Real Contact Research Articles

Determination of Range and Material of Real Contact Part by Measuring Complex Refractive Index in Contact Surface

Determination of Range and Material of Real Contact Part by Measuring Complex Refractive Index in Contact Surface

Simulation of local contact conditions in the secondary shear zone in dry and wet metal cutting

Cutting fluids significantly influence the contact conditions in metal cutting, e.g. stresses or contact areas. Due to the limited accessibility of the chip-tool contact, the identification of contact conditions is challenging. In this paper, a simulation model is created and used to identify the real contact area in dry and wet cutting. Experimentally identified normal stresses and chip-tool roughness serve as input parameters. The results show higher normal stresses in wet cutting, which results in a higher real contact area between rake face and chip.

Koherentna dydaktyka dwuwymiarowa – personalistyczna i zmediatyzowana – pedagogiczną szansą i nadzieją teraźniejszości i przyszłości

Introduction: Didactics is a pedagogical subdiscipline as well as the constant search for a more constructive and effective teaching process - learning in order to better and more effectively guide each other - teacher - student and at the same time student - teacher. The current popandemic situation and, at the same time, a powerful expansion of new media, including educational media, mobilize for the necessary research, how to constructively use the media in didactics to make it a constructive coexistence. We can see that the new media played a very positive role during the pandemic, because if they did not exist, teaching would probably only become self-education or a lack of education, but at the same time we felt even more the priceless value of real contacts and real education. Research Aim : For truly effective 21st century didactics, invaluable interpersonal contact is necessary, this is the most important for motivation, for the desire to learn effectively together, but this process will also be supported by the media, because mediatization is currently one of the strongest processes and the search for constructive coherence of personalism and mediatization this is the main research problem and research goal. Evidence-based Facts : Research in this area is carried out by many eminent researchers (Carr, Pinker, Spitzer, Dijk, Fukuyama, Gergen, Melosik, Baron-Polańczyk, Morbitzer), but they require constant guidance and intensification, because the times are extremely expansive and dynamic. Summary : To sum up, it should be stated that there is a need for continuous and even more expansive didactic modeling so that this personalistic-mediatized coherence would be as fruitful as possible for man and society, and here a great research and didactic effort is needed.

Multiscale in-situ quantification of the role of surface roughness and contact area using a novel Mica-PVS triboelectric nanogenerator

Triboelectric nanogenerators (TENGs) are energy harvesters generating electricity via the triboelectric effect and electrostatic induction. However, the influence of interface mechanics on TENG performance requires attention. Here, we study the effect of random multiscale surface roughness on TENG performance using a novel in-situ optical technique to directly visualise the contact interface. To achieve this, a new type of TENG is developed based on transparent mica in contact with polyvinyl siloxane (PVS). A wide range of surface roughness instances were created on the PVS surface (Sq from 1.5 to 82.5 µm) by replicating 3D-printed masters developed from numerically generated rough surfaces. TENG output was found to be highly sensitive to surface roughness over a wide range of forces and frequencies. The dependence of real contact area on roughness was identified as the underlying cause. In this work, electrical output (and contact area) decreased significantly with increasing roughness. The highest output (smoothest PVS surface) gave open circuit voltage 222.8 V, short-circuit current density 53 mA/m2 and peak-power density 4256 mW/m2: a competitive output given the rapid and simple fabrication, low cost and long durability demonstrated. The new Mica-PVS TENG, the direct technique for TENG interface visualisation and the insights on the role of topography and contact area will be invaluable for future TENG design.

1921. Leveraging Bluetooth Low-Energy Technology to Improve Contact Tracing in Healthcare Settings during the COVID-19 Pandemic

