36 research outputs found
Size effects and idealized dislocation microstructure at small scales: predictions of a phenomenological model of Mesoscopic Field Dislocation Mechanics: Part I
A Phenomenological Mesoscopic Field Dislocation Mechanics (PMFDM) model is
developed, extending continuum plasticity theory for studying initial-boundary
value problems of small-scale plasticity. PMFDM results from an elementary
space-time averaging of the equations of Field Dislocation Mechanics (FDM),
followed by a closure assumption from any strain-gradient plasticity model that
attempts to model effects of geometrically-necessary dislocations (GND) only in
work-hardening
Optimum PID Control of Multi-wing Attractors in A Family of Lorenz-like Chaotic Systems
Multi-wing chaotic attractors are highly complex nonlinear dynamical systems
with higher number of index-2 equilibrium points. Due to the presence of
several equilibrium points, randomness of the state time series for these
multi-wing chaotic systems is higher than that of the conventional double wing
chaotic attractors. A real coded Genetic Algorithm (GA) based global
optimization framework has been presented in this paper, to design optimum PID
controllers so as to control the state trajectories of three different
multi-wing Lorenz like chaotic systems viz. Lu, Rucklidge and Sprott-1 system.Comment: 6 pages, 21 figures; 2012 Third International Conference on
Computing, Communication and Networking Technologies (ICCCNT'12), July 2012,
Coimbator
Modeling dislocation sources and size effects at initial yield in continuum plasticity
Size effects at initial yield (prior to stage II) of idealized micron-sized specimens are modeled within
a continuum model of plasticity. Two different aspects are considered: specification of a density of
dislocation sources that represent the emission of dislocation dipoles, and the presence of an initial,
spatially inhomogeneous excess dislocation content. Discreteness of the source distribution appears to
lead to a stochastic response in stress-strain curves, with the stochasticity diminishing as the number
of sources increases. Variability in stress-strain response due to variations of source distribution is also
shown. These size effects at initial yield are inferred to be due to physical length scales in dislocation
mobility and the discrete description of sources that induce internal-stress-related effects, and not due
to length-scale effects in the mean-field strain-hardening response (as represented through a constitutive
equation)