Real Contact Research Articles

The Significance of Chinese Art Songs by Huang Tzu (1904 - 1938)

Chinese art song, a type of Chinese New Music, was a musical genre referring to the songs composed particularly in the 1920s. It is undeniable that it was a product of the real contact and fusion of Chinese and Western cultures. Imagine listening to music like Schubert or Puccini, you may suddenly realise that the language is not German or Italian, but an exotic language (Mandarin, also mixed with different Chinese dialects). Chinese art songs indeed had such characteristics. Its appearance was epoch-making. Before the 19th century, the gate of Chinese traditional culture was closed and self-sufficient, but due to the invasion of Western powers, this gate soon collapsed. Western culture also swept China along with the military trend in the early 20th century, causing earth-shaking changes in China, in which Western music was also introduced into China. Some intellectuals enlightened by modern thoughts and knowledge believed that in addition to learning western military and technology, they should also absorb their philosophy and culture, so that China could rise in all directions and catch up with Western powers. The theme of this research revolves around one of the intellectuals (composers) of this period, Huang Tzu (1904-1938) who challenged and responded to the culture shock through composing Chinese New Music. After studying in the United States in 1926, he returned to Shanghai, China. Like the intellectuals at that time, in addition to being proficient in various fields like science, he also dabbled in music. Many of Huang Tzu’s music revolved around the concept of "nationality". It refers to an approach: borrowing Western compositional techniques to highlight the values of traditional Chinese aesthetics. This research did not aim at describing the characteristics of music or literature in Chinese art songs itself. Yet, it finally allowed me to discover more about how intellectuals dealt with issues of cultural exchange between the East and the West a hundred years ago. What would be the effects if Western music elements, such as harmony, form, techniques and musical instruments were added to the Chinese traditional music language and habits? From a cultural perspective, what significance did this incur?

Characterisation of the Contact between Cross-Country Skis and Snow: A Micro-Scale Study Considering the Ski-Base Texture

In winter sports, the equipment often comes into contact with snow or ice, and this contact generates a force that resists motion. In some sports, such as cross-country skiing, this resistive force can significantly affect the outcome of a race, as a small reduction in this force can give an athlete an advantage. Researchers have examined the contact between skis and snow in detail, and to fully understand this friction, the entire ski must be studied at various scales. At the macro scale, the entire geometry of the ski is considered and the apparent contact between the ski and the snow is considered and at the micro-scale the contact between the snow and the ski-base textures. In the present work, a method for characterising the contact between the ski-base texture and virtual snow will be presented. Six different ski-base textures will be considered. Five of them are stone-ground ski bases, and three of them have longitudinal linear textures with a varying number of lines and peak-to-valley heights, and the other two are factory-ground “universal” ski bases. The sixth ski base has been fabricated by a steel-scraping procedure. In general, the results show that a ski base texture with a higher Spk value has less real contact area, and that the mutual differences can be large for surfaces with similar Sa values. The average interfacial separation is, in general, correlated with the Sa value, where a “rougher” surface exhibits a larger average interfacial separation. The results for the reciprocal average interfacial separation, which is related to the Couette type of viscous friction, were in line with the general consensus that a “rougher” texture performs better at high speed than a “smoother” one, and it was found that a texture with high Sa and Spk values resulted in a low reciprocal average interfacial separation and consequently low viscous friction. The reciprocal average interfacial separation was found to increase with increasing real contact area, indicating a correlation between the real area of contact and the Couette part of the viscous friction.

Planarization profile modeling using pad bulk deformation and real contact area analysis of macro-scale device pattern

In general, the shape of the polished pattern is not flat but has a rounded curved profile. Unlike micro-patterns that have similar scales to pad asperities, macro-patterns have a very large scale compared to asperities, so bulk deformation must also be considered. To derive the pad bulk deformation, real contact area (RCA) measurements were performed in this study. Based on the preceding contact model, a semi-empirical model for RCA and bulk deformation was derived. After including the constructed pad bulk deformation function in the existing Greenwood–Williamson model, a new model that can derive the material removal rate profile according to the position in the pattern was presented. Unlike the general upper and lower removal rate behavior, this model shows a unique behavior. At the beginning of polishing, the edge shows a higher removal rate than the center, but after a specific step height, the center has a higher removal rate due to the curved shape. Analysis was performed for comparison between the proposed model equation and the experimental value. When the polishing profile in the 10 mm pattern was compared with the previous model and the proposed model, respectively, the existing model did not predict the removal rate distribution according to the position in the pattern. However, this model has the advantage of predicting both over-polishing at the edge of the pattern and high removal rate at the bottom. In addition, it was confirmed through simulation that the 4 mm and 2 mm patterns had excellent matching properties.