Abstract Background COVID-19 rapidly evolved into a global pandemic. Contact tracing with isolation and quarantine contribute to epidemic control but they are time consuming, costly and may be incomplete. We set out to assess the usability and performance characteristics of Bluetooth Low-Energy (BLE) wireless technology for indoor localization applied to contact tracing in healthcare settings. Methods Consented healthcare workers (HCW) from 2 designated COVID-19 wards (one intensive care unit (ICU) and one medical ward) were equipped with coin-sized BLE- emitting beacons. The signal was captured by small embedded computers (anchors) placed at designated locations, time-stamped and transmitted to an edge server via secure Wi-Fi where data were stored and real time contact algorithms were run (Fig.1). We developed experiments mimicking clinical scenarios and tested indoor localization during observed clinical activity for 6 months. We constructed our algorithms based on room structure (e.g. open spaces vs computer rooms) and activity characteristics (e.g. rounding in a large group vs 2 healthcare workers sitting together). We used 1) radio fingerprint localization where an initial virtual radio map was developed, 2) semantic localization which carries additional information such as proximity to a computer to define indirect transmission via fomites, and 3) clustering contact tracing to identify individuals rounding together. Close contact was defined as per the CDC guidelines. Fig. 1System configuration Results Consent rate was 43.3% with 187 HCW enrolled in the study. Consent rate was higher in the ICU and among attendings. All participants were compliant with wearing the beacons for the duration of the study. The performance characteristics for contact tracing using fingerprinting methods were AUROC 0.93, AUPRC 0.96, sensitivity 0.9, specificity 0.77 with F1 score of 0.89 and overall accuracy of 0.85. The clustering contact tracing registered a sensitivity of 0.86, specificity 0.89, F1 score 0.91 and accuracy 0.87. Computation time necessary to generate a list of close contacts as per specified criteria was less than 30 minutes. Conclusion We have developed and tested a reliable and accurate, low-cost and easily deployable system based on BLE technology to improve contact tracing among healthcare workers. Disclosures M Cristina Vazquez Guillamet, MD, AUPH: Stocks/Bonds|BNGO: Stocks/Bonds|OCGN: Stocks/Bonds|SESN: Stocks/Bonds.

MoDLE: high-performance stochastic modeling of DNA loop extrusion interactions

DNA loop extrusion emerges as a key process establishing genome structure and function. We introduce MoDLE, a computational tool for fast, stochastic modeling of molecular contacts from DNA loop extrusion capable of simulating realistic contact patterns genome wide in a few minutes. MoDLE accurately simulates contact maps in concordance with existing molecular dynamics approaches and with Micro-C data and does so orders of magnitude faster than existing approaches. MoDLE runs efficiently on machines ranging from laptops to high performance computing clusters and opens up for exploratory and predictive modeling of 3D genome structure in a wide range of settings.

Elastic Contact Analysis of Shot-Peened Rough Surfaces

Shot peening can effectively improve the mechanical performance of metal components, and thus has been widely employed in the engineering field. During the processing, the surface roughness of treated components will be completely changed, which could strongly affect their tribological behavior. However, few of the existing contact models are directed toward the rough surfaces generated by shot peening. In this study, the normal contact response between a shot-peened surface and a rigid plane is investigated based on the finite element method and the recently developed incremental contact model. The elastic contacts of the rough surfaces experimentally measured on three different shot-peened specimens are considered. Contrary to the conventional rough contact models, it is found that the dependence of the external load on the real contact area for the shot-peened surfaces is not at all linear, even for light loads. The slope of the area–load curve significantly varies at two transition points, which are intrinsically linked to the special structure of shot-peened surfaces.

Asymmetrically interacting dynamics with mutual confirmation from multi-source on multiplex networks

In the early stage of epidemics, individuals’ determination on adopting protective measures, which can reduce their risk of infection and suppress disease spreading, is likely to depend on multiple information sources and their mutual confirmation due to inadequate exact information. Here we introduce the inter-layer mutual confirmation mechanism into the information-disease interacting dynamics on multiplex networks. In our model, an individual increases the information transmission rate and willingness to adopt protective measures once he confirms the authenticity of news and severity of disease from neighbors’ status in multiple layers. By using the microscopic Markov chain approach, we analytically calculate the epidemic threshold and the awareness and infected density in the stationary state, which agree well with simulation results. We find that the increment of epidemic threshold when confirming the aware neighbors on communication layer is larger than that of the contact layer. On the contrary, the confirmation of neighbors’ awareness and infection from the contact layer leads to a lower final infection density and a higher awareness density than that from the communication layer. The results imply that individuals’ explicit disclosure of their infection and awareness status to neighbors, especially those with real contacts, is helpful in suppressing epidemic spreading.

What does a sliding triboelectrical sensor really measure?

