Contact Mechanism of the Ag-doped Trimolybdate Nanowire as An Antimicrobial Agent

Antibacterial Ag-agents are intensively applied as broad spectrum, high-stability, high-efficiency and high-safety inorganic antibacterial agents. We have developed a new kind of antibacterial Ag-agent, namely Ag_2-x(NH_4)xMo_3O_(10) ·3H_2O nanowires(NWs). Carrying Ag atoms in the lattice and Ag-rich nanoparticles on the surface, the Ag-doped NWs show strong antibacterial effects for a variety of bacteria including E.coli, Staphylococcus aureus, Candida albicans and Aspergil lus niger. By performing systematic comparison experiments, we have proven that the main antibacterial effects are neither resulted from the tiny amount of Ag+ions released from the Ag-doped NWs in aqueous solutions, nor resulted from Ag-rich nanoparticles of fragments of the NWs when they are slowly dissolved in the Martin broth. Instead, the effects are mainly resulted from a contact mechanism, under which, the Ag-doped NWs need to be physically in contact with the bacteria to be eliminated. This is a novel phenomenon observed in the interactions between nanomaterials and live cells, which is worthy of further investigation at the molecular scale. As the Ag-doped NWs are not dissolved in pure water or weak acids, one may find practical antibacterial applications in textile industry and food storage industry for these unique nanomaterials.

Friction contact mechanisms of layered surface

In this paper,we firstly review the carbon layered surface prepared with electron cyclotron resonance (ECR) plasma sputtering. Secondly,the friction behavior of carbon layered surface under pin-on-disk testing is described. Furthermore,the contact stress evolution processes of layered surface with and without transfer layer during wear are given for understanding the contact mechanisms. Finally,a three-dimension (3D) local yield map of layered surface is introduced,which is useful to predict the possible contact mechanisms.

Immunology Mechanism of CD4^＋ CD25^ T Regulatory Cells Acting on Effector T Cells

Objective:To detect the inhibiting co-stimulating molecule CTLA4 and cytokines secreted by Treg cells, and explore the immunology mechanism of T regulatory cells acting on effector T cells in co-cultured system(CCS) and separating-cultured system(SCS). Methods: Detecting the percentage of CTLA4 and CD28 expressed on the Treg cells and effector T cells, and then adding Treg cells to mixed lymphocyte reaction(MLR) system in CCS and TransWell Millicell-PCF SCS, at the same time, adding or not adding anti-IL-10 or anti-TGF-β1 to the reacting systems, examining the inhibitory capacity of Treg cells exerting on the MLR. Results: Compared with effector T cells, Treg cells expressed higher level CTLA4 and secreted much more IL-10 and TGF-β1(P<0.01). The inhibitory capacity of Treg cells co-cultured with effector T cells is much stronger than that in separating cultured group(P<0.01). Moreover, the inhibiting rate of Treg cells exerting on effector T cells through secreting IL-10 was more powerful than that through secreting TGF-β1(P<0.01). Conclusion: Both cell-to-cell contact and cytokines secretion mechanisms are involved in CD4 +CD25 + Treg cells operating function. However, the former is more important. Intrestingly, we for the first time point found that IL-10 plays more powerful roles than TGF-β1 in the cytokines secretion mechanism.

Modelling rapid non-destructive test using light weight deflectometer on granular soils across different degrees of saturation

This study introduces an advanced finite element model for the light weight deflectometer(LWD),which integrates contact mechanics with fully coupled models.By simulating LWD tests on granular soils at various saturation levels,the model accurately reflects the dependence of the LWD modulus on dry density,water content,and effective stress.This model addresses and overcomes the limitations of previous finite element models for this specific problem.Simultaneously,this research presents the first experimentally validated fully coupled contact impact model.Furthermore,the research provides a comparative assessment of elastoplastic and nonlinear elastic models and contrasts an enriched node-tosegment method(developed in this study)with the more precise mortar technique for contact mechanics.These comparisons reveal unique advantages and challenges for each method.Moreover,the study underscores the importance of careful application of the LWD modulus,emphasising the need for sophisticated tools to interpret soil behaviour accurately.

Finite Element Analysis of the Contact Mechanics of Ceramic-on-Ceramic Hip Resurfacing Prostheses

Ceramics are good alternative to metal as bearing couple materials because of their better wear resistance. A Finite Element(FE) study was performed to investigate the contact mechanics and stress distribution of Ceramic-on-Ceramic (COC) hip resurfacingprostheses. It was focused in particular on a parametric study to examine the effects of radial clearance, loading,alumina coating on the implants, bone quality, and fixation of cup-bone interface. It was found that a reduction in the radialclearance had the most significant effect on the predicted contact pressure distribution among all of the parameters considered inthis study. It was determined that there was a significant influence of non-metallic materials, such as the bone underneath thebearing components, on the predicted contact mechanics. Stress shielding within the bone tissue was found to be a major concernwhen regarding the use of ceramic as an alternative to metallic resurfacing prostheses. Therefore, using alumina implantswith a metal backing was found to be the best design for ceramic resurfacing prostheses in this study. The loading, bone quality,and acetabular cup fixation conditions were found to have only minor effects on the predicted contact pressure distribution alongthe bearing surfaces.