Modelling tangential friction considering contact pressure distribution of rough surfaces

Frictional interfaces play an important role on the dynamic response of jointed structures. To accurately predict the dynamics of jointed structures, the phenomenological Iwan-type models, which consist of many spring-slider elements in parallel or series, are often used to describe interface frictional behavior. In this paper, a novel tangential friction modelling approach based on the framework of Iwan model is proposed. Specifically, the density function of slider critical slip force, which is vital to deduce the final form of Iwan model, is determined by a new method. The method is based on the real rough surface and contact pressure results due to rough contact are introduced to derive the form of Iwan model. This provides a physical method to derive the density function of slider critical slip force, while in the past the density function is usually assumed artificially without a clear physical meaning. In the proposed method, twofold Weibull mixture model is used to represent the contact pressure distribution of actual rough surfaces. Following this, the corresponding Iwan density function is derived based on the local Coulomb friction. Then substituting Iwan density function into Iwan model, the explicit relationship between the tangential force and the relative displacement is deduced. The proposed modelling approach is applied to sphere-on-sphere contact and the comparison between the simulation and theoretical results shows perfect agreement. Then, the proposed modelling approach is validated against published experimental results for a flat-on-flat contact and a bolted joint. Compared to the classic Iwan model, the proposed model can better match the experimental results at the transition from microslip to macroslip. This study considers the influence of real rough contact characteristics on tangential friction behavior and provides a new tangential friction model deriving method.

Dynamic Redirection for VR Haptics with a Handheld Stick.

This paper proposes a general handheld stick haptic redirection method that allows the user to experience complex shapes with haptic feedback through both tapping and extended contact, such as in contour tracing. As the user extends the stick to make contact with a virtual object, the contact point with the virtual object and the targeted contact point with the physical object are continually updated, and the virtual stick is redirected to synchronize the virtual and real contacts. Redirection is applied either just to the virtual stick, or to both the virtual stick and hand. A user study (N = 26) confirms the effectiveness of the proposed redirection method. A first experiment following a two-interval forced-choice design reveals that the offset detection thresholds are [-15cm, +15cm]. A second experiment asks participants to guess the shape of an invisible virtual object by tapping it and by tracing its contour with the handheld stick, using a real world disk as a source of passive haptic feedback. The experiment reveals that using our haptic redirection method participants can identify the invisible object with 78% accuracy.

Effect of load application method on thermal contact resistance and uniformity of temperature distribution

Traditionally, the research on thermal contact resistance based on real rough surfaces is often limited to the uniform load. This study investigated the effects of the material, surface roughness, pressure load, and temperature on the thermal contact resistance and contact interface temperature distribution non-uniformity under a concentrated load. First, rough surfaces with different surface roughness degrees were generated by using a random generation method, and microscopic contact numerical models of three different materials were established. Then, the real contact area of different pressure loads under uniform and concentrated loads were calculated. Finally, heat transfer analysis was performed at different temperatures based on the microcontact state, the thermal contact resistance and the contact interface temperature distribution non-uniformity were calculated. Compared with the uniform load, the thermal contact resistance and the non-uniformity of the temperature distribution were improved under the concentrated load, and the effect was more obvious under the conditions of a large pressure load and small surface roughness degree. In addition, it was found that the uniformity of the temperature distribution on the contact surface was proportional to the real contact area and temperature instead of the thermal contact resistance except when the real contact area was very small.

