Real Contact Research Articles

A mechanically consistent unified formulation for fluid-porous-structure-contact interaction

Fluid–structure interaction with contact poses profound mathematical and numerical challenges, particularly when considering realistic contact scenarios and the influence of surface roughness. Computationally, contact introduces challenges in altering the fluid domain topology and preserving stress balance. This work introduces a new mathematical framework for a unified continuum description of fluid-porous-structure-contact interaction (FPSCI), leveraging the Navier–Stokes–Brinkman (NSB) equations to incorporate porous effects within the surface asperities in the contact region. Our approach maintains mechanical consistency during contact, circumventing issues associated with contact models and complex interface coupling conditions, allowing for the modeling of tangential creeping flows due to surface roughness. The unified continuum and variational multiscale formulation ensure robustness by enabling stable and unified integration of fluid, porous, and solid sub-problems. Computational efficiency and ease of implementation – key advantages of our approach – are demonstrated by solving two benchmark problems of a falling ball and an idealized heart valve. This research has broad implications for fields reliant on accurate fluid–structure interactions and promising advancements in modeling and numerical simulation techniques.

Friction Performance of Rubber Sealing Disc Inside Pipe Robots for the Production of High-Paraffin Oil

The in-pipe robot is the most commonly used technique in offshore pipelines. The use of rubber sealing discs is important for in-pipe robots to ensure that the robots are moved by fluid pressures inside offshore pipelines. This paper focuses on the measuring and modeling of the wax–oil gel-breaking process at the soft frictional area between sealing discs and the pipe wall. In this study, a detailed characterization of the gel-scraping process and in situ probing portable microscopy are performed. Two contributions are made in this study. First, a direct observation of wax–oil deposition breaking is employed to detect the minute changes at the in-pipe robot. Second, we find that a simple function is possible to describe the relationship between the wax contents and dewaxing efficiency, in which the debris material removal ratio (DRR) is discussed. Thus, the gel deposition-breaking phenomena are quite different under the influence of rubber sealing discs. This result is further confirmed by the real contact ratio measurements. It is important to research the sealing disc further and apply it more in the petroleum industry, especially in in-pipe robots for deepwater pipeline systems.

What do we know about dermal bioaccessibility of metals coated on antibacterial films?

Antibacterial films have gained attention since the outbreak of the COVID-19 pandemic; however, the impact of metals contained in antibacterial films on human safety have not been sufficiently investigated. This study reports on the important features that must be considered when assessing the bioaccessibility of Ag, Cu, and Zn in antibacterial films. Specifically, the effects of the artificial sweat component (i.e., amino acid and pH), surface weathering of antibacterial films, wipe sampling, and sebum were carefully examined. Our findings suggest that amino acids greatly affect bioaccessibility as amino acids act as ligands to facilitate metal ion leaching. In addition, constant exposure to ultraviolet C causes the film surface to oxidize, which significantly increases metal bioaccessibility due to the electrostatic repulsion between metal oxides and organic substrates. The presence of sebum in artificial sweat and physical damage to the film surface had no significant effects. Furthermore, the wipe sampling used to mimic the realistic dermal contact suggests the feasibility of applying this method for the assessment of bioaccessibility of metals in antibacterial films. The method offers significant advantages for evaluating the human safety aspects of skin contact with consumer products in future research.

Failure analysis of soil-rock mixture slopes using coupled MPM-DEM method

A 3-D concurrent MPM-DEM (material point method - discrete element method) scheme is proposed and developed in this paper to simulate soil-rock mixture slopes. The MPM and DEM are treated as two individual parts linked by the coupled contact force. Compared with MPM, the proposed MPM-DEM scheme provides a more realistic contact detection. Compared with DEM, the scheme can model such cases more efficiently and conveniently. Based on the characteristics of the soil-rock mixture, a CPU-GPU concurrent solving scheme is introduced, which can improve the efficiency and make full use of the computational resources of both GPU and CPU. The accuracy of the MPM-DEM scheme is validated by three benchmark examples, i.e., a block sliding on an inclined plane, granular flow impacting blocks, and collapse of hybrid granular columns. The failure mode and sliding distance of soil-rock mixture slopes are analyzed using the proposed MPM-DEM scheme and compared to a pure MPM. Influencing factors such as soil-rock friction and cohesion, rock content, and rock size are studied. The results indicate that this scheme can well capture the soil-rock interface and deal with complex interactions between soil and rock.

