Contact Behavior Research Articles

Investigation on the influence of the slip at the wheel-rail contact patch on the shakedown limit of rail material

Research on factors affecting rolling contact fatigue (RCF) damage of rail materials has become increasingly important since developing effective measures to mitigate RCF damage is crucial. This study focuses on exploring the influence of full slip and partial slip contact modes at the wheel-rail contact patch on the RCF damage behavior and the shakedown limit of the pearlite rail material through wheel-rail RCF rolling-sliding tests. Firstly, based on the wheel-rail adhesion-creep curves in dry, water and oil environments, the creepage required to achieve full slip during the rolling-sliding tests was determined. Then, rolling-sliding tests under full slip contact with different adhesion coefficients were carried out in a dry atmosphere and with the assistance of a third body medium (i.e., oil and water), respectively. Meanwhile, rolling-sliding tests under partial slip contact with the similar contact parameters were performed in a dry atmosphere. The results indicated that RCF damage and wear rates of the rail material under a full slip contact with an adhesion coefficient below the saturation peak on the adhesion-creep curve were significantly less than those under partial slip contact with similar contact parameters. Moreover, under full slip contact with an adhesion coefficient below the saturation peak on the adhesion-creep curve, the pearlite rail materials could exhibit a higher shakedown limit. Furthermore, the influence of full slip and partial slip contact on wheel-rail contact behavior was further analyzed using finite element simulations. Finally, a novel friction modification strategy to mitigate RCF damage and wear of rails was proposed. By applying a specific low-coefficient friction modifier to the wheel-rail interface, the operation of powered wheelsets under controlled creepage conditions that reach the threshold of full slip contact at the wheel-rail contact interface could be employed to achieve the desired adhesion coefficient. Thus, this approach could ensure that the achieved adhesion coefficient met the on-site target adhesion force while reducing RCF damage and wear of rail materials.

Contact behaviors of rough surfaces under tension and bending

Contact behaviors of rough surfaces under tension and bending

Theoretical and experimental approaches for flexible cage dynamic characteristics of four-point contact ball bearing considering multi-point contact behaviors

Multi-point contact often occurs between the balls and raceways of the four-point contact ball bearing (FPCBB) due to operating conditions and manufacturing errors, which can lead to unstable motion and wear of the cage. A dynamic analysis method for FPCBB with a flexible cage under multi-point contact is presented in this paper. Initially, the boundary conditions for different contact points (two-point, three-point, and four-point contact) are clarified through the research of the dynamic interaction and collision mechanisms between the balls and the raceways. Subsequently, based on the structure flexibility, and the collision effect among the balls, cage, and guiding ring, a dynamic model for FPCBB is constructed, and the heightened accuracy and superiority of the model are substantiated through comparative analyses with the conventional rigid cage model. Furthermore, the influence of operating conditions and manufacturing errors on the rotational stability and the wear degree of the cage are explored, and the accuracy and reliability of the model are experimentally verified. The results show that the degree of cage wear is strongly influenced by the contact state, and the maximum wear degree varies at different positions. Reasonable speeds, loads, and manufacturing error range can effectively improve the contact conditions, thereby augmenting cage motion stability and mitigating wear. This research contributes novel insights into the failure analysis and structural optimization of the FPCBB.

Topological van der Waals Contact for Two-Dimensional Semiconductors.

The relentless miniaturization inherent in complementary metal-oxide semiconductor technology has created challenges at the interface of two-dimensional (2D) materials and metal electrodes. These challenges, predominantly stemming from metal-induced gap states (MIGS) and Schottky barrier heights (SBHs), critically impede device performance. This work introduces an innovative implementation of damage-free Sb2Te3 topological van der Waals (T-vdW) contacts, representing an ultimate contact electrode for 2D materials. We successfully fabricate p-type and n-type transistors using monolayer and multilayer WSe2, achieving ultralow SBH (∼24 meV) and contact resistance (∼0.71 kΩ·μm). Simulations highlight the role of topological surface states in Sb2Te3, which effectively mitigate the MIGS effect, thereby significantly elevating device efficiency. Our experimental insights revealed the semiohmic behavior of Sb2Te3 T-vdW contacts, with an exceptional photoresponsivity of 716 A/W and rapid response times of approximately 60 μs. The findings presented herein herald topological contacts as a superior alternative to traditional metal contacts, potentially revolutionizing the performance of miniaturized electronic and optoelectronic devices.

