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High-strength boron steels are widely used in manufacturing the auto bodies and parts of light-weight vehicles, but the high rates of surface scratches and die wear have consistently occurred during hot stamping for these steels. For an in-depth understanding of the tribological characteristics at this interface, the frictional contact behavior and thermomechanical mechanisms of boron steel 22MnB5 against die steel H13 at 800 °C were studied through experiments and finite-element simulations. The coefficient of friction and worn surface topography were investigated by pin-on-disk sliding tests. A three-dimensional thermomechanical finite-element model of a friction pair was established to explore the interfacial dynamic variations. Experimental and simulation results show that severe elastic–plastic deformation occurred on the worn surface of the boron steel, whereas an increase in the load decreased the coefficient of friction within a certain range because the growth rate of shear force was slower than that of the normal force. When the finite-element model was changed from the gradual loading stage to the initial sliding stage, the tangential friction force further increased the plastic deformation on the surface of boron steel. The scratches and furrows were mainly caused by the compression and shear from asperities of the rough surface, as confirmed by the high-frictional-stress regions concentrated on the peaks and flanks of asperities. During the high-temperature and high-pressure experiments, the plasticized and softened surface materials of the boron steel adhered to the die surface readily, resulting in peeling and delamination.

With the advent of Rail cum road motors there are great demanding situations earlier than Indian railways. Railway Engineers had been for all time interested by the metal wheel-Rail and Rubber tire-Rail contacts. These tiny interfaces govern the dynamic overall performance of avenue cum rail motors via the masses it transmits and, like every high-strain attention sector, it's far subjected to severe damage phenomena. The paper deals with modelling and simulation of the static behaviour of a radial mini truck tire of a proposed road cum rail automobile in touch with rails. The Finite element technique via the ANSYS software program is used to obtain the static behaviour of the rubber tire in contact with rail underneath inflation stress values. The primary goal is to carry out a finite detail analysis and computationally compare the overall performance of a stationary rubber tire along with rim on rails with the aid of changing the inflation stress so that corresponding overall performance parameters like equivalent strain in rubber tire and rims, deformation and call patch of rubber tire are expected and the effect of inflation pressure on these parameters can be understood.

The dynamic effects, mainly including the inertia effect and strain-rate effect, on the dynamic wheel–rail contact behavior become more and more serious as the train speed increases. The inertia effect can be automatically taken into account in explicit finite element analysis codes, while the strain-rate effect needs to be considered via inputting the related material parameters. In the present paper, the influence of strain rate on the dynamic wheel–rail contact response for the straight track case was explored, based on a 3D wheel–rail rolling contact finite element model, via LS-DYNA/explicit algorithm. Effects of the axle load and train speed on typical dynamic wheel–rail responses were discussed, and the results indicate that the coupled train speed with strain rate has a non-negligible influence on dynamic contact responses. The strain rate hardening effect increases the maximum contact pressure and stress, and inhibits the plastic deformation of the wheel–rail system. A rate-sensitive factor (RSF) was then introduced to describe the strain rate hardening effect, confirming that the rail is more sensitive to strain rate compared to the wheel. Finally, an error analysis of the wheel–rail Hertz contact theory was conducted, which further verify the differences between elastic and elastic-plastic contact solutions.

Functionally graded surface has been a domain of research interest due to its use in various technologically advanced applications. The work focuses on static and dynamic analysis of rough fractal surface with exponentially graded material properties. The rough fractal surface is modeled in ANSYS with the coordinate points generated using the two variable modified Weierstrass–Mandelbrot function. Material gradation is applied to the rough surface model in such a way that, for any value of the gradation or inhomogeneity parameter, material properties at the top of the rough surface always remain constant. Force–displacement behavior of the fractal surface in contact with a rigid flat surface is determined through finite element simulation. A parameter representing the nonlinearity of the system is extracted from the force–displacement plot. It is found that higher is the inhomogeneity parameter, higher is the nonlinearity of the system. Furthermore, for a certain change in inhomogeneity parameter, the change in nonlinearity is higher for rougher topography. The dynamic contact system is found to be softening in nature, and the softening nature increases with higher inhomogeneity parameter. The phase plot of the vibrating contact system becomes more asymmetric with respect to the velocity axis for higher value of inhomogeneity parameter.

The interaction between geosynthetics and soil is vital for the stability and the bearing capacity of geosynthetic-reinforced soil structures. This contact behavior between geosynthetics and granular soils has been extensively studied in the literature while there is scarcity of it related to geosynthetics and cohesive soils particularly with softening responses. This paper presents a strain-softening model of geobelt–clay interaction based on direct shear test results under two compaction degrees. A theoretical model for evaluating the pullout behavior of a geobelt is proposed by employing the strain-softening model verified by direct shear tests and a hyperbolic model capturing the stress–strain curves of a geobelt calibrated by uniaxial tensile tests. The proposed model is numerically solved and validated by pullout tests. A kind of sensor-enabled geobelt (SEGB) was adopted in all the aforementioned tests. Both test and numerical results show an overall softening trend in terms of front pull-out force versus displacement. Generally, the model proposed can give reasonably good agreement between calculations and test data during the whole pull-out range. Also, the strain distributions measured by SEGBs demonstrate the working process during the pullout tests, which makes SEGBs a potentially new choice for the strain measurements of in-soil geobelts.