Effect of Third-Particle Material and Contact Mode on Tribology Contact Characteristics at Interface

A moving pair with two-body contact is the ideal situation assumed in previous analyses. However, all moving pairs are in a three-body contact state at the start of operation or immediately after the start of operation, such as bearings, ball-screws, gears and engines. This work studies the influence of wear particles (SUJ2), environmental particles (SiO2 and Al2O3) and nano-additives (CuO) on the tribological contact characteristics under different particle concentrations, particle sizes, surface roughnesses and contact modes. The three-body microcontact analysis revealed that the differences in the real contact area, particle contact area and separation of the four-particle materials in the three-body s–s and p–s contact modes are rather small. Under the three-body hybrid contact mode, the difference is relatively large and the sequence of the real contact area value obtained due to the elastic modulus for the four-particle material at this interface is Al2O3 > SUJ2 > CuO > SiO2. The order of the other two contact characteristics is reversed. The difference increases as the particle size or particle concentration increases. The order of the critical load required to transform three kinds of contact modes is SiO2 > CuO > SUJ2 > Al2O3. On the nearly initial three-body hybrid contact mode, the plastic contact area ratio at the interface first increases to a critical value and then decreases as the load increases because the original plastic contact spot area and contact spot number increases with the increase in load. At the same time, the elasto-plastic contact area ratio decreases to a low value and then increases. The elastic contact area ratio at the interface decreases as the load increases. Among the four third-particle materials, the experimental results and theoretical predictions show that the environmental particles, Al2O3, cause the maximum friction and wear observed at the interface.

Tire-pavement friction modeling considering pavement texture and water film

The accurate estimation of tire-pavement friction, especially under wet conditions, is critical to ensure pavement safety. For this purpose, this paper develops a modified tire-pavement friction model which takes the effect of pavement texture and water film into consideration. The influence of pavement texture is quantified by a newly proposed parameter called texture influence coefficient, which is related to the real contact patch of tire-pavement. The water effect is calculated from two parts, namely lubrication effect and hydrodynamic effect. Based on these two steps, a modified average lumped LuGre (ALL) model is developed. The proposed model is calibrated and verified by GripTester data collected under different vehicle velocities and water film thicknesses. The root mean square error between the calculated value of the model and the measured value is 0.023. In addition, the effects of vehicle velocity, slip rate, water film thickness, and pavement type on the friction coefficient are analyzed by numerical calculation. The results show that the friction coefficient reaches the maximum when the slip rate is in the range of [0.15, 0.20]. The increases in the vehicle speed and water film thickness will lead to the decrease in the friction coefficient. Besides, in thin water film (<1 millimeter) conditions, the deterioration effect of water film thickness on the friction coefficient is more remarkable. The results prove that the modified tire-pavement friction model provides a precise and reliable way to estimate the friction coefficient of pavement, which can assist the pavement management systems in risk warning and safety guarantee.

Effects of surface roughness and counter body variables on the dry sliding wear behavior of AISI 4140 steel based on the elastoplastic flattening model

This study aimed to determine the effect of surface roughness and counter body material on the wear behavior of AISI 4140 steel based on the elastoplastic flattening model. Most studies in tribology based on the elastoplastic regime focus on modeling the contact between a sphere and a flat surface. However, these models’ main challenge is determining the real contact area. This study claims that the real contact area can be detected with high accuracy through interface software used in optical microscopy. The sample surfaces were roughened and then supposed to dry sliding wear tests using the AISI 52100 and Al2O3 abrasive counter bodies under varying loads and test durations. It was concluded from the calculations that the sample’s surface roughness value significantly affects the contact pair’s plasticity index and, thus, the sample’s wear behavior against the counter body material. Higher plasticity index values indicating the abrasive effect were obtained with the Al2O3 ball, which has a higher hardness and elasticity modulus than the AISI 52100 steel ball. The surface damage of the sample with a high roughness value was less than the other samples. The COF values obtained with the steel ball were detected as lower than that of the alumina ball. Also, it was seen that the surface roughness parameter and plasticity index values calculated were compatible with the wear characteristics of the test samples. As a result, determining the real contact area between the contacting surfaces and its usability in calculating the elastoplastic flattening model parameters were experimentally tested and verified.

