任意轴对称弹性体吸附接触的广义Maugis模型

通过线性叠加Sneddon方法和Lowengrub-Sneddon方法分别给出的解, 得到了一个弹性半空间 轴对称混合边值问题的一般解,进而研究了两个一般轴对称弹性体的正向无摩擦吸附接触问 题. 考虑任意有效的表面形状(要求中心部分首先进入接触)和任意的表面吸附作用,推广 得到了广义Maugis模型. 该模型是一个半解析的模型,它可以分解成表面形状和表面吸附 作用的分别独立影响的两部分,以及一个关联变形和吸附作用的式子. 利用Dugdale模型近 似表面吸附作用,得到了具有任意有效的表面形状的广义M-D模型. 它在强吸附或软材料条 件下的极限形式是广义JKR模型,而在弱吸附或硬材料下的另一个极限形式是广义DMT模型.     

Sliding of a spherical indenter on a viscoelastic foundation with the forces of molecular attraction taken into account

The problem of sliding of a spherical indenter on a viscoelastic foundation is solved in a quasistatic formulation taking account the forces of adhesive attraction which are considered different at the entrance to and exit from the contact region due to changes in the surface properties during the interaction. It is found that the contact characteristics and the frictional force due to the imperfect elasticity of the foundation depend on the surface and bulk properties of the materials of the interacting bodies and the interaction conditions (load, velocity, etc.).     

Study of the anisotropy of sliding stops of mobile robots

The interaction of mini-robot contact elements with the surface is studied. The values of basic parameters necessary for successful operation of such elements are estimated. A procedure for calculating the value of anisotropic friction typical to adhesive material with haired structure is proposed. The results of this paper can be used to design robots intended for motion in bounded spaces, in particular, in narrow tubes.     

Modeling of friction at different scale levels

We construct a model for studying the common influence of the imperfect elasticity of actual bodies, the microgeometry of their surfaces, and their adhesive interaction on the contact characteristics (the contact pressure distribution, the region of actual contact) and on the sliding friction force. The model is based on the solution of a plane contact problem of sliding of a rigid body with a regular relief on the boundary of a viscoelastic foundation with surface molecular attraction in the gap between the surfaces taken into account. We analyze the influence of the surface microgeometry parameters at different scale levels on the character of the surface interaction (the saturated or discrete contact) and the friction force for different sliding velocities of the contacting bodies.     

Simulations of the spreading of a vesicle on a substrate surface mediated by receptor-ligand binding

A continuum model was introduced for the adhesion of vesicles to substrate surfaces. In the model, the vesicle membrane was assumed to be a closed shell with hyperelasticity. The vesicle cavity is filled with a liquid of fixed volume. The receptors on the membrane are mobile and initially uniformly distributed while the ligands on the substrate surface are fixed and also uniformly distributed. The formation of localized regions of tight binding between receptors and ligands, results in vesicle adhesion to the substrate surface. An adhesive model was introduced to describe the adhesive interaction between the receptors and the ligands. The growth of the adhesion area occurs via recruiting receptors from the non-adhered region through diffusion. Finite-element methods were used to solve the governing equations for the deformation of the vesicle and the receptor diffusion on the membrane surface. Effects of the membrane stiffness, the cohesive parameters and the receptor density on the adhesion kinetics of the vesicle were studied. In addition, the instability of the advancing front of the adhesion was also analyzed.     

A unified treatment of axisymmetric adhesive contact problems using the harmonic potential function method