Dynamic modeling and vibration analysis of bolted flange joint disk-drum structures: Theory and experiment

Bolted flange joint disk-drum structures (BFJDSs) are key components in aero-engines, in which fatigue damage often occurs due to structural vibration. However, no study has so far given an effective theoretical dynamic model of BFJDSs. In this study, an effective dynamic model of BFJDSs is proposed. The present model considers the flange effect, non-uniform contact pressure of bolted joint, and bolt mass. The theoretical expression for describing the stiffness variation of bolted joints is presented. During the modeling process, the energy functions of disk, drum, and flange are obtained according to the Kirchhoff plate, Sanders’ shell, and Euler-Bernoulli beam theories, respectively. The non-uniform artificial spring technique is adopted to simulate the pressure distribution of bolted joint. This method is capable of taking into account the contact pressure, which is closer to real contact situation. The displacement functions of disk and drum are expanded by using the Chebyshev orthogonal polynomials, and the motion equations are obtained by employing the Lagrange equation. Then, the experimental studies are performed on BFJDSs to illustrate the effectiveness of the theoretical model. Finally, the frequency veering and coupling vibration phenomena are revealed. The comparison studies indicate that the established theoretical model can well predict the vibration characteristics of BFJDSs under both bolt looseness and no-looseness conditions. The maximum error can be reduced from 46.81% to 3.61% by using the present dynamic model.

Modeling the line contact on an elastic half-space with the statistical approach: Self-affine fractal roughness and numerical framework

This paper presents a line contact model for describing the normal contact between rough surfaces with self-affine fractal roughness based on the statistical approach. An iterative algorithm combining the Levenberg-Marquardt (LM) method with penalty function is proposed to overcome the limitation of restricted indentation depth. Results show a competitive relationship between the plasticity index and the fractal dimension on the real contact area. Besides, nonlinear characteristics between force and area appear when the elastic modulus of the substrate is larger than that of the asperity. Furthermore, the wavy machining texture leads to a great increase in the maximum pressure. The current work can be used for modeling the transmission interfaces involving line contact, such as gears and cylindrical rotor bearings.

Effect of the interaction time of CO2–H2O on the alterations of coal pore morphologies and water migration during wetting

CO2 geosequestration requires coal property examination for long-term storage sustainability. This study explores pore morphologies and water kinetic during wetting under interactions. Results showed that the CO2–H2O interaction induced intricate modifications in the coal pore architecture over time, causing a decrease in surface roughness and an increase in hydrophobicity of coal after long-term (10 days) and short-term (5 days) treatment. By setting a water intake, capillary force drives the transformation of free water to capillary water and adsorbed water. The adsorption kinetics of coal to water follows the linear driving force (LDF) mass transfer rate law, provided a good agreement with experimental data, validating its applicability to the studied system within the long time limits. As the reaction duration increased, the rate constant increased while the equilibrium adsorption capacity decreased. The modified Wenzel model of hydrophilic surface is proposed to interpret the temporal alterations, showing that untreated coal has substantial contact points on the rough surface, resulting in a smaller apparent contact area than the real contact area, hindering water retention and displaying enhanced wettability. The rule applied hydrophilic surface of both natural wettability adjusted by supercritical carbon dioxide (ScCO2).

Ultrahigh Critical Current Density across Sliding Electrical Contacts in Structural Superlubric State.