For a decade, Triboelectric Nanogenerators (TENG) have been massively developed and optimized either as (i) triboelectric energy harvesters or, (ii) triboelectric self-powered sensors. Unfortunately, it is obvious that the classical tribologists’ concerns – like the optimization of both real contact area, friction laws and wear processes – have never really been integrated so far neither in their development processes nor in their triboelectrical responses. Thus, a question as basic as “What kind of tribological information can we expect from multi-asperity triboelectric sensor rubbing on a plane in dry friction?” does currently not lead to a trivial answer.This paper tries to get out this paradoxical situation by simulating triboelectrical behavior of a multi-asperity real contact area in dry friction. Results reveal that a sliding triboelectric sensor assesses the instantaneous and averaged velocities of every interacting asperities within the contact area, finally probing, in real time, the tribological actual contact area behavior during sliding.

A Bayesian generative neural network framework for epidemic inference problems

The reconstruction of missing information in epidemic spreading on contact networks can be essential in the prevention and containment strategies. The identification and warning of infectious but asymptomatic individuals (i.e., contact tracing), the well-known patient-zero problem, or the inference of the infectivity values in structured populations are examples of significant epidemic inference problems. As the number of possible epidemic cascades grows exponentially with the number of individuals involved and only an almost negligible subset of them is compatible with the observations (e.g., medical tests), epidemic inference in contact networks poses incredible computational challenges. We present a new generative neural networks framework that learns to generate the most probable infection cascades compatible with observations. The proposed method achieves better (in some cases, significantly better) or comparable results with existing methods in all problems considered both in synthetic and real contact networks. Given its generality, clear Bayesian and variational nature, the presented framework paves the way to solve fundamental inference epidemic problems with high precision in small and medium-sized real case scenarios such as the spread of infections in workplaces and hospitals.

A novel and quantitative determination method for the running-in process through dimensionless real contact area

This paper presents a novel and quantitative characterization method for the running-in process through dimensionless real contact area. The traditional running-in criteria, such as coefficient of friction and roughness, can only provide a qualitative assessment of the running-in state. This work investigate the evolution of the running-in process and analyze the running-in period for the friction pairs with varying hardness combinations. In situ experiments for friction pairs with varying hardness combinations were carried out on a pin-on-disc tribometer.The relationship among the real contact area, the fractal dimension D and fractal roughness G was established. The calculations and experimental results indicate that the dimensionless real contact area will have a derivative of 0 that can be utilized to determine the running-in state of friction pairs, as running-in has been completed. Using the dimensionless real contact area, we can analyze the evolution of the friction pairs' running-in period comprehensively and systematically.

Elastic and plastic deformation of surface asperities and their load-carrying mechanisms during the formation of a real contact area

How the contact behaviours of steel engineering surfaces with different roughnesses (Ra = 0.1, 0.6 and 1.0 µm) are affected by the asperity work-hardening and the deformation regime are described here. Large values of the plasticity index Ψ between 20 and 50 indicate that all the surfaces should undergo a full plastic deformation. However, in the loading range up to the yield stress (on a nominal contact area) the rough surfaces exhibited at least 10 % elastic deformation, while for the smooth surfaces the elastic deformation was as much as 44 %. During the loading, the work-hardening increased the hardness of the rough surfaces by up to 63 %, and that of the smooth surfaces by up to 20 %. However, the asperities were able to carry the load that resulted in as much as a 4–10-times-higher contact pressure than the (initial) bulk yield strength. The proposed contact mechanisms for such an increased asperity-load-carrying capacity depend on the surface roughness. For the rough surfaces this is due to the work-hardening, while for the smooth surfaces the dominant mechanisms enhancing the load-carrying capacity are the work-hardening combined with the hydrostatic bulk stresses.

Pore-Level Multiphase Simulations of Realistic Distillation Membranes for Water Desalination.

