Contact Shape Research Articles

A Refined Closed-Form Solution for Laterally Loaded Circular Membranes in Frictionless Contact with Rigid Flat Plates: Simultaneous Improvement of Out-of-Plane Equilibrium Equation and Geometric Equation

Essential to the design and development of circular contact mode capacitive pressure sensors is the ability to accurately predict the contact radius, maximum stress, and shape of a laterally loaded circular membrane in frictionless contact with a concentric circular rigid flat plate. In this paper, this plate/membrane contact problem is solved analytically again by simultaneously improving both out-of-plane equilibrium equation and geometric equation, and a new and more refined closed-form solution is given to meet the need of accurate prediction. The new closed-form solution is numerically discussed in convergence and effectiveness and compared with the previous one, showing that it can greatly improve the prediction accuracy of the contact radius, maximum stress, and shape of the circular membrane in frictionless contact with the rigid flat plate.

Time-domain simulation of charged particle diffraction by an electrostatically biased grating: Transmission tunability and shaping of the quantum point contact for protons

A numerical simulation of a two-dimensional Gaussian wave packet of charged particles has been performed to investigate the diffraction phenomena from a single-, double-, and multi-slit grating biased with an electrostatic potential (Ve0). The wave packet dynamics are obtained by solving the time-dependent Schrödinger’s equation using the generalized finite difference time domain (GFDTD-Q) method for quantum systems. The effect of Ve0 on transmission properties, fringe pattern, motion of the peaks, and wave number distribution in the diffracted wave has been studied. It is found that Ve0 changes the shape of the quantum point contact of diffracting constriction, which controls the allowed quantum states in the diffracted wave and the transmission coefficient Tc can be tuned by Ve0. It is observed that the number of peaks, their relative intensity, and quantization of lateral wavenumber depend upon Ve0. This study will be helpful in optimizing the parameters for material grating-based matter–wave interferometers employing charged particle such as proton beams.

Describing auxin solid state intermolecular interactions using contact descriptors, shape property and molecular fingerprint: comparison of pure auxin crystal and auxin-TIR1 co-crystal

This work reports for the first time, the analysis of intermolecular interactions in crystal structures of auxin (Indole-3-acetic acid) crystallized as pure sample (Aux-A) or co-crystallized with transport inhibitor response 1 (Aux-B). Using crystal packing of pure auxin and a cluster of residues in a radius of 6 Å around this ligand in the transport inhibitor response 1 binding domain, various properties were calculated and mapped on the Hirshfeld surface (HS). The HSs of the two molecules are characterized by close parameters of volume, area, globularity, and asphericity revealing the efficiency of the considered cluster. The HS mapped over descriptors like de, di and dnorm showed red spots corresponding to hydrogen bonds contacts. In addition to the shape index and curvedness descriptors, the results highlight weak interactions stabilizing the auxin structures. The analyses of electrostatic potential, electron density, and deformation density maps confirm the slightly change in the electron donor and acceptor groups localization. Furthermore, the molecular fingerprint analyses revealed a notable discrepancy in the shape and percentage value of the various contacts. Decomposition of the fingerprint shows that the contributions of important contacts (H···H, H···O, and O···O) are higher in Aux-B than in Aux-A. Finally, the quantitative approach by the determination of the molecular interaction energies of the two structures in their respective crystallographic environment revealed that Aux-A is slightly more stabilized than Aux-B.

Timing Matters: How Adolescent Police Contact Shapes Political Lives

Timing Matters: How Adolescent Police Contact Shapes Political Lives

A novel design for enhancing the surface durability of the spur gear systems

In this study, a general mathematical model for defining the gear tooth profile and its geometrical aspects that meet a desirable sliding contact during the meshing cycle is built. This model is based on the path of contact shape predefinition. In the contact path, a straight-line segment through the pitch point and a universal transition curve for the other segments are combined to create a free-form tooth profile with desired radius of curvature in the designed gear. The maximum pressure angle during the meshing cycle and the involute curve length parameter are only introduced to characterize this model. The designed gear in this study is given the title “free-form-gear” since it provided a universal manner of establishing the path of contact that provides desirable sliding conditions during the meshing cycle. The proposed tooth form, interference condition, contact ratio, contact stress, sliding coefficient, and meshing efficiency are derived and investigated in this study. The fillet stress and torsional mesh stiffness of the proposed gear pair are obtained using the finite element method (FEM). The performance of the new gear is compared to that of the standard involute and non-involute gear types. The results indicated that the method proposed in this study can be utilized to construct a gear pair with higher surface durability and strength than typical involute gear of the same size.