In conventional sliding electrical contacts (SECs), large critical current density (CCD) requires a high ratio between actual and apparent contact area, while low friction and wear require the opposites. Structural superlubricity (SSL) has the characteristics of zero wear, near zero friction, and all-atoms in real contact between the contacting surfaces. Here, we show a measured current density up to 17.5 GA/m^{2} between microscale graphite contact surfaces while sliding under ambient conditions. This value is nearly 146 times higher than the maximum CCD of other SECs reported in literatures (0.12 GA/m^{2}). Meanwhile, the coefficient of friction for the graphite contact is less than 0.01 and the sliding interface is wear-free according to the Raman characterization, indicating the presence of the SSL state. Furthermore, we estimate the intrinsic CCD of single crystalline graphite to be 6.69 GA/m^{2} by measuring the scaling relation of CCD. Theoretical analysis reveals that the CCD is limited by thermal effect due to the Joule heat. Our results show the great potential of the SSL contacts to be used as SECs, such as micro- or nanocontact switches, conductive slip rings, or pantographs.

Seepage disturbance mechanism and interface force of cylindrical barrier in fracture

The fluid flow in the crack is disturbed by the contact area. The parallel-plate model with a circular cylindrical contact area is regarded as an idealization of the real contact fracture, and a computational fluid dynamics simulation is performed on it to analyze the interaction between the contact area and the flow around it. The size of the contact area controls the disturbance intensity to the flow velocity magnitude and the disturbance range to the velocity direction. Due to the existence of viscosity, the flow near the wall has a larger shear rate. The intermediate transition region is located between the contact area and the fracture lateral wall and does not contain the region with strong viscous friction caused by the wall. The flow velocity magnitude in the intermediate transition zone changes exponentially in space and has a peak value near the contact area. After the flow bypasses the contact area, the inertial effect caused by the increase in flow velocity magnitude in the local flow channel controls the generation and development of the low-velocity region and the asymmetric degree of the velocity direction distribution. Both the mechanical aperture and the inlet flow velocity affect the stress distribution on the surface of the contact area. The occurrence of the nonlinear flow behavior of fracture seepage and nonlinear change trend of logarithmic drag coefficient curve can be predicted with the same critical Reynolds number. These results provide a useful guide for further exploring the local flow and the surface stress distribution of the local interior geometric property in a single rough-walled fracture on the mesoscopic scale.

Scaling-up laser cladding of rails

With rail travel getting more popular more demands are being put on rail infrastructure. The wheel/rail contact is the one of the main parameters that is key to maintaining a high performing network. With increasing demands for higher loads and higher speeds, wear and rolling contact fatigue (RCF) are the main two problems.New maintenance techniques can overcome some problems, but new solutions that reduce the damage are needed. Laser cladding is one of the best methods for improving wear and RCF of rail steels by adding layers of more durable materials to the rail.In this article full-scale tests of clad layers have been carried out at realistic contact conditions to verify outcomes seen in twin-disc testing to see if the results can be scaled to predict field performance of clad layers. Martensitic Stainless Steel (MSS) and Stellite 6 were used for the clad layers and R260 was used as the base material. Un-clad R260 was used as reference material.Results of full-scale tests in terms of wear rates, sub-surface deformation, hardness and roughness evolution were comparable. This showed that the clad layers deposited on actual rail performed very well compared to un-clad rail and that the tests run at the small-scale were appropriate for predicting full-scale behaviour.

A New Approach for Determining Rubber Enveloping on Pavement and Its Implications for Friction Estimation

The depth to which the pavement texture is enveloped by the tire tread rubber (d) is an important parameter related to contact performance. This study presents a new method (S-BAC), which relies on the ratio between the real contact area and the nominal tire-pavement contact area (S) and the bearing area curve (BAC), to measure the depth on pavements. The tire-pavement contact was simulated by contact between a non-patterned rubber block and pavement specimens. After analyzing the affecting factors, the new method was compared with previous methods by the d values and the application on the relationship between pavement texture parameters and friction. The results reveal that though there is a linear regression between the d obtained with the S-BAC and previous methods, the d values obtained with different methods differ. Applying the S-BAC method can strengthen the relationship between texture parameters and friction more than other methods.

