanisms along with involute ones. In modern drive mechanisms, using pin gears and gears with intermediate rolling elements (IRE) is widespread, which simultaneously use cycloid gears. To a greater extent, pin gears are now being investigated, but IRE gears have their undeniable advantages. Many works are devoted to the study of cycloid toothing for certain gears, but the efficiency, especially that of IRE gears, has practically not been investigated. Therefore, the analysis of power losses in the engagement of a gear with IRE and a free cage (IREFC) is relevant. In this analysis, the authors of the work have used laws of mechanics, methods of energy flows and a secant normal. Mathematical expressions have been obtained to estimate slip speeds and power friction losses in the engagement of a gear with IREFC, and a formula has been derived to determine the efficiency of a mentioned mechanical transmission. The calculation of slip speeds and power losses at the points of contact of a rolling element with cycloid profiles of wheels for selected initial parameters of a gear with IREFC has been presented. The friction power and the overall efficiency of the entire gear engagement have also been calculated. This work shows that power friction losses at the points of contact of a rolling element with cycloid profiles of tooth wheels of a gear with IREFC are not the same. The friction power in the contact of a rolling element with a cycloid profile of a cam is an order of magnitude higher than the friction power in the contact of a rolling element with a cycloid profile of a crown. [ABSTRACT FROM AUTHOR]

In a stack of atomically thin van der Waals layers, introducing interlayer twist creates a moiré superlattice whose period is a function of twist angle. Changes in that twist angle of even hundredths of a degree can dramatically transform the system's electronic properties. Setting a precise and uniform twist angle for a stack remains difficult; hence, determining that twist angle and mapping its spatial variation is very important. Techniques have emerged to do this by imaging the moiré, but most of these require sophisticated infrastructure, time-consuming sample preparation beyond stack synthesis, or both. In this work, we show that torsional force microscopy (TFM), a scanning probe technique sensitive to dynamic friction, can reveal surface and shallow subsurface structure of van der Waals stacks on multiple length scales: the moirés formed between bi-layers of graphene and between graphene and hexagonal boron nitride (hBN) and also the atomic crystal lattices of graphene and hBN. In TFM, torsional motion of an Atomic Force Microscope (AFM) cantilever is monitored as it is actively driven at a torsional resonance while a feedback loop maintains contact at a set force with the sample surface. TFM works at room temperature in air, with no need for an electrical bias between the tip and the sample, making it applicable to a wide array of samples. It should enable determination of precise structural information including twist angles and strain in moiré superlattices and crystallographic orientation of van der Waals flakes to support predictable moiré heterostructure fabrication. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to solve the issues of time-consuming and complicated computation of traditional measures, as well as the underutilization of two-dimensional (2D) phase-trajectory projection matrix, so a new set of features were proposed based on the projection of attractors trajectory to characterize the friction-induced attractors and to reveal the tribological behavior during the running-in process. Design/methodology/approach: The frictional running-in experiments were conducted by sliding a ball against a static disk, and the friction coefficient was collected to reconstruct the friction-induced attractors. The projection of the attractors in 2D subspace was then mapped and the distribution of phase points was adapted to conduct the feature extraction. Findings: The evolution of the proposed moment measures could be described as "initial rapid decrease/increase- midterm gradual decrease/increase- finally stable," which could effectively reveal the convergence degree of the friction-induced attractors. Moreover, the measures could also describe the relative position of the attractors in phase–space domain, which reveal the amplitude evolution of signals to some extent. Originality/value: The proposed measures could reveal the evolution of tribological behaviors during the running-in process and meet the more precise real-time running-in status identification. [ABSTRACT FROM AUTHOR]