High-contact ratio spur gears with conformal contact and reduced sliding

The high-contact ratio (HCR) spur gear is a possible choice for a quiet and smooth gearing system. However, HCR spur gear of the involute type has several constraints, such as high sliding contact under large loads and interference problems in high speed reduction systems, so its benefits may not be fully offered. As a result, the primary goal of this research is to design a non-involute HCR spur gear with reduced sliding contact, enhanced fillet strength, better lubrication conditions, and no interference issues compared to the traditional HCR involute pair. A generalized mathematical model for defining the gear tooth profile and its geometrical aspects is built based on the path of contact shape. The involute curve length parameter and maximum pressure angle during the meshing cycle are only introduced to characterize this model. This model is utilized to create a new non-involute HCR gear pair that provides a free-form tooth profile to meet the design requirements. To demonstrate this method, certain case studies are provided, and the analytical results are validated using the finite element method. The new gear's performance is compared to the traditional involute gear that is currently in use. The results showed that by employing the proposed method, the HCR spur gear can achieve better surface durability and fillet strength.

Uniform Coverage Tool Path Generation for Robotic Surface Finishing of Curved Surfaces

We provide a novel solution to the problem of robot tool path generation to uniformly cover the surface area of a curved surface with varying curvatures by using a circular, flat finishing tool. We first develop a local contact shape descriptor using tools from differential geometry to estimate the contact shape and its area between the finishing tool and the workpiece surface under an applied normal force. Based on this varying contact area as the tool moves on the surface, we describe a tool path planning strategy that provides full and uniform coverage of a free-form or curved surface with the least amount of overlap. As opposed to fixed spacing paths with point contact in most existing approaches, we provide a novel path generation method where the interval spacing between neighboring path segments is determined by the contact area, which is position-dependent and varies along the surface in accordance with its principal curvatures. An efficient bisection method is employed in the proposed off-line path planning strategy. Numerical studies were conducted for ruled and general curved surfaces to compare the contact areas and coverage of the resulting path with paths generated using two other approaches from the literature. Real-time surface finishing experiments with a six degree-of-freedom robot equipped with a surface finishing tool were also conducted for both these surfaces to validate the proposed approach. Results from the numerical studies and experiments are presented and discussed.

Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells.

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm2), increasing the contact area from 28 cm2 to 70 cm2 enhanced power output from 58 mW·m−2 to 107 mW·m−2. For the same contact area (28 cm2), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m−2 to 58 mW·m−2. Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.

Comparative Masticatory Performance of Bilateral Balanced Occlusion and Lingualized Occlusion in Complete Denture Patients

Background: Both natural and artificial dentition has an occlusal scheme defined by the shape and positioning of the occlusal contacts. Complete denture fabrication has used a variety of occlusal designs that might have impact on stability of denture and masticatory function. Objective: To determine comparative masticatory performance of bilateral balanced occlusion and lingualized occlusion in complete denture patients Methodology: This study design was randomized trial carried out at the department of Prosthodontics, Altamash Institute of Dental Medicine for duration of six months. A total of 80 subjects were enrolled in the current study and were divided into two groups. Forty subjects were included in each group. In group LO subjects, complete dentures were provided with Lingualized occlusion whereas in group BBO participants, complete dentures were provided with bilateral balanced occlusion. All the required information’s including demographic features were documented in a predesigned Performa. SPSS version 19 was used to enter and analyze all of the data. Results: The mean weight of masticated peanuts in group LO was 5.30gm with standard deviation of 0.89 while in group BBO, the mean weight of masticated peanuts was 9.45gm with standard deviation of 2.10. The difference was significant statistically between two occlusions schemes (p=0.021). Conclusion: Our study concludes that masticatory efficiency was higher in complete dentures patients with lingualized occlusal than bilateral balanced occlusal scheme.. Keywords: Masticatory performance; Bilateral balanced occlusion; Lingualized occlusion

Crack-front model for adhesion of soft elastic spheres with chemical heterogeneity

Adhesion hysteresis can be caused by elastic instabilities that are triggered by surface roughness or chemical heterogeneity. However, the role of these instabilities in adhesion hysteresis remains poorly understood because we lack theoretical and numerical models accounting for realistic roughness. Our work focuses on the adhesion of soft elastic spheres with low roughness or weak heterogeneity, where the indentation process can be described as a Griffith-like propagation of a nearly circular external crack. We discuss how to describe the contact of spheres with chemical heterogeneity that leads to fluctuations in the local work of adhesion. We introduce a variational first-order crack-perturbation model and validate our approach using boundary-element simulations. The crack-perturbation model faithfully predicts contact shapes and hysteretic force-penetration curves, provided that the contact perimeter remains close to a circle and the contact area is simply connected. Computationally, the crack-perturbation model is orders of magnitude more efficient than the corresponding boundary element formulation, allowing for realistic heterogeneity fields.

