Contact Shape Research Articles

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.

Numerical modeling and analysis of thermal and mechanical behavior for ground wire-clamp system under short-circuit current

In the ground wire-clamp system, aluminum armor tape (AAT) or armor rod (AR) is commonly adopted to avoid the wear damage of ground wire. While under the short-circuit current, damage or even breakage of ground wire in suspension clamp due to overheat may occur. However, there still lacks attention on the investigation about this type of damage. In this paper, a finite element (FE) modeling method of the ground wire-clamp system, which was applicable to two cases with AAT and AR, was proposed to discuss the transient thermal and mechanical behaviors. In the modeling of contact points, an improved contact bridge model considering the contact shape characteristics was proposed. The transient temperature rise experiments for ground wire-clamp systems with AAT and AR were carried out to verify the accuracy of models. The results shows that the improved contact bridge model is conducive to obtaining the accurate calculation results. For the analysis of this type of damage, the generated thermal stress cannot be ignored. In engineering, the ground wire twinned by AAT is at risk of overheat or even breakage under the short-circuit current, while using AR can prevent the ground wire in the suspension clamp from damage of overheat.

Thinking clearly about social aspects of infectious disease transmission.

Social and cultural forces shape almost every aspect of infectious disease transmission in human populations, as well as our ability to measure, understand, and respond to epidemics. For directly transmitted infections, pathogen transmission relies on human-to-human contact, with kinship, household, and societal structures shaping contact patterns that in turn determine epidemic dynamics. Social, economic, and cultural forces also shape patterns of exposure, health-seeking behaviour, infection outcomes, the likelihood of diagnosis and reporting of cases, and the uptake of interventions. Although these social aspects of epidemiology are hard to quantify and have limited the generalizability of modelling frameworks in a policy context, new sources of data on relevant aspects of human behaviour are increasingly available. Researchers have begun to embrace data from mobile devices and other technologies as useful proxies for behavioural drivers of disease transmission, but there is much work to be done to measure and validate these approaches, particularly for policy-making. Here we discuss how integrating local knowledge in the design of model frameworks and the interpretation of new data streams offers the possibility of policy-relevant models for public health decision-making as well as the development of robust, generalizable theories about human behaviour in relation to infectious diseases.

Tactile Interaction Sensor with Millimeter Sensing Acuity.

In this article we report on a 3 × 3 mm tactile interaction sensor that is able to simultaneously detect pressure level, pressure distribution, and shear force direction. The sensor consists of multiple mechanical switches under a conducting diaphragm. An external stimulus is measured by the deflection of the diaphragm and the arrangement of mechanical switches, resulting in low noise, high reliability, and high uniformity. Our sensor is able to detect tactile forces as small as ~50 mgf along with the direction of the shear force. It also distinguishes whether there is a normal pressure during slip motion. We also succeed in detecting the contact shape and the contact motion, demonstrating potential applications in robotics and remote input interfaces. Since our sensor has a simple structure and its function depends only on sensor dimensions, not on an active sensing material, in comparison with previous tactile sensors, our sensor shows high uniformity and reliability for an array-type integration.

두 개의 성형공구를 이용한 무금형 6축 양면점진성형기 개발

Incremental sheet forming (ISF) does not use a partial or full die at the bottom of the die; rather, a hemispherical forming tool presses the sheet layer by layer along the numerically controlled movement path to cause plastic deformation. The ISF is somewhat limited in manufacturing freeform surfaces because the die is installed at the bottom of the sheet material. To compensate for these shortcomings, a double side incremental forming (DSIF) method, which can form both sides of the sheet simultaneously, is required with two independently controlled tools. This machine is composed of a forming part and support part, Equipped with a motion controller capable of 6-axis control, the developed DSIF machine can freely and smoothly form surfaces. To verify its performance, prototype forming was performed, and the 3D contact measurement and shape data were superimposed to compare and analyze the forming accuracy and verify the usefulness of incremental forming.

