Shear bands lie at the root of fracture initiation in bulk metallic glasses and amorphous polymers. For silicate glasses, in contrast, studies have largely emphasized permanent volumetric strain, commonly referred to as densification. Here, we systematically investigate indentation-induced fracture in two distinct families of aluminoborosilicate glasses. The results demonstrate that plastic shear flow plays a decisive role in governing fracture initiation. In addition, molecular dynamics simulations reveal a pronounced composition dependence of softening associated with plastic shear flow, closely mirroring the experimentally observed propensity for strain localization. We conclude that silicate glasses conform to a universal pattern of rupture initiation governed by the localization of shear-deformation, aligning with a broad range of amorphous materials, including bulk metallic glasses and glassy polymers.

In pressure-sensitive adhesive (PSA) tapes, adhesive failure is often accompanied by cavitation and fibrillation. In this paper, we focus specifically on fibrillation. We model the behavior using a single fibril (mono-fibril) configuration with the axisymmetric boundary conditions. Using the finite element method, we simulate the mono-fibril with varying aspect ratios using hyperelastic models such as Arruda-Boyce and Yeoh. First, we explain why the deformation of these fibrils is not purely uniaxial. We then analyze the normalized force-stretch response using appropriate scaling models. Then we examine the impact of changing strain-hardening, inter-fibrillar distance, and bulk modulus on the fibril response. Following this, we investigate fibril debonding using parameters of the Yeoh model fitted to the uniaxial rheological experimental data from two PSA tapes, referred to as PSA types 6A and 6B. Based on this analysis, we derive the power laws for debonding stretch and debonding force for both PSA types. Finally, we compare our findings with experimental data on mono-fibril debonding from the literature.

This work presents a new approach to evaluating the toughness, described by the critical energy release rate (G_c), and ultimate tensile strength (σ_c) of amorphous silica (SiO_2 glass), combining microbeam tests and phase-field calculations. The latter provides a numerical route to brittle fracture without prescribing explicit fracture surfaces a priori, enabling crack initiation and propagation to be tracked. Single-notched microbeams and newly designed bone-shaped microbeams with a notch-free gauge section were fabricated by Focused Ion Beam (FIB) milling nd tested under bending in air, probing the brittle-fracture and strength-controlled regimes, respectively. Both geometries were modeled by Finite Element Analysis (FEA) coupled with a phase-field formulation. We found G_c = 5.1 J/m^2 (critical stress intensity factor K_IC = 0.61 MPa·m^1/2), an intrinsic material length scale ℓ_c = 9.1 nm, and σ_c = 6.8 GPa, consistent with previously reported brittle properties of silica glass. Through a parametric study, we show the effect of notch geometry on the fracture response of the microbeams and the impact of dimensional measurement error on the determined toughness. Unlike conventional micromechanical methods that yield only K_IC, our combined microbeam geometries and phase-field approach simultaneously deliver G_c and σ_c, bridging brittle-fracture characterization and the strength-controlled regime inaccessible to toughness-only techniques.

Electron irradiation enables quantitative control over the plastic flow dynamics of silicate glasses, even far below the glass transition temperature. Through stress-relaxation experiments spanning ambient to near-glass-transition temperatures, we uncover a time-current equivalence that grants direct access to steady-state plastic flow over five decades in strain rate. This equivalence allows reconstruction of the intrinsic plastic-flow curve and quantitative assessment of the roles of network connectivity and temperature. Notably, the observed temperature dependence reveals a striking discrepancy with existing theoretical frameworks, highlighting the need for a comprehensive model of plastic flow dynamics in the glassy state.

The difference between free surface energy and fracture toughness in amorphous silica is studied via multi-scale simulations. We combine the homogenization of a molecular dynamics fracture model with a phase-field approach to track and quantify the various energy contributions. We clearly separate free surface energy localized as potential energy on the surface and damage diffusion over a 16-23 A range around the crack path. The plastic contribution is negligible. These findings, which clarify brittle fracture mechanisms in amorphous materials, align with toughness measurements in silica.