BACKGROUND: Ureteral stents are commonly used in urology. However, complications such as encrustation and infection on the surface of the stent, and injury to the ureteral mucosa can occur after implantation, causing discomfort for patients. OBJECTIVE: We intend to confirm the biosafety of polyvinylpyrrolidone (PVP) hydrophilic coating and its lubrication properties for surface modification of ureteral stents to reduce friction and improve patient comfort. METHODS: Based on our previous studies, we have developed a PVP hydrophilic coating for surface modification of ureteral stents. We firstly investigated the cytotoxicity, intradermal irritation, delayed type hypersensitivity, and acute systemic reactions of stent coating extracts. We further characterized the break strength, retention strength, and dynamic friction of the stent. RESULTS: The cell survival rate of all experimental groups was greater than 70%. No hypersensitivity reaction, systemic toxicity reaction, or obvious intradermal reaction were observed. The above results indicate that the test results of the modified stent meet the requirements of ISO 10993-5: 2009 (Cytotoxicity); ISO 10993-10:2021 (Sensitization and Irritation); ISO 10993-11:2017 (Acute Systemic Toxicity). After soaking in artificial urine for an extended period, there was no obvious change in its super-slip performance. CONCLUSION: Our results confirm the safety and lubrication characteristics of PVP hydrophilic coating for ureteral stent surface modification. The performance of this coating has the potential to reduce complications after stent implantation, thereby improving patient comfort, reducing medical burden, and has a good clinical application prospect. [ABSTRACT FROM AUTHOR]

Ultra-high molecular weight polyethylene (UHMWPE) is esteemed for its superior wear resistance, making it a preferred material in various applications, including artificial joints, dental materials, and mechanical components. This study elucidates the effects of thermo-oxidative aging on the dry tribological performance and wear mechanisms of UHMWPE and zirconia (ZrO2) friction pairs using dynamic friction wear tests, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Results reveal that thermo-oxidative aging significantly compromises wear resistance and alters the degradation mechanisms of UHMWPE. The unaged UHMWPE exhibits exceptional wear resistance, indicated by minimal wear and pronounced polishing effects. Post-aging at 40 °C leads to the formation of fine scratches and rougher wear marks on UHMWPE surfaces, with the predominant wear mechanism transitioning from abrasive wear to fatigue wear as the number of cycles increases. Upon aging at 70 °C, more extensive spalling and pitting damages occur on UHMWPE, indicating more severe thermo-oxidative and wear damages that primarily exhibit fatigue wear and oxidative wear patterns. Notably, aging at 40 °C results in a friction coefficient increase to ∼0.165, whereas aging at 70 °C decreases the friction coefficient to around 0.118, indicating a complex relationship between aging temperature and tribological behavior. This research provides valuable insights into predicting and improving the durability of UHMWPE components used in orthopedic applications, thereby contributing to optimizing orthopedic implant materials for enhanced patient outcomes. [ABSTRACT FROM AUTHOR]

Fault reactivations induced by deep excavation can pose significant challenges to underground construction or resource extraction. Laboratory experiments on rock faults demonstrate that unloading‐induced fault reactivations obey the Coulomb failure criterion derived from loading‐induced events. However, the effect of stress path during unloading on the failure criterion and rupture dynamics of fault reactivations remains poorly understood. Here, we present findings from a series of laboratory experiments aimed at elucidating the effect of the unloading path on the failure criterion and rupture dynamics of fault reactivations. We conducted experiments under various stress conditions, examining two cases of unloading paths. In Case I, we unloaded the minimum principal stress, while in Case II, the maximum principal stress was unloaded. Strain gauges and high‐speed photography were employed to capture the transient dynamic rupture process. Our investigations have yielded new insights into the effect of unloading path on the rupture dynamics when the fault is reactivated. In Case I, we observed fault reactivations resembling those loading‐induced events characterized by forward sliding. Conversely, in Case II, fault reactivations associated with stress reversal produce mild reversed sliding with lower stress drop and rupture velocity. Furthermore, we find that there is a remarkable reduction in static friction for reversed sliding, indicating that the failure criterion for fault reactivation is influenced by the stress path. We demonstrate that enhanced stress heterogeneity, caused by stress reversal, serves as a mechanism for reduced static friction. These findings contribute to our understanding of the mechanisms underlying fault reactivations, particularly those involving reversed sliding. Plain Language Summary: It is known that underground excavation, accompanied by stress release, can trigger fault reactivation, resulting in induced earthquakes. Understanding how unloading affects the activation and rupture dynamics of these induced events is crucial. To investigate the role of unloading path, we conducted laboratory experiments to simulate unloading‐induced fault reactivation on analog material containing a fault. Loadings are applied biaxially at the boundary. We observed that unloading the minimum principal stress (i.e., reducing the minimum loading) could reactivate the fault, generating forward sliding resembling loading‐induced rupture events. Conversely, unloading the maximum principal stress (i.e., reducing the maximum loading) induces reversed sliding, featuring smaller stress drop, coseismic slip, and rupture speed compared to forward sliding. Moreover, the static friction coefficient is reduced prior to reversed sliding. We also found that enhanced stress heterogeneity prior to unloading‐induced reversed sliding can account for the difference in static friction coefficient. Therefore, it is necessary to incorporate the effect of loading path into the studies of fault reactivation. Key Points: Rupture process of unloading‐induced fault reactivation is dictated by the initial stress state and stress pathThe static friction of fault is reduced for the unloading‐induced reversed slidingEnhanced stress heterogeneity caused by stress reversal contributes to reduced static friction [ABSTRACT FROM AUTHOR]