A comprehensive analysis on coast side contact behaviour of thermoplastic gears against steel gear: a FEA approach

PurposeThe research paper comprehensively investigates the gear tooth deflection of standard thermoplastic gears with steel gear as the driver and driven companions. An accurate mapping of characteristic contact regions between the meshing gears was done, and the behaviour of the gear tooth in the premature and prolonged contact zones was studied.Design/methodology/approachThe study employs the finite element method to conduct a quasi-static 2D analysis of meshing gear teeth. The finite element model was created in AutoCAD and analysed using the ANSYS 19.1 simulation package.FindingsIn the polymer-polymer gear combinations, premature and prolonged contact primarily occurs along the addendum radii of meshing gears, whereas a novel contact phenomenon was observed in the coast side for polymer-metal and metal-polymer combinations, exhibiting a path perpendicular to the standard drive side contact. As well, the deflection of the tooth alters the load distribution across the interlocking gears, leading to a decrement in the root stresses.Originality/valueThe Lewis bending equation demonstrates that bending stresses depend solely on the applied load and the geometry of the tooth. It does not consider the effects of deflection. However, the computational results showed that the gear tooth deflection caused by different gear pair combinations also affects the bending stresses. The contact stresses observed in the polymer-polymer gear combination were observed to be within the material’s proportional limit. However, when a steel gear is paired with a polymer gear, the contact stresses exceed the proportional limit due to coast side contact.

Nonlinear friction dynamics of water-lubricated bearings under transient shocks considering cavitation and turbulence effects

This study proposes a transient elastohydrodynamic mixed lubrication (EHML) model for water-lubricated bearings (WLBs) that incorporates cavitation and turbulence effects to evaluate the nonlinear friction dynamic performance under transient shock loads. The generalized average Reynolds equation is discretized using the control volume technique (CVM), and the constrained system is solved using the Fischer-Burmeister-Newton-Schur (FBNS) method. The validity of the model is verified by a comparison of experimental data from published literature. On this basis, the effects of cavitation, turbulence, shock load amplitude, direction, time, and rotational speed on WLB nonlinear friction dynamics characteristics are investigated. The results show that cavitation induces hydrodynamic loss under transient shock conditions, significantly increases contact time and load, and exacerbates the hydrodynamic instability phenomenon. In contrast, the turbulence effect effectively reduces frictional contact. The stability of WLBs under transient shock conditions is closely related to the load offset angle. Reducing the load offset angle improves the anti-shock stability of the bearings. Nevertheless, an increase in the amplitude and duration of the shock load may result in a deterioration of the frictional contact behavior. Increasing the rotational speed appropriately favors accelerating the lubrication regime transition and improving WLB’s anti-shock stability. This study provides a reference for enhancing WLB anti-shock performance and optimizing structural design.

On the time-dependent sliding contact behavior of three-phase polymer matrix smart composites

Abstract Three-phase smart composites consisting of magnetostrictive and piezoelectric reinforcements embedded with a polymer matrix can achieve specific multifunctional properties in response to external stimuli, which are well-suited for the application of sensors, actuators, and electronic devices. The materials exhibit complex behaviors characterized by electro-magneto-viscoelasticity coupling during the contact of these smart structures. This paper proposes a novel hybrid element method (HEM) for numerically analyzing the frictionless sliding contact problem stemming from the viscoelastic behavior and multiphase interactions of polymer matrix smart composites. The study aims to fully investigate the effects of material properties, sliding velocities, and action time on the contact behavior of materials via the integration of the conjugate gradient method (CGM) with the discrete convolution-fast Fourier transform (DC-FFT) algorithm. The analytical viscoelastic frequency response functions (FRFs) are derived by substituting elastic solutions with the time-dependent relaxation modulus. Numerical results show that three-phase polymer matrix smart composites exhibit lower contact pressure and higher surface electric/magnetic potential than three-phase magneto-electro-elastic composites. Sliding velocity and action time strongly influence the distribution of pressure/stress and electric/magnetic potential.