Temporal Cascade Model for Analyzing Spread in Evolving Networks

Current approaches for modeling propagation in networks (e.g., of diseases, computer viruses, rumors) cannot adequately capture temporal properties such as order/duration of evolving connections or dynamic likelihoods of propagation along connections. Temporal models on evolving networks are crucial in applications that need to analyze dynamic spread. For example, a disease spreading virus has varying transmissibility based on interactions between individuals occurring with different frequency, proximity, and venue population density. Similarly, propagation of information having a limited active period, such as rumors, depends on the temporal dynamics of social interactions. To capture such behaviors, we first develop the Temporal Independent Cascade (T-IC) model with a spread function that efficiently utilizes a hypergraph-based sampling strategy and dynamic propagation probabilities. We prove this function to be submodular, with guarantees of approximation quality. This enables scalable analysis on highly granular temporal networks where other models struggle, such as when the spread across connections exhibits arbitrary temporally evolving patterns. We then introduce the notion of “reverse spread” using the proposed T-IC processes, and develop novel solutions to identify both sentinel/detector nodes and highly susceptible nodes. Extensive analysis on real-world datasets shows that the proposed approach significantly outperforms the alternatives in modeling both if and how spread occurs, by considering evolving network topology alongside granular contact/interaction information. Our approach has numerous applications, such as virus/rumor/influence tracking. Utilizing T-IC, we explore vital challenges of monitoring the impact of various intervention strategies over real spatio-temporal contact networks where we show our approach to be highly effective.

Experimental assessment of clayey layers for clogging potential in TBM tunnel driving and the influence of compositional factors

Clogging is common for tunnel boring machines, especially in clayey soil, and when it happens, the cutter heads or even the entire tunnelling device can become completely clogged, causing low excavation efficiency and high project costs. Because clogging stems from the adhesion of the excavated geomaterials, a better understanding of soil adhesion is required if clogging is to be avoided. Reported here are piston pull-out tests conducted to investigate the adhesion of natural clayey soils and artificial soils prepared using pure kaolin, montmorillonite, and silica sand, thereby enabling consideration of the effects of compositional factors (e.g., clay fraction, and mineralogy). The results show that with increasing water content, the adhesion stresses of the studied samples increased initially and then decreased. With increasing clay fraction, the adhesion stresses increased linearly because of the larger real contact area of the interface between the soil and a foreign object. With the addition of montmorillonite, the soil adhesion also increased significantly because of its microstructural properties. An updated semi-empirical diagram is proposed that allows the effects of compositional factors on clogging potential to be evaluated qualitatively. The measured maximum adhesion stresses of the studied samples occurred in the region of strong clogging in the semi-empirical diagram, showing the feasibility of using adhesion stress as an index for assessing the clogging of tunnel boring machines. This study provides valuable experimental data on soil adhesion and a better understanding of the adhesion behavior of clayey soils.

The attitude of the patients of a multidisciplinary hospital to the processes of digitalization in modern healthcare: A cross-sectional continuous study

BACKGROUND: This article is devoted to the impact of the digitalization of modern healthcare on the nature of relationships between a doctor and a patient.&#x0D; AIM: To assess the level of readiness of the patients in the city hospital for the introduction of digital technologies in the system of providing medical services.&#x0D; MATERIALS AND METHODS: The study was based on the results of a questionnaire survey of 154 patients in city hospitals in JulyAugust 2022 in Nizhny Novgorod. The survey questions included studying the use by modern day patients of various methods of digital communication with medical workers, the impact of the availability of medical information on the internet on the level of patients trust on a doctor, and patients opinions about the prospects for solving problems of modern healthcare through digitalization.&#x0D; RESULTS: The results of the survey revealed that 104 (67.5%) patients do not use digital communications, and 94 (61%) have no intention of using them. Among the prospects for the use of digital technologies in healthcare, the most popular for respondents were getting referrals for medical services (n=83, 53.9%), a prescription (n=57, 37%), and documents certifying temporary disability (n=43, 27, 9%). Only 8 (5.2%) respondents systematically check the diagnoses and prescriptions received from the attending physician on the internet and 25 (16.2%) do this from time to time. Only 2 (1.3%) respondents stated that they have a priority level of trust in recommendations from internet sources, and the rest of the patients trust their real attending physicians more.&#x0D; CONCLUSION: A modern patient seeks to receive medical care in real contact with a doctor, considering digital technologies mainly as a tool that addresses formal issues that arise when visiting medical organizations.