Needle insertion in soft tissue has attracted considerable attention in recent years due to its application in minimally invasive surgery such as biopsies, intravenous injection and brachytherapy. In order to ensure the accuracy of surgery, the surgical simulation process requires accurate modeling of the contact behavior between instrument and soft tissue. However, it is difficult to carry out a simulation of the needle deformation in the puncture process. Hence, in this paper, the deformation of the puncture needle specially focusses on muscle puncture surgery in the process of robot-assisted puncture is analyzed and investigated. Interaction during puncture is modeling and simulated using Abaqus to obtain the displacement curve of tissue and the force curve of needle. Insertion experiments are performed to verify the simulation results, and the insertion mechanisms of the soft tissue under different under different diameters of needles, insertion velocities, insertion depth and rotational angles are revealed and discussed. Relevant analysis is performed to direct the real surgery and make it more accurate.

We investigated the interfacial contact behavior of the side-to-side biaxial heterostructure between carbon nanotubes and silver nanowires on an atomic scale. The nanotubes can move along the nanow...

In this paper, an enriched finite element method is presented to model the interaction between the hydraulically-driven fracture and the pre-existing naturally-cemented fault within an impermeable domain. The inflow and continuity equations of the fluid phase are solved throughout the discontinuities in conjunction with the momentum balance equation of the bulk using a sequential manner based on the staggered Newton algorithm. The frictional contact behavior along the overlapped zone of the naturally-cemented fault is modeled through the extended–FEM penalty scheme. The effect of cementation bond along the natural fault is incorporated employing a modified Coulomb law to derive the cementation tractions. Various interaction scenarios are recognized based on a novel approach accounting for the effect of fracturing fluid diversion into the intersected fracture network. Finally, several numerical examples are presented in order to illustrate the performance and accuracy of the proposed computational algorithm. Accordingly, it is shown by increase in natural fracture length, the probability of hydro-fracture arrest is increased. Meanwhile, the shear resistance of the natural interface plays the key role in development of the penetration scenario.

Although crown gear couplings are widely used in rotating machinery, very little is known about their contact behavior and load distribution characteristics. In this study, the manufacturing methods are presented for crown gear coupling. Complete geometrical mathematical models from tools to crown gear coupling are proposed based on the theories of differential geometry and gear mesh. Then, a high-fidelity finite element model verified by tooth contact analysis under light load is employed to investigate load distribution along the crown gear coupling interfaces. The effects of meshing position, torque, and angular misalignment are investigated on load distributions along with crowning amount depending on the displacement circle radius. Finally, it is observed that when the contact position is 0.2 times the width of the tooth, the radius of the displacement circle is the optimal result for the performance of the crown gear coupling.

In the current paper, a novel experimental methodology to characterize the contact behavior on thin plates under bending is presented. The method is based on the experimental measurement of the indentation observed during contact experiments. Tests were conducted using aluminum thin plates and a steel sphere to evaluate the effect of thickness and bending during contact. For this purpose, a non-contact optical technique, 3D Digital Image Correlation (3D-DIC), has been employed to measure the out-of-plane displacements experienced at the rear face of the specimens (opposite where the contact is occurring). An indirect measurement of the experimental contact law is obtained for different plate thicknesses (2 mm, 3 mm, 4 mm, 5 mm and 6 mm) as the contact load increases. An energy balance performed during contact experiments made it possible to evaluate and quantify the applied energy to generate bending and contact deformation. When the specimen thickness increases from 2 mm to 6 mm, contact deformation reaches higher values from the total applied energy. In addition, it is also possible to evaluate the portion of the elastically recovered energy for contact and bending deformation during the unloading. It has been observed that thicker specimens show a lower elastic energy recovery due to bending and a higher elastic energy recovery due to contact. Results clearly show how the ratio between absorbed and applied energy changes as the specimen thickness increases, highlighting the relevance of the proposed method for the characterization of contact behavior in thin plates.

The closure behavior of rock joints is of critical importance to the study of hydromechanical behaviors and geophysical properties of jointed rock masses. Theoretical contact models, used to predict the relations of normal stress versus closure deformation, rely on morphology parameters of rock joint as the input parameters. The relevance of the contact models depends on the inherent assumptions and the accuracy with which the input parameters are determined. In the present study, morphology parameters of three rock joints are determined by the spectral moment approach and peak identification method, respectively. The differences are found to vary significantly depending on the selected method. The phenomenon would be related to the definition of an asperity peak on joint profile. The spectral method only considers the so-called asperity peaks, while the deterministic approach further accounts for the asperity shoulders. Finally, the morphology parameters determined by the two methods are treated as the input parameters of a validated theoretical model. The comparisons between the theoretical curves and the experimental results indicate that parameters determined by the deterministic method would be more reliable.

Waterproof membranes have higher initial strength, faster construction, and better waterproofing than conventional sheet membranes. In addition, their polymer constituents have much higher interfacial adhesion and tensile strength than those of conventional materials. However, despite their advantages, waterproof membranes are not widely used in civil construction. This study evaluates the material properties and interface parameters of a waterproof membrane by considering the results of laboratory experiments and numerical analysis. Since the contact behavior of a membrane at its interface with shotcrete is important for understanding the mechanism of the support it offers known as a shotcrete tunnel lining, modeling should adopt appropriate contact conditions. The numerical analysis identifies the suitability and contact conditions of the waterproof membrane in various conditions.

