In this paper, domain switching in ferroelectric ceramics near the morphotropic phase boundary (MPB), where tetragonal phase and rhombohedral phase coexist, is analyzed by a micromechanical model using an inverse-pole...
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An optimization-based computational model is proposed to study the constrained domain switching in polycrystalline ferroelectrics. Charge screening effect is taken into account thus the depolarization field induced by...
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An optimization-based computational model is proposed to study the constrained domain switching in polycrystalline ferroelectrics. Charge screening effect is taken into account thus the depolarization field induced by polarization switching vanishes. The stress field induced by non-180o switching cannot be compensated and is considered in an Eshelby inclusion manner. Domain switching is realized by an optimization process to minimize the free energy of each grain using fractions of each domain as the optimization variables. This model does not impose any priori domain switching criterion, thus having the similar superiority as the phase field model. Besides the polarization and strain, the domain textures can also be calculated using this model. Simulation results show that very little 900 domain switching can occur in tetragonal PZT ceramics, while in rhombohedral PZT ceramics, about half of non- 1800 switching can be accomplished under moderate electric poling. The large difference in poling difficulties between the tetragonal and rhombohedral PZT ceramics is partial due to the crystal symmetry differences, and also due to the large difference in lattice deformation during P-F phase transitions.
Space-time correlation is a staple method for investigating the dynamic coupling of spatial and temporal scales of motion in turbulent flows. In this article, we review the space-time correlation models in both the Eu...
Space-time correlation is a staple method for investigating the dynamic coupling of spatial and temporal scales of motion in turbulent flows. In this article, we review the space-time correlation models in both the Eulerian and Lagrangian frames of reference, which include the random sweeping and local straining models for isotropic and homogeneous turbulence, Taylor's frozen-flow model and the elliptic approximation model for turbulent shear flows, and the linear-wave propagation model and swept-wave model for compressible turbulence. We then focus on how space-time correlations are used to develop time-accurate turbulence models for the large-eddy simulation of turbulence-generated noise and particle-laden turbulence. We briefly discuss their applications to two-point closures for Kolmogorov's universal scaling of energy spectra and to the reconstruction of space-time energy spectra from a subset of spatial and temporal signals in experimental measurements. Finally, we summarize the current understanding of space-time correlations and conclude with future issues for the field.
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