A unified treatment of axisymmetric adhesive contact problems is provided using the harmonic potential function method for axisymmetric elasticity problems advanced by Green, Keer, Barber and others. The harmonic function adopted in the current analysis is the one that was introduced by Jin et al. (2008) to solve an external crack problem. It is demonstrated that the harmonic potential function method offers a simpler and more consistent way to treat non-adhesive and adhesive contact problems. By using this method and the principle of superposition, a general solution is derived for the adhesive contact problem involving an axisymmetric rigid punch of arbitrary shape and an adhesive interaction force distribution of any profile. This solution provides analytical expressions for all non-zero displacement and stress components on the contact surface, unlike existing ones. In addition, the newly derived solution is able to link existing solutions/models for axisymmetric non-adhesive and adhesive contact problems and to reveal the connections and differences among these solutions/models individually obtained using different methods at various times. Specifically, it is shown that Sneddon’s solution for the axisymmetric punch problem, Boussinesq’s solution for the flat-ended cylindrical punch problem, the Hertz solution for the spherical punch problem, the JKR model, the DMT model, the M-D model, and the M-D-n model can all be explicitly recovered by the current general solution.     

Adhesion-induced instabilities in elastic and elastic-plastic contacts during single and repetitive normal loading

Adhesive interaction in spherical contacts was modeled with the Lennard-Jones (L-J) potential. Elastic adhesive contact was analyzed by the equivalent system of a rigid sphere with reduced radius of curvature and a half-space of effective elastic modulus. The critical gap at the instant of abrupt surface contact (jump-in) and separation (jump-out) was determined from the deformed surface profile of the elastic half-space and geometrical relationships. A finite element model of a rigid sphere and an elastic-plastic half-space was used to examine elastic-plastic adhesive contact. Surface adhesion was modeled by nonlinear springs with a force-displacement relationship governed by the L-J potential. The evolution of the interfacial force and the central gap distance as well as the occurrence of jump-in and jump-out instabilities were investigated in terms of the Tabor parameter, plasticity parameter, and dimensionless maximum normal displacement. The force-displacement response due to several approach-retraction cycles was interpreted in the context of elastic and plastic shakedown behaviors using dimensionless parameters.     

壁虎粘附微观力学机制的仿生研究进展

本文针对壁虎粘附系统最小单元的真实形状, 类似于有限尺寸纳米薄膜的铲状纤维, 综述了对其微观粘附力学机制主要影响因素的多个研究, 主要考虑了有限尺寸纳米薄膜长度、厚度、撕脱角等对撕脱力的影响; 物体表面粗糙度以及环境湿度等对粘附的影响因素; 包括实验、理论及数值模拟的研究及结果比较. 最后给出仿生粘附力学方向仍然存在的主要科学问题及进一步的研究展望.     

Tabor数、粘着数与微尺度粘着弹性接触理论

微电子机械系统（ＭＥＭＳ）等领域的飞速发展,促使我们迈进了一个表面效应在许多现象 中占主导地位的研究领域．本文重点介绍在ＭＥＭＳ中经常遇到的微尺度粘着弹性接触的相关理论． 通过对两个无量纲数——Ｔａｂｏｒ数μ（以及其相应形式）和粘着数θ的分析,以及考虑它们对于粘 着力的影响,指出了粘着弹性接触理论中所隐含的尺度效应,随着特征尺度的减小,粘着弹性接触中 的表面效应愈加明显．     

高速干铣削钛合金时涂层硬质合金刀具磨损机理研究

采用CVD涂层硬质合金可转位立铣刀对钛合金(Ti-6Al-4V)进行了高速干铣削试验,采用扫描电子显微镜(SEM)观察刀具的磨损形貌,通过能谱分析(EDS)分析失效刀具表面的元素分布,并对刀具的主要磨损机理进行了分析.研究结果表明:使用涂层硬质合金刀具高速干铣削Ti-6Al-4V时,刀具的失效机理主要为磨粒磨损、粘结磨损、氧化磨损、扩散磨损和热-机械疲劳磨损的综合作用.刀具刚参与切削时,刀具后刀面会产生粘结和由于摩擦引起的擦伤,粘结层在断续冲击作用下的脱落过程还会造成后刀面涂层的剥落;随着刀具进一步的磨损,涂层剥落、粘结磨损及磨粒磨损伴随整个刀具失效过程,且还会出现氧化磨损、扩散磨损和疲劳裂纹等.切削速度越高,新产生的钛合金切屑就越容易燃烧,使刀具粘结、氧化和扩散以及热-机械疲劳等磨损加剧.     