We investigate the exceptional adhesion performance of pressure-sensitive adhesive (PSA) foam tapes by linking microscale damage mechanisms to macroscopic peel behavior. Using instrumented peel tests, side-view imaging, and microscopy, we show that the key to high adherence lies in a transition from a stiff incompressible composite to a soft dissipative foam, triggered by debonding of the adhesive matrix from embedded hollow glass microspheres. This structural transformation enables large strain energy dissipation while maintaining structural integrity. We extend the equivalent fibril model (EFM) to accurately predict adherence energy in the high-performance regime and identify a master curve between the shape of the debonding region and adherence energy. This "time-temperature-interface equivalence" enables fast, image-based assessment of adhesive performance and provides a unified framework bridging fracture and cohesive zone models. Our findings offer fundamental insights and practical tools for the design and evaluation of advanced structural adhesives.

We present a computationally efficient Python algorithm based on the Boundary Element Method (BEM) for frictionless linear elastic axisymmetric contact of coated solids. The algorithm solves indentation problems using conical, spherical, and cylindrical flat indenters, with results also reported for flat punch indentation on a soft-coated substrate. To validate BEM, we implement Finite Element Method (FEM) simulations, analyzing soft layers with Poisson ratios of 0.25, 0.4, and 0.49, aspect ratios from 0.25 to 10, and modulus mismatches of 10 and 100. BEM and FEM show good agreement for compressible soft layers but diverge as incompressibility increases. For Poisson’s ratio of 0.4999, BEM fails due to confinement effects. We verify FEM results using the Poker-chip test, confirming accuracy in highly confined, nearly incompressible cases. For compressible soft layer and large aspect ratios, we found good agreement between BEM and analytical result of Poker-chip test applicable in that regime.

Indentation experiments have helped understand non-linear mechanical properties of brittle materials such as plasticity, damage and fracture. However, our understanding of stress fields under indentation remains limited due to the general lack of direct measurements. This study introduces a novel approach to characterizing indentation stress fields in silicate glasses by combining high sensitivity birefringence measurements, photoelastic calculations and finite element analysis (FEA). We extensively investigated the elastoplastic response of soda-lime-silicate (SLS) and silica glasses under different indentation conditions, highlighting the effects of composition and indenter geometry on the photoelastic distributions. To predict the photoelastic response under indentation, we carefully calibrated an elastoplastic constitutive relation for silicate glasses using a combination of high-pressure (up to 25 GPa) and nanoindentation experiments. Computed indentation stress fields can then be validated through the comparison of full 3D photoelastic calculations and measured birefringence patterns. One key finding is that the residual stresses arising from the calibrated constitutive relations offered a far more realistic representation of the indentation stress fields than a commonly used approximate analytical elastoplastic model. With this method, stress fields can be investigated not only in oxide glasses but also in any other transparent isotropic material. While the calculated stress fields were generally satisfactory for both glass compositions, they also evidenced that improvements in the constitutive relation are needed for amorphous silica, which is known to undergo significant densification.

We have explored receding contact line dynamics on superhydrophobic surfaces, composed of micropillars arrays. We present here dynamic receding contact angle measurements of water on such surfaces, covering contact line speeds spanning over five decades. We have studied the effect of pillars fraction on dynamical receding contact angles. We compared these measurements to those on smooth surfaces with the same chemical nature and also with similar systems reported in the literature. We show that superhydrophobic surfaces exhibit a significantly lower dependence of contact angle on contact line speed compared to smooth surfaces. Additionally, we observed that a higher surface fraction of pillars leads to a greater dependence of the contact angle on contact line speed, approaching the dependence of the angle on smooth surface. Interestingly, we show that the exact texuration of the surface does not play a fundamental role in the angle-velocity relationships as long as microtextures present the same type of periodic pattern (pillar arrays or microgrid). These results are interpreted in terms of viscous friction reduction on superhydrophobic surfaces, shedding light on the underlying mechanisms governing their unique dynamic behavior. In addition we show that contact angles follow same laws for two different geometries (milimetric sessile drop and a centimetric capillary bridge).