Effects of Contact Area and Contact Shape on Nonlinear Fluid Flow Properties of Fractures by Solving Navier-Stokes Equations

Abstract The influences of contact shape and contact area on nonlinear fluid flow properties through fractures are investigated by solving Navier-Stokes equations. The evolutions of nonlinear relationships between flow rate and hydraulic pressure drop, Forchheimer coefficients, nonlinear factor, critical hydraulic gradient, distributions of flow streamlines, and tracer flow paths at different times are systematically estimated. The results show that the nonlinear relationships between flow rate and hydraulic pressure drop can be well described by Forchheimer’s law, in which the nonlinear term coefficient b is approximately three orders of magnitude larger than the linear term coefficient a. The smaller contact area corresponds to smaller variations in many aspects such as flow rate, critical hydraulic gradient, flow streamlines, and tracer flow paths. The critical hydraulic gradient decreases with the increasing degree of contact shape variations while the contacts have the same mean area. The increase in hydraulic pressure drop can induce significant eddies and decrease the permeability and/or conductivity of fractures. However, the distributions of streamlines and tracer flow paths are not dramatically disturbed under a large hydraulic pressure drop.

Computational investigation of the impact of deep brain stimulation contact size and shape on neural selectivity

Background. Understanding neural selectivity is essential for optimizing medical applications of deep brain stimulation (DBS). We previously showed that modulation of the DBS waveform can induce changes in orientation-based selectivity, and that lengthening of DBS pulses or directional segmentation can reduce preferential selectivity for large axons. In this work, we sought to investigate a simple, but important question from a generalized perspective: how do the size and shape of the contact influence neural selectivity? Methods. We created multicompartment neuron models for several axon diameters and used finite element modeling with standard-sized cylindrical leads to determine the effects on changing contact size and shape on axon activation profiles and volumes of tissue activated. Contacts ranged in size from 0.04 to 16 mm2, compared with a standard size of 6 mm2. Results. We found that changes in contact size are predicted to induce substantial changes in orientation-based selectivity in the context of a cylindrical lead, and changes in contact width or height can alter this selectivity. Smaller contact sizes were more effective in constraining neural activation to small, nearby axons. However, micro-scale contacts enable only limited spread of neural activation before exceeding standard charge density limitations; further, energetic efficiency is optimized by somewhat larger contacts. Interpretations. Small-scale contacts may be optimal for constraining stimulation in nearby grey matter and avoiding orientation-selective activation. However, given charge density limitations and energy inefficiency of micro-scale contacts, we predict that contacts sized similarly to or slightly smaller than segmented clinical leads may optimize energy efficiency while avoiding charge density limitations.

Interconnected drying phenomena in nanoparticle laden water-ethanol binary droplets.

Understanding the evaporation of a multi-component droplet has found immense importance in various technological applications. This study investigates the evaporation behaviour of a colloidal binary droplet system comprising of the ethanol-water mixture and polystyrene nanoparticles. The wetting and evaporation dynamics were studied with an emphasis on the collective influence of ethanol and nanoparticle concentrations. The temporal behaviour of the contact angles, shapes and volumes of the droplets was monitored in order to analyse the evaporative behaviour. With increase of ethanol concentrations, the binary droplet volumes were found to decrease nonlinearly with time. Ethanol being more volatile evaporated in the initial stage. Towards the end of the evaporation process, the evaporation characteristics mimics the behaviour of pure water. Our study shows that the initial contact angle decreases monotonically with increased concentration of ethanol in the mixture. The contact angle is maximum for a particular nanoparticle concentration. Droplets with higher ethanol concentration show higher wettability which in its turn is maximum for low nanoparticle concentrations. This trend shows the interconnected effect of ethanol and nanoparticle concentrations on evaporation. Rim width of the final deposition pattern increases with nanoparticle concentration although it is almost independent of ethanol concentration. Finally, it is noticed that fast evaporation of a relatively more volatile component in a binary mixture droplet leads to nanoparticle segregation for low nanoparticle concentrations. Thus for binary mixtures, the evaporation of the more volatile component, ethanol for our case, offers characteristic differences in the resulting evaporation dynamics from that of pure water which finds applicability for multi-component evaporation processes.

A generic energy‐conserving discrete element modeling strategy for concave particles represented by surface triangular meshes

AbstractA generic energy‐conserving linear normal contact model for concave particles in the discrete element method (DEM) is presented in this article. It is derived based on a recently enhanced general energy‐conserving contact theory for arbitrarily shaped particles. A set of more effective evaluation schemes required in the model are also given, which shows that only the intersection boundary between two contact shapes, instead of their contact region or surfaces, is required to be explicitly obtained, thereby substantially improving both efficiency and applicability of the proposed contact model over the previous version. A surface triangular mesh is used to represent any 3D concave particle. The computational issues associated with the contact of two surface triangulated 3D shapes, including the contact detection, the determination of intersection boundary segments, the computation of contact features and parallelization, critical time step, and friction and damping treatment for multiple contacts are described in detail. Two sets of numerical examples involving various concave 3D shapes with a large number of surface triangles are presented to demonstrate either the superb energy‐conserving property of the proposed model model, or its effectiveness, robustness, and universal nature for wider and more complex problems.