Membrane distillation (MD) is a thermally driven separation process that is operated below boiling point. Since the performance of MD modules is still comparatively low, current research aims to improve the understanding of the membrane structure and its underlying mechanisms at the pore level. Based on existing realistic 3D membrane geometries (up to 0.5 billion voxels with 39nm resolution) obtained from ptychographic X-ray computed tomography, the D3Q27 lattice Boltzmann (LB) method was used to investigate the interaction of the liquid and gaseous phase with the porous membrane material. In particular, the Shan and Chen multi-phase model was used to simulate multi-phase flow at the pore level. We investigated the liquid entry pressure of different membrane samples and analysed the influence of different micropillar structures on the Wenzel and Cassie-Baxter state of water droplets on rough hydrophobic surfaces. Moreover, we calculated the liquid entry pressure required for entering the membrane pores and extracted realistic water contact surfaces for different membrane samples. The influence of the micropillars and flow on the water-membrane contact surface was investigated. Finally, we determined the air-water interface within a partially saturated membrane, finding that the droplet size and distribution correlated with the porosity of the membrane.

Friction Behavior of Rough Surfaces on the Basis of Contact Mechanics: A Review and Prospects.

Contact and friction are closely related as friction cannot happen without contact. They are widely used in mechanical engineering, traffic, and other fields. The real contact surface is not completely smooth, but it is made up of a series of tiny contact asperities as viewed in the micro-scale. This is just the complexity of the contact and friction behaviors of rough surfaces: the overall mechanical behavior is the result of all asperities which are involved during the contact. Due to the multiplicity of surface topography, the complexity of contact scale, and the nonlinearity of the constitutive material, there are still many open topics in the research of contact and friction behavior of rough surfaces. Based on the perspective of the macroscopic and micro-nano scale contact mechanics, this review gives a brief overview of friction for the latest developments and points out the existing issues and opportunities for future studies.

Investigation of Contact Clusters Between Rough Surfaces

We investigate the persistence of micro-contacts between two elastic random rough surfaces by means of a simple model for quasi-static sliding. Contact clusters are calculated with the Boundary Element Method, then surfaces are repeatedly displaced to study the evolution of the original contact area. While the real contact area remains constant due to the rejuvenation of micro-contacts, the original contact clusters are progressively erased and replaced by new ones. We find an approximate exponential decrease of the original real contact area with a characteristic length that is influenced both by statistics of the contact cluster distribution and physical parameters. This study aims to shine light on the microscopic origins of phenomenological rate-and-state friction laws and the memory effects observed in frictional sliding.

MOCMIN: convex inferring of modular low-rank contact networks over COVID diffusion data

SEIR (which consists of susceptible, exposed, infected, and recovered states) is a common diffusion model which could model different disease propagation dynamics across various domains such as influenza and COVID diffusion. As a motivation, across these domains, observing the node states is relatively easier than observing the network edges over which the diffusion is taking place, or it may not even be possible to observe the underlying network. This paper focuses on the problem of predicting modular low-rank human contact network edges only if a SEIR diffusion dynamics spreading among the human on their contact network can be observed. Such contact networks exhibit high modularity where the graph has dense connections between the vertices within modules, but sparse connections between vertices in different modules. We first formulate such inference problem as an optimization problem, discuss its convexity, and propose MOCMIN to optimally infer such unknown contacts of modular human contact network from COVID diffusion data. This modular contact network inference problem is important in the general case where human states such as infected with virus and recovered from virus can be identified more easily than the contacts between humans. Our contributions can be summarized as follows: (1) MOCMIN can handle noisy, incomplete, or undersampled diffusion data while inferring the unknown contact network; (2) The inferred contact networks are highly modular which cannot be ensured by the existing methods; (3) This paper applies MOCMIN to better understand COVID diffusion on contact network. We found MOCMIN to be accurate in modular real human contact network inference from COVID diffusion data under a number of challenging scenarios. As an example, such high school contact network can be inferred by tracking COVID diffusion among humans approximately 5% better than the compared methods by MOCMIN's ability to model modularity of the network. Via such inference, we can also understand the details of COVID diffusion dynamics in real human contact network. Additionally, inferred human contact graphs nearly mimic the true contact network's known graphical properties. Lastly, MOCMIN outperforms the competing approaches while estimating the synthetic networks.

