Adhesion between elastic cylinders based on the double-Hertz model

A cohesive zone model for two-dimensional adhesive contact between elastic cylinders is developed by extending the double-Hertz model of Greenwood and Johnson (1998). In this model, the adhesive force within the cohesive zone is described by the difference between two Hertzian pressure distributions of different contact widths. Closed-form analytical solutions are obtained for the interfacial traction, deformation field and the equilibrium relation among applied load, contact half-width and the size of cohesive zone. Based on these results, a complete transition between the JKR and the Hertz type contact models is captured by defining a dimensionless transition parameter μ, which governs the range of applicability of different models. The proposed model and the corresponding analytical results can serve as an alternative cohesive zone solution to the two-dimensional adhesive cylindrical contact.     

Kinetics of adhesive contact formation between thermoplastic melts and solid surfaces: Effect on bond strength

Formation of an adhesive contact between a polymer melt (or solution) and reinforcing fibers is considered from the viewpoint of kinetics. A two-stage model of this process has been proposed, and an expression for the interfacial bond strength as a function of time and temperature is derived. Experimental data on bond strength in adhesive joints between thermoplastic polymers and reinforcing fibers formed under various conditions were obtained, and the concept of activation energy was used to analyze them. Since the process is controlled by the stage having the larger activation energy, the adhesive contact formation between fibers and polymer solutions is governed by the rate of adhesive bonding, whereas that between fibers and polymer melts is governed by the rate of the melt spreading.     

提高聚氨酯表面硅橡胶涂层粘接性研究

利用表面处理并借助硅烷偶联剂大幅提高了聚氨酯/硅橡胶(PU/SR)的界面粘接性.利用红外光谱、水接触角以及表面元素分析对PU表面处理效果及偶联剂的反应效果进行检测,利用扫描电镜对材料的表面形貌及界面情况进行观察.并对不同方法得到的PU/SR界面进行剪切和振动疲劳测试以考察其粘接效果并进行比较.结果表明,经过硫酸短时处理过的PU表面生成大量羟基,使得亲水性提高,并大大增强了端异氰酸酯基硅烷偶联剂与PU的接枝反应效果.当室温缩合固化的硅橡胶预聚体涂覆到其表面后,以化学键联接在PU表面的硅烷偶联剂又可以与硅橡胶一起缩合,从而有效的提高了PU/SR的界面粘接性.     

First-principles calculations of adhesion,bonding and magnetism of the Fe/HfC interface

First-principles plane-wave pseudopotential calculations of the adhesion, bonding and magnetism of the interface between the ferromagnetic bcc Fe and non-magnetic HfC are performed. The work of adhesion for C- and Hf-site Fe/HfC interfaces is calculated. High adhesion at C-site interface is found and Fe–C polar covalent bonds are formed across the interface. The magnetic moments of Fe atoms at interface are increased in both interfaces. The effect of the magnetism on the electronic structure of Fe/HfC interface is also investigated. It is shown that the change in band of majority-spin leads to enhance the magnetic moment of Fe.     

Mechano-chemical coupling in the adhesion of thin-shell structures

Nonlinear coupling between mechanical and chemical fields at material interfaces can result in complex phenomena that include segregation-driven interface strengthening or weakening and bistability. Spatial nonuniformity of those fields is driven by elastic stresses that develop in the conforming bodies and from surface topography that is the result of patterning or inherent roughness. In this paper, equilibrium states are analyzed as a function of geometrical, material, and chemical properties to understand coupling mechanisms that impact interface strength. In particular, a theoretical model is presented for the finite deformations of a shallow spherical cap adhering to a rigid substrate that is either flat or has topography. The adhesive interactions are taken to be a continuous function of the local shell-substrate separation and the local concentrations of strengthening or weakening chemical species. Equilibrium states characterized by contact radii and energies are presented as a function of the average concentration of surface species (closed system) and the ambient chemical potential (open system). Bistable equilibria, snap transitions, and nonuniform energy, traction, and concentration fields are salient features of the numerical solutions. Interface separation under edge loading conditions is also investigated to determine the geometrical, material, chemical, and rate of the pull-off load and the work of separation. Additionally, adhesion to substrates with sinusoidal topography is analyzed to investigate the impact of patterning or inherent roughness. Important predictions of the later analysis are topography-induced segregation patterns and bistability.     