Fretting is a damaging phenomenon, generally observed when a mating pair is subjected to a small amplitude of oscillatory motion. The contact behavior in fretting is governed by a complex interaction between mechanical properties of mating pair, contact geometry, and loading conditions. In most of the practical applications, dissimilar materials are chosen for a contacting pair with one of the materials having superior material properties than other so as to replace the worn-out or unfit component during the maintenance. In the literature, many researchers have studied the effect of dissimilar materials on fretting behavior but mainly in the context of hardness. As experimental methodology has been adopted in these studies, the effect of dissimilar material properties has been reported in terms of global variables like wear volume or fretting fatigue life, but its influence on underlying local contact tractions could not be studied. In the present work, a two-dimensional finite element analysis has been carried out for a cylinder-on-plate configuration. The effect of dissimilar materials for the mating pair has been studied by modeling elastic–plastic behavior for combinations of three different materials, namely, SS 304, ASTM A302-B, and aluminum. The validation of the finite element model is carried out by comparing the results of elastic analysis with the analytical solutions available in the literature. The pertinent contact parameters in the context of fretting wear, namely, contact pressure, contact slip, and contact stresses are extracted. A frictional dissipation energy density-based approach is used for the qualitative comparison of the fretting damage for different cases and validated with the literature data.

Interaction forces between a robotic cuff and the skin during assisted walking with a lower limb exoskeleton may cause skin injuries over time, such as blisters and ulcers. This study proposes a sensing cuff that can monitor the contact behavior between the exoskeleton and skin during assisted walking, and a functional test and assisted walking experiments were conducted to evaluate the performance of the proposed device. The functional test of the sensing cuff showed good performance of capturing the contact behavior for safety evaluation. The walking experiment involved subjects walking on a treadmill with a lower limb exoskeleton under different conditions (i.e., walking speed and clothing), and the sensing cuff attached to the exoskeleton measured the interaction forces and slip velocity. The magnitude of shear force in the movement direction peaked near the beginning and within 40 – 50% of the gait cycle. The contact safety of the lower limb exoskeleton during assisted walking was then evaluated based on the calculated shear stress. The designed sensing cuff could provide sufficient information regarding contact behavior and contact safety during assisted walking.

It is state of technology in district heating systems to use sand as backfill material for district heating pipes (DHP). In conventional pipeline construction, Temporarily Flowable Backfill Materials (TFB) have been already used for backfilling the pipe zone. TFB consists of the excavated material, cement, water and optionally bentonite. Environmental and economic advantages are that the excavated material can be reused and that TFB requires no compaction. In order to embed district heating pipes in TFB, soil mechanical parameters of the TFB are required. Above all the resistance to temperature-induced axial displacement should be well-known in order to estimate the displacements of the DHP, as well as the stress distribution along the DHP. Compared to sand as a non-cohesive backfill TFB have remarkable adhesive contact stresses which result in considerable resistance forces. In this article, the contact behavior between TFB and DHP is described as well as the effect on the DHP statics. Therefore, the results of various laboratory tests are summarized and presented to understand the interface-resistance-characteristics (IRC) of the DHP/ TFB interface. Then, the deduced IRC was implemented in a computer program for some comparative calculations with sand and TFB. Finally, the results of cyclic loading are presented and discussed.

S-lay is a widely used method for offshore pipe installation. In recent years, S-lay has gradually applied to the deepwater condition. Because of the increasing pipe weight in deep S-lay, there exist severe and complex contact problems between the overbend pipe and roller supports of the stinger. In deep S-lay design, it is difficult to solve this nonlinear mechanics problem, and there remain confusion and difficulties to predict the roller contact forces and the pipe strain level in S-lay design. The present paper develops a refined finite element model with the framework of ABAQUS, which considers the complex surface contact behaviors in the overbend section. The features of the contact state of different rollers within one roller box are discussed, and the resultant support forces from each roller box are calculated and compared with the commercial design code. The overbend strain level of five S-lay cases is investigated and the pipelaying safety is checked by DNV rules. The simulation results show that the proposed model can provide more accurate and reasonable predictions on roller forces and pipe strain distribution for deepwater S-lay design.

Short-time withstanding current is a key parameter of air circuit breakers. Due to the structure of multiple parallel contacts, the outer movable conductors tilt and slide seriously when withstanding the large short-circuit current. This paper is aimed to investigate the contact behavior of the tilted contact. A new designed experimental setup to measure the minimum repulsion current and the contact resistance of the tilted contact is developed. Contact force and tilt angle can also be measured and adjusted. Based on the measured results and the impression marks of the tilted contact, it is concluded that the repulsion force and the contact resistance are increased seriously when the contact is tilted. During the contact tilting process, the contact type is changed from the line contact to the point contact and the contact center is offset to the edge of the movable contact. In addition, with the help of contact bridge model, it is also found that the contact type transition plays a dominant role on the increase of the repulsion force and contact resistance.

Human skin possesses complex deformation behaviour in multi-asperity contact. The deformation interaction under multi-asperity contact is prodigious in the skin contact model, must not be neglected. The phenomenon of non-uniform deformation has to be taken into account in order to properly and accurately develop a contact behaviour model of human skin. In this paper, one tribological model of contact behavior of human skin is developed with the concern of non-uniformation deformation behaviour under multi-asperity contact. Hertz, and DMT based theories were optimized for expatiating upon the tribological interaction between the human skin and the product surface. The model has been utilized to analyze the skin in multi-asperity contact. Results from FEM deformation simulation validated that deformation interaction between asperities is one of the important controlling factors which influences the deformation behaviour of skin in multi-asperity contact. Whilst asperities spacing was decreased, deformation interference was strongly noticed, and multi-asperity contact points were interfering adjacent deformation regime in irregular manner causing non-uniform deformation of skin. Furthermore, the total contact area tended to decrease when lambda spacing decreased.