Implementation of real contact behaviour in the DEM modelling of triaxial tests on railway ballast

In the Discrete Element modelling of soils, the micromechanical behaviour at contacts has often been considered to have a minor influence on the macromechanical response, leaving basic theoretical models (e.g., Hertz) to describe the contact response in the normal direction. A realistic description of the contact response may be crucial especially when investigating small strain ranges. Recent experimental inter-particle loading tests on gravel suggest that the classic contact models fail to reproduce certain mechanical features, especially when roughness is significant. Here, some of these experimental observations, including a softer response than the Hertz model under loading in the normal direction, and plasticity on unloading, are implemented in a DEM model for the simulation of small strain tests on railway ballast. The influence of these features on small strain stiffness is highlighted. A micromechanical analysis is carried out to show how each of the contact-level features introduced affects the macroscopic response. • Classic contact models do not work well for rough surfaces. • Accounting for lower normal stiffness due to contact with asperities and plasticity. • True contact behaviour implemented in numerical DEM simulations of ballast. • Contact behaviour can explain small strain stiffness degradation.

Dual-Arm Visuo-Haptic Optical Tweezers for Bimanual Cooperative Micromanipulation of Nonspherical Objects.

Cooperative manipulation through dual-arm robots is widely implemented to perform precise and dexterous tasks to ensure automation; however, the implementation of cooperative micromanipulation through dual-arm optical tweezers is relatively rare in biomedical laboratories. To enable the bimanual and dexterous cooperative handling of a nonspherical object in microscopic workspaces, we present a dual-arm visuo-haptic optical tweezer system with two trapped microspheres, which are commercially available end-effectors, to realize indirect micromanipulation. By combining the precise correction technique of distortions in scanning optical tweezers and computer vision techniques, our dual-arm system allows a user to perceive the real contact forces during the cooperative manipulation of an object. The system enhances the dexterity of bimanual micromanipulation by employing the real-time representation of the forces and their directions. As a proof of concept, we demonstrate the cooperative indirect micromanipulation of single nonspherical objects, specifically, a glass fragment and a large diatom. Moreover, the precise correction method of the scanning optical tweezers is described. The unique capabilities offered by the proposed dual-arm visuo-haptic system can facilitate research on biomedical materials and single-cells under an optical microscope.

A Revised Continuous Observation Length Model of Rough Contact without Adhesion

The real contact area of rough surfaces has significant importance in many engineering applications, such as tribology, wear, lubrication and seals. A continuous observation length-dependent mechanic model of rough contact without adhesion is proposed, which assumes that the rough surface is divided into ideal subplanes. However, the model ignores the elastoplastic deformation of asperities, and the standard deviation of ideal subplanes’ heights is assumed to vary linearly with continuous observation length, which is not precise for all the surface fractal dimensions. In this work, a revised continuous observation length model is proposed with elastic, elastoplastic and fully plastic stages. The expressions of force and real contact areas are derived. For surfaces with different fractal dimensions, the quadratic polynomial, cubic polynomial and power relationships between standard deviation and observation length are proposed, respectively. In addition, the influences of the dimensionless observation length, fractal dimension and equivalent elastic modulus on the real contact areas in different contact stages are also analyzed. It can be concluded that the quadrate real contact area decreases as the dimensionless observation length decreases, which can be applied to the percolation theory for leak seal problems.

Frictional Anisotropy of Oriented Carbon Nanotubes/Rubber Composites and New Insight Into Its Mechanism From the Perspective of Frictional Interface

Abstract Nanomaterials as reinforcement to enhance the properties of the composite and extend its potential applications have always shown great interest. As 1D materials, aligned carbon nanotubes (CNTs) reinforced composites could show different mechanical properties in different directions. In this paper, the frictional anisotropy of oriented CNTs/rubber composites at both macroscopic and atomic scales was investigated. Both physical experiments and molecular dynamics (MD) simulations were carried out to measure the coefficient of friction (COF) of rubber incorporated with CNTs oriented in different directions. The macroscale and nanoscale results qualitatively show good agreement. The COF and wear rate of CNTs-z/rubber are both lower than that of CNTs-x/ and CNTs-y/rubbers. That is, CNTs perpendicular to the sliding interface could further decrease the COF compared to those that are in the plane parallel to the interface. This may be due to the weaker adhesive ability, smaller real contact area, lower temperature, and higher anti-shearing ability on the interface. This work provides guidelines for the extension of the application and control for the CNTs reinforced composites.