Contact Behavior Research Articles

ABSTRACT We develop new continuum contact model for the micro-scale sliding frictional and adhesive coupling contact problem of the conducting cylindrical indenter on the exponentially functionally graded piezoelectric materials (FGPM) layered half-plane. This model can explain the sliding friction contact behavior with adhesion effects. First, based on the displacement components and the electrical potential equations of the sliding frictional contact problem, the governing equations of the problem have been derived by using the Maugis type of adhesion theory and the extended Amonton’s law of friction. Second, the present problem could be reduced into a set of coupled Cauchy singular integral equations and two displacement difference equations, which can be numerically discretized and solved by a newly developed algorithm. Finally, numerical examples are presented to demonstrate the effectiveness of the method. The effects of the gradient index, the friction coefficient, the adhesive stress, the work of adhesion and the electric charge on the surface electromechanical response of FGPM were carried out systemically. The motivation for this approach is the adsorption behavior of a gecko type micro crawling robot, which can generate frictional forces under tensile normal loads.

ABSTRACTThe rate at which individuals contact each other is central to the transmission of diseases through populations. Most simple models assume homogenous mixing, with all individuals equally likely to contact each other within a population, where contact can either scale with density (the more individuals the more likely contact will occur) or scale independently of density (where individuals maintain contacts regardless of density). However, there is growing evidence that contact rates are non‐homogenous, and both spatial and social structuring are likely to play an important role in producing and maintaining heterogeneous contact behaviour. Additionally, assuming homogenous mixing is a deliberate simplification, yet it can undermine a model's predictive power when spatial or social structure is important, as is often the case for many wildlife diseases. Here, we investigated the relationship between measures of social and spatial behaviour in a non‐territorial rodent species (Mastomys natalensis) which exhibits significant seasonal fluctuations in density and exposure to a mammarenavirus, Morogoro virus (MORV), using an extensive and unique capture‐mark‐recapture dataset. We followed this up with a study to investigate the extent to which spatial overlap may correlate meaningfully with contact rates using miniaturised proximity loggers developed in house. Exposure to MORV was strongly associated with the proportion of home range overlap with other exposed individuals, and negatively associated with the proportion of home range overlap with conspecifics regardless of exposure status. Including spatial autocorrelation suggested that consistent spatial structuring across the study area also played an important role in determining exposure to MORV. Finally, our proximity logger experiment demonstrated that home range overlap may overestimate direct contact behaviour in M. natalensis as individuals showed a high degree of spatial overlap, but most contacts were associated with a small number of individuals.

Reduced interpersonal touch and elevated preferred interpersonal distance are signs of impaired social contact behavior in post-COVID syndrome.

A novel trans-scale reconstruction model for contact behavior analysis of rough surfaces

Polar bear (Ursus maritimus) neonates are highly altricial, and in-den maternal care is required for cub survival and as follows, population health. Study of maternal denning polar bears in managed care can provide valuable insights on mother-cub dynamics. We reviewed video recordings of polar bears in maternal dens from three participating zoos to monitor maternal behavior and cub development. The study subjects included three polar bear mothers with a single cub. During a total of 366 observations, we collected behavioral data on both mother and cub during 30-min observation sessions spaced every 4 h for the first 30 days post-partum. We recorded mother-cub contact and individual behaviors for both the mother and cub. During the first ten days postpartum, cubs spent 60% of the time on their mother, usually in a cradled position, and this behavior decreased to 44% thereafter. Mothers and cubs spent most of the time resting, with mothers occasionally licking and attending to their cubs. Cubs spent approximately 12% of the time nursing. More replicates from ex situ populations will refine our understanding of how the denning environment, maternal care behavior and cub development are correlated with cub survival.

