Contact Edge Research Articles

Nonlinear behavior of disk spring with complex contact state.

Disk springs are widely used as preload and isolation due to their unique mechanical properties. In the prior research, the effect of linear friction on the disk spring was considered, but contact stiffness, another nonlinear contact factor, is ignored. Accordingly, in this paper, the asymmetric displacements of the contact edges are first derived, and the accurate friction dissipations are obtained, as a way to evaluate the effect of friction on the system. Then the velocity of the edges was obtained to establish a dynamic friction model. Meanwhile, the contact displacement and contact stiffness of the edge are obtained by fractal contact theory. Then the nonlinear static and dynamic models of disk spring with friction and contact stiffness are established by the energy method. The load-deflection relationship, stiffness, and hysteresis of disk spring are studied with different contact states. The results show that the model considering contact stiffness and asymmetric friction dissipation can effectively evaluate the static properties of the disk spring. Friction reinforces the nonlinear behavior of the system, while contact stiffness weakens the nonlinearity of the system. And due to the influence of nonlinear contact factors, the transmissibility curves produce multiple resonance peaks.

Numerical-simulation-based Landslide Warning System and Its Application

Landslide early warning is a systematic project involving multidisciplinary integration, i.e. geology, mechanics, engineering, monitoring technology, and information technology. When conducting landslide studies, due to the limitation of failure theory of geological body, landslide warning system is purely based on monitoring data nowadays, so it is difficult to integrate interdisciplinary techniques. A trigger condition based prediction theory and disaster stage judgment approach are introduced, with which the landslide time prediction is converted to the disaster stage judgment. The definition and significance of fracture degree is presented, by which the disaster stage judgment is convert to inner fracture state analysis. At last, the numerical-simulation-based landslide warning system is discussed in detail. This system contains four parts, namely parameter acquisition part, disaster kernel analysis system, current state back analysis part, and landslide reliability evaluation part, respectively. In the first part, the essential parameters and its acquisition method is presented, and then the necessity and advantages of dimensional analysis is discussed. In the second part, the new numerical method named continuous discontinuous element method (CDEM) is introduced, and main features, i.e. Lagrange equation, strain strength distribution criteria, element crack strategy, and indented point & indented edge contact model is introduced. In third part, the inverse analysis method of current parameters of geological body based on monitoring data and numerical simulation is discussed. In the fourth part, the reliability evaluation steps are presented in detail. Finally, the sliding occurrence probability of Liangshuijing landslide in Chongqing, China is discussed, which demonstrated to show the precision and rationality of the proposed landslide warning system.

Contacts between monolayer black phosphorene and metal electrodes: Ohmic, Schottky, and their regulating strategy

Two-dimensional black phosphorene (BP) has attracted much interest for application in electronic devices. Contacts between BP and metal electrodes are critical components of BP-based devices and can dramatically affect device performances. In this paper, we adopted first-principles calculations to explore binding energies, electronic structures, and potential distribution for interface systems of Al-, Au-, Cu-, Ni-, and Ti-monolayer BP in surface contact and edge contact (EC) types. Moreover, we also used density functional theoretical coupled with the nonequilibrium Green’s function method to investigate contact resistances and Schottky barrier heights (SBHs) for transport systems of monolayer BP with Al, Au, Cu, Ni, and Ti electrodes. Our calculated results indicate that the contact type between BP and metals may greatly affect electrical properties of BP–metal contacts. Changing contact type between metal electrodes and BP channel can change the type of Schottky barrier of metal–BP contacts. The contact barrier of metal–BP depends on the metal material. Selecting an appropriate contact type and metal can effectively regulate the contact barrier of metal–BP. Specifically exciting, our estimated lateral SBHs for the Ni–BP system in EC-type agree well with the experimental results. We have provided a new strategy on choosing an appropriate contact type to achieve low contact resistance for the metal–BP interface.

Experimental investigation on the effect of misalignment on the wear failure for spline couplings

The teeth of misaligned spline couplings used in power transmission parts of helicopter and aero-engine often suffer serious abnormal wear faults during service. Through the self-made spline coupling test rig, the mechanism of misalignment on the spline coupling wear was explored. The tooth contact domain of the spline coupling with shaft misalignment is close to the addendum, and the tooth contact domain of the spline coupling with angle misalignment is mainly concentrated on the side of the tooth end. The edge contact effect becomes more serious as the amount of misalignment increases, resulting in abnormal wear at specific positions on the tooth surface. The presence of misalignment increases the vibration intensity of the spline coupling based vibration signal monitoring, which will increase the wear of the teeth. In addition, the difference in system vibration response of different misalignment types can be used to identify the misalignment failure mode of the spline coupling. It can be inferred from the characterization of wear debris that fretting wear is the cause of the failure of the misaligned spline coupling. Tooth modification, surface strengthening modification and lubrication design are necessary as potential solutions to improve the wear resistance of misaligned spline couplings.