Observational study of close contact behaviors in a multinational graduate student office

Understanding human contact behavior plays a crucial role in improving the design of indoor environments, for example, by enhancing thermal comfort, workplace performance and productivity, and controlling infection transmission. Although baseline information for indoor environmental design is available, data on person-to-person contact behavior are limited, especially in populations of diverse nationalities, genders, and age ranges. In this study, we used high-resolution video cameras to collect close contact data for five consecutive school days in a multinational graduate school student office in Japan with a reserved cultural background. We characterized human close-contact behavior using stochastic interactions in terms of interpersonal distance, assortativity, posture, duration, and frequency of contact in a multinational population. Our results showed a remarkable difference compared to the study results from person-to-person contact behavior in an ethnically homogenous population. The interpersonal distance averaged 0.75 m, and the close contact frequency was notably lower, but the close contact duration was significantly longer. Nationality showed stronger homophily. We considered the degree centrality measures of the nodes in the observed networks. The observed contact network links were dense with high reciprocity. High contact heterogeneity was observed in twenty-five percent of the nodes. These data can be used to improve targeted epidemiological analyses for indoor occupant health decision-making, and infection spread prevention strategies.

Investigating the Influence of Medium Size and Ratio on Grinding Characteristics

This study explores the effect of steel ball size and proportion on mineral grinding characteristics using Discrete Element Method (DEM) simulations. Based on batch grinding kinetics, this paper analyzes the contact behavior during grinding, discussing particle breakage conditions and critical breakage energy. The results indicate that while increasing the size of the steel balls leads to higher collision energy, the collision probability decreases significantly; the opposite is true for smaller steel balls. Simulation results with different ball size combinations show that increasing the proportion of smaller balls does not significantly change the collision energy but greatly increases the collision probability, providing a basis for optimizing ball size distribution to improve grinding performance. Furthermore, appropriately increasing the proportion of smaller balls can reduce fluctuations in grinding energy consumption, thereby enhancing collision energy and collision probability while reducing energy costs. Liner wear results demonstrate that larger ball sizes increase liner wear, but different ball size combinations can effectively distribute the forces on the liner, reducing wear.

Simulation of soil-structure interaction using inelasticity-separated finite element method

The soil–structure interaction (SSI) effect is nonnegligible during the nonlinear seismic response analysis of large-scale or underground structures. However, the computation of nonlinear response of a structure considering SSI effect usually is a time-consuming process because the numerical model should involve the structure itself, a wide-range soil domain and the soil–structure interface, especially for large-scale structure. This study aims to incorporate the inelasticity-separated finite element method (IS-FEM), which is an algorithm recently developed for efficient structural nonlinear analysis, to improve the efficiency of the soil-structure interaction system. To this end, an inelasticity-separated contact element model for modeling the nonlinear behavior of soil and structure interface is developed in this study. To derive the inelasticity-separated governing equation of this model, a reference elastic stiffness is defined so that the normal and shear deformation of any point pair in the presented contact element is decomposed into reference linear and reference nonlinear parts according to this reference elastic stiffness. As a result, the problem of inconsistency between the requirement of IS-FEM for constant initial linear elastic stiffness and the existence of inflection point for the stress versus relative displacement relationship of contact behavior can be solved. Then, the Goodman element formulation for depicting the nonlinear contact behavior is introduced and an interpolation scheme to establish the reference nonlinear deformation field in an element is incorporated. By combining the proposed model with existing inelasticity-separated elements, a global analytical model of the soil–structure interaction system can be established within the framework of IS-FEM. Because the nonlinearity usually occur in some local regions of the global model and the use of the IS-FEM only require performing these operations for a small scale matrix representing local nonlinearity, the computational efficiency of nonlinear structural response analysis considering SSI effect can be improved significantly. The applicability and efficiency of the proposed method is finally verified by two numerical examples.

The Effects of Humidity on the Velocity-Dependence and Frictional Ageing of Nanoscale Silica Contacts

This work examines the effect of environmental humidity on rate-and-state friction behavior of nanoscale silica-silica nanoscale contacts in an atomic force microscope, particularly, its effect on frictional ageing and velocity-weakening vs. strengthening friction from 10 nm/s to 100 μm/s sliding velocities. At extremely low humidities (≪1%RH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ll 1\\% RH$$\\end{document}), ageing is nearly absent for up to 100 s of nominally stationary contact, and friction is strongly velocity-strengthening. This is consistent with dry interfacial friction, where thermal excitations help overcome static friction at low sliding velocities. At higher humidity levels (10–40% RH), ageing becomes pronounced and is accompanied by much higher kinetic friction and velocity-weakening behavior. This is attributed to water-catalyzed interfacial Si–O-Si bond formation. At the highest humidities examined (> 40% RH), ageing subsides, kinetic friction drops to low levels, and friction is velocity-strengthening again. These responses are attributed to intercalated water separating the interfaces, which precludes interfacial bonding. The trends in velocity-dependent friction are reproduced and explained using a computational multi-bond model. Our model explicitly simulates bond formation and bond-breaking, and the passivation and reactivation of reaction sites across the interface during sliding, where the activation energies for interfacial chemical reactions are dependent on humidity. These results provide potential insights into nanoscale mechanisms that may contribute to the humidity dependence observed in prior macroscale rock friction studies. They also provide a possible microphysical foundation to understand the role of water in interfacial systems with water-catalyzed bonding reactions, and demonstrate a profound change in the interfacial physics near and above saturated humidity conditions.