Effect of Surrounding Solvents on Interfacial Behavior of Gallium-Based Liquid Metal Droplets.

Gallium-based liquid metal (GaLM) alloys have been extensively used in applications ranging from electronics to drug delivery systems. To broaden the understanding and applications of GaLMs, this paper discusses the interfacial behavior of eutectic gallium-indium liquid metal (EGaIn) droplets in various solvents. No significant difference in contact angles of EGaIn is observed regardless of the solvent types. However, the presence or absence of a conical tip on EGaIn droplets after dispensing could indirectly support that the interfacial energy of EGaIn is relatively low in non-polar solvents. Furthermore, in the impact experiments, the EGaIn droplet bounces off in the polar solvents of water and dimethyl sulfoxide (DMSO), whereas it spreads and adheres to the substrate in the non-polar solvents of hexane and benzene. Based on the dimensionless We number, it can be stated that the different impact behavior depending on the solvent types is closely related to the interfacial energy of EGaIn in each solvent. Finally, the contact angles and shapes of EGaIn droplets in aqueous buffer solutions with different pH values (4, 7, and 10) are compared. In the pH 10 buffer solution, the EGaIn droplet forms a spherical shape without the conical tip, representing the high surface energy. This is associated with the dissolution of the “interfacial energy-reducing” surface layer on EGaIn, which is supported by the enhanced concentration of gallium ion released from EGaIn in the buffer solution.

The Use of Simulation Software using the Discrete Element Method (DEM) for the Process of Materials Comminution

Comminution processes are one of the most common processes for processing energy materials, e.g. coal, biomass, and post-recycling elements. The hitherto unsolved problem is the high energy consumption of machines and the lack of precise descriptions of the phenomenon of comminution in terms of the relationship between the design features of mills and the properties of comminuted materials. The dynamic development of simulation techniques based on advanced models and the method of discrete elements allows for a certain mapping of occurring phenomena. The purpose of the work is to illustrate the possibility of using simulation software based on the discrete element method to model the grinding processes in the shredders grinding assemblies. The paper presents aspects of modeling the shape and size of particles, their interactions and contacts with mills structural elements, as well as aspects of crushing modeling in RockyDem software.

Self-Supervised Contact Geometry Learning by GelStereo Visuotactile Sensing

Vision-based tactile sensors have recently shown promising contact information sensing capabilities in various fields, especially for dexterous robotic manipulation. However, dense contact geometry measurement is still a challenging problem. In this article, we update the design of our previous GelStereo tactile sensor and present a self-supervised contact geometry learning pipeline. Specifically, a self-supervised stereo-based depth estimation neural network (GS-DepthNet) is proposed to achieve real-time disparity estimation, and two specifically designed loss functions are proposed to accelerate the convergence of the network during the training process and improve the inference accuracy. Furthermore, extensive qualitative and quantitative experiments of perceived contact shape were performed on our GelStereo sensor. The experimental results verify the accuracy and robustness of the proposed contact geometry sensing pipeline. This updated GelStereo tactile sensor with dense contact geometric sensing capability has predictable application potential in the field of industrial and service robots.

Boosting the External Quantum Efficiency of AlGaN-Based Metal–Semiconductor–Metal Ultraviolet Photodiodes by Electrode Geometry Variation

Fast aluminum-gallium-nitride–based metal–semiconductor–metal ultraviolet photodiodes were successfully designed, fabricated, and characterized using conventional photolithography techniques. Various electrode geometries were fabricated to investigate the influence of metal contact shapes on the device performance indices with emphasis on the response speed and bias-voltage–independent efficiency. Based on the independently measured Hall mobility and electric field, we evaluated the carrier transit time of the devices as 1.31 ps with bias-voltage–independent external quantum efficiency of 1198% in photoconductive mode at 19.5 V and 70% at 60 V for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> -doped and intrinsic devices, respectively.

Three-dimensional contact stresses of a slick solid rubber tyre on a rigid surface

The main aim of this paper is to quantify the three-dimensional contact stresses imposed by a single slow-moving (or rolling) slick solid rubber tyre on a relatively rough contact surface, such as stiff asphalt concrete or airport concrete surfacing layers. The results indicated the tyre-contact patch of a slick solid rubber tyre to be of rectangular shape for a vertical tyre loading range between 20 kN and 100 kN. The rectangular tyre contact shape was confirmed with static paper prints, as well as an electronically measured contact patch with the stress-in-motion pad device. The study included load calibration using a mass load scale, and a stress-in-motion device. These were used with an existing full-scale accelerated pavement test device, referred to as the heavy vehicle simulator. In addition, simplistic multi-layer linear elastic modelling was used to quantify differences between stress and strain responses of two types of two relatively 'stiff' based pavements, such as an asphalt concrete base and Portland cement concrete base, on similar subbase and subgrade layers. Notable differences were obtained, which could potentially influence further detailed studies on the performance of full-scale slick solid rubber tyres on typical multi-layered pavements.