Asymptotic description of fretting wear and fretting fatigue for incomplete contacts

Looking at wear of incomplete contacts in partial slip we start from an asymptotic description of the contact tractions at the contact edges. We introduce distributed dislocations along the slip zone to account for the profile reduction due to wear and find the long-term time asymptote where the contact is wholly stuck. The resulting stress field is used to find the crack tip stress intensity factors for short contact edge cracks, which are useful in predicting the crack nucleation threshold.

Edge Contact Angle, Capillary Condensation, and Meniscus Depinning.

We study the phase equilibria of a fluid confined in an open capillary slit formed when a wall of finite length H is brought a distance L away from a second macroscopic surface. This system shows rich phase equilibria arising from the competition between two different types of capillary condensation, corner filling and meniscus depinning transitions depending on the value of the aspect ratio a=L/H. For long capillaries, with a<2/π, the condensation is of type I involving menisci which are pinned at the top edges at the ends of the capillary characterized by an edge contact angle. For intermediate capillaries, with 2/π<a<1, depending on the value of the contact angle the condensation may be of type I or of type II, in which the menisci overspill into the reservoir and there is no pinning. For short capillaries, with a>1, condensation is always of type II. In all regimes, capillary condensation is completely suppressed for sufficiently large contact angles. We show that there is an additional continuous phase transition in the condensed liquidlike phase, associated with the depinning of each meniscus as they round the upper open edges of the slit. Finite-size scaling predictions are developed for these transitions and phase boundaries which connect with the fluctuation theories of wetting and filling transitions. We test several of our predictions using a fully microscopic density functional theory which allows us to study the two types of capillary condensation and its suppression at the molecular level.

Experimental Study on the Damage and Deterioration Behaviour of Deep Soft Rock under Water-Rock Interaction

The ageing disintegration, the damage, and failure mechanism of water-saturated soft rock are of significance to hazard prevention for deep mining. In this paper, indoor experiments, including disintegration behaviour tests in water, uniaxial compression failure tests of rock samples with different water contents, and variations in the microstructure of mudstone under saturated water contents, were conducted. The investigation results show that the saturated water content of mudstone is 16.96% and that the rock mass bursts completely after being immersed in water for 72 h. With increasing water content, the uniaxial strength and elastic modulus at the prepeak stage present significant attenuation. However, Poisson’s ratio varies little, which indicates that the swelling of cemented mudstone is not obvious when meeting water. In addition, the failure pattern of mudstone changes from overall splitting failure to block fragmentation failure. Due to ion-exchange adsorption and the wedging action of water molecules, the edge of contact between particles changes from staggered to smooth, which leads to the expansion of pores, the loosening of mudstone structures, and a decrease in mechanical strength. Therefore, the diffusion, migration, and particle expansion of illite and other clay minerals in mudstone are the main factors leading to the structural damage and strength reduction of weakly cemented rock under water-rock interactions.

High-Performance and Ultralow-Noise Two-Dimensional Heterostructure Field-Effect Transistors with One-Dimensional Electrical Contacts

Two-dimensional heterostructure field-effect transistors (2D-HFETs) with one-dimensional electrical contacts to atomically thin channels have recently shown great device performance, such as reduced contact resistance, leading to ballistic transport and enhanced carrier mobility. While a number of low-frequency noise studies exists on bare graphene devices supported on silicon dioxide gate insulators with surface contacts, such studies in heterostructure devices comprising epitaxial graphene on hexagonal boron nitride (hBN) with edge contacts are extremely limited. In this article, we present a systematic, temperature-dependent study of electrical transport and low-frequency noise in edge-contacted high-mobility HFET with a single atomic-layer graphene channel encapsulated by hBN and demonstrate ultralow noise with a Hooge parameter of ≈10–5. By combining measurements and modeling based on underlying microscopic scattering mechanisms caused by charge carriers and phonons, we directly correlate the high-performance, temperature-dependent transport behavior of this device with the noise characteristics. Our study provides a pathway towards engineering low-noise graphene-based high-performance 2D-FETs with one-dimensional edge contacts for applications such as digital electronics and chemical/biological sensing.