45钢/PA66配副干滑动摩擦磨损性能研究

采用45钢销和尼龙PA66盘,运用正交试验法在MMW-1A万能摩擦磨损试验机上研究干滑动摩擦条件下速度、载荷和金属销表面粗糙R_a对45钢/PA66配副摩擦学性能的影响. 通过极差分析与方差分析发现:载荷、粗糙度对摩擦系数与磨损量有显著影响,而速度影响相对较小. 当载荷为50 N,速度为11.25 m/s,R_a为0.60 μm时,摩擦系数与磨损量最小. 基于正交试验的最优结果,开展控制变量试验,试验结果表明:载荷小于90 N时,PA66以黏着磨损为主;载荷为90 N时,PA66磨损形式为犁削磨损和黏着磨损. 载荷为140 N时,PA66的磨损形式为黏着磨损并伴有胶合现象的产生. R_a小于0.46 μm时,PA66以黏着磨损为主;R_a为0.46 μm时,PA66的磨损形式为黏着磨损和犁削磨损且在对偶金属销表面上形成连续的转移膜;R_a大于0.46 μm时,PA66以犁削磨损为主.      

Identifying traction–separation behavior of self-adhesive polymeric films from in situ digital images under T-peeling

In this paper procedures are developed to identify traction–separation curves from digital images of the deformed flexible films during peeling. T-peel tests were performed for self-adhesive polymeric films. High quality photographs of the deformed shape within and outside the zone of adhesive interaction were made in situ by the digital light microscope. The deformed line is approximated by a power series with coefficients computed by minimizing a least squares functional. Two approaches to identify the traction–separation curve for the given deformation line are proposed. The first one is based on the energy integral of the non-linear theory of rods and allows the direct evaluation of the adhesion force potential. The second one utilizes the complementary energy type variational equation and the Ritz method to compute the adhesion force. The accuracy of both approaches is analyzed with respect to different approximations for the deformed line and the force of interaction. The obtained traction vs. axial coordinate and the traction–separation curves provide several properties of the adhesive system including the maximum adhesion force, the length of the adhesive zone and the equilibrium position, where the adhesive force is zero while the separation is positive.     

粘着摩擦系数的分形几何研究

计及作用于接触斑点上的切向力，通过比较作用于接触斑点上的法向弹性载荷与法向塑性载荷，确定了区分弹性接触与塑性接触区域的临界接触斑点面积．总的粘着摩擦系数被表示为弹性接触区与塑性接触区的粘着摩擦系数的组合．假设屈服压力及局部粘着摩擦系数不依赖于接触斑点且等于塑性接触区中的平均值，则总的粘着摩擦系数可用简单的表达式描述．分形几何参数及归一接触面积对于粘着摩擦系数的效应已通过算例表明，研究中，分别考虑了忽略与计及接触斑点的微粒间的相互作用，两种情况的结果完全不同．     

EXPERIMENTAL INVESTIGATIONS OF STRENGTH,TOUGHNESS AND FAILURE MECHANISM OF THE METAL/EPOXY/METAL ADHESIVE SYSTEM

本文系统地开展了金属/环氧/金属胶结体系的强韧机理及失效行为实验研究,针对铝合金圆棒与铝合金圆棒通过环氧树脂胶层的各种斜截面方向粘结,实验观测了该体系的拉伸变形和失效行为,测量了界面失效载荷对胶层厚度和粘结界面倾斜角的依赖关系;通过引入胶结界面平均正应力、平均剪应力、平均正应变、平均剪应变等概念,可对界面失效强度进行测量,获得界面强度与界面粘结角度以及胶层厚度的关系,进而获得了铝合金/环氧胶层/铝合金体系的强度失效面以及胶结界面的断裂能和胶结体系的能量释放率.上述研究结果为深入认识金属胶结体系的强韧性能和失效机制提供了科学依据,对金属胶结体系的优化设计和性能评判具有重要指导意义.研究结果表明,铝合金/环氧胶层/铝合金体系的拉伸失效总体呈弹脆性破坏特征,失效表现为胶层粘结界面的断裂,失效强度和界面断裂能在胶层厚度为百微米量级时表现出强烈的尺度效应：界面粘结强度随着胶层厚度的减小而显著增大,临界状态的平均正应力和平均剪应力在强度破坏面上近似位于同一圆上,界面断裂能随着胶层厚度的减小而显著减小;与此同时,界面失效强度和界面断裂能也密切依赖于界面粘结角度.     