EPM–MRE: Electropermanent Magnet–Magnetorheological Elastomer for Soft Actuation System and Its Application to Robotic Grasping

Conventional soft robotic grippers have been developed based on soft pneumatic actuators or using smart soft materials, but they need external pressure sources, are easily deteriorated or used in millimetric-scale, which leads to increase of the independency, instability, and vulnerability. In this study, we propose an EPM-MRE (Electropermanent Magnet-Magnetorheological elastomer) actuation system, which strengthens the independency and stability of soft actuation by non-contact magnetic force. We established its fundamental principle and investigated parameter design through developing a suction cup as a robotic gripper. We prototyped an EPM-MRE actuated suction cup based on magnetic-charge and tensile modeling as well as optimized the structure of EPM by introducing axisymmetric EPM with frustum pole and suction cup by introducing bi-silicone structure to uniformly activate MRE membrane. The activation of EPM by different current pulses and suction force affected by contact shapes and air gaps were tested. Evaluations showed that the suction cup could be activated with 10 ms and generate a maximum suction force of 9.2 N at a steady state with 0 J energy consumption. In conclusion, the EPM-MRE soft actuation system can be used as a robotic gripper.

Nonballistic transport characteristics of superconducting point contacts

In the "ballistic" regime, the transport across a normal metal (N)/superconductor (S) point-contact is dominated by a quantum process called Andreev reflection. Andreev reflection causes an enhancement of the conductance below the superconducting energy gap, and the ratio of the low-bias and the high-bias conductance cannot be greater than 2 when the superconductor is conventional in nature. In this regime, the features associated with Andreev reflection also provide energy and momentum-resolved spectroscopic information about the superconducting phase. Here we theoretically consider various types of N/S point contacts, away from the ballistic regime, and show that even when the superconductor under investigation is simple conventional in nature, depending on the shape, size and anatomy of the point contacts, a wide variety of spectral features may appear in the conductance spectra. Such features may misleadingly mimic theoretically expected signatures of exotic physical phenomena like Klein tunneling in topological superconductors, Andreev bound states in unconventional superconductors, multiband superconductivity and Majorana zero modes.

The Importance of Not Being Too Attached: Pharmaceutical Equipment Characteristics and Bacterial Attachment

In this article the author provides an overview of the characteristics of microbial attachment and the essential considerations when developing a contamination control strategy. This review paper assesses the factors affecting finish and roughness, primarily in relation to microbial attachment to stainless steel, while considering other related variables like contact height and shape of surface defects

Effect of Roughness on Capillary Contact Shapes in Tangential Shear: Experiments

Effect of Roughness on Capillary Contact Shapes in Tangential Shear: Experiments

On the fretting fatigue crack nucleation of complete, almost complete and incomplete contacts using an asymptotic method

In this work, the fretting crack nucleation of an aeronautical Ti-10V-2Fe-3Al titanium alloy is investigated. The main difficulty when designing complex industrial systems, especially helicopters rotor parts, lies in the prediction of the assembly interfaces behaviour. Those areas can be subjected to fretting loading characterized by a very confined multiaxial high stress gradient, leading to fatigue crack nucleation. This kind of failure reduces the parts potential lifetime and increases therefore the security margin that can be considered.The aim of this paper is to provide a criterion to prevent crack nucleation on industrial contacts configurations. To reach this objective, this study focuses on the geometrical conditions, loadings and material properties linked to crack initiation. Two dedicated fretting test campaigns are used to study crack initiation conditions with various contact shapes and loadings on the same material. The crack initiation conditions are compared with a contact mechanics representation based on asymptotic methods. This method allows the stress field evaluation at the hot spot location by using the problem’s eigenvalues.The combination of the asymptotic method with contact mechanics and the Goodman approach allows to represent the key parameters of the fretting fatigue crack initiation. They include the impacted material volume, the shear intensity and the bulk stress. A fretting fatigue crack initiation criterion is proposed. It is based on classical material properties and the bulk stress ratio Rσ0 only and is applicable to all sorts of contact shapes. The main interests of this prediction method are the absence of size effect parameters for industrial contacts and its efficiency, as it is only based on analytical formulations.