Contact Pairs Research Articles

Enhanced photovoltaic response in WSe2 photodetector with asymmetric two-dimensional contacts

Asymmetric contact pairs with different work functions provide an efficient method to extract photogenerated carriers in optoelectrical devices. Specifically, vertical optoelectrical devices based on two-dimensional (2D) materials utilize graphene layers as the bottom and top contacts. Whereas an additional terminal is required for electrostatic doping in either top or bottom graphene to enlarge the built-in electric field. Herein, we present an enhanced photovoltaic response in a vertical WSe2 photodetector utilizing asymmetric 2D contacts. A graphite layer and a degenerate SnSe2 are used as the top and bottom contacts, respectively, with a significant difference in their work functions. By establishing a large built-in electric field across the vertical WSe2 layer, a strong photovoltaic effect is achieved, resulting in an open-circuit voltage of 0.37 V and a short-circuit current of 0.42 μA under 532 nm illumination. The device shows high-performance photodetection characteristics, with a responsivity of 32.04 A W−1, external quantum efficiency of 7475%, and specific detectivity of 3.61 × 1012 Jones. Furthermore, the device can generate a maximum output electrical power of 70.9 nW, enabling a high-power conversion efficiency of 3.5%.

Comparative analysis of thermal interface materials for effective thermal management of electronic devices

ABSTRACT Thermal interface materials (TIM) employed to electronic devices enhances interfacial heat dissipation and thermal contact conductance (TCC). This study compares the performance of TIMs (silicon grease, phase change material (PCM) and composite PCM) on a copper-aluminum contact pair under varying range of contact pressure (0.1 to 0.4 MPa) and interface temperature (35 to 65 °C). Composite PCM is prepared by mixing aluminum powder to PCM in different mass concentrations (4, 8 and 25 wt.%). Result shows that addition of aluminum powder > 8 wt.% to PCM reduces its heat storage capacity and delays heat transfer. Moreover, TCC with silicon grease outperforms PCM by 108%, while CPCM (8 wt. %) is 144% more efficient but costlier than others.

The Effect of Temperature on the Current-Carrying Tribological Behaviour of C/Cu Contact Pairs in High Humidity Environments

The Effect of Temperature on the Current-Carrying Tribological Behaviour of C/Cu Contact Pairs in High Humidity Environments

An enhanced polar-based GPGPU-parallelized contact detection algorithm for 3D FDEM and its application to cracking analysis of shield tunnel segmental linings

This study introduces the three-dimensional combined finite-discrete element method (3D FDEM) to perform cracking analysis of segmental linings under extreme conditions. Considering the complex contact interactions of segments, this study first proposes a polar-based GPGPU-parallelized contact detection algorithm to handle memory issues confronted by existing FDEM algorithms. Initially, a spatial decomposition approach based on the polar coordinate system is implemented during the broad search phase. Each tetrahedral element is positioned within suitable search cells according to the axis-aligned bounding box. Subsequently, element pairs within each search cell are iteratively traversed, and potential contact pairs are identified using the judge cell criteria. After the broad search, a narrow search phase is executed to determine all real contacts. Following the above implementation, a load-structure model encompassing soil spring and external pressure calculations is then proposed. Based on the shape functions and coordinate transformation, the formulations of soil springs and external loads are derived and parallelized in the 3D FDEM framework. Three numerical tests are presented to validate the effectiveness of the proposed approach. Simulation results confirm the suitability of the proposed method for cracking analysis of segmental linings. Compared to the existing methods, it reduces GPU memory usage by 56 ∼ 76 % without extending time, which enhances the computational scale of 3D FDEM simulations. Furthermore, the proposed method is applied to two engineering scenarios, i.e., straight and curved segmental linings, both considering the absence and presence of contact defects between segments. The results show that contact defects can significantly reduce the resistance of the structural system comprising bolts and concrete segments for straight and curved scenarios.

A study of fretting fatigue in a contact pair of DZ125/GH4169: its mechanical behavior and life prediction

In this paper, the fretting fatigue test of DZ125/GH4169 contact pair was carried out. Observation and analysis of the wear and fracture were needed to get the fretting damage law. A hardness parameter was introduced to modify the existing life prediction model. The specimen was exposed to both normal and fatigue loads, as indicated by the results, which resulted in the formation of a black oxide layer that stuck to the contact zone's edge. Oxide spalling formed grits and abrasive wear, accelerating the loss of fatigue resistance. At high temperatures, the oxidation was intensified. The life prediction results were all within the double error band. The error range was reduced and the life prediction effect was significantly improved.