This paper describes the results of an experimental investigation on the coefficient of friction at the interface of a PVC–sand–PVC layer that is utilised as part of a low-cost geotechnical seismic isolation devised to be used in low-income countries. The PVC–sand–PVC configuration consists of two smooth PVC surfaces enclosing a single layer of sand grains, with surface densities between 0.5 kg/m2 and 3 kg/m2, which aim to facilitate relative sliding at friction resistance between 0.15 and 0.30 depending on the design acceleration, by acting like "non-perfectly rounded ball bearings". The latter isolation method has been extensively studied both numerically and experimentally by means of large-scale testing at the shaking table of the EQUALS Earthquake Laboratory of the University of Bristol. However, in the light of the construction of the first building worldwide to be designed and constructed in Nepal with the particular low-cost PVC–sand–PVC sliding interface, it was deemed necessary to reliably assess the mean and dispersion of the coefficient of friction as a function of vertical pressure, sand density and degree of saturation. The results of the tests performed using an improved direct shear apparatus are presented herein using sand samples and PVC sheets that were locally resourced in Nepal to be used in construction. The results indicate that the variation of friction is reasonably low and in any case within the desirable range, irrespectively of the parameters examined, thus establishing confidence to the forthcoming design of the novel isolated building. [ABSTRACT FROM AUTHOR]

The protolith of the hanging wall and footwall of a fault plays a crucial role in influencing the sliding stability of the fault, and different protoliths have different tendencies toward sliding instability. To investigate the influence of protoliths on fault sliding stability, simulated fault friction sliding tests were conducted on five types of rocks: fine sandstone, limestone, marble, basalt, and granite, under various loading conditions. The test results demonstrate that, under the same loading conditions, basalt and granite exhibit a greater inclination toward unstable sliding during fault simulation, primarily displaying regular stick–slip and regular inclusion chaotic stick–slip behaviors. On the other hand, fine sandstone, limestone, and marble are predominantly characterized by stable sliding behaviors. The order of sensitivity for the influencing factors on sliding mode is the type of protolith, followed by initial normal stress, and then displacement loading rate. Based on the type of protolith and loading conditions (initial normal stress and displacement loading rate), the sliding mode can change during the sliding process of the simulated rock faults, transitioning from stable sliding to chaotic stick–slip, and then to regular stick–slip. Alternatively, the sliding mode can shift from regular inclusion chaotic stick–slip to regular stick–slip, or from regular stick–slip to stable sliding. Finally, the complexity of sliding patterns in different types of protoliths is analyzed from the perspectives of mineral composition and microstructure, elucidating the underlying mechanisms behind three sliding patterns: stable sliding, chaotic stick–slip, and regular stick–slip. Furthermore, the degree to which different types of rocks tend toward stick–slip behavior can be ranked as follows: rock mineral composition, mineral particle size, and structure among rock minerals. These research findings contribute to a deeper understanding of fault sliding behavior. Highlights: Experimental studies have shed light on the influence of protolith type on the stability of fault sliding, revealing that different rock types exhibit a preference for stick–slip behavior in the following descending order: rock mineral composition, mineral grain size, and structure among rock minerals. Further investigations have identified that basalt and granite tend to display unstable sliding, whereas fine sandstone, limestone, and marble are predominantly characterized by stable sliding. Intriguingly, a novel fault sliding mode named regular inclusion chaotic stick–slip has been uncovered. By delving into the mineral composition and microstructure, a comprehensive understanding of the underlying causes for the intricate variations in sliding modes across different protolith types has been attained. [ABSTRACT FROM AUTHOR]