Interfacial layer with a dibenzofulvene-bridged triphenylamine core for efficient and stable inverted perovskite solar cells

Considering the energy level cascade, introducing a hole transport layer (HTL) between the NiOx and perovskite layers has become a common and effective strategy to enhance the performance of inverted perovskite solar cells (PSCs). Herein, we designed and synthesized three hole-transporting interfacial layers (TPAD, TPAO, and TPAS) based on a dibenzofulvene-bridged triphenylamine (TPA) core to fabricate efficient and stable inverted NiOx-based PSCs. Dibenzofulvene, known for its sp²-hybridized structure, offers superior planarity and molecular stacking, and it easily bonds with triphenylamine derivatives, resulting in unique light-harvesting and charge mobility properties for optoelectronic applications. Specifically, diphenylamine, dimethoxy diphenylamine, and dimethylthio diphenylamine were used as end-capping units for TPAD, TPAO, and TPAS, respectively. The NiOx-based inverted PSC devices fabricated with TPAS as an interfacial layer effectively modified NiOx to improve energy level alignment, enhance film quality and crystallinity, and improve carrier transport, leading to a high-quality perovskite layer and superior interface contact behavior. Consequently, this device yielded a highly efficient cell performance of 20.30 %, surpassing those using TPAD (19.29 %) and TPAO (18.78 %) as interfacial layers, and significantly outperforming devices using only NiOx (17.69 %). Additionally, the champion cell exhibited negligible hysteresis and long-term stability. These findings demonstrate a facile approach to preparing multifunctional TPA-based hole transport materials and showcase the efficient performance of inverted cells based on a triphenylamine dibenzofulvene-based interfacial layer, contributing to the development of high-efficiency inverted PSCs.

Modeling properties of chromosome territories using polymer filaments in diverse confinement geometries

Interphase chromosomes reside within distinct nuclear regions known as chromosome territories (CTs). Recent observations from Hi-C analyses, a method mapping chromosomal interactions, have revealed varied decay in contact probabilities among different chromosomes. Our study explores the relationship between this contact decay and the particular shapes of the chromosome territories they occupy. For this, we employed molecular dynamics (MD) simulations to examine how confined polymers, resembling chromosomes, behave within different confinement geometries similar to chromosome territory boundaries. Our simulations unveil so far unreported relationships between contact probabilities and end-to-end distances varying based on different confinement geometries. These findings highlight the crucial impact of chromosome territories on shaping the larger-scale properties of 3D genome organization. They emphasize the intrinsic connection between the shapes of these territories and the contact behaviors exhibited by chromosomes. Understanding these correlations is key to accurately interpret Hi-C and microscopy data, and offers vital insights into the foundational principles governing genomic organization.

Doping of Porous Transport Layers to Optimize Electrical Contact Behaviour in PEM Water Electrolysis Cells