Constitutive model of disordered grid interpenetrating structure of flexible microporous metal rubber

In this study, the disordered grid interpenetrating structure (DGIS) of wire turns in flexible microporous metal rubber (FMP-MR) for vibration and noise reduction is investigated, and an effective constitutive model is developed to dynamically capture the nonlinear mechanical behavior of FMP-MR. In this model, a micro spring element with adaptive deformation (MSEAD) model with random spatial distribution is employed, based on the phenomena of irregular overlapping and interlacing of material turns. The spatial distribution of micro springs and the evolution of the contact area morphology in FMP-MR are taken into consideration and introduced as key variables in model development. The concept of combined probability distribution (CPD) of micro spring pairs between wire turns in FMP-MR is proposed to characterize the random combination mode of material turns. Eventually, based on the micro-patterns of wire turns in FMP-MR, a constitutive model including macroscopic parameters, such as shape, density, wire diameter, helix pitch, and wire elastic modulus, and microstructure parameters, such as spatial distribution of wire turns, contact shape, and friction coefficient is developed for the first time. By analyzing and discussing the fitting degree of quasi-static compression experimental results and the model constitutive curves, the validity of the proposed constitutive model is quantitatively confirmed by residual analysis. According to the results, the FMP-MR constitutive model based on DGIS can effectively reflect the nonlinear mechanical behavior and complex micro-contact friction phenomena of the material.

A heuristic approach to detect CAD assembly clusters

Mechanical assemblies are very complex structures, made of many parts of various shapes and sizes with different usages. Consequently, it is challenging to manage them during all the manufacturing processes, from the design to the assembly and the recycling. Aiming to simplify the assembly structure and reduce the number of parts to deal with simultaneously, in literature many works exist on subassemblies identification starting from the CAD assembly model. However, the methods provided loose sight of many details associated with the parts, as well as the fact that the treated model represents a real mechanical assembly which respects precise engineering rules. At this regard, this work introduces a novel methodology to detect meaningful clusters in CAD assembly models. The logic applied relies on engineering knowledge, both of mechanical assemblies’ components and of assembling techniques, and on the leveraging of the semantics of components. In particular, referring to general design rules, we have identified some heuristics to exploit to partition the assembly into different types of clusters, such as the symmetry along an axis and the presence of fasteners or welds. It results that the assembly’s parts are meaningfully grouped, considering, at the same time, their shape, functionality, and type of contact.

Soft Body Belt-Type Touch Sensor With Impact Resistance: A Study of Dynamic Behavior

We report the development of a novel soft body touch sensor capable of measuring contact force along its length. The sensor can be embedded in soft objects and on curved surfaces for smart furniture, interactive electronics, and general robotics applications. The sensor uses pneumatic transduction principle and achieves both high sensitivity and impact loading tolerance. The development is motivated by the needs of consumer electronics industries for smart furniture and interactive toys. The current work fills a gap of existing soft-bodied touch sensors. The main sensor body is completely polymeric and contains no conductive or semiconducting material elements. It exhibits high pass frequency response to reject common mode contact forces or shape variations. The central question addressed by this paper is dynamic behavior of this sensor under normal and impact touch force. In this study we developed a theoretical model for the sensor output and validated with experimental measurements. We modeled sensor behavior under two operational regimes of different unloading speed. Depending on the rate of change, the sensor could be in force limited relaxation mode or elastic relaxation (free relaxation) mode. Measurements have been performed to capture time constants of occupant behavior in a smart cushion application.

Experimental investigation of cold adhesion failure physical mechanism of gold plated contact within the Micro-Electromechanical-Relay

Gold plated contacts are widely used in the Micro-Electromechanical-Relay to improve electric contact reliability. However, the cold adhesion phenomenon between gold plated surfaces is prone to cause normally closed contacts operating failure. In this paper, a novel test rig for measuring dynamic force and contact resistance between spring contact and rod shape contact during breaking process is introduced. The dynamic contact force, displacement and contact resistance during contact breaking process are obtained. From these waveforms, the adhesion force between two contacts in each break is estimated. In order to reveal the failure phenomena occurred in the mechanical vibration screening tests, fretting between the closed contact pairs is generated with different amplitudes and cycles by using the motorized stage. Subsequently, the effects of fretting behaviors on cold adhesion of gold plated contact pairs are investigated explicitly. Next, the associated failure physical model is built with the help of mechanical adhesion theory to explain the nature of surface adhesion. Furthermore, surface quality of gold coating and static contact force are also verified as the key factors influencing the adhesion phenomena. Surface morphologies of contacts prove the substantial increase of adhesion force correlates closely with the features of micro asperities.