We report a new approach on the phenomenon of plastic flow induced by electron irradiation in amorphous silica, revealing that the total injected electric charge is the governing parameter of the mechanical response: micropillar relaxation tests conducted under electron irradiation showed a one-to-one relationship between the injected electric charge and the measured mechanical stress level, regardless of the applied current. Moreover, by performing these tests at high temperature, we have found that the effects of electronic processes and temperature are decoupled. This result suggests that under the present irradiation/temperature conditions, the density of flow defects is controlled only by irradiation, while the plastic rearrangement of the defects depends only on temperature.

Polyvinylbutyral (PVB) is a polymer with sizeable viscoelastic dissipation at room temperature. It is often used in laminated glass to impart shock resistance to glazings. We have investigated adhesion rupture in glass/PVB interfaces in the through crack tensile test (TCT) geometry, representative of laminated glass rupture. We find that even though, in the high velocity range, interfacial rupture apparently follows the linear viscoelastic predictions, at low velocity a much richer behavior appears: the system bifurcates, the front undulates, and at still lower velocities, it stops. Such instabilities cannot be explained by linear viscoelastic fracture. Prompted by the measured tensile response of PVB at high strain rates/low temperatures, we have explored steady state viscoplastic fracture, using a generic numerical model. The results show that the TCT geometry enhances the viscoplastic response in the rupture process. They also demonstrate that with viscoplasticity, the rupture energy decreases with velocity, a characteristic which indeed accounts for the observed crack front instabilities. We further discuss the implications of these findings for a better understanding of adhesion and rupture in soft matter and their connection to viscoplasticity.

The aim of this work is to analyse and understand the densification process of silica glasses at the micrometer scale under micro-indentation. The density evolution at micro-scale of silica glass following a micro-indentation exhibits a high maximum density change, up to 21% in contrast to normal glasses such as float glass, which have a low densification change. In the case of silica glass, it is observed that the evolution of the densification in the lateral dimension is gradual, as for high Poisson’s ratio glasses. However, we find that along the central axis, the evolution with depth is quite different : It presents two regions. In the area immediately below the indenter, the densification is high and almost constant. Just under this imprint, there is a relatively sharp transition to the purely elastic region. Our present study, based on Brillouin diffusion measurements, allows us to improve the description of the imprint for normal/anomalous glass and to explain the location of median cracks in the silica imprint: in the transition zone between densified and undensified regions.

For drug delivery systems, the mechanical properties of drug carriers are suspected to play a crucial role in the delivery process. However, there is a lack of reliable methods available to measure the mechanical properties of drug carriers, which hampers the establishment of a link between delivery efficiency and the mechanical properties of carriers. Lipid nanoparticles (LNPs) are advanced systems for delivering nucleic acids to target cell populations for vaccination purposes (mRNA) or the development of new drugs. Hence, it is crucial to develop reliable techniques to measure the mechanical properties of LNPs. In this article, we used AFM to image and probe the mechanical properties of LNPs which are loaded with two different biopolymers either pDNA or mRNA. Imaging the LNPs before and after indentation, as well as recording the retraction curve, enables us to obtain more insight into how the AFM tip penetrates into the particle and to determine whether the deformation of the LNPs is reversible. For pDNA, the indentation by the tip leads to irreversible rupture of the LNPs, while the deformation is reversible for the mRNA-loaded LNPs. Moreover, the forces reached for pDNA are higher than for mRNA. These results pave the way toward the establishment of the link between the LNP formulation and the delivery efficiency.

