15 research outputs found
Scaling Behaviour and Complexity of the Portevin-Le Chatelier Effect
The plastic deformation of dilute alloys is often accompanied by plastic
instabilities due to dynamic strain aging and dislocation interaction. The
repeated breakaway of dislocations from and their recapture by solute atoms
leads to stress serrations and localized strain in the strain controlled
tensile tests, known as the Portevin-Le Chatelier (PLC) effect. In this present
work, we analyse the stress time series data of the observed PLC effect in the
constant strain rate tensile tests on Al-2.5%Mg alloy for a wide range of
strain rates at room temperature. The scaling behaviour of the PLC effect was
studied using two complementary scaling analysis methods: the finite variance
scaling method and the diffusion entropy analysis. From these analyses we could
establish that in the entire span of strain rates, PLC effect showed Levy walk
property. Moreover, the multiscale entropy analysis is carried out on the
stress time series data observed during the PLC effect to quantify the
complexity of the distinct spatiotemporal dynamical regimes. It is shown that
for the static type C band, the entropy is very low for all the scales compared
to the hopping type B and the propagating type A bands. The results are
interpreted considering the time and length scales relevant to the effect.Comment: 35 pages, 6 figure
Coherent Hydrodynamic Coupling for Stochastic Swimmers
A recently developed theory of stochastic swimming is used to study the
notion of coherence in active systems that couple via hydrodynamic
interactions. It is shown that correlations between various modes of
deformation in stochastic systems play the same role as the relative internal
phase in deterministic systems. An example is presented where a simple swimmer
can use these correlations to hunt a non-swimmer by forming a hydrodynamic
bound state of tunable velocity and equilibrium separation. These results
highlight the significance of coherence in the collective behavior of
nano-scale stochastic swimmers.Comment: 6 pages, 3 figure