The in-plane metal contacted 5.1 nm Janus WSSe Schottky barrier field-effect transistors

Edge contact between two-dimensional materials and metal can achieve small contact resistance because of strong interaction. In this work, we investigated the electronic transport of in-plane (IP) heterojunctions based on Ti/WSSe and Sn/WSSe using first-principle calculations. The results showed the interface bonding and metallization on the IP Ti/WSSe and Sn/WSSe contact interface, indicating the Ohmic contacts between Ti, Sn and WSSe. Then, we constructed a double-gate model to investigate the performance of the IP Ti and Sn contacted 5.1 nm WSSe Schottky barrier field-effect transistors (SBFETs). The calculated on-state current of the IP Ti contacted 5.1 nm WSSe SBFETs is 406.3 μA μm−1. However, the on-state current of the Sn contacted 5.1 nm WSSe SBFETs reaches up to 1104.2 μA μm−1, which is far beyond the requirements of the International Technology Roadmap for Semiconductor HP application targets. Our study will provide a guide for high-performance transistors based on IP metal/WSSe configurations in the future.

On the Interaction of Viscoelasticity and Waviness in Enhancing the Pull-Off Force in Sphere/Flat Contacts

Motivated by roughness-induced adhesion enhancement (toughening and strengthening) in low modulus materials, we study the detachment of a sphere from a substrate in the presence of both viscoelastic dissipation at the contact edge, and roughness in the form of a single axisymmetric waviness. We show that the roughness-induced enhancement found by Guduru and coworkers for the elastic case (i.e. at very small detachment speeds) tends to disappear with increasing speeds, where the viscoelastic effect dominates and the problem approaches that of a smooth sphere. This is in qualitative agreement with the original experiments of Guduru’s group with gelatin. The cross-over velocity is where the two separate effects are comparable. Viscoelasticity effectively damps roughness-induced elastic instabilities and makes their effects much less important.Graphical

Research on quality detection method for axis-hole interference fit based on laser ultrasound

The interference fit quality determines the equipment’s service performance. In this work, interference fit assembly quality was evaluated using a laser ultrasonic method, including the assembly state of the interference fit. The power spectral density was used to calculate the power of the guided waves, and an interference assembly state evaluation method was proposed. Contact edge micro-cracks were identified by acquiring the full-field waveform propagation diagram, and these cracks were located by coupling the scanning area with the crack location. The center coordinate error for crack detection, which can basically determine the exact crack location, ranged between 0.09 mm and 0.15 mm. The length and width measurement errors ranged from 0.01 mm to 0.04 mm and 0.02 mm to 0.09 mm, respectively. The relationship curve between the guided wave power and interference was obtained experimentally. This method provides a new method for detection of the interference assembly structure state and the micro-cracks.

Numerical investigation for failure load and contact stress beneath RC square footing resting on cohesionless soil

The contact pressure distribution below, reinforced concrete footing, does not solely depend on the type of soil, but also on the change of the footing stiffness after cracking. This paper presents a numerical simulation and validation for full-scale square reinforced concrete footing rested on sand soil using a nonlinear finite element program “ABAQUS 6.14” to investigate the effect of concrete damage plasticity on contact stress distribution beneath the footing. It was found that, as long as the foundation stiffness decreases during the loading cycle for the footing, the percentage of the contact stresses at the footing edges to the contact stresses under the column center are reduced. A parametric study is conducted on square concrete footings with various reinforcement ratios resting on sand soil to investigate the effect of increasing reinforcement ratio on the failure load, and the shape of the contact stress below the footing before and after cracking. The results determine the impact of increasing the steel reinforcement ratio from 0.15 % to 0.30 % on the footing performance, and the corresponding increases in the ratio between central to edge contact stress. The findings further indicate that contact stress distribution below square footing was not consistent with the theoretical assumption.

