388 research outputs found
Simulation of textures and Lankford values for face centered cubic polycrystaline metals by using a modified Taylor model
This report presents a modified Taylor model is presented which statistically considers grain interaction in a polycrystalline aggregate in terms of a standard deviation for the symmetric part of the velocity gradient. The model can be solved using a Newton iteration method. We simulate crystallographic rolling textures and the anisotropy arising from uniaxial tension tests (Lankford values for different directions in the rolling sheet plane). The results reveal in part a good agreement with experimental data
Studying the effect of grain boundaries in dislocation density based crystal plasticity finite element simulations
AbstractA dislocation density based constitutive model for the face centered cubic crystal structure has been implemented into a crystal-plasticity finite element framework and extended to consider the mechanical interaction between mobile dislocations and grain boundaries by the authors [Ma, A., Roters, F., Raabe, D., 2006a. A dislocation density based constitutive model for crystal-plasticity FEM including geometrically necessary dislocations. Acta Materialia 54, 2169–2179; Ma, A., Roters, F., Raabe, D., 2006b. On the consideration of interactions between dislocations and grain boundaries in crystal-plasticity finite element modeling – theory, experiments, and simulations. Acta Materialia 54, 2181–2194]. The approach to model the grain boundary resistance against slip is based on the introduction of an additional activation energy into the rate equation for mobile dislocations in the vicinity of internal interfaces. This energy barrier is derived from the assumption of thermally activated dislocation penetration events through grain boundaries. The model takes full account of the geometry of the grain boundaries and of the Schmid factors of the critically stressed incoming and outgoing slip systems. In this study we focus on the influence of the one remaining model parameter which can be used to scale the obstacle strength of the grain boundary
Grain boundary mechanics in Crystal Plasticity Finite Element Modeling
Crystal mechanics-FEM 3D EBSD Materials science of arthropods: lobste
Monte Carlo Dynamics of driven Flux Lines in Disordered Media
We show that the common local Monte Carlo rules used to simulate the motion
of driven flux lines in disordered media cannot capture the interplay between
elasticity and disorder which lies at the heart of these systems. We therefore
discuss a class of generalized Monte Carlo algorithms where an arbitrary number
of line elements may move at the same time. We prove that all these dynamical
rules have the same value of the critical force and possess phase spaces made
up of a single ergodic component. A variant Monte Carlo algorithm allows to
compute the critical force of a sample in a single pass through the system. We
establish dynamical scaling properties and obtain precise values for the
critical force, which is finite even for an unbounded distribution of the
disorder. Extensions to higher dimensions are outlined.Comment: 4 pages, 3 figure
Higher correlations, universal distributions and finite size scaling in the field theory of depinning
Recently we constructed a renormalizable field theory up to two loops for the
quasi-static depinning of elastic manifolds in a disordered environment. Here
we explore further properties of the theory. We show how higher correlation
functions of the displacement field can be computed. Drastic simplifications
occur, unveiling much simpler diagrammatic rules than anticipated. This is
applied to the universal scaled width-distribution. The expansion in
d=4-epsilon predicts that the scaled distribution coincides to the lowest
orders with the one for a Gaussian theory with propagator G(q)=1/q^(d+2 \zeta),
zeta being the roughness exponent. The deviations from this Gaussian result are
small and involve higher correlation functions, which are computed here for
different boundary conditions. Other universal quantities are defined and
evaluated: We perform a general analysis of the stability of the fixed point.
We find that the correction-to-scaling exponent is omega=-epsilon and not
-epsilon/3 as used in the analysis of some simulations. A more detailed study
of the upper critical dimension is given, where the roughness of interfaces
grows as a power of a logarithm instead of a pure power.Comment: 15 pages revtex4. See also preceding article cond-mat/030146
Crystal Plasticity and Fresh Lobster
Mechanics of few crystals Mechanics of many crystals 3D electron microscopy Chitin-composite
Origin of the roughness exponent in elastic strings at the depinning threshold
Within a recently developed framework of dynamical Monte Carlo algorithms, we
compute the roughness exponent of driven elastic strings at the
depinning threshold in 1+1 dimensions for different functional forms of the
(short-range) elastic energy. A purely harmonic elastic energy leads to an
unphysical value for . We include supplementary terms in the elastic
energy of at least quartic order in the local extension. We then find a
roughness exponent of , which coincides with the one
obtained for different cellular automaton models of directed percolation
depinning. The quartic term translates into a nonlinear piece which changes the
roughness exponent in the corresponding continuum equation of motion. We
discuss the implications of our analysis for higher-dimensional elastic
manifolds in disordered media.Comment: 4 pages, 2 figure
Depinning transition and thermal fluctuations in the random-field Ising model
We analyze the depinning transition of a driven interface in the 3d
random-field Ising model (RFIM) with quenched disorder by means of Monte Carlo
simulations. The interface initially built into the system is perpendicular to
the [111]-direction of a simple cubic lattice. We introduce an algorithm which
is capable of simulating such an interface independent of the considered
dimension and time scale. This algorithm is applied to the 3d-RFIM to study
both the depinning transition and the influence of thermal fluctuations on this
transition. It turns out that in the RFIM characteristics of the depinning
transition depend crucially on the existence of overhangs. Our analysis yields
critical exponents of the interface velocity, the correlation length, and the
thermal rounding of the transition. We find numerical evidence for a scaling
relation for these exponents and the dimension d of the system.Comment: 6 pages, including 9 figures, submitted for publicatio
Stochastic boundary conditions in the deterministic Nagel-Schreckenberg traffic model
We consider open systems where cars move according to the deterministic
Nagel-Schreckenberg rules and with maximum velocity , what is an
extension of the Asymmetric Exclusion Process (ASEP). It turns out that the
behaviour of the system is dominated by two features: a) the competition
between the left and the right boundary b) the development of so-called
"buffers" due to the hindrance an injected car feels from the front car at the
beginning of the system. As a consequence, there is a first-order phase
transition between the free flow and the congested phase accompanied by the
collapse of the buffers and the phase diagram essentially differs from that of
(ASEP).Comment: 29 pages, 26 figure
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