Soft Elastic Bodies Research Articles

Elasticity-associated rebinding rate of molecular bonds between soft elastic media

A quantitative understanding of how cells interact with their extracellular matrix via molecular bonds is fundamental for many important processes in cell biology and engineering. In these interactions, the deformability of cells and matrix are usually comparable with that of the bonds, making their rebinding events globally coupled with the deformation states of whole systems. Unfortunately, this important principle is not realized or adopted in most conventional theoretical models for analyzing cellular adhesions. In this study, we considered a new theoretical model of a cluster of ligand-receptor bonds between two soft elastic bodies, in which the rebinding rates of ligands to receptors are described, by considering the deformation of the overall system under the influence of bond distributions. On the basis of theory of continuum and statistical mechanics, we obtained an elasticity-associated rebinding rate of open bonds in a closed analytical form that highly depends on the binding states and distributions of all other bonds as well as on the overall deformation energy stored in the elastic bodies and all closed bonds. On the basis of this elasticity-associated rebinding rate and by performing Monte Carlo simulations, we uncovered new mechanisms underlying the adhesion stability of molecular-bond clusters associated with deformable elastic bodies. Moreover, we revealed that the rebinding processes of molecular bonds is not only dependent on interfacial separation but is related to overall energy. This newly proposed rebinding rate may substantially improve our understanding of how cells adapt to their microenvironments by adjusting their mechanical properties through cytoskeleton remodeling.

Adhesive contact of randomly rough surfaces: experimental and numerical investigations

The contact mechanics of soft matters is strongly affected by short-range adhesive interactions, which can lead to large deformations and contact instabilities.In this work, we present both experimental and numerical investigations of the adhesive contact between soft elastic bodies with a Greenwood and Williamson (GW)-like roughness. To investigate the coalescence of neighbour contact spots, surfaces have been designed with overlapping spherical asperities. Normal contact experiments are carried out by using a home-built device. Numerical simulations are performed with the Interacting and Coalescing Hertzian Asperities (ICHA) model, conveniently modified to take account of adhesion according to the Johnson, Kendall & Roberts (JKR) theory.

Roughness-Induced Adhesive Hysteresis in Self-Affine Fractal Surfaces

It is known that in the presence of surface roughness, adhesion can lead to distinct paths of loading and unloading for the area–load and penetration–load relationships, thus causing hysteretic loss. Here, we investigate the effects that the surface roughness parameters have on such adhesive hysteresis loss. We focus on the frictionless normal contact between soft elastic bodies and, for this reason, we model adhesion according to Johnson, Kendall, and Roberts (JKR) theory. Hysteretic energy loss is found to increase linearly with the true area of contact, while the detachment force is negligibly influenced by the maximum applied load reached at the end of the loading phase. Moreover, for the micrometric roughness amplitude hrms considered in the present work, adhesion hysteresis is found to be affected by the shorter wavelengths of roughness. Specifically, hysteresis losses decrease with increasing fractal dimension and cut-off frequency of the roughness spectrum. However, we stress that a different behavior could occur in other ranges of roughness amplitude.

Simulations of microscopic propulsion of soft elastic bodies.

Using simulations that realistically model both hydrodynamic and elastic behavior, we study the motion of a microscopic, driven elastic sphere immersed in water. We first confirm the "jittery" relaxation recently predicted theoretically for an externally driven elastic sphere. The sphere is then divided in two and each section is driven internally with the two sections 180° out of phase. With periodic and perfectly symmetric driving, the elastic sphere spontaneously breaks symmetry and can attain macroscopic average swimming velocities to the right or left, the direction depending only on the initial state. With asymmetric driving the elastic sphere swims in one direction and the maximum speed is obtained with a 1/3:2/3 split. At high drive frequencies close to elastic resonances of the sphere, the motion can be quite efficient. At low drive frequencies the propulsion speed becomes independent of the elastic constants of the sphere and less efficient, but still substantial. Inertia is found to be an important driver of the behavior despite the small size of the spheres. As we model the full three-dimensional elasticity and compressible hydrodynamics, our simulations give not just qualitative indications but quantitative predictions for the motion.

Adaptive tactile control for in-hand manipulation tasks of deformable objects

Tactile sensors are key components for a robot hand system, which are usually used to obtain the object’s features. The use of tactile sensors to obtain information from the objects is an open topic of research. In this paper, a new strategy for in-hand extraction of object’s properties and for control of the interaction forces with robot fingers, mainly based on tactile data, is presented. The scope of this strategy is to grasp and manipulate solid objects, including rigid and soft bodies. Assuming that the hand is in an initial configuration in which the object is grasped, the properties’ extraction approach is executed. After the extraction of properties is finished, the object can be classified in regard to a general body listing: rigid body, soft elastic body, or soft plastic object. Once the object is classified, for in-hand manipulation tasks, the contact points between the object grasped and the fingers are maintained using the information given by the tactile sensors in order to perform manipulation tasks. Each task is defined by a sequence of basic actions, in which the contact points and applied forces are adapted depending on the action to be performed and the estimated features for the object. The presented approach tries to imitate the behavior of human beings, in which the applied forces by the fingers are changed when the human estimates the rigidity of a body and when the fingers react to unexpected movements of the object to keep the contact points.