This paper develops a new test method to investigate the factors that influence contact behavior between fully cracked concrete surfaces. This test considers 36 specimens of recycled aggregate concrete (RAC) and conventional concrete. The material variables were the aggregate type (natural coarse aggregate (NCA) and recycled coarse aggregate (RCA)), surface roughness, and curing time before splitting (7 d and 28 d). Experimental results indicated that by increasing the gap between cracked surfaces from 0 mm to 4 mm, the maximum shear load was reduced, by 16.9–79% for different cases. Curing time and aggregate type were strong factors that affected the crack propagation and the contact behavior. Furthermore, for conventional concrete, increasing the curing time of concrete increased the maximum shear load by 0.47 times to 2.86 times; for RAC with higher quality RCA in this test, the shear load decreased by 21.8–65% with the increasing of curing time. The surface roughness has a positive effect on shear load, especially when the surface roughness increases greatly in this study. Walraven’s model predicted stronger effect of interface roughness than shown by the results of these experiments, suggesting that these specimens had limited aggregate interlock. The results suggest that the Walraven model might be modified by an appropriate factor to better account for aggregate properties.

Modifying hydrogels with catechol functionality is a promising approach for improving their mechanical and interfacial properties in water, particularly in biological environments. However, the effects of this modification on hydrogels' contact behavior with soft tissues are not well-studied due to the complexity of hydrogels and lack of suitable techniques to probe this behavior. In addition, modification can alter the mechanical properties of hydrogels, resulting in consequences for adhesive strength as well. In this work, we report an investigation of the contact behavior of alginate hydrogels with and without conjugation of catechol functionality, aiming to elucidate the role of catechol modification on wet adhesion of alginates to a model tissue-like material, gelatin. To directly characterize this soft-on-soft contact, which has commonly been a challenge, we developed an indentation-based contact adhesion measurement using alginate hydrogel beads as the testing probe. We found that3% conjugation of catechol can significantly improve the adhesion of alginate to gelatin by half an order of magnitude, with this adhesion depending heavily on contact time and pH. In contrast, the reduced elastic modulus from modification resulted in lower adhesive strength on rigid substrates. These findings provide valuable insight into the effects of catechol modification of hydrogels, especially in their interaction with tissue-like soft substrates, as well as a simple method for the direct measurement of time- and pH-dependent hydrogel adhesion behavior underwater.

Concrete-filled steel tubular (CFT) columns and high-strength steel have been increasingly used in construction. However, the application of high-strength steel in CFT columns has not been permitted in many design codes. This paper reports an experimental investigation on the behavior of rectangular CFT beam-columns using high-strength steel. The influences of the in-fill concrete, eccentricity ratio and the width-to-thickness ratio on the resistance of the test columns are discussed. The contact behavior is studied using the finite element analysis. Chinese code DB 29-57 adopts the assumption that the concrete bears the axial load only, and the steel tube withstands the bending moment and part of the axial load. A new N-M interaction approach is developed based on the foresaid assumption to account for the plastic behavior of high-strength steel. The approach is verified by the experimental results and the available current design codes to be reasonably conservative, and it can be employed to design rectangular CFT beam-columns using high-strength steel.

The present study establishes a solving model for analyzing the interwire wear evolution of a wire rope strand subjected to cyclic bending load, in which the frictional contact and sliding between the wires are considered simultaneously. A wear experiment between the wires is conducted to study the wear behavior of the wires. Meanwhile, the proposed model is verified experimentally. Then the interwire wear and its effect on the contact behavior of the strand are analyzed. The results show that the interwire wear only happens on the side further from the curvature center of the bended strand than its neutral layer, and no wear happens when the wires are apart from each other or the interwire slippage is zero. As the wear process goes on, the wear region extends only along the normal direction of the core-wire contact line, and the maximum wear depth occurs at the middle position between the neutral layer and the furthest location from the curvature center. The contact pressure is distributed uniformly along the normal direction of contact line, but a significant stress concentration and local deformation happen at the position furthest from the curvature center of the bended strand.

In order to calculate analytically the contact status for rail grinding by abrasive belt with an axis deflection, as well as considering limitations of using Hertz contact theory for that, a numerical contact model (NCM) based on the local geometrical relationship between contact wheel and rail surface was developed. The effectiveness and accuracy of the proposed model have been validated by the corresponding finite element model (FEM) by comparing the contact boundary and contact stress distribution. Comparative cases at two typical grinding positions with different attitudes were involved, and the effects of applying axis deflection on contact behavior were investigated in detail. The results from NCM and FEM both agreed belt grinding with an axis deflection was able to enlarge the contact width of the belt and the total grinding force under the premise of ensuring required width of grinding trace on the rail. The model provides insights into understanding contact behavior under actual working conditions and gives a theoretical basis for future researches based on contact analysis.

In this paper we define two feature representations for grasping. These representations capture hand-object geometric relationships at the near-contact stage — before the fingers close around the object. Their benefits are: 1) They are stable under noise in both joint and pose variation. 2) They are largely hand and object agnostic, enabling direct comparison across different hand morphologies. 3) Their format makes them suitable for direct application of machine learning techniques developed for images.We validate the representations by: 1) Demonstrating that they can accurately predict the distribution of $\epsilon$-metric values generated by kinematic noise. I.e., they capture much of the information inherent in contact points and force vectors without the corresponding instabilities. 2) Training a binary grasp success classifier on a real-world data set consisting of 588 grasps.