The paper addresses enhanced braking efficiency in electromechanically driven vehicle wheels on pneumatic tires through the robust Simple Adaptive Control method. The sliding friction is modeled as dry, semi-dry, and fluid friction, accounting for uneven motion, self-oscillations, and elastic properties of the pneumatic tire. A robust simple adaptive control method is proposed, utilizing signal-parametric adaptation algorithms with implicit reference models. The control objective aims to ensure the convergence of a quadratic performance index within a finite time. The control algorithm combines parametric and signal components, with simulations demonstrating its efficiency. [ABSTRACT FROM AUTHOR]

The friction performance of tread rubber is related to the safety of the vehicle during driving, especially in terms of shifting speeds, cornering, and changing environmental factors. The experimental design used in this paper employed a self-developed automatic multi-working-condition friction tester to investigate the correlation between the friction coefficient of three tread formulations and various factors, including speed, pressure, temperature, side deflection angle, and lateral camber. This experimental study demonstrates that the coefficient of friction decreases with increasing load and increases with increasing sliding velocities due to changes in adhesion friction. Due to the increasing and decreasing changes in rubber adhesion and hysteresis friction caused by temperature, the coefficient of friction shows a tendency to increase and then decrease with the increase in temperature; thus, temperature has an important effect on the coefficient of friction. Based on the basic theory of friction and experimental research, the Dorsch friction model was modified in terms of temperature, and the analytical relationship between the rubber friction coefficient and the combined variables of contact pressure, slip velocity, and temperature was established, which is more in line with the actual situation of rubber friction. The model predictions were compared with the experimental results, and the error accuracy was controlled within 5%. This verifies the accuracy of the model and provides a theoretical basis for the study of rubber friction. [ABSTRACT FROM AUTHOR]

The frictional properties of the coarse aggregate used in asphalt concrete are a major contributor to the friction of the surface mixes. Selecting an aggregate that is not only polish and crush resistant to withstand the mechanical degradation and grinding under traffic loading, but also has a low friction loss rate and reasonable friction life is vital. A laboratory aggregate test program was carried out to evaluate the polishing/friction and crushing performance of 25 different aggregate sources from different locations. Two widely used friction test methods, i.e., British pendulum testing (BPT) and dynamic friction testing (DFT) in conjunction with the three-wheel polishing testing (TWPD) and the aggregate crushing value test (ACV) were used to quantify the polishing and crushing resistance of aggregates, respectively. Several frictional and crushing test parameters were introduced, analyzed, and finally, a correlation analysis was performed to relate different aggregate friction, polishing, and crushing test parameters. All three tests showed low variability when replicate samples were compared. A strong correlation (R value of 0.92) was found between the friction loss rate and the ACV test parameters and a linear correlation with R2 of greater than 0.80 was observed between the final friction life of the aggregate and the BPT test parameters. The ACV and TWPD/BPT tests can be potentially considered as an alternative test for friction evaluation of the coarse aggregates in case the DFT device is not available, with some loss in the sensitivity in characterizing marginal materials. [ABSTRACT FROM AUTHOR]