BackgroundLong-term effects of COVID-19 can place burden on individuals, healthcare, and society. We aimed to evaluate the importance of a wide range of potential risk factors for being diagnosed with post-COVID-19 condition (PCC).MethodsWe used data from national and regional registers and databases for all adult residents in the two largest regions in Sweden. Individuals with a first COVID-19 between 1 August 2020 and 9 February 2022 were included and followed until PCC diagnosis, censoring (death or migration), or 30 November 2023. Using Cox proportional hazards models and backwards stepwise selection, we evaluated a large set of risk factors including sociodemographic data, comorbidities, healthcare contact behaviors, COVID-19-related factors, as well as PCC in family and cohabitants (as proxies for genetics and shared environment).ResultsWe include 810,851 individuals (age range 18-106 years and 53.3% women), of whom 1.4% are diagnosed with PCC during follow-up. Female sex, older age, being born outside Sweden, higher educational attainment, essential workers, having comorbidities such as thromboembolic disease, asthma, fibromyalgia, depression/anxiety, and stress-related disorders, being infected earlier in the study period, experiencing severe acute COVID-19, not being vaccinated before COVID-19, and having a relative or a cohabitant with PCC are associated with an increased risk of being diagnosed with PCC.ConclusionsIn this large population-based cohort study, our exploratory analysis reveals several risk factors for being diagnosed with PCC. Our findings can serve as a basis for future targeting of preventive measures against PCC.

Real close contact behavior based respiratory infectious diseases transmission in rural China

A Multi-perspective Exploration of Contact Behavior in Orthotropic Layer Resting on Isotropic Half-Plane

To clarify the regulatory laws of the fines content (FC) and particle size ratio (SR) on the mechanical properties of sand–fines mixtures and reveal the underlying microscopic mechanical mechanisms, this study takes sand–fines mixtures composed of natural river sand and silt as the research object. It systematically investigates the macro-mechanical behaviors and micro-interaction mechanisms of the mixtures by combining laboratory triaxial tests and discrete element method (DEM) simulations. First, through conducting triaxial drained shear tests on mixtures with three particle size ratios (SR = 9.1, 18.7, and 39.7) under seven fines contents (FC = 0%, 10%, 20%, 30%, 50%, 70%, and 100%), it is found that both the peak friction angle (φps) and critical-state friction angle (φcs) of sand–fines mixtures show a “first increase, then decrease” trend with the increase in FC. The peak inflection points of their variation curves are the threshold fines content related to SR; meanwhile, a fines content below this threshold has an inhibitory effect on dilatancy, while that above this threshold exerts a promotive effect on dilatancy. Subsequently, by exploring the microscopic contact behaviors of sand–fines mixtures, it is observed that, under the fines content corresponding to the highest peak strength, the strong contact network and weak contact network inside the material form an optimal coordination between efficient load-bearing and stable support. This coordination enables the macro-strength of the mixture to reach the peak at this fines content. In addition, by modifying the weight coefficient of fabric anisotropy, a unique linear relationship between the fabric anisotropy of strong contacts and the stress ratio can be established, confirming that the strong contact network plays a core mechanical role in mixtures with different FC values.

Abstract This study investigates the mechanisms of friction-induced vibration under periodic stress distribution variations using an improved fretting friction model. A fretting friction test system integrated with a total reflection method was developed to analyze interfacial contact behavior under dynamic loading conditions. An improved fretting friction model was established, incorporating three critical nonlinear parameters: hysteretic friction coefficient, tangential stiffness fluctuations, and stress distribution. Through systematic validation, the model demonstrates high-fidelity replication of experimental steady-state amplitude-frequency responses. Key findings reveal that stress distribution non-uniformity governs vibration response irregularity, and increased uniformity intensifies stick-slip instabilities. Near the stick-slip transition threshold, distinct vibration anomalies emerge due to the coupled effects of stress heterogeneity, friction hysteresis, and stiffness variations during state transitions. Furthermore, the magnitude of the normal contact force systematically alters the dominant interfacial contact mechanism. The different interfacial contact states at various frequencies lead to distinct steady-state responses. This shift elevates resonance frequencies and amplifies higher-order resonant peaks. The fretting friction model provides a predictive framework for vibration control under dynamic interfacial loading.

This study investigates the thermoelastic frictional contact and wear behavior during reciprocating sliding of a conductive cylindrical punch on a functionally graded piezoelectric material (FGPM)-coated half-plane. The thermo-electro-elastic properties of the coating vary continuously along the thickness direction according to arbitrary gradient functions, with thermal parameters being temperature-dependence. A theoretical framework for the coupled thermo-electro-elastic frictional contact problem is developed and solved using the finite element method. A sequential coupling approach is employed to integrate thermoelastic frictional contact with piezoelectric effects. Furthermore, wear on the coating surface is modeled using an improved Archard formulation, accounting for its impact on thermal sliding frictional contact characteristics. Numerical simulations examine the influence of wear, cycle number, friction coefficient, gradient index and gradient form on the coupled thermo-electro-elastic response of the FGPM coating structure. The numerical results demonstrate the gradient index and gradient form can effectively mitigate thermo-electrical contact-induced damage and reduce friction and wear in piezoelectric materials.

