Resolving a controversy about adhesion in sliding contacts

Sphere and cylinder contact mechanics during slip

Using molecular dynamics (MD) we study the dependency of the contact mechanics on the sliding speed when an elastically soft slab (block) is sliding on a rigid substrate with a ${\rm sin} (q_0 x)$ surface height profile. The atoms on the block interact with the substrate atoms by Lennard-Jones potentials. We consider contacts with and without adhesion. We found that the contact area and the friction force are nearly velocity independent for small velocities ($v < 0.25 \ {\rm m/s}$) in spite of the fact that the shear stress in the contact area is rather non-uniform. For the case of no adhesion…

Friction and Adhesion mediated by supramolecular host-guest complexes

The adhesive and frictional response of an AFM tip connected to a substrate through supramolecular host-guest complexes is investigated by dynamic Monte Carlo simulations. The variation of the pull-off force with the unloading rate recently observed in experiments is here unraveled by evidencing a simultaneous (progressive) break of the bonds at fast (slow) rates. The model reveals the origin of the observed plateaus in the retraction force as a function of tip-surface distance, showing that they ensue from the tip geometrical features. In lateral sliding, the model exhibits a wide range of dy…

软接触中的粘附在超过临界剪切位移后达到最小值

Adhesion in soft contacts is minimum beyond a critical shear displacement

研究弹性体球体与刚性板软接触的粘附力，发现预剪切会显著降低脱粘力，当剪切位移超过临界值（约10%整体滑动位移）时，脱粘力降至初始值的10%-15%并保持恒定。

纳米级的液体如何影响粘附力？

How do liquids confined at the nanoscale influence adhesion?

液体在粘附和滑动摩擦中起重要作用。它们在人体内起润滑剂的作用，特别是在关节中。然而，在许多生物附着系统中，它们像粘合剂一样起作用，例如促进昆虫在天花板或垂直墙壁上移动。在这里，我们使用分子动力学来研究如何限制在纳米级的液体影响固体之间的粘附与光滑和粗糙的表面。我们表明，单层的液体可能会强烈影响的粘附。

含运动大肠杆菌的液滴表现出降低的粘附和异常润湿行为

Motile Escherichia coli-laden Droplets Exhibit Reduced Adhesion and Anomalous Wetting Behavior

研究通过实验发现，含活大肠杆菌的液滴比含死菌的液滴表面粘附力更低，且浓度越高粘附力越小，原因是活菌的鞭毛运动抵抗蒸发驱动流，产生集体动力学，促进接触线解钉，从而降低粘附。

随机粗糙表面弹性固体间的毛细粘附

Capillary adhesion between elastic solids with randomly rough surfaces

本文研究了两个具有随机粗糙表面的弹性固体之间的接触面积和粘附功与相对湿度的关系。假设表面是亲水的，并且在固体之间的界面处形成毛细桥。对于具有相对光滑表面的弹性硬固体，当刚好有足够的液体填充固体之间的界面空间时，实际接触面积以及因此滑动摩擦最大，这通常发生在$d_{\rm K} \approx 3 h_{\rm rms}$中，其中$d_{\rm K}$是毛细管桥的高度，而$h_{\rm rms}$是（组合）表面粗糙度轮廓的均方根粗糙度。对于弹性软固体，实际接触面积在非常低的湿度下最大（即，小$d_{\rm K}$），其中毛细管桥能够将固体拉至几乎完全接触。在这两种情况下，当$d_{\rm K} >> h_{\rm rms}$对应于高相对湿度时，粘附功最大（并且等于$2γ{\rm cos}θ$，其中$γ$是液体表面张力，$θ$是液-固接触角）。

滑动还是滚动？表征单颗粒接触

Sliding or Rolling? Characterizing single-particle contacts

本文利用胶体探针原子力显微镜同步测量微粒接触中的法向、切向力及滑动、滚动，揭示粗糙度与黏附对滚动摩擦和流变行为的微观影响。

Torsional Instabilities in the Delamination of Soft Adhesives

Soft adhesive contacts are ubiquitous in nature and are increasingly used in synthetic systems, such as flexible electronics and soft robots, due to their advantages over traditional joining techniques. While methods to study the failure of adhesives typically apply tensile loads to the adhesive joint, less is known about the performance of soft adhesives under shear and torsion, which may become important in engineering applications. A major challenge that has hindered the characterization of shear/torsion-induced delamination is imposed by the fact that, even after delamination, contact with…

基于混合单元法的多铁涂层摩擦粘着接触

Frictional Adhesive Contact of Multiferroic Coatings Based on the Hybrid Element Method

该研究采用 HEM、MD 模型、AD-CGM 与 DC-FFT 分析刚性绝缘球滑动时多铁涂层的摩擦粘着接触，揭示涂层厚度及摩擦对力电磁场和前后缘对称性的影响。

粘弹性材料的粘着接触力学

Adhesive contact mechanics of viscoelastic materials

本研究提出稳态滑动下粘弹性材料粗糙粘着接触理论，揭示粘弹性与粘着相互作用对接触面积、拉脱力及摩擦的影响规律，发现接触边缘能量释放率的非单调趋势，结果获实验支持。

On the presence of a critical detachment angle in gecko spatula peeling -- A numerical investigation using an adhesive friction model

A continuum-based computational contact model is employed to study coupled adhesion and friction in gecko spatulae. Nonlinear finite element analysis is carried out to simulate spatula peeling from a rigid substrate. It is shown that the "frictional adhesion" behavior, until now only observed from seta to toe levels, is also present at the spatula level. It is shown that for sufficiently small spatula pad thickness, the spatula detaches at a constant angle known as the critical detachment angle irrespective of the peeling and shaft angles. The spatula reaches the same energy states at the jump…

On mixed-mode fracture mechanics models for contact area reduction under shear load in soft materials

The fundamental problem of friction in the presence of macroscopic adhesion, as in soft bodies, is receiving interest from many experimentalists. Since the first fracture mechanics `purely brittle' model of Savkoor and Briggs, models have been proposed where the mixed mode toughness is interpreted with phenomenological fitting coefficients introducing weaker coupling between modes than expected by the "purely brittle" model. We compare here two such previously proposed models and introduce a third one to show that the transition to sliding is very sensitive to the form of the mixed-mode model.…

On the dependency of rubber friction on the normal force or load: theory and experiment

In rubber friction studies it is often observed that the kinetic friction coefficient μ depends on the nominal contact pressure p. We discuss several possible origins of the pressure dependency of μ: (a) saturation of the contact area (and friction force) due to high nominal squeezing pressure, (b) non-linear viscoelasticity, (c) non-randomness in the surface topography, in particular the influence of the skewness of the surface roughness profile, (d) adhesion, and (e) frictional heating. We show that in most cases the non-linearity in the μ(p) relation is mainly due to process (e) (frictional…

An asperity-based statistical model for the adhesive friction of elastic nominally flat rough contact interfaces

Contact mechanics-based models for the friction of nominally flat rough surfaces have not been able to adequately capture certain key experimentally observed phenomenona, such as the transition from a static friction peak to a lower level of sliding friction and the shear-induced contact area reduction that has been observed in the pre-sliding regime especially for soft materials. Here, we propose a statistical model based on physically-rooted contact mechanics laws describing the micromechanics of individual junctions. The model considers the quasi-static tangential loading, up to full slidin…