Like metallic materials, fiber metal laminate (FML) lets the material has a simple metal structure behavior but with such advantages as specialized strength properties, impact, fire resistance, weight savings, corrosion resistance, and metal fatigue. The main focus of this article is to indicate the dynamic response of circular size-dependent circular plates made of FML material via 3D-elasticity theories. The size-dependent structure is simulated by coupling the modified nonlocal couple stress and 3D-elasticity theories (MNCS-3DET). For accurate modeling of the elastic substrate, torsional and linear spring and Pasternak foundation are modeled using the equations of horizontal friction force and torsional interaction. Harmonic differential quadrature method and Chebyshev–Gauss–Lobatto grid distribution points are coupled for solving the partial differential equations of the current micro/nano-structure. Novelties of this work consider the effects of MCS-3DET, torsional interaction, horizontal friction force, and FML material in the construction of the circular micro/nanoplate. In the results section, the outputs are verified with other published articles, and the outcomes show that the MCS-3DET parameter, elastic foundation coefficient, horizontal friction force coefficient, and geometry have an essential role in the dynamic stability of the FML micro/nano-structure. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to investigate the metabolic cost (C), mechanical work, and kinematics of walking on a multidirectional treadmill designed for locomotion in virtual reality. Methods: Ten participants (5 females, body mass 67.2 ± 8.1 kg, height 1.71 ± 0.07 m, age 23.6 ± 1.9 years, mean ± SD) walked on a Virtuix Omni multidirectional treadmill at four imposed stride frequencies: 0.70, 0.85, 1.00, and 1.15 Hz. A portable metabolic system measured oxygen uptake, enabling calculation of C and the metabolic equivalent of task (MET). Gait kinematics and external, internal, and total mechanical work (WTOT) were calculated by an optoelectronic system. Efficiency was calculated either as WTOT/C or by summing WTOT to the work against sliding frictions. Results were compared with normal walking, running, and skipping. Results: C was higher for walking on the multidirectional treadmill than for normal walking, running, and skipping, and decreased with speed (best-fit equation: C = 20.2–27.5·speed + 15.8·speed2); the average MET was 4.6 ± 1.4. Mechanical work was higher at lower speeds, but similar to that of normal walking at higher speeds, with lower pendular energy recovery and efficiency; differences in efficiency were explained by the additional work against sliding frictions. At paired speeds, participants showed a more forward-leaned trunk and higher ankle dorsiflexion, stride frequency, and duty factor than normal walking. Conclusion: Walking on a multidirectional treadmill requires a higher metabolic cost and different mechanical work and kinematics than normal walking. This raises questions on its use for gait rehabilitation but highlights its potential for high-intensity exercise and physical activity promotion. [ABSTRACT FROM AUTHOR]

This study explores the rheological and tribological behavior of water-based lubricants (WBLs) as potential alternatives for electric vehicle (EV) applications. As the transportation sector increasingly shifts towards EVs to reduce carbon emissions, the demand for efficient lubricants becomes critical. WBLs here are defined as fluids containing a minimum of 50 wt% water mixed with glycerol, ethylene glycol (MEG), polyethylene glycol (PEG), or one of two polyalkylene glycols (PAGs). Rheological properties were investigated and compared with traditional lubricating oils. Results demonstrate distinctive rheological characteristics in WBLs, with viscosity–temperature responses resembling traditional oils with lowered pressure–viscosity coefficients. Nevertheless, WBLs exhibit promising film-forming capabilities in highly loaded contacts. Additionally, in sliding contacts, WBLs generally display lower friction coefficients compared to traditional oils, with PEG exhibiting the lowest value near 0.1. These findings suggest that WBLs may offer advantages in reducing friction and energy loss in EV applications. Furthermore, sliding wear tests indicate low wear rates in WBLs such as PEG, PAG, and glycerol, supporting their potential as viable lubrication options. The study highlights the importance of high-pressure rheology and tribochemistry in wear mechanisms among the different lubricants. [ABSTRACT FROM AUTHOR]