Simulation on metal-rubber contact behavior based on a reconstructed 3D topography of rough surfaces

A contact model with refined surface topography is important to the frictional wear study of rubber seal. But the traditional modeling method relies on the measurement of surface characteristics of rubber material, which increases the cost due to high-precision instruments and complex data processing. In the paper, a new modeling method on reconstructing the 3D surface topography is proposed. The coordinate cloud of the surface is generated based on the random distribution of asperity height, which is established according to the initiate parameters of the surface roughness. The metal-rubber assembly model with 3D topography of rough surfaces are built. The simulation on metal-rubber contact behavior is conducted in ANSYS. The result shows a power-exponent relation is between the real contact area and the external pressure, and three contact states of no contact, adhesion and slippage are defined to describe the dynamic distribution of real contact area. The authors proved the reliability of the topography reconstruction method by an indentation experiment on rubber material. The area ratio reflects not only the change rule of contact area under an increasing pressure, but also the difference of contact behavior of the contact pairs under different surface roughness.

Study on current-carrying tribological characteristics of C-Cu sliding electric contacts under water accumulation from rainfall condition

Pantograph-OCS system sliding electrical contact is the only way for train energy transmission, which determines the safety and stability of energy transfer. And the current-carrying wear is the core factor that affecting the service performance of C-Cu contact pairs. C-Cu mate pairs often work for a long time in rainy/humid environments due to its exposed nature of work, and the contact interface often accumulates a large amount of water. Existing operating experience has shown that the carbon sliding plate of the pantograph experiences abnormal wear and frequent failure during rainfall, resulting in a significant decrease in service performance and lifespan. This article found that the thickness of the water film at the contact interface has a significant impact on the current carrying friction and wear performance of C-Cu contact pairs. When the thickness of the water film exceeds a certain range, the carbon skateboard will cause abnormal wear under high current, with the wear amount being more than three times the minimum value. The contact resistance also increases by 53.9%, which is related to the obstruction of current transmission. It also proves that the water film lubrication effect can be restored during the process of rainfall decreasing from large to small. The research can help to provide a suitable maintenance policy for pantograph and catenary system during the rainy season.

Механический тепловой ключ криогенного магнитного рефрижератора

This work study the operating parameters of a cryogenic mechanical thermal switch, a detachable contact pair made of a alloy GdNi2 disk and a copper cylinder. The mechanical thermal switch operates in a vacuum in the temperature range of 8-325 K with a pressure of 250-350 kPa. The time of thermal equilibrium is studied at different contact areas with and without an indium thermal interface at an initial temperature difference of 0.8-10 K in the contact pair in the temperature range from 8 to 122 K. The temperature relaxation value is 33.7...39.9 seconds at a temperature difference of 3±0.14 K in the range of 50...122 K. Reducing the nominal contact area from 177 mm2 to 2.5 mm2 increases the temperature relaxation time at a temperature of 73.3 K from 36.6 to 63.5 seconds. This temperature range corresponds to the maximum magnetocaloric effect near the Curie temperature of the GdNi2 alloy. The values of the heat that must be removed to maintain the required temperature of the cooling object in a cryogenic magnetic refrigerator have been obtained.

A Hybrid Discrete-Finite Element method for continuous and discontinuous beam-like members including nonlinear geometric and material effects

This paper introduces a novel formulation, called Hybrid Discrete-Finite Element (HybriDFEM) method, for modelling one-directional continuous and discontinuous planar beam-like members, including nonlinear geometric and material effects. In this method, the structure is modelled as a series of distinct rigid blocks, connected to each other through contact pairs distributed along the interfaces. Each of those contact pairs are composed of two nonlinear multidirectional springs in series, which can represent either the deformation of the blocks themselves, or the deformation of their interface. Unlike the Applied Element Method, in which contact pairs are composed of one single spring, the current approach allows capturing phenomena such as sectional deformations or relative deformations between two blocks composed of different materials. This method shares similarities with the Discrete Element Methods in its ability to model contact interfaces between rigid or deformable units, but does not require a numerical time-domain integration scheme. More importantly, its formulation resembles that of the classical Finite Elements Method, allowing one to easily couple the latter with HybriDFEM. Following the presentation of its formulation, the method is benchmarked against analytical solutions selected from the literature, ranging from the linear-elastic response of a cantilever beam to the buckling and rocking response of continuous flexible columns, and rigid block stackings. One final example showcases the coupling of a HybriDFEM element with a linear beam finite element.