Properties Analysis of Disk Spring with Effects of Asymmetric Variable Friction

The primary objective of this fundamental research is to investigate the mechanical properties of the disk spring when the friction at the contact edges is asymmetric and varies with the load. The contact mechanics study shows that the static friction and static friction coefficient on fractal surfaces change depending on the normal load. In this paper, a fractal contact model based on the W-M function is used to explore the connection between the static friction and the normal load. Subsequently, taking into account the asymmetry of the contact surface at the edge, the variable static friction coefficient is brought into the existing model to obtain an improved static model of the disk spring. Different fractal dimensions, frictional states and free heights are considered under quasi-static loading condition, the relative errors between this paper and the method using Coulomb friction are also calculated, and experimental validation was performed. The static stiffness and force hysteresis of the disk spring for different forms of asymmetric variable friction are discussed. It is shown that using the variable friction model can improve the computational accuracy of the disk spring model under small loads and help to improve the design and control accuracy of preload and vibration isolation equipment using the disk spring as a component.

Effects of cutting edge radius in vibration assisted micro machining

It is important for vibration-assisted machining (VAM) to incorporate the cutting edge radius (re) at microscale machining to understand the tool-workpiece contact relationship and the underlying cutting mechanism. re is absent so far in the analysis of VAM conducted by various researchers. It is difficult to understand the tool edge contact mechanism with the workpiece at microscale cutting simply by theoretical or mathematical analysis. Hence, the contact phenomenon for both 1D and 2D VAM has been investigated through finite element (FE) simulation using the Coupled Eulerian-Lagrangian (CEL) approach. Practical experiments with varying re are conducted to verify the observations. The chip thickness increases in 1D VAM with increased re which remains unchanged in 2D VAM. Although the cutting force increases at a different rate for both 1D and 2D VAM, the thrust force is significantly higher in 2D VAM. Ploughing increases significantly in 2D VAM than 1D VAM. The workpiece surface improves in 2D VAM whereas the change is very little in 1D VAM. The experimental findings with varying re support the FE simulation model of contact relationship and evaluate the cutting performance with re in both 1D and 2D VAM.

Delamination-fretting wear failure evaluation at HAp-Ti-6Al–4V interface of uncemented artificial hip implant

Present research aims to develop a finite element computational model to examine delamination-fretting wear behaviour that can suitably mimic actual loading conditions at HAp-Ti-6Al–4V interface of uncemented hip implant femoral stem component. A simple finite element contact configuration model based on fretting fatigue experimental arrangement subjected to different mechanical and tribological properties consist of contact pad (bone), HAp coating and Ti–6Al–4V substrate are developed using adaptive wear modelling approach adopting modified Archard wear equation to be examined under static simulation. The developed finite element model is validated and verified with reported literatures. The findings revealed that significant delamination-fretting wear is recorded at contact edge (leading edge) as a result of substantial contact pressure and contact slip driven by stress singularity effect. The delamination-fretting wear behaviour is promoted under higher delamination length, lower normal loading with higher fatigue loading, increased porous (cancellous) and cortical bone elastic modulus with higher cycle number due to significant relative slip amplitude as the result of reduced interface rigidity. Tensile-compressive condition (R=−1) experiences most significant delamination-fretting wear behaviour (8 times higher) compared to stress ratio R=0.1 and R=10.

Metallization-Induced Quantum Limits of Contact Resistance in Graphene Nanoribbons with One-Dimensional Contacts.

Graphene has attracted a lot of interest as a potential replacement for silicon in future integrated circuits due to its remarkable electronic and transport properties. In order to meet technology requirements for an acceptable bandgap, graphene needs to be patterned into graphene nanoribbons (GNRs), while one-dimensional (1D) edge metal contacts (MCs) are needed to allow for the encapsulation and preservation of the transport properties. While the properties of GNRs with ideal contacts have been studied extensively, little is known about the electronic and transport properties of GNRs with 1D edge MCs, including contact resistance (RC), which is one of the key device parameters. In this work, we employ atomistic quantum transport simulations of GNRs with MCs modeled with the wide-band limit (WBL) approach to explore their metallization effects and contact resistance. By studying density of states (DOS), transmission and conductance, we find that metallization decreases transmission and conductance, and either enlarges or diminishes the transport gap depending on GNR dimensions. We calculate the intrinsic quantum limit of width-normalized RC and find that the limit depends on GNR dimensions, decreasing with width downscaling to ~21 Ω∙µm in 0.4 nm-wide GNRs, and increasing with length downscaling up to ~196 Ω∙µm in 5 nm-long GNRs. We demonstrate that 1D edge contacts and size engineering can be used to tune the RC in GNRs to values lower than those of graphene.

