38 research outputs found
Evidence of Deep Water Penetration in Silica during Stress Corrosion Fracture
We measure the thickness of the heavy water layer trapped under the stress corrosion fracture surface of silica using neutron reflectivity experiments. We show that the penetration depth is 65–85 Å, suggesting the presence of a damaged zone of ~100 Å extending ahead of the crack tip during its propagation. This estimate of the size of the damaged zone is compatible with other recent results
Cleaved surface of i-AlPdMn quasicrystals: Influence of the local temperature elevation at the crack tip on the fracture surface roughness
Roughness of i-AlPdMn cleaved surfaces are presently analysed. From the
atomic scale to 2-3 nm, they are shown to exhibit scaling properties hiding the
cluster (0.45 nm) aperiodic structure. These properties are quantitatively
similar to those observed on various disordered materials, albeit on other
ranges of length scales. These properties are interpreted as the signature of
damage mechanisms occurring within a 2-3 nm wide zone at the crack tip. The
size of this process zone finds its origin in the local temperature elevation
at the crack tip. For the very first time, this effect is reported to be
responsible for a transition from a perfectly brittle behavior to a nanoductile
one.Comment: 8 page
Nonlinear Waves in Disordered Diatomic Granular Chains
We investigate the propagation and scattering of highly nonlinear waves in
disordered granular chains composed of diatomic (two-mass) units of spheres
that interact via Hertzian contact. Using ideas from statistical mechanics, we
consider each diatomic unit to be a "spin", so that a granular chain can be
viewed as a spin chain composed of units that are each oriented in one of two
possible ways. Experiments and numerical simulations both reveal the existence
of two different mechanisms of wave propagation: In low-disorder chains, we
observe the propagation of a solitary pulse with exponentially decaying
amplitude. Beyond a critical level of disorder, the wave amplitude instead
decays as a power law, and the wave transmission becomes insensitive to the
level of disorder. We characterize the spatio-temporal structure of the wave in
both propagation regimes and propose a simple theoretical interpretation for
such a transition. Our investigation suggests that an elastic spin chain can be
used as a model system to investigate the role of heterogeneities in the
propagation of highly nonlinear waves.Comment: 10 pages, 8 figures (some with multiple parts), to appear in Physical
Review E; summary of changes: new title, one new figure, additional
discussion of several points (including both background and results
Failure mechanisms and surface roughness statistics of fractured Fontainebleau sandstone
In an effort to investigate the link between failure mechanisms and the
geometry of fractures of compacted grains materials, a detailed statistical
analysis of the surfaces of fractured Fontainebleau sandstones has been
achieved. The roughness of samples of different widths W is shown to be self
affine with an exponent zeta=0.46 +- 0.05 over a range of length scales ranging
from the grain size d up to an upper cut-off length \xi = 0.15 W. This low zeta
value is in agreement with measurements on other sandstones and on sintered
materials. The probability distributions P(delta z,delta h) of the variations
of height over different distances delta z > d can be collapsed onto a single
Gaussian distribution with a suitable normalisation and do not display
multifractal features. The roughness amplitude, as characterized by the
height-height correlation over fixed distances delta z, does not depend on the
sample width, implying that no anomalous scaling of the type reported for other
materials is present. It is suggested, in agreement with recent theoretical
work, to explain these results by the occurence of brittle fracture (instead of
damage failure in materials displaying a higher value of zeta = 0.8).Comment: 7 page
Toughening and asymmetry in peeling of heterogeneous adhesives
The effective adhesive properties of heterogeneous thin films are
characterized through a combined experimental and theoretical investigation. By
bridging scales, we show how variations of elastic or adhesive properties at
the microscale can significantly affect the effective peeling behavior of the
adhesive at the macroscale. Our study reveals three elementary mechanisms in
heterogeneous systems involving front propagation: (i) patterning the elastic
bending stiffness of the film produces fluctuations of the driving force
resulting in dramatically enhanced resistance to peeling; (ii) optimized
arrangements of pinning sites with large adhesion energy are shown to control
the effective system resistance, allowing the design of highly anisotropic and
asymmetric adhesives; (iii) heterogeneities of both types result in front
motion instabilities producing sudden energy releases that increase the overall
adhesion energy. These findings open potentially new avenues for the design of
thin films with improved adhesion properties, and motivate new investigation of
other phenomena involving front propagation.Comment: Physical Review Letters (2012)
Morphology of two dimensional fracture surface
We consider the morphology of two dimensional cracks observed in experimental
results obtained from paper samples and compare these results with the
numerical simulations of the random fuse model (RFM). We demonstrate that the
data obey multiscaling at small scales but cross over to self-affine scaling at
larger scales. Next, we show that the roughness exponent of the random fuse
model is recovered by a simpler model that produces a connected crack, while a
directed crack yields a different result, close to a random walk. We discuss
the multiscaling behavior of all these models.Comment: slightly revise
Damage accumulation and hysteretic behavior of MAX phase materials
The compressive response of fully dense and 10 vol% porous Ti_(2)AlC MAX phase materials subjected to quasi-static uniaxial and cyclic loading including their repeatable hysteretic behavior is presented. Damage accumulation in the form of kink bands and microcracking is characterized using ultrasonics and scanning electron microscopy under different levels of compressive loading. The observations and measurements are correlated quantitatively using a model based on friction between the crack faces, which is the main dissipation process. The model is shown to capture the hysteretic behavior of Ti_(2)AlC MAX phase and quantitatively reproduce the experimentally measured stress–strain curves