1,720,996 research outputs found
Rough frictional contact of elastic thin layers: The effect of geometrical coupling
No full textThe rough contact behavior of thin layers in the presence of interfacial friction is investigated by means of an innovative fundamental elastic solution. A certain degree of geometrical coupling between normal and tangential elastic field is found which, depending on the layer thickness, may lead to larger contact areas compared to the frictionless case. A specific focus has been devoted to investigate the behavior of the local quantities at the interface, in terms of both the displacement field and the gap distribution. We found that significant thinner gaps are predicted due to elastic coupling and frictional interactions, which may lead to larger hydraulic impedance of the contact interface. The latter result is specifically interesting for applications such as seals, where lubrication and leakage are the governing phenomena
A Winkler solution for the axisymmetric Hertzian contact problem with wear and finite element method comparison
No full textContact problems with wear are often modelled according to the Reye-Archard law that applies locally to the wearing parts. In the transient regime, for geometries where the contact area cannot be assumed to be constant, a simple solution is possible when using the Winkler simplifying assumption. Here, we obtain such a solution in the axisymmetric contact problem, for an initially Hertzian geometry. Also, we explore the possibility to improve the solution by assuming that the Winkler constant adapts to the changing size of the contact. The correction is relevant in intermediate regimes before the solution tends to a 'rigid' asymptotic regime, independent of the elastic modulus. Comparison with a full finite element method simulation shows that the error in either contact area or peak pressure tends to be reduced from the initial error intrinsic in the Winkler assumption; however, the improvement remains small
A note on wear of elastic sliding parts with varying contact area
No full textWear of sliding parts in the transient regime depends on elastic behavior of the bulk of the materials, and in general the contact area cannot be assumed to be constant, so that the problem is nonlinear. Here we look at the simple example of the classical Hertzian geometry, obtaining a simple solution for transient to uniform pressure (which is also the "rigid" limit solution) assuming out-of-plane sliding, and the approximation of the "Winkler foundation" in plane strain. Wear is assumed to vary according to the Reye-Archard law, which applies locally and only to the wearing indenter. As a further improvement, we give a more refined solution using a Winkler constant which adapts to the changing size of the contact
Tuning the periodic V-peeling behavior of elastic tapes applied to thin compliant substrates
No full textIn this paper, we investigate the periodic peeling behavior of opposing symmetric peeling fronts involving an elastic tape peeled off from a deformable substrate of finite thickness, backed onto a rigid foundation. We treat the problem by means of an energetic formulation, and we found that, depending on the values of the initial detached length l, substrate thickness h, and peeling periodicity λ, the translational invariance of the peeling process is lost and restored, as the elastic interaction between the peeling fronts is limited by the substrate thickness. Indeed, given h and λ, a critical value of the detached length can be found, which is able to prevent unstable peeling of the tape under a fixed applied load, thus resulting in enhanced adhesion strength, with respect to the classical Kendall's solution for peeling from a rigid substrate. On the other hand, given the geometrical system configuration (i.e. the detached length l) the load necessary to trigger the peeling can be minimized by conveniently tuning the ratio h/λ. This feature might be of interest for the development of innovative designs for future biomedical devices, such as Transdermal Drug Delivery Systems or wound dressing, requiring low peel adhesion for safe successive removals
Adhesive contact mechanics of viscoelastic materials
Full text linkIn this study, we propose a theory of rough adhesive contact of viscoelastic materials in steady-state sliding. By exploiting a boundary formulation based on Green's function approach, the unknown contact domain is calculated by enforcing the local energy balance at the contact edge, thus considering also the non-conservative work of internal stresses which is directly related to the odd part of the Green's function. Theoretical predictions indicate that viscoelasticity may enhance the adhesive performance depending on the sliding velocity, thus leading to larger contact area and pull-off force compared to the equivalent adhesive elastic case The interplay between viscoelasticity and adhesion also affects the overall friction. Indeed, at low velocity, friction is strongly enhanced compared to the adhesiveless viscoelastic case, mainly due to the small-scale viscoelastic hysteresis induced by the adhesive neck close to the contact edge At higher velocity, the effect of viscoelastic hysteresis occurring at larger scales (bulk material) leads to even higher friction. Under these conditions, in the presence of adhesion, the small-scale and large-scale viscoelastic contributions to friction cannot be separated. Finally, in contrast with usual predictions for crack propagation/healing in infinite systems, we found a non-monotonic trend of the energy release rates at the trailing and leading contact edges, which is consistent with the finiteness of the contact length. All the presented results are strongly supported by existing experimental evidences
Effect of In-Plane Stress on the Frictional Behavior of Thin Layers
No full textUsually, 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
Effect of thickness and boundary conditions on the behavior of viscoelastic layers in sliding contact with wavy profiles
Full text linkIn this work, the sliding contact of viscoelastic layers of finite thickness on rigid sinusoidal substrates is investigated within the framework of Green's functions approach. The periodic Green's functions are determined by means of a novel formalism, which can be applied, in general, to either 2D and 3D viscoelastic periodic contacts, regardless of the contact geometry and boundary conditions. Specifically, two different configurations are considered here: a free layer with a uniform pressure applied on the top, and a layer rigidly confined on the upper boundary. It is shown that the thickness affects the contact behavior differently, depending on the boundary conditions. In particular, the confined layer exhibits increasing contact stiffness when the thickness is reduced, leading to higher loads for complete contact to occur. The free layer, instead, becomes more and more compliant as thickness is reduced. We find that, in partial contact, the layer thickness and the boundary conditions significantly affect the frictional behavior. In fact, at low contact penetrations, the confined layer shows higher friction coefficients compared to the free layer case; whereas, the scenario is reversed at large contact penetrations. Furthermore, for confined layers, the sliding speed related to the friction coefficient peak is shifted as the contact penetration increases. However, once full contact is established, the friction coefficient shows a unique behavior regardless of the layer thickness and boundary conditions
Modelling the non-steady peeling of viscoelastic tapes
Full text linkWe present a model to study the non-steady V-shaped peeling of a viscoelastic thin tape adhering to a rigid flat substrate. Geometry evolution and viscoelastic creep in the tape are the main features involved in the process, which allows to derive specific governing equations in the framework of energy balance. Finally, these are numerically integrated following an iterative scheme to calculate the process evolution assuming different controlling conditions (peeling front velocity, peeling force, tape tip velocity). Results show that the peeling behavior is strongly affected by viscoelasticity. Specifically, for a given applied force, the peeling can either be prevented, start and stop after some while, or endlessly propagate, depending on the original undeformed tape geometry. Viscoelasticity also entails that the interface toughness strongly increases when the tape tip is fast pulled, which agrees to recent experimental observations on tougher adhesion of natural systems under impact loads, such as see waves and wind gusts
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