The present study investigated several properties such as friction, hardness, penetration work, and cutting forces in soaps formulated with apple and carrot pomace at varying concentrations of 5%, 10%, and 15%. To gain insights into the molecular-level alterations within the formulated soap samples, they were spectroscopically analyzed using Fourier-transform infrared spectroscopy. The sliding friction analyses revealed that the investigated extrudate additives had no significant impact on the frictional forces of the soaps. However, notable differences were observed in the cutting force, hardness, and penetration work between the control and pomace-added samples. Excluding the control samples, no statistically significant distinctions were found between the cutting force, hardness, and work of penetration of soaps containing apple pomace and carrot pomace. Moreover, the quantity of pomace incorporated did not induce any significant variations in the results. The obtained samples were characterised at the molecular level using FTIR Fourier transform infrared spectroscopy. On the other hand, alterations in band intensities suggested improved molecular packing of the compounds within the samples due to the presence of the additives. [ABSTRACT FROM AUTHOR]

The fiber/resin interfacial mechanical properties in low‐temperature environments are crucial for composite materials, and a temperature‐friction cohesive zone model is proposed in this paper. This model combines the temperature effect, the interfacial friction effect, and the interfacial debonding. The mechanical characteristics of the fiber/matrix interface are described using this model. The proposed model has been implemented in ABAQUS using the VUMAT subroutine. To verify this model, microdroplet debonding experiments were conducted at temperatures 298, 193, and 77 K. The results of the simulation and the experiment matched well. The proposed model takes temperature differences as a parameter and can characterize the interfacial mechanical response at different temperatures. In addition, the temperature, friction, interface parameters, and microdroplet size effects on the mechanical properties of the fiber/matrix interface were investigated. The results show that interfacial friction and temperature differences have a significant impact on the interfacial mechanical properties. The microdroplet size also has an influence on interfacial shear strength. Highlights: A temperature‐friction cohesive zone model is proposed.Cryogenic microdroplet debonding tests were conducted.The finite element method results are stable and close to the regression line of tests.The temperature difference changes the stress state of the interface.The interfacial sliding friction force has a large dispersion. [ABSTRACT FROM AUTHOR]

This paper investigates the sliding surface failure characteristics, earth pressure distribution law and stability safety factor of inverted T-type retaining wall by using the finite element limit analysis software OptumG2, the effects of width of wall heel plate, width of wall toe plate, thickness of bottom plate, soil–wall interface friction angle, soil cohesion and soil internal friction angle of filling on the failure characteristics of sliding surface, the earth pressure distribution law and stability safety factor of retaining walls are analyzed, The stability safety factor of the retaining wall showed a gradually increasing trend as the width of wall heel plate and wall toe plate increased; as the bottom plate thickness increases, the stability safety factor of the retaining wall gradually increases; as the soil-wall interface element reduction coefficient rises, that is, the internal friction angle of the soil-wall gradually increases to the soil internal friction angle, the stability safety factor of the retaining wall gradually increases; as the soil cohesion and internal friction angle increase, the stability safety factor of the retaining wall progressively increases. The safety factor of retaining wall increases by 0.45 for every 0.5m increase in the width of the wall heel plate; the safety factor of the retaining wall increases by 0.29 when the width of the wall toe plate increases by 0.5m; for every 0.5m increase in the width of wall plate thickness, the safety factor of the retaining wall is increased by 0.62; for every 0.25 increase in soil-wall interface element reduction coefficient, the safety factor of the retaining wall increases by 0.29; for every increase of 5KPa in soil cohesion, the safety factor of the retaining wall increased by 1.16; for every 5° increases in soil internal friction angle, the safety factor of retaining wall increases by 0.6. The research is significant for studying the failure laws and stability of retaining walls and providing references for retaining wall design. [ABSTRACT FROM AUTHOR]