Mechanics and mechanism of cut resistance of protective materials

A sliding sharp edge penetrating material is one of the most dangerous cases of cutting because it requires the smallest applied load. A better understanding of the cutting mechanism is a fundamental step to develop new and more performing protective materials. This study aims at analyzing cutting mechanics and mechanism in the presence of friction. The International Standard ISO 13997 cut test method consists in measuring the distance that a straight blade slides horizontally to cut through a material under a constant applied normal force and was used to investigate cutting phenomena.In practice, cut resistance of a material is contributed by the intrinsic strength of material and the frictional distribution. Two types of friction distributions are involved in cutting: a macroscopic friction induced by the gripping of the material and by the applied normal load on the two sides of the blade; and the other the sliding friction associated with cut through of the material that occurs along the face of the blade tip. For most materials, frictional forces due to lateral gripping could be several times greater than the friction due to the applied normal force. Thus, the cutting energy required for breaking molecular chains is much smaller than the energy dissipated for friction. The elastic modulus, the structure of the material as well as the sliding velocity have significant influence on the friction. Therefore all these properties can affect the cutting resistance results.     

Mechanochemistry in cancer cell metastasis

In this review, we introduced the mechanical factors in cancer cell metastasis, intracellular mechanical sensors and methods to measure the mechanical forces of tumor cells for evaluating the mechanochemistry in cancer metastasis.     

Adhesion in the contact of a spherical indenter with a layered elastic half-space

With the emergence of micro- and nano-technology, the contact mechanics of MEMS and NEMS devices and components is becoming more important. Thus it is important to gain a better understanding of the role of coatings and thin films on micro- and nano-scale contact phenomena, and to understand the interactions of measurement devices, such as an atomic force microscope (AFM), with layered media.More specifically, in this work the frictionless contact, with adhesion, between a spherical indenter and an elastic-layered medium is investigated. This configuration can be viewed as either a single contact model or as a building block of a multi-asperity rough surface contact model. As the scale decreases to the nano level, adhesion becomes an important issue. The presence of adhesion affects the relationships among the applied force, the penetration of the indenter, and the size of the contact area. This axisymmetric problem includes the effect of adhesion using a Maugis type of adhesion model. This model spans the range of the Tabor parameter between the JKR and DMT regions. The key parameters in this analysis are the elastic moduli ratio of the layer and the substrate, the dimensionless layer thickness, and the Maugis adhesion parameter. The results can be applied to a rigid or to an elastic indenter.     

The adhesive contact of viscoelastic spheres

We have formulated the restricted self-consistent model for the adhesive contact of linear viscoelastic spheres. This model is a generalization of both the Ting (J. Appl. Mech. 33 (1966) 845) approach to the viscoelastic contact of adhesionless spheres and the restricted self-consistent model for adhesive axisymmetric bodies. We also show how the model can be used in practice by giving a few examples of numerical solutions.     

Non-slipping adhesive contact between mismatched elastic spheres: A model of adhesion mediated deformation sensor

A generalized JKR model is established for non-slipping adhesive contact between two dissimilar elastic spheres subjected to a pair of pulling forces and a mismatch strain. We discuss the full elastic solution to the problem as well as the so-called non-oscillatory solution in which tension and shear tractions along the contact interface is decoupled from each other. The model indicates that the mismatch strain has significant effect on the contact area and the pull-off process. Under a finite pulling force, a pair of adhering spheres is predicted to break apart spontaneously at a critical mismatch strain. This study suggests an adhesion mediated deformation sensing mechanism by which cells and molecules can detect mechanical signals in the environment via adhesive interactions.