A deterministic adhesive model for the contact between an elastic layered medium with surface roughness and a smooth elastic microsphere was developed on the basis of the Lennard–Jones surface force law. Through numerical simulations, the adhesive contact behavior of the layered medium with the measured three-dimensional (3D) surface topography was comparatively analyzed with that of the homogeneous medium. Furthermore, the contact characteristics of the layered medium with pre-assigned roughness parameters were investigated with the aid of a computer-generated technique for simulating surface roughness. Results showed that the pull-off force for the contact problem involving rough surfaces was influenced by the contact location, and the average value for the contact between an alumina (SiO2) microsphere and a diamond-like carbon/silicon (DLC/Si)-layered medium was smaller than that for the contact between a SiO2 microsphere and a Si homogeneous half-space. In addition, the effect of the diamond-like carbon (DLC) layer on reducing adhesion was smaller than that of the surface roughness. Finally, the average pull-off force for a DLC/Si-layered medium with computer-generated surface roughness rapidly decreased; however, it eventually became almost unchangeable with the increase in the root-mean-square (RMS) deviation.

The rough contact behavior of thin layers in the presence of interfacial friction is investigated by means of an innovative fundamental elastic solution. A certain degree of geometrical coupling between normal and tangential elastic field is found which, depending on the layer thickness, may lead to larger contact areas compared to the frictionless case. A specific focus has been devoted to investigate the behavior of the local quantities at the interface, in terms of both the displacement field and the gap distribution. We found that significant thinner gaps are predicted due to elastic coupling and frictional interactions, which may lead to larger hydraulic impedance of the contact interface. The latter result is specifically interesting for applications such as seals, where lubrication and leakage are the governing phenomena.

In this study, we established a performance analysis model of two types of ball continuously variable transmissions (CVT), conformal type and non-conformal type, by modifying the rheological model based on the elastohydrodynamic contact behavior for the existing toroidal traction drive to suit the working mechanism of ball CVTs. The main purpose of this study is, based on our analysis model, to identify the tendency of performance change according to design factors of ball CVTs and to compare the performance between two ball CVTs. Performance was analyzed in terms of torque capability, torque density and efficiency; factors affecting performance were selected through analysis of individual shapes and operating conditions. In this process, all design and performance factors were expressed as dimensionless quantities. It was confirmed that the conformal ball CVT has superior traction capability compared to the non-conformal ball CVT. In addition, by solving an example problem for ball CVT design and describing the process of designing optimal ball CVTs, it was proved that this study is applicable to real on-site problems.

The inter-wire contact effect on mechanical performances of a wire rope strand is studied with a new semi-analytical method. The mathematical model of the wire rope strand subjected to axial tension and torsion loads is established first, into which the wire deformation parameters considering the combining effects of Poisson's ratio and inter-wire contact are incorporated. Then this model is solved to achieve the mechanical performances for the wire rope with the semi-analytical method, in which the conjugate gradient method and fast Fourier transform are simultaneously used for calculating the contact deformation, contact pressure and inside stress of the wires caused by the inter-wire contact. The numerical results show that the proposed method is accurate and efficient in evaluating the inter-wire contact behavior. And the large axial load results in the large contact pressure and deformation. The contact deformation results in a reduction in the stiffness of the strand with a lay angle larger than 20°.

The behavior of an elastic layer in contact with a wavy rigid substrate is analyzed depending on layer thickness, substrate geometry, energy of adhesion, for given value of remote applied load or penetration. Two different slab configurations are considered: (i) a free layer with uniform pressure acting on the upper boundary, and (ii) a confined layer with uniform displacement assigned to the upper boundary. These two different geometries have been considered as exemplar cases which are of great relevance in a large number of applications of crucial importance as structural adhesives, pressure sensitive adhesives, coatings and protective adhesives. Our study shows that the layer thickness affects the contact behavior differently depending on the constraints configuration. In particular, reducing the thickness of the layer makes the latter more or less compliant depending on the considered configuration. Thus, the free layer becomes more sticky and, as the layer thickness is reduced, an increasingly large amount of external work needs to be provided to detach the layer from the substrate. On the contrary, the confined layer significantly stiffens by decreasing the layer thickness. This leads to an increase of the pull-off force for detachment accompanied by a decrease of the energy needed to bring the layer and substrate apart.

The contact resistance between Au/Mo and HgCdTe was investigated. The influence of thermal annealing on metal–semiconductor contact on short and middle-wavelength HgCdTe is also discussed in this paper. The specific contact resistance ρc (300 K, 80 K) of Au/Mo/HgCdTe was measured by the transmission line method. Good ohmic contacts can be formed with Au/Mo on long-wavelength infrared p-HgCdTe (x = 0.23) with a low specific contact resistivity of 3.78E−04 Ωcm2 measured at 80 K. For the mid-wavelength infrared p-HgCdTe (x = 0.30), the metal–semiconductor contact is ohmic, and the minimum specific contact resistivity of 7.40E−04 Ωcm2 is obtained after annealing at 120°C/10 min. The as-deposited contact between Au/Mo and the short-wavelength infrared HgCdTe (x = 0.47) shows non-ohmic behavior. After annealing at 120°C/5 min, although the contact behavior is still a Schottky contact, the contact resistance decreases. For the n-HgCdTe (x = 0.27), the metal–semiconductor contact is ohmic with a specific contact resistivity of 5.70E−04 Ωcm2 at 80 K.