Applying the method of virtual elements to solving contact problems of shells of revolution interacting with surfaces of inconsistent shape

An approach based on the method of virtual elements is used to solve the contact problem for a thin shell of revolution lying on a rigid foundation. In this case, the surface of the base has a shape inconsistent with the surface of the shell. The method makes it possible to determine the contact area and the contact pressure from the contact area unknown in two coordinate directions. Since the contact area is not known in advance, the problem is structurally nonlinear. A thin isotropic shell is described by the classical theory based on the Kirchhoff–Love hypotheses. The base is taken absolutely rigid, but with the presence of an elastic gasket. The shell equations are integrated by S. K. Godunov’s method of discrete orthogonalization. To determine the forces of interaction between the shell and the base, a mixed method of structural mechanics is used. With this aim in view, the maximum possible contact area is discretized by virtual rectangular elements. A constant value of the contact pressure is assumed on each element obtained in this area, and the contact pressure is assumed to be zero on the elements in the area where the shell leaves the base. Based on the assumptions, a system of linear algebraic equations is constructed, which determines the contact pressure and deflection of the shell circumference axis. Since the shell can move away from the base, iterative procedures are applied to search for the real contact area, which depends on the geometric and elastic parameters of the shell and the magnitude of the external load. As an example, the contact interaction of a cylindrical shell (part of the shell of a tank car) lying on a rigid base with a gasket is considered. It is shown how the contact area and contact pressure change depending on the rigidity of the gasket and the difference between the radii of the shell and the base (inconsistency in the shape of the surfaces).

DEM study of an “avatar” railway ballast with real particle shape, fabric and contact mechanics

In this paper we show DEM simulations of static and cyclic large triaxial tests on a sample of railway ballast. The sample is reconstructed from X-Ray tomography images of an untested laboratory sample, recovered by impregnation with an epoxy resin. Measurements of both shape and fabric are carried out; the sample shows a high anisotropy of particle orientations due to the preparation procedure and a high shape heterogeneity. A DEM model is then generated using clumps to model single particles, preserving the shape of each particle and the fabric of the sample. Results of static and cyclic simulations are shown and compared with previous simulations on numerically generated samples, showing the importance of an accurate representation of the whole range of particle shapes, as well as confirming the effect of particle anisotropy on the mechanical response.Graphical

A consecutive joint shear strength model considering the 3D roughness of real contact joint surface

A consecutive joint shear strength model for soft rock joints is proposed in this paper, which takes into account the degradation law of the actual contact three-dimensional (3D) roughness. The essence of the degradation of the maximum possible dilation angle is the degradation of the 3D average equivalent dip angle of the actual contact joint asperities. Firstly, models for calculating the maximum possible dilation angle at the initial and residual shear stress stages are proposed by analyzing the 3D joint morphology characteristics of the corresponding shear stages. Secondly, the variation law of the maximum possible dilation angle is quantified by studying the degradation law of the joint micro convex body. Based on the variation law of the maximum possible dilation angle, the maximum possible shear strength model is proposed. Furthermore, a method to calculate the shear stiffness degradation in the plastic stage is proposed. According to the maximum possible shear strength of rock joints, the shear stress-shear displacement prediction model of rock joints is obtained. The new model reveals that there is a close relationship between joint shear strength and actual contact joint roughness, and the degradation of shear strength after the peak is due to the degradation of actual contact joint roughness.

An ultrasonic array-based method for the in-situ monitoring of contact area and wear under severe sliding conditions

Determining the very nature of an interface within a sliding contact is a central question in tribology. Contacts between asperities, normal and shear stresses and resulting real contact area are important characteristics governing friction losses but also wear. Despite the fundamental nature of these quantities, being able to experimentally and in-situ measure them is still a real challenge. This is even truer as far as extreme contact conditions are concerned, i.e. operating under high temperatures and/or contact pressures and/or sliding velocities.This work presents the development of a method for in-operando contact monitoring of a sliding contact. Based on an ultrasonic array of 32 elements, this approach uses wave propagation to assess the contact area and wear between two metallic materials. Each element of the probe is individually pulsed with a given sequence to construct a picture of the contact zone based on the reflected signals. A numerical model is first developed to study the propagation of the ultrasonic waves through a friction pin and its interaction with the contact interface. The influence of contact stresses and contact size on the ultrasonic signals is investigated in order to establish a method for online estimating the contact area.The experimental set-up is then described with the integration of an ultrasonic array on an open tribometer. A multi-channel pulser receiver is employed to control the probe while a dedicated software is used for processing the signals and monitoring in real time the data. Finally, an experimental campaign is performed with a cemented carbide pin sliding on a AISI 1045 steel to validate the methodology.

