365 research outputs found
Dynamics of the peel front and the nature of acoustic emission during peeling of an adhesive tape
We investigate the peel front dynamics and acoustic emission of an adhesive
tape within the context of a recent model by including an additional
dissipative energy that mimics bursts of acoustic signals. We find that the
nature of the peeling front can vary from smooth to stuck-peeled configuration
depending on the values of dissipation coefficient, inertia of the roller, mass
of the tape. Interestingly, we find that the distribution of AE bursts shows a
power law statistics with two scaling regimes with increasing pull velocity as
observed in experiments. In this regimes, the stuck-peeled configuration is
similar to the `edge of peeling' reminiscent of a system driven to a critical
state.Comment: Accepted for publication in Phys. Rev. Let
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
Adhesive Contact to a Coated Elastic Substrate
We show how the quasi-analytic method developed to solve linear elastic
contacts to coated substrates (Perriot A. and Barthel E. {\em J. Mat. Res.},
{\bf 2004}, {\em 19}, 600) may be extended to adhesive contacts. Substrate
inhomogeneity lifts accidental degeneracies and highlights the general
structure of the adhesive contact theory. We explicit the variation of the
contact variables due to substrate inhomogeneity. The relation to other
approaches based on Finite Element analysis is discussed
Hidden Order in Crackling Noise during Peeling of an Adhesive Tape
We address the long standing problem of recovering dynamical information from
noisy acoustic emission signals arising from peeling of an adhesive tape
subject to constant traction velocity. Using phase space reconstruction
procedure we demonstrate the deterministic chaotic dynamics by establishing the
existence of correlation dimension as also a positive Lyapunov exponent in a
mid range of traction velocities. The results are explained on the basis of the
model that also emphasizes the deterministic origin of acoustic emission by
clarifying its connection to sticks-slip dynamics.Comment: 5 pages, 10 figure
Interplay of internal stresses, electric stresses and surface diffusion in polymer films
We investigate two destabilization mechanisms for elastic polymer films and
put them into a general framework: first, instabilities due to in-plane stress
and second due to an externally applied electric field normal to the film's
free surface. As shown recently, polymer films are often stressed due to
out-of-equilibrium fabrication processes as e.g. spin coating. Via an
Asaro-Tiller-Grinfeld mechanism as known from solids, the system can decrease
its energy by undulating its surface by surface diffusion of polymers and
thereby relaxing stresses. On the other hand, application of an electric field
is widely used experimentally to structure thin films: when the electric
Maxwell surface stress overcomes surface tension and elastic restoring forces,
the system undulates with a wavelength determined by the film thickness. We
develop a theory taking into account both mechanisms simultaneously and discuss
their interplay and the effects of the boundary conditions both at the
substrate and the free surface.Comment: 14 pages, 7 figures, 1 tabl
Relation between composition, microstructure and oxidation in iron aluminides
The relation between chemical composition, microstructure and oxidation properties has been investigated on various FeAl based alloys, the aim being to induce changes in the microstructure of the compound by selective oxidation of aluminium. Oxidation kinetics that was evaluated on bulk specimens showed that, due to fast diffusion in the alloys, no composition gradient is formed during the aluminium selective oxidation. Accordingly, significant aluminium depletion in the compound could be observed in the thinnest part of oxidised wedge-shape specimens. Another way to obtain samples of variable aluminium content was to prepare diffusion couples with one aluminide and pure iron as end members. These latter specimens have been characterised using electron microscopy and first results of oxidation experiments are presented
Missing physics in stick-slip dynamics of a model for peeling of an adhesive tape
It is now known that the equations of motion for the contact point during
peeling of an adhesive tape mounted on a roll introduced earlier are singular
and do not support dynamical jumps across the two stable branches of the peel
force function. By including the kinetic energy of the tape in the Lagrangian,
we derive equations of motion that support stick-slip jumps as a natural
consequence of the inherent dynamics. In the low mass limit, these equations
reproduce solutions obtained using a differential-algebraic algorithm
introduced for the earlier equations. Our analysis also shows that mass of the
ribbon has a strong influence on the nature of the dynamics.Comment: Accepted for publication in Phys. Rev. E (Rapid Communication
Spreading of Latex Particles on a Substrate
We have investigated both experimentally and theoretically the spreading
behavior of latex particles deposited on solid substrates. These particles,
which are composed of cross-linked polymer chains, have an intrinsic elastic
modulus. We show that the elasticity must be considered to account for the
observed contact angle between the particle and the solid substrate, as
measured through atomic force microscopy techniques. In particular, the work of
adhesion computed within our model can be significantly larger than that from
the classical Dupr\'{e} formula.Comment: 7 pages, 7 figures, to appear in Europhys. Let
Self-stresses and Crack Formation by Particle Swelling in Cohesive Granular Media
We present a molecular dynamics study of force patterns, tensile strength and
crack formation in a cohesive granular model where the particles are subjected
to swelling or shrinkage gradients. Non-uniform particle size change generates
self-equilibrated forces that lead to crack initiation as soon as strongest
tensile contacts begin to fail. We find that the coarse-grained stresses are
correctly predicted by an elastic model that incorporates particle size change
as metric evolution. The tensile strength is found to be well below the
theoretical strength as a result of inhomogeneous force transmission in
granular media. The cracks propagate either inward from the edge upon shrinkage
and outward from the center upon swelling
Dynamics of stick-slip in peeling of an adhesive tape
We investigate the dynamics of peeling of an adhesive tape subjected to a
constant pull speed. We derive the equations of motion for the angular speed of
the roller tape, the peel angle and the pull force used in earlier
investigations using a Lagrangian. Due to the constraint between the pull
force, peel angle and the peel force, it falls into the category of
differential-algebraic equations requiring an appropriate algorithm for its
numerical solution. Using such a scheme, we show that stick-slip jumps emerge
in a purely dynamical manner. Our detailed numerical study shows that these set
of equations exhibit rich dynamics hitherto not reported. In particular, our
analysis shows that inertia has considerable influence on the nature of the
dynamics. Following studies in the Portevin-Le Chatelier effect, we suggest a
phenomenological peel force function which includes the influence of the pull
speed. This reproduces the decreasing nature of the rupture force with the pull
speed observed in experiments. This rich dynamics is made transparent by using
a set of approximations valid in different regimes of the parameter space. The
approximate solutions capture major features of the exact numerical solutions
and also produce reasonably accurate values for the various quantities of
interest.Comment: 12 pages, 9 figures. Minor modifications as suggested by refere
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