23 research outputs found
Sliding without slipping under Coulomb friction: opening waves and inversion of frictional force
An elastic layer slides on a rigid flat governed by Coulomb's friction law.
We demonstrate that if the coefficient of friction is high enough, the sliding
localizes within stick-slip pulses, which transform into opening waves
propagating at intersonic speed in the direction of sliding or, for high
Poisson's ratios, at supersonic speed in the opposite direction. This sliding
mode, characterized by marginal frictional dissipation, and similar to carpet
fold propagation, may result in inversion of the frictional force direction; at
longer time intervals the system demonstrates stick-slip behavior. The
mechanism is described in detail and a parametric study is presented.Comment: 17 pages, 4 figures, 1 tabl
Electrical and Thermal Conductivity of Complex-Shaped Contact Spots
This paper explores the electrical and thermal conductivity of complex
contact spots on the surface of a half-space. Employing an in-house Fast
Boundary Element Method implementation, various complex geometries were
studied. Our investigation begins with annulus contact spots to assess the
impact of connectedness. We then study shape effects on "multi-petal" spots
exhibiting dihedral symmetry, resembling flowers, stars, and gears. The
analysis culminates with self-affine shapes, representing a multi-scale
generalization of the multi-petal forms. In each case, we introduce appropriate
normalizations and develop phenomenological models. For multi-petal shapes, our
model relies on a single geometric parameter: the normalized number of
"petals". This approach inspired the form of the phenomenological model for
self-affine spots, which maintains physical consistency and relies on four
geometric characteristics: standard deviation, second spectral moment, Nayak
parameter, and Hurst exponent. As a by product, these models enabled us to
suggest flux estimations for an infinite number of petals and the fractal
limit. This study represents an initial step into understanding the
conductivity of complex contact interfaces, which commonly occur in the contact
of rough surfaces.Comment: 40 pages, 28 figure
The role of phase interface energy in martensitic transformations: a lattice Monte-Carlo simulation
To study martensitic phase transformation we use a micromechanical model
based on statistical mechanics. Employing lattice Monte-Carlo simulations and
realistic material properties for shape-memory alloys (SMA), we investigate the
combined influence of the external stress, temperature, and interface energy
between the austenitic and martensitic phase on the transformation kinetics and
the effective material compliance. The one-dimensional model predicts well many
features of the martensitic transformation that are observed experimentally.
Particularly, we study the influence of the interface energy on the
transformation width and the effective compliance. In perspective, the obtained
results might be helpful for the design of new SMAs for more sensitive smart
structures and more efficient damping systems.Comment: 10 pages, 3 figures, 22 reference
Wave propagation through an elastically asymmetric architected material
A one-dimensional wave propagation through elastically asymmetric media is
investigated. A class of metamaterials possessing an arbitrary elastic
asymmetry is proposed. This asymmetry results in different wave speeds of
tensile and compressive components of elastic waves. The faster component can
overtake the slower one resulting in their dissipative annihilation through
energy cascades. Efficient absorbing assemblies are presented and analysed
numerically. The length of the asymmetric part needed to damp a harmonic signal
is determined analytically and validated numerically. Transmission properties
for random self-affine wave-packets are studied: a universal scaling for the
transmission factor variation with the length of the asymmetric part was
established.Comment: 23 pages, 13 figure
The existence of a critical length scale in regularised friction
We study a regularisation of Coulomb's friction law on the propagation of
local slip at an interface between a deformable and a rigid solid. This
regularisation, which was proposed based on experimental observations, smooths
the effect of a sudden jump in the contact pressure over a characteristic
length scale. We apply it in numerical simulations in order to analyse its
influence on the behaviour of local slip. We first show that mesh convergence
in dynamic simulations is achieved without any numerical damping in the bulk
and draw a convergence map with respect to the characteristic length of the
friction regularisation. By varying this length scale on the example of a given
slip event, we observe that there is a critical length below which the friction
regularisation does not affect anymore the propagation of the interface
rupture. A spectral analysis of the regularisation on a periodic variation of
Coulomb's friction is conducted to confirm the existence of this critical
length. The results indicate that if the characteristic length of the friction
regularisation is smaller than the critical length, a slip event behaves as if
it was governed by Coulomb's law. We therefore propose that there is a domain
of influence of the friction regularisation depending on its characteristic
length and on the frequency content of the local slip event. A byproduct of the
analysis is related to the existence of a physical length scale characterising
a given frictional interface. We establish that the experimental determination
of this interface property may be achieved by experimentally monitoring slip
pulses whose frequency content is rich enough.Comment: 21 pages, 7 figure
On the Propagation of Slip Fronts at Frictional Interfaces
The dynamic initiation of sliding at planar interfaces between deformable and
rigid solids is studied with particular focus on the speed of the slip front.
Recent experimental results showed a close relation between this speed and the
local ratio of shear to normal stress measured before slip occurs (static
stress ratio). Using a two-dimensional finite element model, we demonstrate,
however, that fronts propagating in different directions do not have the same
dynamics under similar stress conditions. A lack of correlation is also
observed between accelerating and decelerating slip fronts. These effects
cannot be entirely associated with static local stresses but call for a dynamic
description. Considering a dynamic stress ratio (measured in front of the slip
tip) instead of a static one reduces the above-mentioned inconsistencies.
However, the effects of the direction and acceleration are still present. To
overcome this we propose an energetic criterion that uniquely associates,
independently on the direction of propagation and its acceleration, the slip
front velocity with the relative rise of the energy density at the slip tip.Comment: 15 pages, 6 figure
Monitoring Greenland ice sheet buoyancy-driven calving discharge using glacial earthquakes
Since the 2000s, Greenland ice sheet mass loss has been accelerating, followed by increasing numbers of glacial earthquakes (GEs) at near-grounded glaciers. GEs are caused by calving of km-scale icebergs which capsize against the terminus. Seismic record inversion allows a reconstruction of the history of GE sources which captures capsize dynamics through iceberg-to-terminus contact. When compared with a catalog of contact forces from an iceberg capsize model, seismic force history accurately computes calving volumes while the earthquake magnitude fails to uniquely characterize iceberg size, giving errors up to 1 km ³ . Calving determined from GEs recorded ateight glaciers in 1993–2013 accounts for up to 21% of the associated discharge and 6% of the Greenland mass loss. The proportion of discharge attributed to capsizing calving may be underestimated by at least 10% as numerous events could not be identified by standard seismic detections (Olsen and Nettles, 2018). While calving production tends to stabilize in East Greenland, Western glaciers have released more and larger icebergs since 2010 and have become major contributors to Greenland dynamic discharge. Production of GEs and calving behavior are controlled by glacier geometry with bigger icebergs being produced when the terminus advances in deepening water. We illustrate how GEs can help in partitioning and monitoring Greenland mass loss and characterizing capsize dynamics
Accéleration des calculs du contact en éléments finis par H-matrices
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