70 research outputs found
Experimental study of the effect of disorder on subcritical crack growth dynamics
The growth dynamics of a single crack in a heterogeneous material under
subcritical loading is an intermittent process; and many features of this
dynamics have been shown to agree with simple models of thermally activated
rupture. In order to better understand the role of material heterogeneities in
this process, we study the subcritical propagation of a crack in a sheet of
paper in the presence of a distribution of small defects such as holes. The
experimental data obtained for two different distributions of holes are
discussed in the light of models that predict the slowing down of crack growth
when the disorder in the material is increased; however, in contradiction with
these theoretical predictions, the experiments result in longer lasting cracks
in a more ordered scenario. We argue that this effect is specific to
subcritical crack dynamics and that the weakest zones between holes at close
distance to each other are responsible both for the acceleration of the crack
dynamics and the slightly different roughness of the crack path.Comment: 4 pages, 5 figures, accepted in Physical Review Letters
(http://prl.aps.org
Strong dynamical effects during stick-slip adhesive peeling
We consider the classical problem of the stick-slip dynamics observed when
peeling a roller adhesive tape at a constant velocity. From fast imaging
recordings, we extract the dependencies of the stick and slip phases durations
with the imposed peeling velocity and peeled ribbon length. Predictions of
Maugis and Barquins [in Adhesion 12, edited by K.W. Allen, Elsevier ASP,
London, 1988, pp. 205--222] based on a quasistatic assumption succeed to
describe quantitatively our measurements of the stick phase duration. Such
model however fails to predict the full stick-slip cycle duration, revealing
strong dynamical effects during the slip phase.Comment: Soft Matter 201
The cooperative effect of load and disorder in thermally activated rupture of a two-dimensional random fuse network
A random fuse network, or equivalently a two-dimensional spring network with
quenched disorder, is subjected to a constant load and thermal noise, and
studied by means of numerical simulations. Rupture is thermally activated and
the lifetime follows an Arrhenius law where the energy barrier is reduced by
disorder. Due to the non-homogeneous distribution of forces from the stress
concentration at microcrack tips, spatial correlations between rupture events
appear, but they do not affect the energy barrier's dependence on the disorder;
they affect only the coupling between the disorder and the applied load
Physics of sub-critical crack growth in a fibrous material: experiments and model
Communication 4271 http://www.icf11.com/proceeding/EXTENDED/4721.pdfWe are interested in slow rupture processes observed when a material is submitted to a constant load below a critical rupture threshold. It is well known that the delay time (or lifetime) of the material before complete macroscopic rupture strongly depends on the applied stress. Thermodynamics has slowly emerged as a possible framework to describe delayed rupture of materials since early experiments have shown temperature dependence of lifetime with an Arrhenius law. On the other hand, efforts are made to describe slow rupture dynamics from rheological properties of the material such as viscoelasticity and plasticity. To shed light on this problem, it is important to compare experiments and models to distinguish between the different theoretical descriptions. For this purpose, we have studied experimentally the slow growth of a single crack in a fibrous material made of fax paper. Specifically, we have observed that the crack grows by steps of various sizes whose distribution is rather complex and evolves as a function of the crack length. In spite of this complexity, a statistical average of the growth dynamics reveals a very simple behaviour. We show that a model of thermally activated dynamics is able to reproduce many experimental observations. In particular, we show that the average dynamics is in good agreement with the experimental data. In addition, we find that the distribution of step sizes follows sub-critical point statistics with a power law and a stress-dependent exponential cut-off diverging at the critical rupture threshold. The exponent of the power law predicted by the model (3/2) seems to be slightly too large. Leaving the exponent as a free parameter gives a value 1.23+/-0.1. We stress that the material heterogeneity appears in the model only as a characteristic mesoscopic length scale. The fact that a simple model of thermally activated crack dynamics is able to reproduce with a good accuracy our experimental findings may open new perspectives in the description of slow rupture dynamics
Imaging the stick-slip peeling of an adhesive tape under a constant load
Using a high speed camera, we study the peeling dynamics of an adhesive tape
under a constant load with a special focus on the so-called stick-slip regime
of the peeling. It is the first time that the very fast motion of the peeling
point is imaged. The speed of the camera, up to 16000 fps, allows us to observe
and quantify the details of the peeling point motion during the stick and slip
phases: stick and slip velocities, durations and amplitudes. First, in contrast
with previous observations, the stick-slip regime appears to be only transient
in the force controlled peeling. Additionally, we discover that the stick and
slip phases have similar durations and that at high mean peeling velocity, the