The line contact behavior of multiscale meshing interfaces necessitates synergistic investigation spanning nano-to centimeter-scale ranges. When nominally smooth gear teeth surfaces come into contact, the mechanical–thermal coupling effect at the meshing interface actually occurs over a collection of microscale asperities (roughness peaks) exhibiting hierarchical distribution characteristics. The emergent deformation phenomena across multiple asperity scales govern the self-organized evolution of interface conformity, thereby regulating both the load transfer efficiency and thermal transport properties within the contact zone. The fractal nature of the roughness topography on actual meshing interfaces calls for the development of a cross-scale theoretical framework that integrates micro-texture optimization with multi-physics coupling contact behavior. Conventional roughness characterization methods based on statistical parameters suffer from inherent limitations: their parameter values are highly dependent on measurement scale, lacking uniqueness under varying sampling intervals and instrument resolutions, and failing to capture the scale-invariant nature of meshing interface topography. A scale-independent parameter system grounded in fractal geometry theory enables essential feature extraction and quantitative characterization of three-dimensional interface morphology. This study establishes a progressive deformation theory for gear line contact interfaces with fractal geometric characteristics, encompassing elastic, elastoplastic transition, and perfectly plastic stages. By systematically investigating the force–thermal coupling mechanisms in textured meshing interfaces under multiscale conditions, the research provides a theoretical foundation and numerical implementation pathways for high-precision multiscale thermo-mechanical analysis of meshing interfaces.

The use of polymer gears is increasingly becoming popular due to their lightweight, low noise, and low manufacturing cost. However, wear is a critical issue affecting their durability and reliability. This study aims to investigate the wear behavior of asymmetric polymer gears using experimental and numerical methods. The experiments involve conducting wear tests under varying load, speed, and temperature conditions. The numerical method involved an explicit dynamic algorithm to simulate the gear contact and wear behavior. In the current approach of the dynamic contact of gears, the contact forces generated are highly non-linear and time dependent in nature. Also, stress concentration is observed only at the point/line of contact, which accelerates the wear rate. Hence, in order to effectively capture these phenomena, explicit dynamic analysis is best suited for capturing the wear behavior of gear pairs under a given operating domain. While Implicit methods are best suited for static analysis where the response of the system is not time dependent. The simulation model is validated using experimental data, and the wear behavior is analyzed using wear rate, contact pressure, and contact stress. The weight loss percentage method has been used to analyze the wear amount on the gears. The results show that the wear rate increases with increasing load and speed, while decreasing with increasing temperature. A temperature rise of 4°C–5°C has been observed for a running time of 6 h. Thus, temperature rise may not lead to a major wear in Nylon 6 gears. The numerical results show good agreement with the experimental data, with around 5% variation, indicating that finite element analysis can be a reliable method for predicting the wear behavior of polymer gears.

This research introduces three theoretical probabilistic models to predict the ultimate resistance of T- and Y-nodes enhanced with collar plates in compressive, tensile, and bending loads. The study commenced with the creation and validation of a finite element (FE) model, incorporating 18 experimental results from the author and other researchers to ensure model accuracy. Following this, 630 FE simulations were carried out to evaluate the behavior of the retrofitted nodes. In the numerical simulations, welds connecting the reinforcement plate to the chord, as well as those between the brace and the reinforcement plate, were explicitly incorporated. Additionally, the contact behavior at the interface between the collar plate and the chord was modeled to accurately capture their interaction. The simulation data provided a strong basis for developing probabilistic models. 14 functions were fitted to the generated histograms. The appropriateness of the proposed distributions was verified through three statistical tests: Anderson-Darling, Chi-square, and Kolmogorov-Smirnov. Of the tested models, the Johnson SB was found to be the most accurate for modeling the resistance under compression. Also, for the enhanced connections under tensile and in-plane bending loads, the Generalized Extreme Value model was established. These findings demonstrate the potential of the proposed probabilistic framework to enhance the understanding and assessment of the behavior of strengthened T- and Y-shaped joints, within the scope and assumptions of the current study.