A high overall efficiency is crucial for large-scale polymer electrolyte membrane water electrolysers. Due to the harsh environment at the anode, a titanium oxide layer with high electrical resistivity passivates porous transport layers (PTL). A common used way to overcome this problem is noble metal coating (e.g. with platinum, gold or iridium). [1] For the very first time, we present a new and inexpensive way of maintaining the high conductivity of PTLs by doping the titanium surface that faces the catalyst layer. Sun et al. [2] modelled the conductivity of doped titanium oxide for different elements. With respect to their results and Koech et al. [3] we chose tin, niobium, antimony and yttrium as dopants. The implantation was carried out at the Ion Beam Center of the HZDR in Dresden, Germany. All doped PTLs displayed a lower cell voltage than the undoped reference as visible in figure 1a). While tin improves in the range of 2-3 % at a current density of 2A/cm², the other dopants best results reach values of over 4 % with niobium achieving the best performance with 4.4 % improvement (see figure 1b) for comparison). Figure 1c) shows the high frequency resistance (HFR) originating from impedance measurements. The observable improvement of up to 11.4% at 2A/cm² proves the fact that the advantage corresponds to a better contact resistance due to a lower resistance of the doped titanium oxide layer. The improvement in percent presents figure 1d).The measurement results show that doping can have a great impact on the contact resistance of titanium PTLs. These results open a new opportunity in the manipulation of porous transport layers for enhanced contact behaviour, where no experimental publications exist yet. Especially in comparison to noble metal coatings like iridium, doping has an enormous cost advantage when using non noble metals with the potential of lowering the overall electrolyser system costs while increasing its efficiency.[1] Liu, C., Shviro, M., Gago, A. S., Zaccarine, S. F., Bender, G., Gazdzicki, P., Morawietz, T., Biswas, I., Rasinski, M., Everwand, A., Schierholz, R., Pfeilsticker, J., Müller, M., Lopes, P. P., Eichel, R.-A., Pivovar, B., Pylypenko, S., Friedrich, K. A., Lehnert, W., Carmo, M., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Adv. Energy Mater. 2021, 11, 2002926. https://doi.org/10.1002/aenm.202002926[2] Hu Sun, Zhu-tian Xu, Di Zhang. First-principles calculations to investigate doping effects on electrical conductivity and interfacial contact resistance of TiO2, Applied Surface Science, Volume 614, 2023, 156202, ISSN 0169-4332, https://doi.org/10.1016/j.apsusc.2022.156202.[3] Koech, R.K.; Ichwani, R.; Oyewole, D.; Kigozi, M.; Amune, D.; Sanni, D.M.; Adeniji, S.; Oyewole, K.; Bello, A.; Ntsoenzok, E.; et al. Tin Oxide Modified Titanium Dioxide as Electron Transport Layer in Formamidinium-Rich Perovskite Solar Cells. Energies 2021, 14, 7870. https://doi.org/10.3390/en14237870 Figure 1

Role of Trapped Molecules at Sliding Contacts in Lattice-Resolved Friction.

Understanding atomic friction within a liquid environment is crucial for engineering friction mechanisms and characterizing surfaces. It has been suggested that the lattice resolution of friction force microscope in liquid environments stems from a dry contact state, with all liquid molecules expelled from the area of closest approach between the tip and substrate. Here, we revisit this assertion by performing in-depth friction force microscopy experiments and molecular dynamics simulations of the influence of surrounding water molecules on the dynamic behavior of the nanotribological contact between an amorphous SiO2 probe and a monolayer MoS2 substrate. An analysis of simulation and experimental stick-slip patterns demonstrates the entrapment of water molecules at the contact interface. These trapped water molecules behave as an integral component of the probe and participate in its interaction with the substrate, affecting the dynamics of the probe and preventing long slips. Significantly, surrounding water from the capillary or layer exhibits a replenishing effect, acting as a water reservoir during sliding. This phenomenon facilitates the preservation of lattice-scale resolution across a range of applied normal loads.

Experimental investigation of junction growth of rough contacts using X-ray computed tomography

The real contact area (RCA) of randomly rough contacts has received a great deal of attention because it correlates strongly with friction, lubrication, sealing, and conductivity. Simulations have revealed that the RCA associated with deterministic normal squeezing loads increases when tangential loads are also applied, in a phenomenon called junction growth. However, experimental investigations of the junction growth of randomly rough contacts are rare. Here, we used X-ray computed tomography (CT) to measure junction growth when two aluminum alloy surfaces were in contact. A high-resolution experimental setup was used to apply loads and observe contact behaviors at a resolution of 4 µm. The RCA and average contact gaps were computed using a three-dimensional (3D) geometric model constructed from gray CT images using the Otsu thresholding method. The results showed that the RCA increased as the normal load increased. The RCA increased by 22.67% after a tangential load was applied (junction growth), and the average gap decreased by 14.01% after a tangential load was applied. Thus, X-ray CT accurately measured the junction growth as a novel quantitative method.