This project investigates the corrosion tendency of various machining fluids on Al6061 alloy for a sustainable cutting process. Also, the surface of the machining workpiece was analysed to understand the effect of the carbon nanotubes (CNTs) on the surface morphology that assists the cutting conversion of the sliding friction to the rolling process. The study used a two-step process to create machining fluid with CNT nanoparticles at different percentage concentrations. The soluble oil (sample B1), mineral oil (sample B2), 0.2-g/l-CNTs nano-mineral machining fluid (sample B3), 0.4-g/l-CNTs nano-mineral machining fluid (sample B4), and 0.6-g/l-CNTs nano-mineral machining fluid (sample 5) makes up the corrosion study medium. The corrosion study was conducted using polarisation resistance and potentiodynamic corrosion techniques. After the corrosion study, the Vickers micro-hardness machine was employed to evaluate the surface hardness of the normal face region subjected to the corrosion study. The SEM and EDS were also used to investigate the microstructure and elemental composition of the machining fluid impacts on the Al 6061 alloy. The results show that the soluble oil has a high corrosion rate of 0.03590591 (mm/year), with a list polarisation resistance rate of 8,432.83 (Ω) compared to the other machining fluid employed in this study. Furthermore, the 0.6-g/l-CNTs nano-mineral machining fluid has the lowest corrosion rate of 0.0013197 (mm/year) and the highest polarisation resistance of 32,941.67 (Ω). The 0.6-g/l-CNTs presence in the mineral oil increases the rheological and tribological properties, which results in an outstanding performance in the corrosion study. Furthermore, the CNTs hardened the surface of the workpiece due to the carbon element deposition during the implementation of the cutting fluid. [ABSTRACT FROM AUTHOR]

In engineering practice, creating window openings in partition infill walls is a common requirement for infilled frames. However, the intervention of infill walls may interrupt the desired cyclic behavior of the infilled frame, and worst yet, the inevitable window opening might further aggravate such negative interaction. To protect the openings from the detrimental multiple diagonal struts mechanism of the traditional infill wall with a window opening under lateral loadings, this research presents a novel infill wall system with a window opening for semi-rigid steel frames. Three half-scaled specimens are subjected to quasi-static cycle tests: a bare steel frame, a steel frame infilled with a traditional infill wall with a window opening, and a precast infill wall with a window opening and sliding joints in a steel frame. Experimental results show that the proposed infill system with a window opening can release adverse crack development or opening deformation of the window opening by mitigating the detrimental multiple diagonal struts effect in conventional infill walls with window openings under lateral loadings. In this way, the developed infilled frame exhibits similar cyclic behavior to the designed bare steel frame with higher energy dissipation capacity. Furthermore, parametric analysis results reveal that the friction factor of the sliding joints has a significant effect on enhancing the bearing capacity of the proposed infill system, while the change of opening sizes and locations of the window opening has negligible impact on the cyclic behavior of the developed infill system. [ABSTRACT FROM AUTHOR]

Background: Shear forces related to friction are one of the risk factors shown to increase the likelihood of wheelchair users developing pressure injuries (PIs), especially in the buttocks region. Thus, reducing the coefficient of friction between the seat and the person's pants could be a means toward reducing the incidence of PIs. Objective: This study aimed to: (1) determine the coefficients of friction of seven commonly worn pant fabrics and two seat cover fabrics and (2) investigate the effects of a deformable seat cushion on the measurement of the coefficients of friction. Methods: A mechanical system (termed sled) had a pants fabric secured to its bottom and was placed on top of a custom seat pan with seat cover. The seat pan was tilted from horizontal until the sled system started to slide on the seat pan. The coefficient of friction between the two fabrics was calculated using kinematics data obtained from a motion capture system. Results: The office fabric seat cover produced smaller coefficient of friction than the vinyl seat cover for all of the pant fabrics. Women's khakis demonstrated one of the smallest coefficients of friction, and denim demonstrated one of the largest coefficients of friction consistently across both seats covers. Conclusion: Replacing traditional vinyl seat covers in wheelchairs with a fabric closer to an office seat fabric is one approach to reducing frictional forces at the seat interface. Although optimal pant fabrics can be identified for shear force reduction, the results also depend on the seat cover fabric. [ABSTRACT FROM AUTHOR]

