arXiv subjects

Nicola Menga

Publications and source records attributed to Nicola Menga.

12 recordsLinked to original sources

arXiv2026

Theory of fracture initiation and propagation in viscoelastic media

Crack initiation and propagation are fundamental problems in materials science, often leading to catastrophic failure. While fracture in elastic solids occurs instantaneously above a critical load, viscoelastic materials may sustain high loads for a finite time before cracks start to propagate. This phenomenon, known as delayed fracture, has been widely observed experimentally but is still only partially understood theoretically. In this study, we present a rigorous framework based on the Lagrange--d'Alembert principle of virtual work (PVW) to predict both the viscoelastic delay time and the subsequent crack evolution under arbitrary loading histories. We derive how the delay time depends on the applied remote load and validate the theory through quantitative comparison with experiments, using directly measured delay times together with DMA-based viscoelastic characterization of the material. Very good agreement is obtained over a broad range of loading and delay times. Our results also show that crack propagation starts at finite speed and that load-dependent steady-state conditions are soon established. Finite element analyses further support the proposed framework and clarify the role of finite-ranged adhesion forces at fixed adhesion energy, showing that shorter interaction ranges yield results in quantitative agreement with theory. We also present, for the first time, a rigorous J-integral formulation valid for linear viscoelastic solids under arbitrary, time-varying loading histories. The result restores path independence and yields a generalized Griffith criterion that naturally predicts delayed fracture initiation in non-conservative materials. Remarkably, fracture initiation can be described without specifying the detailed stress distribution within the process zone, as long as it remains small relative to the crack length.

cond-mat.soft↗

arXiv2025

Anisotropic shrinkage and finite strains in confined frictional contacts

We report on an experimental investigation of the interplay between friction, contact geometry and finite strains for smooth frictional contacts between rigid spherical glass probes and flat silicone substrates. Using both bulk and layered substrates under various loading conditions (normal force, radius of the probe), we show that shear-induced anisotropic shrinkage of the adhesive contact area under steady-state sliding is an effect of finite-elasticity conditions and is drastically affected by the level of geometric confinement. The resulting non-linear coupling between the normal and lateral directions is also investigated by measuring the changes in the indentation depth (conv. normal load) during the stiction of the adhesive contacts under imposed normal load (conv. indentation depth) conditions, with strong effects of contact confinement. From a comparison with adhesiveless linear contact mechanics calculations, we show that the experimental observations can only be accounted for by the occurrence of finite strains/displacements conditions. Accordingly, measurements of the in-plane surface displacements at the surface of the rubber substrates confirm that strain levels well in the neo-Hookean range are experienced during steady-state frictional sliding.

cond-mat.soft↗

arXiv2024

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

We study the frictional adhesive contact of a rigid insulating sphere sliding past a multiferroic coating deposed onto a rigid substrate, based on the hybrid element method (HEM). The adhesion behavior is described based on the Maugis-Dugdale (MD) model. The adhesion-driven conjugate gradient method (AD-CGM) is employed to calculate the distribution of unknown pressures, while the discrete convolution-fast Fourier transform (DC-FFT) is utilized to compute the deformations, surface electric and magnetic potentials as well as the subsurface stresses, electric displacements, and magnetic inductions. We found that the coating thickness affect the contact stiffness and the interplay between friction and adhesion. More importantly, friction and gap-dependent MD adhesion affects elastic, electric, and magnetic behavior of the interface, breaking the symmetry between leading and trailing edges behaviors in all the investigated fields. Indeed, increasing the friction coefficient, the contact shape is no longer circular, the pressure distribution shifts towards the leading edge, the electric/magnetic surface potentials distributions sharpen at the leading edge, and the subsurface stress fields concentrates at the trailing edges.