Determination of the Normal Contact Stiffness and Integration Time Step for the Finite Element Modeling of Bristle-Surface Interaction

In finite element modeling of impact,it is necessary to define appropriate values of the normal contact stiffness,Kn,and the Integration Time Step(ITS).Because impacts are usually of very short duration,very small ITSs are required.Moreover,the selection of a suitable value of Kn is a critical issue,as the impact behavior depends dramatically on this parameter.In this work,a number of experimental tests and finite element analyses have been performed in order to obtain an appropriate value of Kn for the interaction between a bristle of a gutter brush for road sweeping and a concrete surface.Furthermore,a suitable ITS is determined.The experiments consist of releasing a steel bristle that is placed vertically at a certain distance from a concrete surface and tracking the impact.Similarly,in the finite element analyses,a beam is modeled in free fall and impacting a surface;contact and target elements are attached to the beam and the surface,respectively.The results of the experiments and the modeling are integrated through the principle of conservation of energy,the principle of linear impulse and momentum,and Newton’s second law.The results demonstrate that,for the case studied,Kn and the impact time tend to be independent of the velocity just before impact and that Kn has a very large variation,as concrete is a composite material with a rough surface.Also,the ratio between the largest height of the bristle after impact and the initial height tends to be constant.

Theoretical analysis of thermoviscoelastic contact between friction lining and wire rope in mine friction hoists

Serious accidents of mine hoists caused by high-speed sliding between friction lining and wire rope are often seen in coal mines.In order to solve this problem,we analyzed the contact characteristics between friction lining and wire rope.Then we carried out a dynamic mechanical analysis(DMA) to explain the change in mechanical properties of the friction lining as function of temperature and load frequency and found that temperature has a stronger effect on the mechanical properties than the frequency.We used multiple regression analysis to obtain the thermoviscoelastic constitutive relations of the friction lining.As well we derived the analytic solution for the thermoviscoelastic contact radius and pressure by combining the theory of viscoelastic contact mechanics with thermoviscoelastic constitutive relations.

Sedimentation of short cylindrical pollutants with mechanical contacts

Lattice Boltzmann method and elastic particle collision model were used to investigate the sedimentation of short cylindrical pollutant particles with mechanical contacts for varying bulk number density ε and terminal Reynolds number ReT. The corresponding experiments were performed as a comparison. The clusters of pollutant particles with an inverted “T” structure were observed, the pollutant particles for high ε and large ReT scattered wider than that for low ε and small ReT. The sedimentation velocities increased suddenly at the initial stage, then decreased drastically, after that swayed around and approached to a steady value. The time to steady state did not depend on ε and ReT. The effect of particle interactions was to hinder the average sedimentation velocity, and hindrance was directly proportional to ε. The orientation distributions of pollutant particles depended on ReT and ε, especially on the former. Both the standard deviations of vertical and horizontal velocity, the former was larger than the latter, were nearly independent on ε and ReT.

Exact analysis of the orientation-adjusted adhesive full stick contact of layered structures with the asymmetric bipolar coordinates

The adhesion failure has become one dominant factor in determining the reliability and service life of miniaturized devices subject to loadings with arbitrary orientations.This article establishes an adhesive full stick contact model between an elastic half-space and a rigid cylinder loaded in any direction.Using the Papkovich-Neuber functions,the Fourier integral transform,and the asymmetric bipolar coordinates,the exact solution is obtained.Unlike the Johnson-Kendall-Roberts(JKR)model,the present adhesive contact model takes into account the effects of the load direction as well as the coupling of the normal and tangential contact stresses.Besides,it considers the full stick contact which has large values of the friction coefficient between contacting surfaces,contrary to the frictionless contact supposed in the JKR model.The result shows that suitable angles can be found,which makes the contact surfaces difficult to be peeled off or easy to be pressed into.

On the contact width in generalized plain strain JKR model for isotropic solids

Adhesive contact model between an elastic cylinder and an elastic half space is studied in the present paper, in which an external pulling force is acted on the above cylinder with an arbitrary direction and the contact width is assumed to be asymmetric with respect to the structure. Solutions to the asymmetric model are obtained and the effect of the asymmetric contact width on the whole pulling process is mainly discussed. It is found that the smaller the absolute value of Dundurs＇ parameter 13 or the larger the pulling angle O, the more reasonable the symmetric model would be to approximate the asymmetric one.