The dynamics of piezoelectric stick–slip actuators is important for structural optimization and positioning control, yet challenging to model because of the potentially inconsistent stepping of these actuators in the forward and backward directions. This step inconsistency is found to be strongly associated with the inconsistent dynamic response of the piezoelectric feeding element arising from the contact behavior between the piezoelectric stack and its flexure-based preload mechanism. With this understanding, an improved dynamical model for the typical stick–slip actuator is established in which a non-smooth contact model is introduced. A prototype was built and tested, and with it the contact behavior was proved to cause the inconsistent responses of the piezoelectric feeding element, which in turn was verified to cause the inconsistent stepping characteristics of the stick–slip actuator. The simulated results obtained using the proposed model were in good agreement with the stepping curves of the slider in bi-directional motion under different working conditions. The proposed model provides a new perspective to explain and model the step inconsistency for stick–slip actuators in bi-directional motion, and has great potential in aiding the design and control of stick–slip actuators for bi-directional driving.

Tolerance analysis is an important approach for evaluating the accuracy and function of mechanical products. Research on tolerance analysis has mainly focused on the transfer and accumulation of geometric deviations during assembly, while the effects of contact behavior have not been considered in detail. Therefore, this paper presents a tolerance analysis approach to spur gears that takes into account the effects of contact behavior between mating tooth surfaces on transmission performance. Machining and assembly errors are represented based on the concept of skin model shapes. The contact behavior between mating tooth surfaces is calculated using the boundary element method (BEM) to perform tooth contact analysis (TCA). The proposed tolerance analysis approach is applied to a pair of spur gears as an example. The manner in which the transmission error, tooth contact pattern and contact pressure distribution are affected by machining and assembly errors is discussed. This research demonstrates the notable effects of contact behavior between mating tooth surfaces on transmission performance and provides a potential method for the tolerance analysis of other mechanisms.

The surface roughness induced by geometric irregularities (asperities) has substantial influence on the contact stiffness, which further affects the working performance and service life of mechanical equipment. In this study, an elastic–plastic contact law between a sinusoidal asperity and a rigid smooth flat is first studied, which is then applied on a statistical model to simulate the contact behavior of a pair of 18CrMo4 steel surfaces to investigate the influences of morphology parameters on the contact stiffness. The analysis shows that smaller shape ratios [Formula: see text] and larger wavelengths [Formula: see text] induce larger normal contact stiffness [Formula: see text] for surfaces with identical roughness, wherein the roughness is defined by the mean value of asperity heights [Formula: see text] and the standard deviation of asperity heights [Formula: see text]. The normal contact stiffness increases as [Formula: see text] decreases under the same loading conditions, while the normal contact stiffness increases as [Formula: see text] decreases for surfaces with a fixed [Formula: see text]. Besides, the normal pressure and normal contact stiffness derived from the proposed contact model are validated. The results demonstrate the potential of the proposed model in contact design due to its ability of establishing the relations between the normal contact stiffness and surface morphology parameters.

This paper presents an analysis for the PIM behavior on coaxial connector using statistical method. A novel PIM prediction method for coaxial connector considering random contact behavior is proposed and demonstrated. In this work, by using numerical approximation to reconstruct the micro contact force on contact surface based on Monte-Carlo and micro-measurement, the fluctuated PIM level on contact unit can be calculated based on the contact height distribution. In experiment, the tested PIM of coaxial connector was compared with predication. A good agreement between theoretical prediction and test proves the proposed PIM prediction method is efficient. It gives a confidence interval for the potential PIM levels on coaxial connector, which provides a new way to predict the fluctuated PIM behavior.

Extensive investigations have been carried out in the present paper to understand polymer gear performance, i.e., wear and contact behaviors. The experimental results and possible wear mechanisms for polymer gears run against themselves have been presented, especially the wear rate of the polymer gears under different running speeds and loads. The tested samples were made of three different materials (acetal, nylon, and polycarbonate (PC)) and the effects of two different manufacturing techniques were also investigated (i.e., machine-cut and injection-molded polymer gears). The polymer gear performances (wear and life) were recorded using a uniquely designed and built test rig for this purpose. The testing results have been compared with the existing literature for polymer fatigue and wear theory. Further extensive investigations have been carried out to understand the wear phenomena on tooth flank surface profile of these gears and the data obtained have been discussed.

Tethered Space Net (TSN) is one of the most promising solutions for active space debris removal. However, due to the flexibility, its deployment dynamics is complex and not completely understood. Moreover, the purpose of research on deployment dynamics is to draw some conclusions about preferable releasing conditions, which can make the net successfully wrap the target after contacting the target. Therefore, in this paper, a different way, the contact behavior based opinion, is proposed to analyze the deployment dynamics of TSN. Three critical contact parameters are put forward and influence of initial deployment conditions on these three parameters is investigated by simulation results. Finally, some conclusions for preferable releasing condition are given for TSN based on three critical contact parameters.