An Investigation Into the Grinding Characteristics and Wear Evolution of Micro-Elastic Composite Grinding Pads

Abstract This paper introduces a novel micro-elastic composite grinding pad for material removal. The study also developed a new grinding wear formula grounded in microcontact mechanics, which is crucial in examining the evolution of interface characteristics under optimal parameter combinations. The results showed that the material removal rate (MRR), reduction of roughness height (σ), and peak curvature radius (ρ) increase were the highest in the initial stage, followed by a slight increase in the real-contact area in the second stage. This research suggests that abrasive particles primarily detach from the elastic pad in the second stage. The plasticity index (ψ) decreases during grinding, which suggests a transition from an elastic–plastic mixed contact interface to a predominantly elastic contact interface. This shift in the interface mechanics explains the gradual reduction in wear at the grinding interface. Both the plasticity index and the MRR are consistent throughout the grinding process. However, the plasticity index is a more effective index of interface wear than the conventional H/E ratio because it considers the surface roughness’s shape and size, which is essential in mild grinding operations. The findings of this study can be used to improve the design and performance of micro-elastic composite grinding pads and to optimize the grinding process for improved efficiency and sustainability.

Modeling of the Combined Effect of the Surface Roughness and Coatings in Contact Interaction

The model of indentation of a spherical punch with a rough surface into a thin elastic layer lying on an elastic half-space has been developed. A numerical-analytical solution is suggested based on the two-scales approach. At macroscale, the integral equation of the second kind is reduced to calculate the nominal contact characteristics, taking into account the surface layer thickness and its mechanical characteristics, as well as additional compliance due to surface roughness calculated from the microscale analysis. The influence of the punch roughness and the surface layer mechanical and geometrical characteristics on the nominal contact pressure distribution, on the nominal contact area and the indentation depth, as well as on the real contact area and pressures at the individual contact spots, is analyzed. The developed contact model can be used to analyze the indentation of the punch into the layered elastic base, taking into account the roughness of the punch surface, and can also be used to give a complete analysis of the roughness effect on the contact process at both scale levels. The results can be used to control the indentation of the rough-coated bodies.

Flexible Bayesian inference on partially observed epidemics.

Individual-based models of contagious processes are useful for predicting epidemic trajectories and informing intervention strategies. In such models, the incorporation of contact network information can capture the non-randomness and heterogeneity of realistic contact dynamics. In this article, we consider Bayesian inference on the spreading parameters of an SIR contagion on a known, static network, where information regarding individual disease status is known only from a series of tests (positive or negative disease status). When the contagion model is complex or information such as infection and removal times is missing, the posterior distribution can be difficult to sample from. Previous work has considered the use of Approximate Bayesian Computation (ABC), which allows for simulation-based Bayesian inference on complex models. However, ABC methods usually require the user to select reasonable summary statistics. Here, we consider an inference scheme based on the Mixture Density Network compressed ABC, which minimizes the expected posterior entropy in order to learn informative summary statistics. This allows us to conduct Bayesian inference on the parameters of a partially observed contagious process while also circumventing the need for manual summary statistic selection. This methodology can be extended to incorporate additional simulation complexities, including behavioural change after positive tests or false test results.

Analysis and prediction of contact characteristics of rock fracture surfaces under normal loading

The real contact area of rock fractures is smaller than the nominal area, and actual stresses on contacts are significantly higher. Evaluating contact characteristics and predicting potential contact areas are crucial for understanding mechanical and hydraulic properties of geological fractures under compression or shear. We measured the real contact area of mated tensile fractures using pressure-sensitive films and studied their contact characteristics and evolution under different normal stresses through point cloud analysis. It is revealed that the initial aperture of mated tensile fractures determines the contact state. Under conditions of low normal stress, regions exhibiting higher mean curvature are more susceptible to contact formation, particularly when aperture sizes are comparable. This propensity is further influenced by the directional orientation of the normal vector components within these regions. Increasing normal stress leads to faster development of new contacts in regions with smaller initial apertures. Additionally, we predicted contact characteristics and real contact area of tensile fractures using back propagation artificial neural network. Comparison between predictions and laboratory measurements demonstrated accurate prediction of contact distribution and area values by the neural network. Our findings enable the prediction of real stress states, potential failure areas, and hydraulic conductivity of rock fractures in slope and underground rock engineering.