Wind resistance performance analysis of metal roof system of the long-span integrated photovoltaic building

Wind resistance is an important factor in the operation of Building Integrated Photovoltaic (BIPV) systems, especially for long-span roofs, where lifting of the roof can result in significant economic losses. This paper proposes a periodic boundary numerical simulation method for long-span metal roof systems to address the problem of meshes and contact pairs in the numerical simulation of wind resistance. In order to calibrate the BIPV metal roof's material parameters, indoor tensile test was conducted, and the results of the global metal roof model were compared with those of the single metal roof model with periodic boundaries for verification of periodic boundary efficiency and accuracy. The wind-resistant capacity of laboratory and long-span sizes for the BIPV metal roof system are compared, and a conversion formula between them is proposed to enable the rapid calculation from the laboratory to long-span roof system. The results show that the periodic boundary is suitable for the analysis of wind resistance of the long-span BIPV metal roof. Wind resistance of the long-span BIPV metal roof system is 1.77 kPa, whereas that of the laboratory size is 4.50 kPa. According to the proposed formula, the wind-resistant capacity of the long-span metal roof can be converted from the laboratory test, which can provide technical support for the design of BIPV systems.

Development of CASRock for modeling multi-fracture interactions in rocks under hydro-mechanical conditions

The interaction between multiple fractures is important in the analysis of rock fracture propagation, fracture network evolution and stability and integrity of rocks under hydro-mechanical (HM) coupling conditions. At present, modeling the mechanical behavior of multiple fractures is still challenging. Under the condition of multiple fractures, the opening, closing, sliding, propagation and penetration of fractures become more complicated. In order to simulate the HM coupling behavior of multi-fracture system, the paper presents a novel numerical scheme, including mesh reconstruction and topology generation algorithm, to efficiently and accurately represent fractures and their propagation process, and a potential function-based algorithm to address contact problem. The fracture contact algorithm does not need to set contact pairs and thus is suitable for complex contact situations from small to large deformations induced by HM loading. The topology of fracture interfaces is constructed by the dynamic adding algorithm, which makes the mesh reconstruction more rapid in the modeling of fracturing process, especially in the case of multiple fractures intersections. The numerical scheme is implemented in CASRock, a self-developed numerical code, to simulate the propagation process of rock fractures and the interaction of multiple fractures under the condition of HM coupling. To verify the suitability of the code, a series of tests were performed. The code was then applied to simulate hydraulic fracture propagation and fracture interactions caused by fluid injection. The ability of this method to study fracture propagation, multi-fracture interaction and fracture network evolution under hydro-mechanical coupling conditions is demonstrated.

Adaptive ANCF method described by arbitrary Lagrange-Euler formulation with application in variable-length underwater tethered systems moving in limited spaces

The nonlinear effect of the variable-length cable may dominate the design of Remotely Operated Vehicles (ROVs) due to the interaction between the flexible cable and surroundings, especially when moving in limited spaces. This paper develops a novel adaptive Absolute Nodal Coordinate Formulation (ANCF) described by Arbitrary Lagrange-Euler (ALE) formulation to investigate the nonlinear dynamics of variable-length underwater tethered systems going across obstacles. The adaptive element techniques are adopted to efficiently simulate the moving contact. Fine meshes are generated autonomously to capture the detailed contact behaviors in contact areas while coarse meshes emerge in non-contact areas, thus significantly reducing DOFs and contact pairs. Additionally, the precontact searching algorithm based on the axis-aligned bounding box (AABB) is employed for the acceleration of the contact detection, which is crucial when element number increases as the mass flow. Combined with the experimental records and analytical solutions in two numerical examples, the accuracy and efficiency of the proposed methodology are further assessed by a comprehensive comparison among the fine, coarse, and adaptive mesh results. The numerical algorithm provides an efficient means for developing a feed-forward controller to compensate the nonlinear cable effects on ROVs when moving in limited space.