Approximate Tangent Plane Method for Calculating Surface Deformation in Elastic Contact Problems

A flew numerical method for constructing a pressure distribution to calculate surface elastic deformationcaused by normal contact pressure is developed in this paper. The pressure distribution over one of nonequidistantrectangles is fitted by an approximate tangent plane(ATP), which is formed by five pressure samples. Because thepressure distribution could be expressed as an one order linear polynomial, the iterative expression of elasticdeformation deduced by this method is simple, and the numerical accuracy is higher.

Contact radius of stamps in reversible adhesion

A mechanics model is developed for the contact radius of stamps with pyramid tips in transfer printing.This is important to the realization of reversible control of adhesion,which has many important applications,such as climbing robots,medical tapes,and transfer printing of electronics.The contact radius is shown to scale linearly with the work of adhesion between the stamp and the contacting surface,and inversely with the plane-strain modulus of the stamp. It also depends on the cone angle and tip radius of the stamp,but is essentially independent of details of the tip geometry.

A numerical model to simulate the transient frictional viscoelastic sliding contact

Sliding motion has always been one of the major concerns when it comes to the analysis of viscoelastic contact problems.A new model simulating the transient sliding contact of smooth viscoelastic surfaces is developed in this paper.By taking the dry contact friction and the coupling between shear tractions and normal pressure into account,the effect of the early partial slip period,which is often neglected in the study of viscoelastic sliding contact problems,is investigated numerically.Compared with solutions based on the frictionless assumption,the steady-state pressure profile is found to be slightly different under the effect of the partial slip regime,including a lower peak pressure and the shift of the contacting region in the direction opposite to the sliding motion.Furthermore,the time required for the viscoelastic contact to reach its steady state is delayed owing to the partial slip period preceding the global sliding motion.

Adhesive Contact of Elastic Solids with Self-Affine Fractal Rough Surfaces

The elastic adhesive contact of self-affine fractal rough surfaces against a rigid flat is simulated using the finite element method. An array of nonlinear springs, of which the force-separation law obeys the Lennard–Jones potential, is introduced to account for the interfacial adhesion. For fractal rough surfaces, the interfacial interaction is generally attractive for large mean gaps, but turns repulsive as the gap continuously shrinks. The interfacial interactions at the turning point corresponding to the spontaneous contact are shown for various surfaces. For relatively smooth surfaces, the probability density distributions of repulsion and attraction are nearly symmetric. However, for rougher surfaces, the simulation results suggest a uniform distribution for attraction but a monotonously decreasing distribution with a long tail for repulsion. The pull-off force rises with increasing ratio of the work of adhesion to the equilibrium distance, whereas decreases for solids with a higher elastic modulus and a larger surface roughness. The current study will be helpful for understanding the adhesion of various types of rough solids.

Penetration depth for yaw-inducing bursting layer impacted by projectile

In order to accurately estimate the anti-penetration capacity of yaw-inducing bursting layer with irregular barriers on surface impacted by projectile,the theoretical model of attack angle and angular velocity for projectile impacting on irregular barrier was achieved according to the macroscopic relation of contact force versus contact time,in which the main factors such as the relative geometrical characteristics of projectile and irregular barrier,material property and impact velocity of projectile influencing on yaw-inducing effectiveness were considered.On the basis of considering synthetically the influences of attack angle,impact velocity,impact angle of projectile and uncontrolled free surface of target,the theoretical formulation of penetration depth for bursting layer with irregular barriers on surface impacted by projectile was presented by expressing the stress of an optional point on the nose of projectile according to the relation of stress versus velocity.The theoretical results indicate that in the case of oblique impact embodying effect of attack angle,the penetration depth is reduced with the increase of impact angle,attack angle or angular velocity,and penetration trajectory is also deflected obviously.The effectiveness of angular velocity influencing on penetration depth is increased with impact velocity increasing.The theoretical results are in good agreement with test data for low impact velocity.

Modeling of Mechanical Behavior of Fractal Rock Joint

The present study shows that naturally developed fracture surfaces in rocks display the properties of self-affine fractals. Surface roughness can be quantitatively characterized by fractal dimension D and the intercept A on the log-log plot of variance: the former describes the irregularity and the later is statistically analogues to the slopes of asperities. In order to confirm the effects of these fractalparameters on the properties and mechanical behavior of rock joints, which have been observed in experiments under both normal andshear loadings, a theoretic model of rock joint is proposed on the basis of contact mechanics. The shape of asperity at contact is assumed to have a sinusoidal form in its representative scale r, with fractal dimension D and the intercept A. The model considers different local contact mechanisms, such as elastic deformation, frictional sliding and tensile fracture of the asperity. The empirical evolution law of surface damage developed in experiment is implemented into the model to up-date geometry of asperity in loading history. The effects of surface roughness characterized by D, A and re on normal and shear deformation of rock joint have been elaborated.