An improved terramechanics model for a robotic soil surface sampler

Robotic systems have been developed and deployed for sample collection and geotechnical measurements of soil characteristics. A custom scoop-type robotic soil sampler has been designed and built for sampling operations. An earlier terramechanics model for scoop samplers proposed by Mori et al. is limited to describing the interaction forces in loose sands. This paper proposes an extended model which captures the interaction of a scoop-type sampler with a wider range of soils, including cohesive and adhesive mediums, and accounts for the effects of surcharge. The proposed model was compared to the Mori model in both simulation and laboratory experiments. The forces predicted by each model agree closely for loose sand, but differ in cohesive and adhesive mediums. The proposed model was experimentally tested on dry sand and on centrifuged tailings, a cohesive and adhesive soil. In both cases, the proposed model showed close agreement between measured and predicted forces.     

Mechanics of adhesive contact at the nanoscale: The effect of surface stress

At small length scales, the adhesion and surface effect are of great significance, both of which play important roles in the contact between two elastic solids. In this study, the classical Johnson–Kendall–Roberts (JKR) adhesive contact theory is generalized to the nanoscale at which the surface effect is considered. The influence of the surface stress on the JKR adhesive contact is investigated by employing the non-classical Boussinesq fundamental solutions. It is found that, compared with the classical theory, the pull-off force increases while the critical contact radius decreases as a result of the surface effect. Numerical results show that a relative error of 10% can be introduced in the pull-off force when the indenter radius is less than 20 nm. A detailed theoretical analysis of this interesting phenomenon is presented based on dimensional analysis, and two scaling laws for the adhesive contact at the nanoscale are constructed. These two new scaling laws reveal that the pull-off force is relevant to the elastic properties of the bulk materials, which is different from the classical adhesive contact theory. The present work is promising for the engineering applications in micro-electro-mechanical systems (MEMS) and nano-intelligent devices.     

Modeling of the random packing of a loose layer of polydisperse spherical particles

A method for calculating the loose packing structure of polydisperse spherical particles with a predetermined size distribution function is proposed. The coordinates of the particle centers in the loose layer are determined as the result of random fall of single spheres on a substrate under the action of gravity, assuming the inelastic collision of the spheres and considering the force of their adhesive interaction, and also assuming that the motion of one sphere on the surface of the other is pure slip. Numerical simulation is used to obtain the pattern of arrangement of polydisperse spherical particles in the loose powder layer, whose porosity depends on the particle size distribution function. The results are compared with experimental data.     

电解质吸附对水基带电表面黏着的影响

为研究界面黏着,利用表面力仪在高离子强度电解质水溶液中测量负电云母表面之间的法向力.在纯水中,因范德华吸引,两表面跳跃至直接接触(间距0?),分离两表面时测得界面黏着力为-46.7 m N/m.在0.1 mol/L K₂SO₄中,因K₊离子牢固吸附于云母,表面间距稳定于5?,黏着力仅-2.9 m N/m;在0.1 mol/L Ca(NO₃)₂中,云母表面吸附的Ca₂⁺离子产生显著短程水合排斥,但在较低载荷下解吸附,导致两表面直接接触,黏着力高达-40.7 m N/m.加入Ca(OH)₂于0.1 mol/L K₂SO₄仅产生微弱短程排斥,黏着状态几乎与纯K₂SO₄水溶液中相同.聚电解质PCE从0.1 mol/L K₂SO₄中吸附于云母表面且诱导远程空间位阻排斥,但在中等载荷下解吸附,导...