662 research outputs found
Fluctuation phenomena in crystal plasticity - a continuum model
On microscopic and mesoscopic scales, plastic flow of crystals is
characterized by large intrinsic fluctuations. Deformation by crystallographic
slip occurs in a sequence of intermittent bursts ('slip avalanches') with
power-law size distribution. In the spatial domain, these avalanches produce
characteristic deformation patterns in the form of slip lines and slip bands
which exhibit long-range spatial correlations. We propose a generic continuum
model which accounts for randomness in the local stress-strain relationships as
well as for long-range internal stresses that arise from the ensuing plastic
strain heterogeneities. The model parameters are related to the local dynamics
and interactions of lattice dislocations. The model explains experimental
observations on slip avalanches as well as the associated slip and surface
pattern morphologies
Size scaling of strength in thin film delamination
We investigate by numerical simulation the system size dependence of the
shear delamination strength of thin elastic films. The films are connected to a
rigid substrate by a disordered interface containing a pre-existing crack. The
size dependence of the strength of this system is found to depend crucially on
the crack shape. For circular cracks, we observe a crossover between a
size-independent regime at large crack radii which is controlled by propagation
of the pre-existing crack, and a size-dependent regime at small radii which is
dominated by nucleation of new cracks in other locations. For cracks of finite
width that span the system transversally, we observe for all values of the
crack length a logarithmic system size dependence of the failure stress. The
results are interpreted in terms of extreme value statistics.Comment: 10 pages, 4 figure
Slip avalanches in crystal plasticity: scaling of the avalanche cutoff
Plastic deformation of crystals proceeds through a sequence of intermittent
slip avalanches with scale-free (power-law) size distribution. On macroscopic
scales, however, plastic flow is known to be smooth and homogeneous. In the
present letter we use a recently proposed continuum model of slip avalanches to
systematically investigate the nature of the cut-off which truncates scale-free
behavior at large avalanche sizes. The dependence of the cut-off on system
size, geometry, and driving mode, but also on intrinsic parameters such as the
strain hardening rate is established. Implications for the observability of
avalanche behavior in microscopic and macroscopic samples are discussed.Comment: 12 pages, 4 figure
Some Limitations of Dislocation Walls as Models for Plastic Boundary Layers
It has recently become popular to analyze the behavior of excess dislocations
in plastic deformation under the assumption that such dislocations are arranged
into walls with periodic dislocation spacing along the wall direction. This
assumption is made plausible by the fact that periodic walls represent minimum
energy arrangements for dislocations of the same sign, and it allows to use the
analytically known short-ranged stress fields of such walls for analyzing the
structure of plastic boundary layers. Here we show that unfortunately both the
idea that dislocation walls are low-energy configurations and the properties of
their interactions depend critically on the assumption of a periodic
arrangement of dislocations within the walls. Once this assumption is replaced
by a random arrangement, the properties of dislocation walls change completely.Comment: To appear in: Proceedings of the International conference on
numerical analysis and applied mathematics (ICNAAM) 2011, 4 pages, to appear
in APS proceeding
Depinning of a dislocation: the influence of long-range interactions
The theory of the depinning transition of elastic manifolds in random media
provides a framework for the statistical dynamics of dislocation systems at
yield. We consider the case of a single flexible dislocation gliding through a
random stress field generated by a distribution of immobile dislocations
threading through its glide plane. The immobile dislocations are arranged in a
"restrictedly random" manner and provide an effective stress field whose
statistical properties can be calculated explicitly. We write an equation of
motion for the dislocation and compute the associated depinning force, which
may be identified with the yield stress. Numerical simulations of a discretized
version of the equation confirm these results and allow us to investigate the
critical dynamics of the pinning-depinning transition.Comment: 8 pages, 4 figures. To appear in the proceedings of the
Dislocations2000 meeting (published by Materials Science and Engeneering A
- …