61 research outputs found
Competing failure mechanisms in thin films: Application to layer transfer
We investigate the origin of transverse cracks often observed in thin films obtained by the layer transfer technique. During this process, two crystals bonded to each other containing a weak plane produced by ion implantation are heated to let a thin layer of one of the material on the other. The level of stress imposed on the film during the heating phase due to the mismatch of thermal expansion coefficients of the substrate and the film is shown to be the dominent factor in determining the quality of the transferred layer. In particular, it is shown that if the film is submitted to a tensile stress, the microcracks produced by ion implantation are not stable and deviate from the plane of implantation making the layer transfer process impossible. However, if the compressive stress exceeds a threshold value, after layer transfer, the film can buckle and delaminate, leading to transverse cracks induced by bending. As a result, we show that the imposed stress σ_m —- or equivalently the heating temperature -— must be within the range −σ_c<σ_m<0 to produce an intact thin film where σ_c depends on the interfacial fracture energy and the size of defects at the interface between film and substrate
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
Scaling exponents for fracture surfaces in homogenous glass and glassy ceramics
We investigate the scaling properties of post-mortem fracture surfaces in
silica glass and glassy ceramics. In both cases, the 2D height-height
correlation function is found to obey Family-Viseck scaling properties, but
with two sets of critical exponents, in particular a roughness exponent
in homogeneous glass and in glassy
ceramics. The ranges of length-scales over which these two scalings are
observed are shown to be below and above the size of process zone respectively.
A model derived from Linear Elastic Fracture Mechanics (LEFM) in the
quasistatic approximation succeeds to reproduce the scaling exponents observed
in glassy ceramics. The critical exponents observed in homogeneous glass are
conjectured to reflect damage screening occurring for length-scales below the
size of the process zone
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
Unified scenario for the morphology of crack paths in two-dimensional disordered solids
A combined experimental and numerical investigation of the roughness of intergranular cracks in two-dimensional disordered solids is presented. We focus on brittle materials for which the characteristic length scale of damage is much smaller than the grain size. Surprisingly, brittle cracks do not follow a persistent path with a roughness exponent ζ≈0.6-0.7 as reported for a large range of materials. Instead, we show that they exhibit monoaffine scaling properties characterized by a roughness exponent ζ=0.50±0.05, which we explain theoretically from linear elastic fracture mechanics. Our findings support the description of the roughening process in two-dimensional brittle disordered solids by a random walk. Furthermore, they shed light on the failure mechanism at the origin of the persistent behavior with ζ≈0.6-0.7 observed for fractures in other materials, suggesting a unified scenario for the geometry of crack paths in two-dimensional disordered solids
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)
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
Two-dimensional scaling properties of experimental fracture surfaces
The morphology of fracture surfaces encodes the various complex damage and
fracture processes occurring at the microstructure scale that have lead to the
failure of a given heterogeneous material. Understanding how to decipher this
morphology is therefore of fundamental interest. This has been extensively
investigated over these two last decades. It has been established that 1D
profiles of these fracture surfaces exhibit properties of scaling invariance.
In this paper, we present deeper analysis and investigate the 2D scaling
properties of these fracture surfaces. We showed that the properties of scaling
invariance are anisotropic and evidenced the existence of two peculiar
directions on the post-mortem fracture surface caracterized by two different
scaling exponents: the direction of the crack growth and the direction of the
crack front. These two exponents were found to be universal, independent of the
crack growth velocity, in both silica glass and aluminum alloy, archetype of
brittle and ductile material respectively. Moreover, the 2D structure function
that fully characterizes the scaling properties of the fracture surface was
shown to take a peculiar form similar to the one predicted by some models
issued from out-of-equilibrium statistical physics. This suggest some promising
analogies between dynamic phase transition models and the stability of a crack
front pinned/unpinned by the heterogenities of the material.Comment: 4 page
Crackling dynamics in material failure as the signature of a self-organized dynamic phase transition
We derive here a linear elastic stochastic description for slow crack growth
in heterogeneous materials. This approach succeeds in reproducing
quantitatively the intermittent crackling dynamics observed recently during the
slow propagation of a crack along a weak heterogeneous plane of a transparent
Plexiglas block [M{\aa}l{\o}y {\it et al.}, PRL {\bf 96} 045501]. In this
description, the quasi-static failure of heterogeneous media appears as a
self-organized critical phase transition. As such, it exhibits universal and to
some extent predictable scaling laws, analogue to that of other systems like
for example magnetization noise in ferromagnets
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
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