Papers by Keyword: Contact Mechanics

Abstract: We present our recent study on adhesive contacts of viscoelastic materials sliding against rigid substrates. Ultimately, the theory addresses the combined effect of viscoelasticity and adhesion in sliding contacts, with specific focus on the sliding frictional behavior. Compared to the adhesiveless case, we show that a significant enhancement of hysteretic friction occurs in the presence of adhesion, in agreement with long-standing experimental evidence. The presented formulation allows to investigate the effect of sliding velocities ranging from extremely slow to very high, thus taking into for local viscoelasticity, occurring at the edges of the contacts (crack tips), and bulk viscoelasticity, occurring in the bulk deformable material.

Abstract: Usually, contact mechanics focus on semi-infinite solids, so that any interaction between normal and in-plane deformation is commonly disregarded. However, when dealing with layers of finite thickness, this assumption is no longer valid, and the specific geometry of the contact pair plays a key role in determining the normal-tangential coupling. In this study, we focus on the exemplar case of a thin deformable layer in frictional sliding contact with a rough profile, where the interplay between tangential friction and normal pressure may lead to significantly different contact behavior compared to the uncoupled case, both in terms of contact area size and frictional response.

Abstract: Contact problem for viscoelastic aging pipe with a longitudinally nonuniform thin elastic internal coating and a rigid cylindrical insert is considered in the paper. The basic integral equation with integral operators of different types (mixed integral equation) is given. It's analytical solution for contact stresses in insert area is presented. The solution is constructed in such a way that the function describing the inner coating nonuniformity is distinguished by a separate factor. This fact allows one to perform accurate calculations even in cases where the coating properties are described by rapidly changing and even discontinuous functions. Other known analytical methods do not allow one achieving such a results.

Abstract: It is popular to wear the contact lens nowadays. Also, the output value of the contact lens is estimated more than 4 billion NT dollar every year. Because the phenomena of the contact lenses are very complicated, the relevant mechanisms are not well understood. Thus, the security of contact lens needs to be further investigated. In the lubricated mechanism of the contact lens, there is a layer of tear between the contact lens and cornea. The contact lens’ behavior is akin to that of a slider bearing. The lens represents the slider, the eye plays the role of the stationary pad, and the tear film is the lubricant. Hence, hydrodynamics and contact mechanisms of a contact lens are quite a fascinating subject that is relevant to the science of tribology. In the paper, the lubrication mechanisms include the partial hydrodynamic lubrication (contact lens roughness), contact mechanics and Newtonian fluid mechanics have been established. The parameters of roughness, flow factor, tear film geometry, and hydrodynamic pressure distribution are discussed. The developed technology increases the safety of contact lens.

Abstract: Piezoelectric materials exhibit an electromechanical coupling which allows for their use assensors or energy harvesting devices (direct piezoelectric effect) or actuators and shape control de-vices (inverse piezoelectric effect). They are applied in many technological sectors of current interestsuch as the aerospace and automotive industries, and they are generally constructed in block form orin a thin laminated composite. The study of the integrity of such materials in their various forms andsmall sizes is still a challenge nowadays. To gain a better understanding of these systems, this workpresents a crack surface contact formulation which makes it possible to study the integrity of theseadvanced materials under more realistic crack surface multifield operational conditions. The formu-lation uses the BEM for computing the elastic influence coefficients and contact operators over theaugmented Lagrangian to enforce contact constraints on the crack surface, in the presence of electricfields. The capabilities of this methodology are illustrated solving a benchmark problem.

Abstract: The contact stress field is addressed that is developed at the indenting edge of a keyless shaft-hub interference fit, in the case that both bending and shear forces are applied, and in the absence of friction. The combined effect of a set of elementary load cases is assessed for the sharp notch case in terms of a generalized stress intensity factor, with the aid of Finite Elements and for a class of shaft-hub geometries. In fact, linearity is preserved in the case of a sharp edged bore up to the incipient detachment condition; such event, which may occur as a result of e.g. excessive bending loads, may be forecast based on the proposed framework. Contact stresses in the case of rounded edge may be subsequently predicted by scaling an appropriate local solution; fatigue analysis may then be performed in the case of rotating or fluctuating loads. An exhaustive design table is finally compiled to assist the designer in dimensioning an interference fit in the presence of an arbitrary combination of time varying bending and shear forces.

Abstract: For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.

Abstract: This work presents a numerical formulation to compute wear in ber-reinforced composite materials that are subjected to fretting wear contact conditions. The formulation is based on authors' previous works [1, 2] and presents contact and wear constitutive laws which consider micromechanical aspects such as the ber orientation relative to the sliding direction, the ber volume fraction or the ber length. The formulation uses the Boundary Element Method (BEM) for computing the elastic in uence coef cients and contact operators over the augmented Lagrangian to enforce contact constraints. The proposed formulation is applied to compute and study wear in different carbon berreinforced bulk and fi lm con gurations.

Abstract: Gecko has a special micro hair on its foot to attach to a surface and climb walls. Mimicking its hair, easily detachable adhesive devices have been developed creating micro-structures on the surfaces. Adhesion strength of these devices changes with peeling direction. Therefore, this dependency enables a compatibility of strong adhesion and easy detachment. In this study, the effect of peeling speed on the adhesive strength of the devices is experimentally investigated.

Abstract: In computational contact mechanics, the contact constraints are usually applied using the Lagrange multiplier method, the penalty method, or alternative variants. Traditional contact approaches discretise the contact constraints in a weak sense, providing a stable interpolation scheme. However, they demand complicated search algorithms for contact detection at the interface between the intersecting bodies, and they usually lead to formulations that yield highly nonlinear tangent matrices, particularly for cases with realistic soil models and frictional contact. Recently, a new contact method based on the concept of a third medium has been developed, which overcomes the drawbacks of the conventional contact mechanics techniques. This new scheme is based on a space filling mesh in which the contacting bodies can move and interact. Contact constraints are enforced by changing the mechanical properties of medium with respect to the movements of the bodies. This new method has been developed for contact bodies undergoing large deformations using a hyper-elastic material law. In this study, the method is further extended to solve geomechanics problems in which the material behaviour is elastoplastic and the soil is subjected to large deformations. Potential merits of the third medium contact concept for analysing the geotechnical problems by the finite element method will also be addressed.