The primary objective of the paper is to observe and characterize the flow attributes of gravity-driven dry granular media in vertical cylindrical tubes. Particle packing fractions of ∼60% were the prime focus in the current study as the targeted application is the use of dense particulate media as heat transfer fluids (HTF). Experimental and computational studies were previously conducted to understand the influence of different geometrical parameters on the flow physics [1], [2]. Flowrate, particulate velocity, and packing fraction profiles were studied for different inertial numbers and preliminary observations were made about the corresponding regimes. However, flow characteristics that could have a direct implication on the heat transfer behavior remained unexplored. Hence, the current effort serves as an extension of our previous studies. The three-dimensional computer simulations were conducted by implementing the Discrete Element Method (DEM) for the Lagrangian modelling of particles. Hertz-Mindilin models were used for the soft-particle formulations of inter-particulate contacts. Since the particle contact behavior plays an important role in the conduction heat transfer of these regimes [3], the particle-wall residence times and near-wall packing fractions are studied in the current work. Particle fluctuations, which lead to flow agitation that effect heat transfer [4] are also studied. It was observed that the intermittent nature of the flow resulted in the propagation of wave-like structures in the upstream direction. The characteristics of this phenomenon and its possible influence on the heat transfer physics is also discussed.

For soft materials with Young's moduli below 100 kPa, quantifying mechanical and interfacial properties by small scale indentation is challenging because in addition to adhesion and elasticity, surface tension plays a critical role. Until now, microscale contact of very soft materials has only been studied by static experiments under zero external loading. Here we introduce a combination of the colloidal probe technique and confocal microscopy to characterize the force-indentation and force-contact radius relationships during microindentation of soft silicones. We confirm that the widespread Johnson-Kendall-Roberts theory must be extended to predict the mechanical contact for soft materials. Typically a liquid component is found within very soft materials. With a simple analytical model, we illustrate that accounting for this liquid surface tension can capture the contact behavior. Our results highlight the importance of considering liquid that is often associated with soft materials during small scale contact.

Oscillating microprobes avoid high stress and the sticking effect during contact between microprobe and measured surface. The full performance and application scope of oscillating microprobes can be explored and utilized once the reliable prediction of the microprobe contact behavior is understood. Here, an improved contact model considering adhesion forces, surface roughness, and viscoelastic damping for oscillating microprobes is presented and it is validated by exemplary measurements utilizing a uniaxially oscillating electrostatic microprobe. These results show that the nondestructive identification of material classes seems to be feasible by evaluating the phase shift between the sinusoidal signals of sensor and actuator, respectively.

As for the interesting new building blocks, the Ag nanowires (AgNWs) and single-walled carbon nanotubes (SWNTs) as the interesting new building blocks are viewed as the promising candidates for the next-generation interconnects due to their most remarkable electrical, thermal, optical, mechanical, and other properties. The axial nanowelding of head-to-head style and side-to-side style is relatively simulated with the molecular dynamics method. As for the head-to-head structural style, SWNTs will move toward the AgNWs and contact with the head of AgNWs. And, the part of the Ag nanowire may be subsequently encapsulated in SWNT with the core-filling Ag atom chain as the final atomic contact configuration during nanowelding, which is related to the nanowelding temperature. When the SWNTs and AgNWs are arranged by the side-to-side contact style, the SWNTs will move along the SWNT surface and may eventually catch up with the AgNW being neck and neck. Aiming at the final axial atomic configurations and the contact behavior during nanowelding process, the related dominant mechanism is revealed in this paper.

Mobile opportunistic networks (MONs) have been attracting increasing amounts of attention in recent years. Characterizing user contact behavior provides a baseline to evaluate the performance of these networks. However, because the contact distribution of nodes in MONs is conventionally modeled from a large-scale perspective, i.e., by aggregating all node pairs, the contact features of nodes with multiple social relationships are not reflected. Thus, it is not clear whether friends and strangers have similar or different contact behaviors. In this study, we aggregated the contact information of users from the real world, and discovered that two phenomena exist: (1) Most friends or strangers make contact at public hotspots, rather than private hotspots; (2) The distribution of intra-contact time (ICT) exhibits different decay factors---the ICT distribution of strangers is predominantly faster than that of friends.

Opportunistic networking differs from more conventional architectures by the lack of existing network infrastructure, which can cause intermittent connectivity or increased communication delay between nodes. From a message routing perspective,solving these problems require a different set of techniques thanthose used in more traditional network schemes. Forwarding algorithms in these scenarios aim to improve performance metrics such as message delivery ratio and message delay time, while trying to keep the number of message copies small. A common approach used for testing the performance of opportunistic protocols relies on existing opportunistic contact traces. These datasets are widely available on the Internet, and provide a convenient way of simulating realistic usage scenarios. As such, studying the contact patterns between nodes can lead to useful observations to take into account on future experiments. This paper presents the results of a study on four different datasets. First, we describe the main characteristics of each trace. Then, we propose a graphical representation of the contact behavior for each pair of nodes. The next step was to perform an analysis in terms of the distribution of connectivity among nodes, having found that the contacts follow a roughly lognormal distribution and noting that a small group of nodes is usually much more popular than the rest. We have also made a temporal analysis over the duration of each collection experiment. It was noticeable that individual nodes have very similar contact patterns over time, as well as revealing some cyclic variation over time (namely over weekends). Using dataset derived time-varying graph models, a significant performance decrease was achieved with simple remotion of few critical nodes, FEDER through the Competitiveness Factors Operational Programme - COMPETE FCT - Foundation for Science and Technology under the Project: FCOMP-01-FEDER-0124-022674

A finite element model has been developed for analyzing of the dynamic response of sandwich plates with partially damaged facesheet-to-core interface. The effect of intermittent dynamic contact between the fragments detached at the damaged interface is taken into account for simulation of sandwich plates' vibrations. Transient and forced dynamic responses of the sandwich plates damaged by debonding have been obtained by using the ABAQUS/Explicit code. The influence of the local strongly nonlinear contact behavior on the global dynamics of the sandwich plates is examined.