Wide bandgap semiconductors for high-power and high-frequency applications drain a lot of scientific interest. Among them AlGaN/GaN heterostructure with its related 2D electron gas is a key element for advanced microelectronics devices. Nonetheless, Schottky contacts on AlGaN/GaN heterostructure typically show a non- ideal behavior due to concomitant conduction mechanisms and high ideality factor. This study investigates the electrical behavior of molybdenum Schottky contacts on AlGaN/GaN heterostructures grown on silicon, focusing on the temperature dependence of the electrical parameters. Despite limited adoption of molybdenum as a Schottky metal, its application result in a contact that exhibits a conduction dominated by thermionic emission (TE) with an ideality factor of 1.26 at room temperature. This conduction behavior, uncommon for AlGaN/GaN Schottky contacts, enabled a detailed analysis of the barrier inhomogeneities. The concentration of inhomogeneities justifying the observed electrical behavior is 2 × 109 cm− 2, in good agreement with the density of dislocations in the heterostructure.

Metal–semiconductor heterojunctions are fundamental to modern electronics, serving as the key interface for charge transport and enabling diverse functionalities in electronic and optoelectronic devices. In this work, we computationally design the electrical contact architecture by vertically integrating two-dimensional TaS2 and Sc2CF2 materials using first-principles predictions. The TaS2/Sc2CF2 heterostructure is predicted to be energetically and thermally stable at room temperature and characterized by weak van der Waals interactions. Additionally, the integration of TaS2 with Sc2CF2 enhances the mechanical rigidity of the heterostructure. More interestingly, the TaS2/Sc2CF2 heterostructure forms a Schottky contact with an electron barrier of 0.36 eV. Furthermore, it exhibits remarkable tunability in electronic properties and contact behavior under an applied electric field. Specifically, the electric field induces a transition from Schottky to ohmic contact, as well as a conversion from n-type to p-type Schottky contact. This tunability signifies a barrier-free charge injection process, making the TaS2/Sc2CF2 heterostructure a promising candidate for next-generation electronic and optoelectronic devices.

The influence of cosine-shaped subgrade settlement (CSSS) at different positions on the structure of unit slab ballastless track (USBT) of high-speed railway (HSR) is studied in this paper. The pre-developed general mapping model of the track structure deformation and interlayer contact behavior evolution of HSR is used, the CSSS description function is incorporated, and the deformation equations for each layer of the USBT structure under CSSS are derived. The incremental approach method is used to solve the statically indeterminate equation with contact nonlinearity, and then the influence of CSSS at different positions on the track structure deformation and interlayer contact behavior evolution is analyzed. The results show that the transfer pattern of track deformation is related to the position of settlement, and the structure deformation is more sensitive to the settlement at the position of the slab joint. Under the CSSS, the vertical deformation of the track structure remains synchronized and is transmitted upward layer by layer. The type of track irregularity differs between the subgrade settlement area and the area outside of it. In the area of uneven subgrade settlement and its small area on both sides, the debonding position of the track slab-base slab and track system-subgrade system mainly appears at the position of the slab joint, which presents the distribution law of “smaller at the near end, larger at the far end”.

Flexible piezoresistive sensors are crucial for wearable electronics and intelligent robotics due to their high sensitivity and wide linear range. However, achieving both wide linear range and high sensitivity remains challenging. A high-performance MXene-based flexible piezoresistive pressure sensor featuring hierarchical structural engineering is reported. The sensor integrates a microsphere-regulated barrier layer to modulate contact behavior, a MXene/MWCNTs-PDMS composite for stable conductivity, and an outer PDMS membrane with inverted conical microstructures to enhance sensitivity. This design achieves an ultra-wide detection range with a three-stage linear response (0-1228.75kPa) and an excellent sensitivity (up to 9041.8kPa-1), maintaining stability over 5000 cycles at 625kPa. The device demonstrates reliable detection of physiological signals and material recognition, offering a scalable solution for wearable electronics and intelligent robotics. This work is expected to provide new insights into the design of next-generation high-performance flexible sensing systems.

Influence of laser-induced discrete hardening units on gear surface fatigue resistance: Investigation from contact behavior and lubrication state

Effect of coating plasticity parameters on the fretting wear behavior of electrical contacts