Thermal contact damage is inevitable under the influence of friction. The frictional continuous contact model of the thermoelectric (TE) layer loaded by a rigid indenter is considered. Considering the complexity of friction and size effect, the nonlinear contact problem is reducedis transformed into solving the Cauchy singular integral equation (SIE) of the second kind by using the convolution formula and the superposition principle. The contact stress between the rigid indenter and the TE layer were affected by the external load, friction coefficient, TE material parameters. The results show that the softer TE layer can relieve the contact stress of the upper interface of TE. The change of friction coefficient and TE layer thickness can reduce the pressure at the rear end of the indenter. Properly adjusting these parameters can prevent the destruction and contact damage of the TE layer during the friction contact process. [ABSTRACT FROM AUTHOR]

In this work, a new inertia modulated meta-structure is proposed to enable time-dependent inertia parameters, and thereby realize non-reciprocal wave propagation via spatiotemporal modulation. The designed cell structure is composed of an oscillatory disk and a mass that slides in a guide embedded in the disk frictionlessly with prescribed motion. Effective moment of inertia and damping coefficients of the rocking motion of the cell structure are rendered time-dependent due to the inertia and Coriolis forces of the periodically sliding mass, which allows us to implement the expected spatiotemporal modulation upon a super-cell. Non-reciprocal propagation behavior of the proposed meta-structure is verified via the theoretical solution of the dispersion relation as well as the dynamic response of a finite array. Effects of modulation parameters, including the frequency, amplitude, and phase, on the unidirectional propagation characteristic are thoroughly investigated. [ABSTRACT FROM AUTHOR]

• Calibration of red clay with different water contents based on EDEM software. • The Hertz-Mindlin with JKR Cohesion model was used to model red clay soil's physical properties. • Experimental studies provide insights into the impact of soil moisture content on its properties. • Technical references for future research on soil-tool interactions were provided. Distinct physical properties of red clay soil in hilly and mountainous regions of southwest China, including high adhesiveness and density, challenge the operation of agricultural machinery. A scarcity of accurate discrete element simulation parameters for this soil type restricts computational modeling. The study was focused on red clay soil with a moisture content of 12.50% ± 1% and a measured repose angle of 35.54°. The soil's inherent physical properties were identified through experimental assessments. Soil contact mechanical parameters were obtained from the GEMM database, and optimal contact parameter ranges were determined using Steepest Ascent Experiments, with the simulated soil particle repose angle serving as the response value. A second-order regression model was developed using a quadratic regression rotation orthogonal combination test. By taking the actual repose angle as the optimization criterion, parameters were optimized. The optimal contact mechanical parameters in EDEM simulations were identified as: JKR surface energy at 8.981 J/m2, recovery coefficient at 0.474, dynamic friction coefficient at 0.196, and static friction coefficient at 0.45. The model yielded a repose angle of 36.21°, closely corresponding with the observed value, with a relative error of 1.80%. The parameters calibrated in this study offer a valuable reference for future soil-tool interaction studies and tillage implement optimization in these regions. [ABSTRACT FROM AUTHOR]

Frictional contact problem of a layer-substrate structure is an important topic in coating optimization design. The present work carries out a comprehensive analysis on the coupling effect of coefficient of friction, Poisson's ratio, and layer thickness on contact stresses distribution. A physical property namely full decoupling under interaction between material and geometric couplings is explicitly observed. Eccentricity in contact could be virtually diminished, and symmetrization on contact pressure of non-Hertzian type is presented at a specific Poisson's ratio. Additionally, position of tensile peak within in-plane surface stress could not be affected by friction under the full decoupling effect. Coupling effects of Poisson's ratio, friction coefficient, and layer thickness on eccentric contact involving soft bonded coating are studied systematically. A physical property namely full normal-tangential decoupling at a specific Poisson's ratio in thin coating is explicitly observed and analyzed comprehensively. The tensile peak of in-plane stress as a crack initiator at the coating surface is studied under the full decoupling effect mentioned above. [ABSTRACT FROM AUTHOR]