One-Dimensional Edge Contacts to Two-Dimensional Transition-Metal Dichalcogenides: Uncovering the Role of Schottky-Barrier Anisotropy in Charge Transport across MoS2 /Metal Interfaces

Low-resistance ohmic contacts are a prerequisite for implementing two-dimensional transition-metal dichalcogenides (2D TMDs) in a host of applications. Edge contacts offer unique advantages, yet their electrical properties are not fully understood. Employing an $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ framework, the authors find that edge contacts to monolayer MoS${}_{2}$ are pinned to a charge-neutrality level close to the valence band and are $p$-type---unlike typical $n$-type top contacts. This anisotropy in Fermi-level pinning complicates conduction through metal-TMD interfaces and affects design guidelines for low-resistance contacts. Challenges, potential mitigating solutions, and opportunities that leverage this anisotropy are discussed.

Effects of different edge contacts on the photocatalytic and optical properties of blue phosphorene/arsenene lateral heterostructures

Recent advances in the synthesis and characterization techniques of atomic-scale thicknesses of crystals have enabled the fabrication of various two-dimensional lateral heterostructures (LHSs). In this paper, we systematically investigate the geometrical structures, electronic properties, band alignments, and optical properties of phosphorene/arsenene LHSs using first-principles calculations based on density functional theory. First, we constructed four stable phosphorene/arsenene LHSs with different edge contacts, named A–Z, Z–A, A–A and Z–Z phosphorene/arsenene LHSs. We then investigated the electronic structures of the different edge contacts. Interestingly, the calculated electron localization functions show that the most stable six-membered rings and previously reported five-membered and seven-membered rings are formed at the interface of the blue phosphorene/arsenene LHSs. Moreover, the band edge alignments and optical absorption properties show that A–A and Z–A phosphorene/arsenene LHSs have band-edge conditions suitable for photocatalytic water decomposition, which provides a possibility for their application in the area of photocatalytic water decomposition. These results provide a route for applications of these heterostructures in future optoelectronic and semiconductor devices, and also pave the way for the design of new blue phosphorene/arsenene LHSs and the exploration of their potential applications in optoelectronic devices.

Interface Engineering of Electrical Contacts

Highly conductive nanoscale electrical contacts suffer from strong current crowding at the contact edges, which can lead to nonuniform heat deposition; the formation of local hot spots, aggravation of electromigration; and, in the worst-case scenario, lead to thermal runaway and breakdown of the device. These effects severely affect the overall device properties, reliability, and lifetime. Devices based on thin-film junctions, nanotubes or nanowires, and two-dimensional (2D) materials are especially sensitive to current transport at electrical contacts, due to their reduced dimensions and increased geometrical confinement for current flow. Here, we demonstrate a method to mitigate current crowding, by engineering the interface layer properties and geometry. Based on a self-consistent transmission-line model, we show that the distribution of the contact current greatly depends on the properties of the interfacial layer between two contacting members. Current steering and redistribution can be realized by strategically designing the specific contact resistivity, ${\ensuremath{\rho}}_{c}$, along the contact length. For similar contact members, parabolically varying ${\ensuremath{\rho}}_{c}$ along the contact interface significantly reduces the edge-current crowding in ohmic contacts. Similarly, the nonuniform current distribution of 2D semiconductor-3D metal contacts can be decreased, and the current-transfer length can be increased by varying the Schottky barrier height along the interface. It is also found that introducing a nanometer- or subnanometer-scale thin insulating tunneling gap between contact members can greatly reduce current crowding, while maintaining a similar total contact resistance.

Microcapsule mechanics: Quasi-static compressive properties and the effect of liquid core

Liquid-filled microcapsules with a core-shell structure have been developed and widely applied in multi-functional materials. Mechanical properties of microcapsules play a vital role in production, collection and re-processing. Nevertheless, their mechanical behaviors have not been comprehensively understood. In this study, poly urea-formaldehyde (PUF) shelled microcapsules with paraffin oil are selected for experiments. Intrinsic mechanical properties of the shell material obtained from nanoindentation test and uniaxial compression test show remarkably good consistence. Both experimental and simulation results unprecedentedly reveal that the liquid core has a significant effect on the mechanical properties of a microcapsule by enhancing the stability and facilitating the stretching of the shell under compression, especially at large deformations. Moreover, the relationship between the rising hydrostatic pressure and the structural deformation is found to nicely follow up a quadratic function. When the structural deformation increases, plasticity successively appear at the circular contact area, contact edge, and non-contact area of the shell.