Host feeding patterns of Nyssorhynchus darlingi (Diptera: Culicidae) in the Brazilian Amazon

Nyssorhynchus darlingi (Root) is the dominant malaria vector in the Brazilian Amazon River basin, with additional Anophelinae Grassi species involved in local and regional transmission. Mosquito blood-feeding behavior is an essential component to define the mosquito-human contact rate and shape the transmission cycle of vector-borne diseases. However, there is little information on the host preferences and blood-feeding behavior of Anophelinae vectors in rural Amazonian landscapes. The barrier screen sampling (BSS) method was employed to sample females from 34 peridomestic habitats in 27 rural communities from 11 municipalities in the Brazilian Amazon states of Acre, Amazonas, Pará and Rondônia, from August 2015 to November 2017. Nyssorhynchus darlingi comprised 97.94% of the females collected resting on barrier screens, and DNA sequence comparison detected 9 vertebrate hosts species. The HBI index ranged from 0.03–1.00. Results revealed the plasticity of Ny. darlingi in blood-feeding on a wide range of mainly mammalian hosts. In addition, the identification of blood meal sources using silica-dried females is appropriate for studies of human malaria vectors in remote locations.

An energy-conserving contact theory for discrete element modelling of arbitrarily shaped particles: Contact volume based model and computational issues

The contact volume based energy-conserving contact model is presented in the current paper as a specialised version of the general energy-conserving contact model established in the first paper of this series (Feng, 2020). It is based on the assumption that the contact energy potential is taken to be a function of the contact volume between two contacting bodies with arbitrary (convex and concave) shapes in both 2D and 3D cases. By choosing such a contact energy function, the full normal contact features can be determined without the need to introduce any additional assumptions/parameters. By further exploiting the geometric properties of the contact surfaces concerned, more effective integration schemes are developed to reduce the evaluation costs involved. When a linear contact energy function of the contact volume is adopted, a linear contact model is derived in which only the intersection between two contact shapes is needed, thereby substantially improving both efficiency and applicability of the proposed contact model. A comparison of this linear energy-conserving contact model with some existing models for discs and spheres further reveals the nature of the proposed model, and provides insights into how to appropriately choose the stiffness parameter included in the energy function. For general non-spherical shapes, mesh representations are required. The corresponding computational aspects are described when shapes are discretised into volumetric meshes, while new developments are presented and recommended for shapes that are represented by surface triangular meshes. Owing to its additive property of the contact geometric features involved, the proposed contact model can be conducted locally in parallel using GPU or GPGPU computing without occurring much communication overhead for shapes represented as either a volumetric or surface triangular mesh. A set of examples considering the elastic impact of two shapes are presented to verify the energy-conserving property of the proposed model for a wide range of concave shapes and contact scenarios, followed by examples involving large numbers of arbitrarily shaped particles to demonstrate the robustness and applicability for more complex and realistic problems.

Can past intergroup contact shape support for policies in a pandemic? Processes predicting endorsement of discriminatory Chinese restrictions during the COVID-19 crisis

A survey of 340 UK residents was conducted when the COVID-19 virus first reached the UK in February 2020. We measured past experiences of positive and negative intergroup contact with Chinese people as predictors of intergroup threat and emotions in the context of the pandemic; and how these processes in turn predicted support for discriminatory policies designed to restrict the freedom of Chinese people in the UK. We tested a novel threat-matching hypothesis which draws upon models of outgroup-specific social perception to predict that the emotional processes underlying contact effects will depend on the specific threat posed by the outgroup. In the present epidemiological context, Chinese people posed a salient threat to individuals’ physical health and welfare. Accordingly, we show that whilst intergroup contact predicted both fear and anger towards the outgroup, the indirect effect of contact on support for Chinese restriction policies via fear was significantly stronger than the indirect effect via anger. Our findings provide a more nuanced understanding of how specific threat and emotions drive intergroup contact effects, and offer important insights for efforts to maintain positive intergroup relations in the face of the crisis.

Evolutionary dynamics in the Anthropocene: Life history and intensity of human contact shape antipredator responses.