slip phase actually lasts longer than the stick phase. Depending on the mean
peeling velocity, we also observe that the velocity change between stick and
slip phase ranges from a rather sudden to a smooth transition. These new
observations can help to discriminate between the various assumptions used in
theoretical models for describing the complex peeling of an adhesive tape. The
present imaging technique opens the door for an extensive study of the velocity
controlled stick-slip peeling of an adhesive tape that will allow to understand
the statistical complexity of the stick-slip in a stationary case
Intermittent stick-slip dynamics during the peeling of an adhesive tape from a roller
We study experimentally the fracture dynamics during the peeling at a
constant velocity of a roller adhesive tape mounted on a freely rotating
pulley. Thanks to a high speed camera, we measure, in an intermediate range of
peeling velocities, high frequency oscillations between phases of slow and
rapid propagation of the peeling fracture. This so-called stick-slip regime is
well known as the consequence of a decreasing fracture energy of the adhesive
in a certain range of peeling velocity coupled to the elasticity of the peeled
tape. Simultaneously with stick-slip, we observe low frequency oscillations of
the adhesive roller angular velocity which are the consequence of a pendular
instability of the roller submitted to the peeling force. The stick-slip
dynamics is shown to become intermittent due to these slow pendular
oscillations which produce a quasi-static oscillation of the peeling angle
while keeping constant the peeling fracture velocity (averaged over each
stick-slip cycle). The observed correlation between the mean peeling angle and
the stick-slip amplitude questions the validity of the usually admitted
independence with the peeling angle of the fracture energy of adhesives.Comment: Forthcoming in Physical Review
Fracture Surfaces as Multiscaling Graphs
Fracture paths in quasi-two-dimenisonal (2D) media (e.g thin layers of
materials, paper) are analyzed as self-affine graphs of height as a
function of length . We show that these are multiscaling, in the sense that
order moments of the height fluctuations across any distance
scale with a characteristic exponent that depends nonlinearly on the order of
the moment. Having demonstrated this, one rules out a widely held conjecture
that fracture in 2D belongs to the universality class of directed polymers in
random media. In fact, 2D fracture does not belong to any of the known kinetic
roughening models. The presence of multiscaling offers a stringent test for any
theoretical model; we show that a recently introduced model of quasi-static
fracture passes this test.Comment: 4 pages, 5 figure
A dynamical law for slow crack growth in polycarbonate films
We study experimentally the slow growth of a single crack in polycarbonate
films submitted to uniaxial and constant imposed stress. For this visco-plastic
material, we uncover a dynamical law that describes the dependence of the
instantaneous crack velocity with experimental parameters. The law involves a
Dugdale-Barenblatt static description of crack tip plastic zones associated to
an Eyring's law and an empirical dependence with the crack length that may come
from a residual elastic field
The effects of time correlations in subcritical fracture. An acoustic analysis
The fracture dynamics of heterogeneous materials is a rich subject with obvious practical interests, especially the subcritical fracture, where a material breaks through a series of successive, non-correlated and localized fracture events until the arriving to a critical situation where the whole material fails. Paper has been a common model material to study this phenomenon, and high-resolution and high-speed visualization are the usual ways to follow the dynamics of the process. However, visualization presents many limitations, especially for long experiences. That is one of the reasons why we are coupling acoustics to the measurements in an attempt to establish it as the main source of information. Acoustics presents a much better temporal resolution and captures a higher number of events than visualization. By thresholding the amplitude of the acoustic signal, it is possible to get similar activities in both measurements. The waiting times between events and the energy of the events are both distributed in power laws with exponents which are similar for the two different kind of measurements (visualization and acoustics), corroborating that the recorded acoustic data corresponds indeed to the fracture process
Repulsion and Attraction between a Pair of Cracks in a Plastic Sheet
We study the interaction of two collinear cracks in polymer sheets slowly growing towards each other, when submitted to uniaxial stress at a constant loading velocity. Depending on the sample’s geometry—specifically, the initial distances d between the two cracks’ axes and L between the cracks’ tips—we observe different crack paths with, in particular, a regime where the cracks repel each other prior to being attracted. We show that the angle θ characterizing the amplitude of the repulsion—and specifically its evolution with d—depends strongly on the microscopic behavior of the material. Our results highlight the crucial role of the fracture process zone. At interaction distances larger than the process zone size, crack repulsion is controlled by the microscopic shape of the process zone tip, while at shorter distances, the overall plastic process zone screens the repulsion interaction.Peer reviewe
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