A novel analytic model for sealing performance of static metallic joint considering the yield hardening effect

The static metallic joints’ sealing performance is deeply impacted by the plastic deformation and the interfacial separation of the contact surfaces with self-affine roughness. The yield hardening effect, unavoidable at the contact interface, is of vital importance to the plastic deformation and the distribution of the interfacial separation. However, most of the previous research ignores the effect of yield hardening, assuming that the contact surfaces are elastic-perfectly plastic. To address the problem, a novel analytic model for investigating the sealing performance under the effect of yield hardening has been developed in this paper. The upper boundary of contact stress in the conventional Persson model has been enlarged from a constant nominal yield stress to a maximum yield stress that varies with contact strain, making the model adaptable to actual scenarios with yield hardening effects. Utilizing the measured data of contact surfaces as input, the corresponding leakage rates are calculated. Besides, the contact stress distribution as well as the real contact area at the interface is also discussed. The sealing experiments are carried out accordingly, verifying that the proposed model owns the ability to predict the leakage rate under the effect of yield hardening.

Contact of Rough Surfaces: An Incremental Model Accounting for Strain Gradient Plasticity

In the contact of rough surfaces, most contact patches are at the scale of micrometers, and thus, their contact deformation can be dominated by the size-dependent plasticity. In this paper, we propose a new strategy to analyze the role of strain gradient plasticity in the contact response between a realistic rough surface and a rigid plane, which modifies the incremental contact model based on the mechanism-based gradient plasticity (MSGP) theory. For several different rough surfaces with their topography measured experimentally, the relations between applied load and real contact area are derived in a simple but effective way. It is found that strain gradient plasticity significantly increases the level of mean contact pressure. The hardening effect caused by strain gradient plasticity weakens somewhat as the contact area increases. Compared with previous methods, the present model might be more efficient and of wider application.

Simplified Calculation Model for Contact Resistance Based on Fractal Rough Surfaces Method

Electrical contact resistance (ECR) is critical to evaluate the stability and reliability of electrical connections. In this paper, a simplified contact model is established for rough surfaces based on the fractal theory and Monte Carlo method, which can overcome the difficulty of constructing the resistance networks for traditional contact models. The model reveals the influence of fractal parameters D and G on the surface morphology and contact characteristics. The established surface method can simulate Gaussian and non-Gaussian isotropic surfaces. Then the contact resistance considering a contaminated film is calculated, which provides a quantitative analysis of the change and the influencing factors. The accuracy of the calculation method in this paper is ensured by comparing the existing experimental data and finite element results. The results show that the contact surface with D of 1.5 has the largest real contact area and the smallest contact resistance. The model has accurate calculation results when dimensionless contact load F* is less than 4 × 10−3.

Factors affecting knitted fabric slipperiness and smoothness

In this study, the factors affecting the slipperiness and smoothness of knitted fabrics were statistically analyzed to facilitate the effective design and development of knitted fabrics. Both slipperiness and smoothness are important properties of a fabric, with impacts on clothing comfort, sports records and the medical or safety performance of textile products. In this study, the average value of frictional coefficient (MIU) of a knitted fabric, which is correlated with the slipperiness of the fabric, and the fluctuations of the average frictional coefficient (MMD), which is correlated with the smoothness of the fabric, were measured by using a friction tester (KES-SE). The friction coefficient of the knitted fabric was found to depend on three factors: linearity of the loop arrangement, fuzziness and real contact area of the fabric. The contribution ratio of each factor to fabric slipperiness was calculated. In addition, the friction coefficient of the fabric was highly correlated with its course or wale densities. On the other hand, the smoothness of the fabric was affected by the linearity of fabric loop arrangement, but not by fabric fuzziness or the real contact area.