Humans profoundly impact landscapes, ecosystems, and animal behavior. In many cases, animals living near humans become tolerant of them and reduce antipredator responses. Yet, we still lack an understanding of the underlying evolutionary dynamics behind these shifts in traits that affect animal survival. Here, we used a phylogenetic meta-analysis to determine how the mean and variability in antipredator responses change as a function of the number of generations spent in contact with humans under 3 different contexts: urbanization, captivity, and domestication. We found that any contact with humans leads to a rapid reduction in mean antipredator responses as expected. Notably, the variance among individuals over time observed a short-term increase followed by a gradual decrease, significant for domesticated animals. This implies that intense human contact immediately releases animals from predation pressure and then imposes strong anthropogenic selection on traits. In addition, our results reveal that the loss of antipredator traits due to urbanization is similar to that of domestication but occurs 3 times more slowly. Furthermore, the rapid disappearance of antipredator traits was associated with 2 main life-history traits: foraging guild and whether the species was solitary or gregarious (i.e., group-living). For domesticated animals, this decrease in antipredator behavior was stronger for herbivores than for omnivores or carnivores and for solitary than for gregarious species. By contrast, the decrease in antipredator traits was stronger for gregarious, urbanized species, although this result is based mostly on birds. Our study offers 2 major insights on evolution in the Anthropocene: (1) changes in traits occur rapidly even under unintentional human "interventions" (i.e., urbanization) and (2) there are similarities between the selection pressures exerted by domestication and by urbanization. In all, such changes could affect animal survival in a predator-rich world, but through understanding evolutionary dynamics, we can better predict when and how exposure to humans modify these fitness-related traits.

Comparative Analysis on the Properties of Yarns Formed by Different Contact-shaped Strands Passing through Static Rod and Self-adjustable Disk Surfaces

ABSTRACT An energy-efficient method that improved spun-yarn properties was previously reported, however, the improvements differed as the varying contact-shaped strands passed through the static rod and self-adjustable disk contact surfaces. Thus, models of three strand-contacting shapes were built: straight, convexing-up, and concaving-down. Then, the influence of the strand-contact shapes on the spun-yarn properties was theoretically analyzed, while spinning with a static rod and self-adjustable disk contact surfaces. The conducted experiments disclosed that the yarn hairiness was significantly reduced for all three models of the strand-contact shapes, with rod and disk surfaces in the yarn-formation zone. The spun-yarn tenacity was slightly enhanced only for the strands passing through the convexing-up and concaving-down contact shapes. The experimental results were consistent with the theoretical analysis.

Evaluation of the incremental compliances of non-elliptical contacts by treating them as external cracks

The incremental normal compliance of a contact of “irregular” (non-elliptical) shape between two elastic half spaces is considered. The contact is modeled as external crack. An approximate expression for the stress intensity factor (SIFs) around its boundary, in conjunction with Rice (1975) theorem that interrelates SIFs and crack compliances, are used to evaluate the crack compliance. The results cover a broad class of contact shapes, including – but not limited to - all convex ones. Bounds, similar to Hill's comparison theorem in micromechanics, are formulated for the compliances of contacts. The cross-property elasticity-conductivity relation yields similar results for contact conductance. The methodology is illustrated on several examples.

Extensive sequence and structural evolution of Arginase 2 inhibitory antibodies enabled by an unbiased approach to affinity maturation

Affinity maturation is a powerful technique in antibody engineering for the in vitro evolution of antigen binding interactions. Key to the success of this process is the expansion of sequence and combinatorial diversity to increase the structural repertoire from which superior binding variants may be selected. However, conventional strategies are often restrictive and only focus on small regions of the antibody at a time. In this study, we used a method that combined antibody chain shuffling and a staggered-extension process to produce unbiased libraries, which recombined beneficial mutations from all six complementarity-determining regions (CDRs) in the affinity maturation of an inhibitory antibody to Arginase 2 (ARG2). We made use of the vast display capacity of ribosome display to accommodate the sequence space required for the diverse library builds. Further diversity was introduced through pool maturation to optimize seven leads of interest simultaneously. This resulted in antibodies with substantial improvements in binding properties and inhibition potency. The extensive sequence changes resulting from this approach were translated into striking structural changes for parent and affinity-matured antibodies bound to ARG2, with a large reorientation of the binding paratope facilitating increases in contact surface and shape complementarity to the antigen. The considerable gains in therapeutic properties seen from extensive sequence and structural evolution of the parent ARG2 inhibitory antibody clearly illustrate the advantages of the unbiased approach developed, which was key to the identification of high-affinity antibodies with the desired inhibitory potency and specificity.