First mushroom-shaped adhesive microstructure:A review

This letter reviews the adhesive and frictional properties of the first mushroom-shaped adhesive microstructure （MSAMS）, which has come a long way from inspiration by the attachment devices evolved in beetles to a large-scale industrial production. It was shown to have an that about twice higher pull-off force compared to a smooth control made from the same material measured on smooth substrates. Pull-off forces measured underwater are even higher than those in air. Moreover, it retained adhesive performance over thousands of attachment cycles and initial adhesive capability could be recovered by washing after being contaminated. In shearing, MSAMS exhibits reduced and stabilized friction in comparison with a smooth control, which demonstrated pronounced stick-slip motion, and shows zero pull-off force in a sheared state, allowing the adhesion to be switched on and off. The presence of a fluid in the contact zone showed adhesion enhancement on both smooth and rough substrates. All these features lead us to conclude that MSAMS may have practical potential in a variety of applications.

Experimental investigation on surface deformation of soft half plane indented by rigid wedge

In this work, the mechanical behavior of a block of soft material subject to large deformation from a series of wedge-shaped indenters is evaluated. Data fields acquired from digital image correlation （DIC） are compared with the existing theoretical models. The slope angles of the wedges vary from 5° to 73.5°, and the minimum measure- ment uncertainties of the DIC system are established in advance to define the accuracy. It is concluded that the assumptions underpinning the analytical theory make it difficult to characterize large deformation of soft materials during contact. The strain fields are also obtained from the measured displacement field and verify the previously postulated existence of two deformation sectors, namely, a so-called shrinkage sector symmetric to the loading axis and an expansion sector, which become smaller with the increasing load and decreasing wedge angle.

Pressure-Driven Contact Mechanics Evolution of Cathode Interfaces in Lithium Batteries

The interfacial instability due to periodic volume expansion of electrodes in the charging and discharging process directly affects the contact performance and interface impedance between the electrodes and the solid-state electrolyte(SSE).The existing work has studied the local stress state behavior on a single spatial scale or only focused on the interfacial influence of electrochemical characteristics at a specific time.In this paper,a semi-analytical method-based chemoelastic contact model was developed to study the evolution behavior of the cathode/SSE interface,and the stress and displacement fields subjected to contact forces were calculated by means of the discrete convolution-fast Fourier transform algorithm.The interface evolution subjected to mechanical pressure was analyzed for the local influence of the stress at one position at a specified time on the contact behavior at the present time and position,and the global influence of those at other positions at a later time.Based on this model,the mechanical-chemical coupling effect of lithium intercalation on interface stability was quantitatively studied,and the mechanism of enhancing interfacial contact stability by mechanical load was further explored.The results show that a larger current causes the contact toward the center,while a larger mechanical force leads to a smaller pressure peak.With the increase in mechanical force,the compressive stress in the contact area decreases significantly,while the tensile stress outside the contact area increases slightly.Based on the model results,a transition map was constructed with bonder equation(P/I=25MPa·cm^(2)/mA)to define whether an interfacial contact is stable or not.Quantitatively,applying a mechanical pressure P/I>25MPa·cm^(2)/mA can maintain a stable interfacial contact between the SSE and the cathode.The proposed model provides a theoretical basis in the chemomechanics view for the understanding of using pressure to suppress diffusion-induced contact instability in lithium batteries.

Mechanical Analysis of Interface in Coating Structure under Conical Concave Indenter with FEM

The evaluation of mechanical properties of coating structures has always been a very important topic in the fields of mechanics, materials, and machinery. The traditional evaluation methods are easy to produce deviation, because the ratio of coating thickness to substrate thickness is too small. Therefore, accurate analysis and calculation is particularly important. Indentation technology is an important means of coating structure analysis and measurement, the basis of standardized application and analysis of coating structure, and a classical method for accurate analysis and calculation of coating structure. The finite element method is a very good means to analyze and study this kind of problems because of its applicability. Based on the finite element method, this paper analyzes and studies the interface connection form, substrate, and local delamination effects of the indentation behavior of the coating structure under the conical concave indenter. In this paper, the finite element method, which is more convenient for analysis and calculation, is used to analyze the influence of interface connection form, substrate, and local delamination on the coating structure. The results of force displacement, interface normal stress, and interface shear stress are analyzed in detail, and the effects of the three effects on the coating structure are proved. The significance of this study is reflected in: based on the analysis of the three effects of interface connection form, substrate, and local delamination, the mechanical properties of the coating structure are more in-depth, which provides some reference for mechanical engineers to design and test the coating structure.