We report experiments on piles of cohesionless granular materials showing the effect construction history static stress distributions. Stresses under are monitored by sensitive capacitive techniques. The formed either pouring material from a funnel with small outlet (localized source), or large sieve (homogeneous rain). Localized sources yield profiles clear dip near center pile; homogeneous rain have no dip. show that scale linearly pile height. Experiments wedge-shaped similar but weaker effects.

We experimentally determine ensemble-averaged responses of granular packings to point forces, and we compare these results recent models for force propagation in a material. use 2D arrays consisting photoelastic particles: either disks or pentagons, thus spanning the range from ordered disordered packings. A key finding is that spatial ordering particles factor response. Ordered have propagative component does not occur

We present precise and reproducible mean pressure measurements at the bottom of a cylindrical granular column. If constant overload is added, linear in nonmonotonic column height. The results are {\em quantitatively} consistent with local, relation between stress components, as was recently proposed by some us. They contradict simplest classical (Janssen) approximation, may pose rather severe test competing models.

We report experiments on a vibrated bidimensional granular layer showing peak pattern formation. measure the dispersion relation and observe two regimes of selection: at low frequency, parametric excitation vertical shearing waves, high crossover to selection with constant wavelength. The amplitude patterns is proportional vibration. study instability onset frequency we find evidence burst waves taking place in subcritical region defined by acceleration values. \textcopyright{} 1996 American...

We introduce a shear experiment that quantitatively reproduces the main laws of seismicity. By continuously and slowly shearing compressed monolayer disks in ringlike geometry, our system delivers events frictional failures with energies following Gutenberg-Richter law. Moreover, foreshocks aftershocks are described by Omori interevent times also follow exactly same distribution as real earthquakes, showing existence memory past events. Other features earthquakes qualitatively reproduced...

We analyze the statistical distribution function for height fluctuations of brittle fracture surfaces using extensive experimental data sampled on widely different materials and geometries. compare a direct measurement to an analysis based structure functions. For length scales $\ensuremath{\delta}$ larger than characteristic scale $\ensuremath{\Lambda}$ that corresponds material heterogeneity size, we find increments $\mathrm{\ensuremath{\Delta}}h=h(x+\ensuremath{\delta})\ensuremath{-}h(x)$...

We propose an approach based on the combination of different techniques in order to discriminate various reinforcement effects vulcanized natural rubber elastomers with cross-link densities, filled carbon black or silica: mechanical response, independent measurements density by proton multiple-quantum NMR, and chain segment orientation under stretching X-ray scattering. show that, while modulus measured dynamical decreases as strain amplitude increases (Payne effect), response elastomer...

We report experiments on the rise time T of a single large sphere within sinusoidally vibrated bed (amplitude a) uniform particles (diameter d). At fixed acceleration, we identify three distinct behavioral regimes both from visual observations and typical increase with frequency f. observe two convective separated by critical and, for low high f, ``nonconvective'' regime. In latter, crystallizes size dependent is evidenced. show relevance nondimensional parameter $a/d$ deduce scaling law...

We study experimentally the slow growth of a single crack in fibrous material and observe stepwise dynamics. model as lattice where is pinned by elastic traps grows due to thermally activated stress fluctuations. In agreement with experimental data we find that distribution step sizes follows sub-critical point statistics power law (exponent 3/2) stress-dependent exponential cut-off diverging at critical rupture threshold.

The modelling of the adherence energy during peeling Pressure Sensitive Adhesives (PSA) has received much attention since 1950's, uncovering several factors that aim at explaining their high on most substrates, such as softness and strong viscoelastic behaviour adhesive, low thickness adhesive layer its confinement by a rigid backing. more recent investigation adhesives probe-tack methods also revealed importance cavitation stringing mechanisms debonding, underlining influence large...