cond-mat.soft↗

arXiv2024

Modelling viscoelastic adhesion and friction in sliding contact mechanics

We present our recent study on rough adhesive contacts of viscoelastic materials in steady-state sliding, focusing on the interplay between adhesion and viscoelasticity by means of a novel energy approach. We investigate tribological features over a wide range of velocity values, exploring the effect of small- and large- scale viscoelasticity on the overall contact behavior. The former is associated with viscoelastic dissipation close to the adhesive neck at the contact edges; the latter refers to material hysteresis involving the entire bulk of the solid. Depending on the sliding velocity, we predict highly enhanced adhesive strength compared to the purely elastic conditions, increased friction compared to the adhesiveless case, and non-monotonic trend of the energy release rates at the contact leading and trailing edges. Most of our results are supported by existing experiments.

cond-mat.soft↗

arXiv2024

Viscoelastic peeling of thin tapes with frictional sliding

Peeling is one of the most common detachment mechanisms adopted in industrial applications. However, although several experimental investigations have proven the possible occurrence of relative sliding at the interface close to the peeling front, a comprehensive model considering the effect of both the tape viscoelasticity and frictional interfacial dissipation on the peeling behavior is lacking. The present study aims at providing a theoretical framework to investigate the peeling process of a thin viscoelastic tape from a rigid substrate in the presence of frictional sliding at the interface. It shows that, under certain conditions, significantly tougher adhesive performance can be achieved compared to stuck elastic conditions with no interfacial sliding, and that the delamination resistance of the system strongly depends on the propagation velocity.

cond-mat.soft↗

arXiv2024

Interfacial performance evolution of ceramics-in-polymer composite electrolyte in solid-state lithium metal batteries

The incorporation of ceramics into polymers, forming solid composite electrolytes (SCEs) leads to enhanced electrical performance of all-solid-state lithium metal batteries. This is because the dispersed ceramics particles increase the ionic conductivity, while the polymer matrix leads to better contact performance between the electrolyte and the electrode. In this study, we present a model, based on Hybrid Elements Methods, for the time-dependent Li metal and SCE rough interface mechanics, taking into account for the oxide (ceramics) inclusions (using the Equivalent Inclusion method), and the viscoelasticity of the matrix. We study the effect of LLTO particle size, weight concentration, and spatial distribution on the interface mechanical and electrical response. Moreover, considering the viscoelastic spectrum of a real PEO matrix, under a given stack pressure, we investigate the evolution over time of the mechanical and electrical performance of the interface. The presented theoretical/numerical model might be pivotal in tailoring the development of advanced solid state batteries with superior performance; indeed, we found that conditions in the SCE mixture which optimize both the contact resistivity and the interface stability in time.

cond-mat.soft↗

arXiv2024

Enhancement of adhesion strength in viscoelastic unsteady contacts

We present a general energy approach to study the unsteady adhesive contact of viscoelastic materials. Under the assumption of infinitely short-range adhesive interactions, we exploit the principle of virtual work to generalize Griffith local energy balance at contact edges to the case of a non conservative (viscoelastic) material, subjected to a generic contact time history. We apply the proposed energy balance criterion to study the approach retraction motion of a rigid sphere in contact with a viscoelastic halfspace. A strong interplay between adhesion and viscoelastic hysteretic losses is reported which can lead to strongly increased adhesion strength, depending on the loading history. Specifically, two different mechanisms are found to govern the increase of pulloff force during either approach retraction cycles and approach, full relaxation, retraction tests. In the former case, hysteretic losses occurring close to the circular perimeter of the contact play a major role, significantly enhancing the energy release rate. In the latter case, instead, the pulloff enhancement mostly depends on the glassy response of the whole (bulk) material which, triggered by the fast retraction after relaxation, leads to a sort of frozen state and results in a flat punch like detachment mechanism (i.e., constant contact area). In this case, the JKR theory of adhesive contact cannot be invoked to relate the observed pulloff force to the effective adhesion energy, i.e. the energy release rate G, and strongly overestimates it. Therefore, a rigorous mathematical procedure is also proposed to correctly calculate the energy release rate in viscoelastic dissipative contacts.