Over the last half-century, linear viscoelastic models for crack growth in soft solids have flourished but their predictions have rarely been compared to experiments. In fact, most available models are either very approximate or cast in forms which are not quite suitable for the analysis of actual data. Here, we propose a linear viscoelastic approach which consistently exploits the dynamic mechanical analysis data. We apply this method to four sets of results documenting fracture or adhesion rupture in soft solids with various degrees of viscoelasticity. For elastomers, the results reproduce the well-known inconsistency of the process zone size. In more viscoelastic systems, however, the present approach is able to match the measured velocity dependence of the rupture energy with physically acceptable process zone sizes. Moreover, our predictions agree with the damage zone sizes measured by mechanoluminescence. Building on these results, we discuss various issues arising when evaluating the linear viscoelastic contribution to the rupture/adhesion energy in soft solids: data quality, physical interpretation of the parameters, validity of simpler approximations and limitations of the present approach.

Solidification is a heterogeneous transformation from liquid to solid, which usually combines transport, phase transition and mechanical strain. Predicting the shapes resulting from such a complex process is fascinating and has a wide range of implications from morphogenesis in biological tissues to industrial processes. For soft solids initially at equilibrium, elastic stresses, whether tensile or compressive, can be induced by heterogeneous volumetric deformations of the material. These stresses trigger surface instabilities leading to variations of curvature and shape of the solids. In this article, we study the shape evolution of elongated droplets of polymer and particle suspensions undergoing a solidification process caused by the inward diffusion of a gelling agent from the surface. We show experimentally and numerically that there appears a layer of gelled material growing at the surface. Due to volume contraction, this layer induces tensile stresses and drives a flow in the ungelled liquid core, resulting in the relaxation of the droplets toward spherical shapes. Over time, the thickness of this elastic membrane grows, hence the bending stiffness required to change its shape eventually balances the surface stresses, which arrests the relaxation process. These results provide general rules to understand the shape of solidifying materials combining both tension and bending driven deformations.

Interfaces between a water droplet and a network of pillarsproduceeventually superhydrophobic, self-cleaning properties. Consideringthe surface fraction of the surface in interaction with water, itis possible to tune precisely the contact angle hysteresis (CAH) tolow values, which is at the origin of the poor adhesion of water droplets,inducing their high mobility on such a surface. However, if one wantsto move and position a droplet, the lower the CAH, the less precisewill be the positioning on the surface. While rigid surfaces limitthe possibilities of actuation, smart surfaces have been devised withwhich a stimulus can be used to trigger the displacement of a droplet.Light, electron beam, mechanical stimulation like vibration, or magnetismcan be used to induce a displacement of droplets on surfaces and transferthem from one position to the targeted one. Among these methods, onlyfew are reversible, leading to anisotropy-controlled orientation ofthe structured interface with water. Magnetically driven superhydrophobicsurfaces are the most promising reprogramming surfaces that can leadto the control of wettability and droplet guidance.

Les verres usuels, dits « silicatés », sont des matériaux irremplaçables car transparents, rigides et de faible cout. Mais ils ont un talon d’Achille : leur résistance mécanique, à tel point qu’ils sont l’archétype même du matériau fragile, qui reste élastique jusqu’à rupture. Cependant, à la fin des années 1940, on a observé avec étonnement que leur indentation à l’échelle du micromètre laisse une empreinte, trace incontestable d’une déformation plastique !Réconcilier cette plasticité à l’échelle locale avec l’idée de rupture fragile reste une question ouverte, tant la description de l’écoulement plastique dans les amorphes est complexe. La conjonction de nouvelles techniques expérimentales et numériques a permis des progrès que nous décrivons ici.

For partially wetting fluids, previous results suggest that the thickness and the dewetting velocity of gravity driven films are uniquely determined by the triple line dynamics. In contrast, when flushing aqueous liquids through polymer tubes, our measurements show that the dewetting velocity and thickness can be selected. The control parameter is pressure, i.e. the macroscopic curvature of the meniscus. Our results demonstrate directly the major role played by the macroscopic geometry in the stability of the triple line in a dynamic meniscus as predicted by Eggers (Phys. Rev. Lett. 93, 094502 (2004)).