By combining direct imaging and acoustic emission measurements, the subcritical propagation of a crack in heterogeneous material is analyzed. Both methods show that fracture proceeds through succession discrete events. However, macroscopic opening captured by images results from accumulation more-elementary events detected acoustics. When energy cumulated over large time scales corresponding to image acquisition rate, similar statistics recovered. High frequency monitoring reveals...

come from teaching and research institutions in France or abroad, public private centers.L'archive ouverte pluridisciplinaire

Fracture paths in quasi-two-dimensional (2D) media (e.g., thin layers of materials or paper) are analyzed as self-affine graphs h(x) height h a function length x. We show that these multiscaling, the sense nth order moments fluctuations across any distance l scale with characteristic exponent depends nonlinearly on moment. Having demonstrated this, one rules out widely held conjecture fracture 2D belongs to universality class directed polymers random media. In fact, does not belong known...

The fatigue durability of polyamide 6,6 has been studied for various maximal stresses. We focus on the identification microscopic mechanisms responsible damaging in regime. show that apparent stiffness, or dynamic modulus, decreases linearly as a function logarithm number cycles during tests, except at very end lifetime, prior to failure. This suggests progressive, accumulative, and generalized damage material. mechanism characterized scales with electron microscopy X-ray scattering. These...

The growth dynamics of a single crack in heterogeneous material under subcritical loading is an intermittent process, and many features this have been shown to agree with simple models thermally activated rupture. In order better understand the role heterogeneities we study propagation sheet paper presence distribution small defects such as holes. experimental data obtained for two different distributions holes are discussed light that predict slowing down when disorder increased; however,...

Using a high-speed camera, we follow the propagation of detachment front during peeling an adhesive tape from flat surface. In given range velocity, this displays multiscale unstable dynamics, entangling two well-separated spatiotemporal scales, which correspond to microscopic and macroscopic dynamical stick-slip instabilities. While periodic release stretch energy whole peeled ribbon drives classical macro-stick-slip, show that micro-stick-slip, due regular transverse dynamic fractures...

We study the propagation of sound through a bidimensional granular medium consisting photoelastic disks, which are packed into different crystalline and disordered structures. Acoustic sensors placed at boundaries system capture acoustic signal produced by local well-controlled mechanical excitation. By compressing system, we find that speed ballistic part wave behaves as power law applied force with both exponent prefactor sensitive to internal geometry contact network. This information,...

The observed repulsive behavior of two initially collinear cracks growing towards each other and leading to a hook-shaped path questioned recently the validity principle local symmetry within linear elastic fracture mechanics theory. Our theoretical numerical work solves this dilemma, providing precise geometric conditions for existence phase. We moreover reveal multiscale repulsive-attractive transition, explaining its ubiquitous occurrence, but also difficulty predict final cracks'...

We study the dielectric relaxation of polycarbonate (PC) at room temperature under imposed strain rate γ̇, above yield stress, and up to 13% strain. find that response stretched PC behaves as if it was heated a just below its glass transition temperature, Tg ≈ 423 K for PC. Indeed, in frequency range our experiment (10–2 103 Hz), superimposes Ta(γ̇) < Tg, which is function rate. Specifically we observe Ta dominant time τα(Ta) rest related γ̇ such way ∼ 1/γ̇ beyond point. In experiment, 10–5...

While of paramount importance in material science, the dynamics cracks still lacks a complete physical explanation. The transition from their slow creep behavior to fast propagation regime is notable key, as it leads full failure if size avalanche reaches that system. We here show simple thermodynamics approach can actually account for such complex crack dynamics, and particular non-monotonic force-velocity curves commonly observed mechanical tests on various materials. consider thermally...

The d10 coinage metal coordination polymers (CPs) are known to display photophysical properties which can be tuned depending on the functionality of ligand. Three new CPs made metals and methyl thiosalicylate, [M(o-SPhCO2Me)]n (M = Cu, Ag, Au), reported. They all constructed from one-dimensional metal-sulfur networks, in Cu Ag three-coordinated sulfur atoms, whereas Au is only two-coordinated. It results that both Cu(I) Ag(I) show orange photoemission at room temperature, Au(I) one exhibits...

We discuss the results of a series experiments performed on heterogeneous materials where we have measured acoustic emission (AE) signals preceding macroscopic failure that correspond to precursory rupture events. mainly focus polyurethane foams whose heterogeneities (pores) constitute arrest points for microcracks. The released AE energy is always power law distributed independently material porosity, loading history (creep and tensile) mechanical properties (from brittle ductile with...