Numerical Research on the Pullout Failure of GFRP Bolt

The fiber pullout is a main failure after the fiber is broken in the tension of glass fiber reinforced polymer (GFRP) bolt. In this paper, the numerical analysis is done on the distribution of both fiber normal force and interface shear stress. The results show that, on the ideal interface, the fiber pullout occurs from the lower end to the upper end of the matrix gradually, and both the normal stress of the fiber and the shear stress of the ideal interface gradually increase from the lower end to the upper end. With the increase of the interface layer thickness, the shear stress concentration area on the interface is enlarged while the stress applied is reduced, and the displacement of GFRP deformation is increasing sharply. This means that the capacity of GFRP deformation is enhanced. As a soft elastic body, the interface layer with a smaller elastic modulus can make the fiber stress and the interface shear stress sharply small and well dispersed. In addition, the load can be effectively transferred to the reinforced phase fibers in a bigger interfacial layer elastic modulus with a certain strength.

Numerical and Experimental Procedures for Development of a Dual Body Dynamics to Study the Ball Impact on a Tennis Racquet

The dynamic interaction of the ball/tennis racquet is studied in this work. The elasticity and mass of both accessories have critical importance in the optimized performance of tennis players. This is a leading class of sport and leisure activity having gained high prestige due to historical links to nobles/monarchy society. For the best achievements of the accessories developed for the practice of this sport, advanced lightweight materials allowing high stiffness/mass ratios have been studied constantly. In this work, a numerical model based on dynamic equilibrium concepts of soft elastic bodies in collision was proposed to model the behavior of the ball/racquet pair during the shot. High speed video recording techniques were also implemented to validate the results obtained from the numerical model.

102 軟弾性体の粒子法シミュレーションにおける時間積分法に関する研究(GS01 計算力学)

102 軟弾性体の粒子法シミュレーションにおける時間積分法に関する研究(GS01 計算力学)

On the modeling of the non-linear response of soft elastic bodies

In this short note we articulate the need for a new approach to develop constitutive models for the non-linear response of materials wherein one is interested in describing the Cauchy–Green stretch as a non-linear function of the Cauchy stress, with the relationship not in general being invertible. Such a material is neither Cauchy nor Green elastic. The new class of materials has several advantages over classical elastic bodies. When linearized under the assumption that the displacement gradient be small, the classical theory leads unerringly to the classical linearized model for elastic response, while the current theory would allow for the possibility that the linearized strain be a non-linear function of the stress. Such bodies also exhibit a very desirable property when viewed within the context of constraints. One does not need to introduce a Lagrange multiplier as is usually done in the classical approach to incompressibility and the models are also more suitable when considering nearly incompressible materials. The class of materials considered in this paper belongs to a new class of implicit elastic bodies introduced by Rajagopal [19,20]. We show how such a model can be used to interpret the data for an experiment on rubber by Penn [18].

Stress and deformation in soft elastic bodies due to intermolecular forces

Intermolecular interaction within one and between two incompressible, soft elastic bodies is studied at a continuous level. We show that the macroscopic effect of the interaction can be characterized by a deformation-dependent Maxwell stress. The divergence of the Maxwell stress gives the body force, while the inner product of it with the outward normal of a body generates the surface traction. Accordingly, we can replace the contribution of intermolecular forces to the deformation and stress in the body by that of either the body force or the surface traction. Both approaches are proved to be equivalent, in the sense that the resulting displacements are the same and the stresses are linked by an exact correspondence relation. If the deformation induced by the interaction is small, the equations are simplified up to the first order of the displacement gradient. Two examples are given as well to illustrate some features of local stress distribution in a body caused by self and other-body interactions.

Specific adhesion of a soft elastic body on a wavy surface

This paper aims at developing a stochastic-elastic model of a soft elastic body adhering on a wavy surface via a patch of molecular bonds. The elastic deformation of the system is modeled by using continuum contact mechanics, while the stochastic behavior of adhesive bonds is modeled by using Bell's type of exponential bond association/dissociation rates. It is found that for sufficiently small adhesion patch size or stress concentration index, the adhesion strength is insensitive to the wavelength but decreases with the amplitude of surface undulation, and that for large adhesion patch size or stress concentration index, there exist optimal values of the surface wavelength and amplitude for maximum adhesion strength.

A regularization method for calculating engineering loads from strain data

A preliminary study of a new method of determining interface pressures in contact zones between hard and soft elastic bodies from measurements of strain away from the contact zone is carried out using a single beam with a known load on its topside and strain gauges spaced out along its underside. The beam is such that it can be modelled by simple beam theory. To reconstruct the load from the strain data a regularization scheme of projection type based on the non-negativeness of the pressure distribution is developed. The distribution is represented as a series of basis functions, here either Bernstein polynomials or quadratic B-splines, the coefficients in the series being determined by solving a constrained optimization problem. This method of reconstruction is applied to known theoretically simulated loads with random noise added and to experimental loads, and ways of determining good values of the regularization parameter, the number of basis functions, given. The reconstructions obtained are very satisfactory and give confidence in the application of the method to unknown loads.