Development of a GPU-based multisphere DE–FE coupling method for interaction simulations between an off-road tire and a gravel terrain

For decades, growing interest has been devoted to simulating the tire–soil interaction phenomena using discrete element/finite element (DE–FE) coupling methods. In contrast to the widely used approach that idealizes soils as spherical DEs, a newly developed multisphere DE–FE method has been demonstrated to be more accurate in reproducing such phenomena; however, it requires considerable computational cost for large-scale tire–soil interaction simulations. Therefore, this study aims to develop an efficient graphics processing unit (GPU)-based multisphere DE–FE method based on a CUDA FORTRAN programming environment. To this end, two-level grids are introduced for the parallelization of contact detection for targeted multisphere DEs and subspheres, which helps to find contact pairs for the targeted subspheres of a multisphere DE in an efficient manner. In contrast to existing GPU-based parallelization techniques, which typically use atomic operations to avoid memory access conflicts, this study presents a parallelization strategy to process a contact pair between bounding spheres using one GPU thread to efficiently handle with owner-member relationships between multisphere DEs and their subspheres. In the parallelization for force calculation, our method introduces an efficient technique that utilizes one GPU thread to process a contact pair between subspheres, or between subspheres and FE segments, to reduce the number of repeated calculations. Finally, the developed GPU-based method is applied to analyze the travelling behaviors of a complex-patterned off-road tire on a gravel terrain, and the effectiveness and computational efficiency of this method are validated via indoor soil-bin experimental outcomes as well as serial and parallel simulation results. It is found that a speedup of approximately 38 has been achieved with the aid of the developed method.

Fretting Behavior of WC-Co-Cr Coatings Against QT Steel in Bolted Joint

Fretting damage on contacting surfaces introduces major challenges in mechanical assemblies. Thermal sprayed hardmetal coatings are extensively used for surface modification in tribological applications under demanding conditions and may also be subjected to fretting-inducing loading. In the present work, the fretting behavior of High Velocity Oxy-Fuel (HVOF) and High Velocity Air–Fuel (HVAF) sprayed WC-10Co-4Cr coatings against quenched and tempered (QT) steel was studied by using a single bolt joint-type fretting experiment. This experimental approach was selected to obtain realistic data on the fretting fatigue performance of the contact pairs (both coating-to-steel and coating-to-coating). Experimental results were completed with continuum-scale linear elastic finite element method (FEM) calculations.

Compatible relative open books on relative contact pairs via generalized square bridge diagrams

Using square bridge position, Akbulut-Ozbagci and later Arikan gave algorithms both of which construct an explicit compatible open book decomposition on a closed contact 3-manifold which results from a contact (±1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\\pm 1)$$\\end{document}-surgery on a Legendrian link in the standard contact 3-sphere. In this article, we introduce the “generalized square bridge position” for a Legendrian link in the standard contact 5-sphere and partially generalize this result to the dimension five via an algorithm which constructs relative open book decompositions on relative contact pairs.

Three-Dimensional Accurate Geometric Modeling and Mechanical Analysis of Wire Mesh for Deployable Antennas

Wire meshes are widely used in deployable antennas, and the structure of the wire mesh directly affects the structural and electrical properties of the antenna. This study proposes a set of automated geometric modeling and mechanical analysis processes to realize the automated mechanical analysis and design of complex wire mesh structures. First, considering the tilt in the wire mesh structure owing to the traction of the underlap on the loop, a three-dimensional (3D) geometric model of the repeating unit of the wire mesh structure was established using periodic cubic spline curves. Subsequently, a method using sensitivity matrix adjustment is proposed to eliminate the interstructure inlay phenomenon, and an optimization model is established. The vector superposition method established a 3D geometric model of the overall wire mesh structure without an inlay problem. Finally, a finite element model of the wire mesh considering the contact problem was established by the adaptive matching method for contact pairs of the finite element model of the wire mesh. Mechanical simulation experiments were carried out on the model, comparing the theoretical analysis with the experimental results and verifying its reasonableness.

Regulating Microstructure and Macroscopic Properties in Saturated Salt Solutions Containing Disordered Anions and Cations by Magnetic Field.

Saturated aqueous salt solutions have diverse applications in food production, mineral processing, pharmaceuticals, and environmental monitoring. However, the random and disordered arrangement of ions in these solutions poses limitations across different fields. In this study, we employ magnetic fields to regulate the disordered arrangement by a comprehensive methodology combining contact angle measurement, Raman spectroscopy, X-ray diffraction, and molecular dynamics simulations on saturated KCl solutions. Our findings reveal that weak magnetic fields impede the formation of K-Cl contact pairs and disrupt hydrogen bond networks, particularly DDAA and free OH types. However, they facilitate the interaction between water molecules and ions, leading to an increase in the number of K-O and Cl-H contact pairs, along with an expansion in ion hydration radius. These changes affect macroscopic properties, including the interaction with solid substrates and potential solubility increases. Our experimental and simulation results mutually validate each other, contributing to a theoretical framework for studying magnetic field-material interactions.