cond-mat.soft↗

arXiv2023

Significance of Elastic Coupling for Stresses and Leakage in Frictional Contacts

We study how the commonly neglected coupling of normal and in-plane elastic response affects tribological properties when Hertzian or randomly rough indenters slide past an elastic body. Compressibility-induced coupling is found to substantially increase maximum tensile stresses, which cause materials to fail, and to decrease friction such that Amontons law is violated macroscopically even when it holds microscopically. Confinement-induced coupling increases friction and enlarges domains of high tension. Moreover, both types of coupling affect the gap topography and thereby leakage. Thus, coupling can be much more than a minor perturbation of a mechanical contact.

cond-mat.soft↗

arXiv2022

Theory of viscoelastic adhesion and friction

We present a novel theory of the adhesive contact of linear viscoelastic materials against rigid substrates moving at constant velocity. Despite the non-conservative behavior of the system, the closure equation of the contact problem can be rigorously formulated in the form of a local energy balance. In the case of adhesiveless contacts, this is equivalent to enforce the stationarity of the total energy stored into the viscoelastic material. However, in the presence of interfacial adhesion, the appearance of non-conservative terms leads to different values of the energy release rates G1 and G2 at the contact trailing and leading edges, respectively. Specifically, the present theory predicts a non-monotonic trend of G1 and G2 as function of the indenter velocity, as well as a very significant enhancement of hysteretic friction due to the coupling between adhesion and viscoelasticity, compared to the adhesiveless case. Both predictions are in very good agreement with existing experimental data.

cond-mat.soft↗

arXiv2021

The role of interfacial friction on the peeling of thin viscoelastic tapes

We study the peeling process of a thin viscoelastic tape from a rigid substrate. Two different boundary conditions are considered at the interface between the tape and the substrate: stuck adhesion, and relative sliding in the presence of frictional shear stress. In the case of perfectly sticking interfaces, we found that the viscoelastic peeling behavior resembles the classical Kendall behavior of elastic tapes, with the elastic modulus given by the tape high-frequency viscoelastic modulus. Including the effect of frictional sliding, which occurs at the interface adjacent to the peeling front, makes the peeling behavior strongly dependent on the peeling velocity. Also, at sufficiently small peeling angles, we predict a tougher peeling behavior than the classical stuck cases. This phenomenon is in agreement with recent experimental evidences indicating that several biological systems (e.g. geckos, spiders) exploit low-angle peeling to control attachment force and locomotion.

cond-mat.soft↗

arXiv2020

Do uniform tangential interfacial stresses affect adhesion?

We present theoretical arguments, based on linear elasticity and thermodynamics, to show that interfacial tangential stresses in sliding adhesive contacts does not affet at all the adhesive behavior of the system, which then follows the classical JKR solution. Our finding explains the experimental observation of Vorvolakos and Chaudhury in 2003, who found that the contact area of a PDMS sphere remains constant during sliding and is in agreement with the JKR solution, at least up to velocity of 1mm/s, and of Carpick et al. Carpick, who observed that the friction force between a platinum-coated atomic force microscope (AFM) tip and the surface of mica in ultrahigh vacuum (UHV) varies with load in proportion to the contact area predicted by the Johnson-Kendall-Roberts (JKR). We show that a reduction of the contact area, experimentlly observed at higher sliding speeds, can be caused by a reduction of the density of adhesive bonds as the velocity is increased, or caused by the repulsive energy term associated with the stress spatial fluctuation at the interface. This may explain why adhesion is completely masked at relatively large sliding velocities. This version of the paper follows the publication of the Corrigendum: Nicola Menga, Giuseppe Carbone, Daniele Dini: Corrigendum to "Do uniform tangential interfacial stresses enhance adhesion?" [Journal of the Mechanics and Physics of Solids 112 (2018) 145--156], Journal of the Mechanics and Physics of Solids, 133, 103744, https://doi.org/10.1016/j.jmps.2019.103744, available on line since 8 October 2019.

cond-mat.mtrl-sci↗

arXiv2019

Tuning the periodic V-peeling behavior of elastic tapes applied to thin compliant substrates

In 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.

cond-mat.soft↗