Surface Design of 3D-printed Polyether Ether Ketone for Abrasive Wear Resistance

The surface features of additively manufactured polymer parts differ compared to extruded polymer parts and decide their performance in terms of power transmission applications. Layer thickness is one of the important process parameters chosen based on the part complexity and production speed, influencing the surface features. The abrasive wear performance of high-performance polyether ether ketone (PEEK), which determines the performance of power transmission elements such as bearings and gears, is reported in this article. The layer thickness employed in fabrication, which varies from 0.1 mm to 0.35 mm, influences the surface roughness, real contact area, and hardness of the as-printed PEEK. The friction coefficient and wear resistance of a printed part are influenced by the layer thickness employed, indicating the need for a proper choice of layer thickness for power transmission applications. Samples printed with a layer height of 0.25 mm and higher exhibited an increase of friction coefficient and wear loss due to the weak surface integrity. The friction and wear characteristics of additive manufactured samples are compared with extruded samples. Wear debris accommodation in the grooves of the as-printed surfaces accelerates the wear due to three-body abrasion in high layer thickness samples. The micromechanisms of wear damage in different layer thickness samples are discussed. The observations indicate the strong influence of layer thickness and facilitate the selection of appropriate layer thickness for the required friction coefficient in a particular application.

Compressing the Chronology of a Temporal Network with Graph Commutators.

Studies of dynamics on temporal networks often represent the network as a series of "snapshots," static networks active for short durations of time. We argue that successive snapshots can be aggregated if doing so has little effect on the overlying dynamics. We propose a method to compress network chronologies by progressively combining pairs of snapshots whose matrix commutators have the smallest dynamical effect. We apply this method to epidemic modeling on real contact tracing data and find that it allows for significant compression while remaining faithful to the epidemic dynamics.

High Friction of Paper Wipers in Partially Wet Conditions: Effect of Three-dimensional Nonuniform Wetting

In wet paper wiper, three-dimensional nonuniform wetting may occur and affect frictional behavior. This study aims to clarify the frictional behavior of wet paper wiper in order to develop guidelines for controlling the frictional behavior of similar products such as clothing and sponges. Friction tests were conducted between a paper wiper and a flat glass while varying the water content of the paper wiper. The friction coefficient reached a maximum at a certain water content depending on the normal load and sliding velocity conditions. This high-friction effect may be attributed to meniscus formation at the contact interface and inside the paper wiper specimen, because the negative pressure due to the meniscus can promote the expansion of the real contact area.

Resolving Multi-Asperity Contacts at the Nanoscale through Super-Resolution Fluorescence Imaging.

Contact mechanics, spanning nanometer to tectonic scales, faces long-standing challenges arising from multiscale random roughness, which hinders experimental validation of theories. Understanding multi-asperity rough contacts is vital for addressing catastrophic consequences of these contacts failing such as earthquakes and for diverse technological applications. To visualize such contacts, we introduce a super-resolution microscopy method utilizing spontaneous millisecond ON/OFF fluorescence blinking of contact-sensitive molecular rotor molecules immobilized on a glass coverslip. This technique achieves ∼55 nm lateral imaging resolution for rough poly(methyl methacrylate) and glass spheres on glass contacts. For soft polymer spheres due to large plastic deformation, the resolution improvement does not significantly affect the area of real contact. However, for hard glass spheres, the real contact area is found to be 2.4 times smaller than that found by diffraction-limited imaging. This study highlights, through direct visualization, the impact of material stiffness on the nanoscale structure within the area of real contact.

Analysis of the discrete contact characteristics based on the Greenwood-Williamson model and the localization principle

The contact of a rigid body with nominally flat rough surface and an elastic half-space is considered. To solve the contact problem, the Greenwood-Williamson statistical model and the localization principle are used. The developed contact model allows us to investigate the surface approach and the real contact area with taking into account the asperities interaction. It is shown that the mutual influence of asperities changes not only contact characteristics at the macroscale, but also the contact pressure distribution at the microscale. As follows from the results, the inclusion in the contact model of the effect of the mutual influence of asperities is especially significant for studying the real contact area, as well as the contact characteristics at high applied loads. The results calculated according to the proposed approach are in a good agreement with the experimentally observed effects, i.e., the real contact area saturation and the additional compliance exhaustion.