In the real world application of railguns, the launch efficiency is one of the most important parameters. This efficiency directly relates to the capacity of the electrical energy storage that is needed for the launch. In this study, the rail/armature contact behavior for two different armature technologies was compared. To this end, experiments using aluminum c-shaped armature and copper brush armature type projectiles were performed under same initial conditions. The c-shaped armature type showed a superior behavior with respect to electrical contact to the rails and in acceleration. A 300 g projectile with a c-shaped armature reached a velocity of 3100 m/s and an overall launch efficiency including the power supply of 41%. This is to be compared to 2500 m/s and 23% for the launching of a projectile using a brush armature., Presented at the 18th Electromagnetic Launch Technology Symposium October 24-28, 2016, at Wuhan University, Wuhan, China submitted to the IEEE Transactions on Plasma Physics Special Issue Electromagnetic Launch 2016

The use of bolted sleeve joints has been proposed for assembling pultruded glass fiber-reinforced polymer (GFRP) tubular profiles into space lattice shell structures. Such joint configurations may introduce a semi-rigid end condition and further affect the capacity of the connecting members in compression. Three batches of specimens assembled with pultruded GFRP profiles of different lengths and bolted sleeve joints at both ends were prepared and tested under static axial compression. A detailed three-dimensional finite element model considering bolt geometry, contact behavior, bolt pretension, initial geometric imperfection, and failure criterion for fiber-reinforced polymer (FRP) composites was developed and validated with experimental results showing good comparisons. It was found that the bolted sleeve joints exhibited semi-rigid behavior and that the failure modes and the effective length factor were dependent on member slenderness. The relationship between effective length factor and member ...

A theory of reciprocating contacts for linear viscoelastic materials is presented. Results are discussed for the case of a rigid sphere sinusoidally driven in sliding contact with a viscoelastic half-space. Depending on the size of the contact, the frequency and amplitude of the reciprocating motion, and on the relaxation time of the viscoelastic body, we establish that the contact behavior may range from the steady-state viscoelastic solution, in which traction forces always oppose the direction of the sliding rigid punch, to a more elaborate trend, never observed before, which is due to the strong interaction between different regions of the path covered during the reciprocating motion. Practical implications span a number of applications, ranging from seismic engineering to biotechnology., Comment: 8 pages, 5 figures, accepted for publication on Physical Review E, March 22, 2016

International audience; The first stage of the RTM process concerns the preforming of the part. During the preforming of multilayered reinforcements, frictions between the plies occur. An experimental device designed to analyze the ply/ply, ply/tool, and yarn/ yarn frictions has been built. Specific contact behavior for ply/ply friction is directly related to shocks taking place between overhanging yarns of each sample. Within the signal, two particular periods can be exhibited. This work shows for four different architecture woven fabrics that the two periods are directly related to the meso-architecture of the studied woven fabrics and more precisely to the characteristics of the fabric unit cell. The friction response appears to be very sensitive to the relative positioning and orientation of the samples. It can also lead to manufacturing defects such as unweaving or wrinkles. Up to now, finite element codes predicting the forming behavior of woven reinforcement fabrics do not take into account this friction coefficient evolution to model accurately the process. This point could therefore be addressed in future works on this topic with the view to optimize the multi-ply forming of composite parts.

Objective The purpose of this study was to investigate the in-vivo time-dependent contact behavior of tibiofemoral cartilage of human subjects during the first 300 s after applying a constant full body weight loading and determine whether there are differences in cartilage contact responses between the medial and lateral compartments. Design Six healthy knees were investigated in this study. Each knee joint was subjected to full body weight loading and the in-vivo positions of the knee were captured by two orthogonal fluoroscopes during the first 300 s after applying the load. Three-dimensional models of the knee were created from MR images and used to reproduce the in-vivo knee positions recorded by the fluoroscopes. The time-dependent contact behavior of the cartilage was represented using the peak cartilage contact deformation and the cartilage contact area as functions of time under the constant full body weight. Results Both medial and lateral compartments showed a rapid increase in contact deformation and contact area during the first 20 s of loading. After 50 s of loading, the peak contact deformation values were 10.5 ± 0.8% (medial) and 12.6 ± 3.4% (lateral), and the contact areas were 223.9 ± 14.8 mm[superscript 2] (medial) and 123.0 ± 22.8 mm[superscript 2] (lateral). Thereafter, the peak cartilage contact deformation and contact area remained relatively constant. The respective changing rates of cartilage contact deformation were 1.4 ± 0.9%/s (medial) and 3.1 ± 2.5%/s (lateral); and of contact areas were 40.6 ± 20.8 mm[superscript 2]/s (medial) and 24.0 ± 11.4 mm[superscript 2]/s (lateral), at the first second of loading. Beyond 50 s, both changing rates approached zero. Conclusions The peak cartilage contact deformation increased rapidly within the first 20 s of loading and remained relatively constant after ~50 s of loading. The time-dependent response of cartilage contact behavior under constant full body weight loading was significantly different in the medial and lateral tibiofemoral compartments, with greater peak cartilage contact deformation on the lateral side and greater contact area on the medial side. These data can provide insight into normal in-vivo cartilage function and provide guidelines for the improvement of ex-vivo cartilage experiments and the validation of computational models that simulate human knee joint contact., National Institutes of Health (U.S.) (R01 AR055612), National Institutes of Health (U.S.) (F32 AR056451), Massachusetts General Hospital. Dept. of Orthopaedic Surgery