An improved mathematical model of gas–water two-phase flows in fractured horizontal wells accounting for physical contact behaviors of fractures with total factor characteristics

In water-bearing gas reservoirs, water existence affects gas production performances due to two-phase flows occurring in matrix and fracture systems. Under the background of staged multi-cluster fractured horizontal wells, this work focuses on an improved gas–water two-phase flow model accounting for physical contact behaviors of fractures with total factor characteristics. Combining a point-convergence method with fractal theory and applying Laplace transform and Stehfest numerical inversion, analytical solutions of this proposed model are solved to validate against the field production data and numerical simulation results. Subsequently, the analytical nephograms of formation pressure and water saturation at different stages are given for the first time, throughout which formation pressure and water saturation distributions at different locations of the fractured reservoir embedded with segmented multi-cluster tree-shaped fracture networks are visually exhibited. The results demonstrate that draining area evolution is limited to each segment at early stage and mid-stage, whereas these multi-cluster segments are really integrated into the whole draining area at late stage. Thus, the moving boundary of fracture-controlled unit is also delineated based on water saturation nephograms and expands with continuous production from 65 to 180 m in the y axis direction, contributing to the effective fracturing area for a high productivity. Furthermore, the share of free gas and adsorbed gas are 83% and 17% at early stage, while free gas and adsorbed gas account for 57% and 43% of total gas at the late stage. Those findings contribute to high-efficient and sustainable development of unconventional gas resources.

The stick-slip bending behavior of the multilevel helical structures: A 3D thin rod model with frictional contact

The multilevel helical structures in various engineering and natural fields offer excellent deformation flexibility and load bearing capabilities. Understanding the interplay between the local frictional contact and the geometric characteristics of the helical structure under complex external loads has attracted considerable interest. In this work, the effect of local frictional contact behaviors on the bending in multilevel helical structures is investigated by using a combination of theoretical modeling, finite element (FE) simulations, and experiments. In the case of pure bending, the kinematic parameters of the bent multi-stage helix are derived concisely by the idea of the kinematic analogy. The bending stiffness of the multi-stage helix is further obtained. In the case of the combined tension/torsion and bending, the 3D thin rod model incorporating Coulomb’s friction is established to describe the mechanical responses. It is found that the relationship between equivalent bending stiffness and the laying angle exhibits nonlinearity. A comparison with the classical Papailiou model reveals that, for helical structures at large laying angles, the influence of friction is primarily determined by the internal force in the tangential direction, which is the core assumption of the Papailiou model. However, in the case of small laying angles, the helical twisting characteristics and the contribution of the internal forces and moments in the other two directions (normal and binormal directions) to the friction cannot be ignored. Subsequently, a multilevel frictional contact transmission formulation is proposed according to the force action–reaction principle. Based on the above formulation, the non-simplified thin rod equations with Coulomb’s friction are extended to describe the multilevel stick-slip bending behaviors of the second stage cable (3*3). The dissipation capacity of helical structures is evaluated quantitatively under the hysteretic bending. Finally, the theoretical model is verified by FE simulations and experimental results. This work provides insights for unveiling the intrinsic relationship between the nonlinear bending and local frictional contact behaviors in the multilevel helical structures.

Examining the adaptive elastic anisotropy of granular materials

Changes of granular material anisotropy with stress are a function of numerous microscale attributes, such as contact network, particle size uniformity and shape. Such influences are often represented with fabric variables. Although multiple choices for fabric exist, the question of which variable best explains why and how granular materials adapt to stress is still open. In this study, the effectiveness of different fabric variables in tracking stress-induced anisotropy is compared. The analysis is restricted to a simple, yet fundamental, range of behavioir: elastic deformation. Both particle-scale simulations and continuum analyses are deployed. Analyses based on the discrete-element method (DEM) reveal that, depending on the contact behaviour, anisotropy may emerge even if the topology of the grain contact network is unchanged. The inspection of these results through a continuum-scale hyperelastic constitutive law further reveals that the computed trends cannot be captured without an evolving fabric variable. A comparison between such fabric and multiple microstructural indicators extracted from DEM simulations suggests that elastic stress-induced anisotropy is primarily a manifestation of changes in the anisotropic particle contact area distribution in response to the current magnitude and orientation of force chains. These results not only offer opportunities to enhance current continuum elastic models for granular materials, but can also be used to design testing strategies quantifying changes in fabric anisotropy through multi-scale measurements.

Study on the frictional contact behavior of plain cotton fabric with metal

This study investigated the frictional contact behavior of the plain cotton fabric with the metal through linear friction experiments and real contact analysis. It established a theoretical calculation model of the contact area based on the characteristics of contact behavior. The results indicate that the contact between the cotton fabric and the metal is a multi-point contact, with the contact occurring on the fabric knuckles. The contact behavior is mainly influenced by the normal load, fabric knuckle size, and the number of fabric knuckles. The theoretical calculation model of the contact area considers the multi-scale structural characteristics of cotton fabrics and validates the applicability of the friction adhesion theory to cotton fabrics. The effects of normal load and velocity on the tribological characteristics of cotton fabrics are explained based on the number of contact points.