Integrated Genomic and Social Network Analyses of SARS-CoV-2 Transmission in the Healthcare Setting.

Infection prevention (IP) measures are designed to mitigate the transmission of pathogens in healthcare. Using large-scale viral genomic and social network analyses, we determined if IP measures used during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic were adequate in protecting healthcare workers (HCWs) and patients from acquiring SARS-CoV-2. We performed retrospective cross-sectional analyses of viral genomics from all available SARS-CoV-2 viral samples collected at UC San Diego Health and social network analysis using the electronic medical record to derive temporospatial overlap of infections among related viromes and supplemented with contact tracing data. The outcome measure was any instance of healthcare transmission, defined as cases with closely related viral genomes and epidemiological connection within the healthcare setting during the infection window. Between November 2020 through January 2022, 12 933 viral genomes were obtained from 35 666 patients and HCWs. Among 5112 SARS-CoV-2 viral samples sequenced from the second and third waves of SARS-CoV-2 (pre-Omicron), 291 pairs were derived from persons with a plausible healthcare overlap. Of these, 34 pairs (12%) were phylogenetically linked: 19 attributable to household and 14 to healthcare transmission. During the Omicron wave, 2106 contact pairs among 7821 sequences resulted in 120 (6%) related pairs among 32 clusters, of which 10 were consistent with healthcare transmission. Transmission was more likely to occur in shared spaces in the older hospital compared with the newer hospital (2.54 vs 0.63 transmission events per 1000 admissions, P < .001). IP strategies were effective at identifying and preventing healthcare SARS-CoV-2 transmission.

Exploring the influence and mechanism of hardfacing STL12 on impact wear performance at high temperature and heavy load

As one of the most important contact pairs of an engine, the performance improvement of the valve and seat insert contact pair is of great concern. In this study, commonly used industry tempered seat inserts and hardfacing seat inserts were selected (named tempered group and hardfacing group respectively). The impact wear performance test was carried out, under conditions consistent of temperature of 650 °C, load of 30 kN, frequency of 12 Hz, and stroke of 1 mm. The wear process of the wear zone was investigated using 3D scanner, optical microscope (OM), scanning electron microscope (SEM), and X-ray photo-electron spectroscopy (XPS). The wear mechanism of the wear area was analyzed according to macro profile and micro wear morphology. The results showed that after the impact test, a layer of oxide film was formed on the surface of the hardfacing seat insert, which isolated direct contact of the valve and the seat insert, greatly improving the wear performance of the pairs. In addition, the hardness of the hardfacing seat insert was higher than the tempered seat insert, this further reduced the weight loss between the contact pairs. The weight loss of hardfacing group was 0.36 g and tempered group was 1.62 g, the weight loss of hardfacing group was reduced by 77.78 % compared with that of tempered group. So in conclusion the impact wear performance of the hardfacing pair is better than the tempered pair.

Prediction of contact resistance of electrical contact wear using different machine learning algorithms

H62 brass material is one of the important materials in the process of electrical energy transmission and signal transmission, and has excellent performance in all aspects. Since the wear behavior of electrical contact pairs is particularly complex when they are in service, we evaluated the effects of load, sliding velocity, displacement amplitude, current intensity, and surface roughness on the changes in contact resistance. Machine learning (ML) algorithms were used to predict the electrical contact performance of different factors after wear to determine the correlation between different factors and contact resistance. Random forest (RF), support vector regression (SVR) and BP neural network (BPNN) algorithms were used to establish RF, SVR and BPNN models, respectively, and the experimental data were trained and tested. It was proved that BP neural network model could better predict the stable mean resistance of H62 brass alloy after wear. Characteristic analysis shows that the load and current have great influence on the predicted electrical contact properties. The wear behavior of electrical contacts is influenced by factors such as load, sliding speed, displacement amplitude, current intensity, and surface roughness during operation. Machine learning algorithms can predict the electrical contact performance after wear caused by these factors. Experimental results indicate that an increase in load, current, and surface roughness leads to a decrease in stable mean resistance, while an increase in displacement amplitude and frequency results in an increase in stable mean resistance, leading to a decline in electrical contact performance. To reduce testing time and costs and quickly obtain the electrical contact performance of H62 brass alloy after wear caused by different factors, three algorithms (random forest (RF), support vector regression (SVR), and BP neural network (BPNN)) were used to train and test experimental results, resulting in a machine learning model suitable for predicting the stable mean resistance of H62 brass alloy after wear. The prediction results showed that the BPNN model performed better in predicting the electrical contact performance compared to the RF and SVR models.