196 research outputs found
Switching of both local ferroelectric and magnetic domains in multiferroic Bi0.9La0.1FeO3 thin film by mechanical force
Cross-coupling of ordering parameters in multiferroic materials by multiple
external stimuli other than electric field and magnetic field is highly
desirable from both practical application and fundamental study points of view.
Recently, mechanical force has attracted great attention in switching of
ferroic ordering parameters via electro-elastic coupling in ferroelectric
materials. In this work, mechanical force induced polarization and
magnetization switching were investigated in a polycrystalline multiferroic
Bi0.9La0.1FeO3 thin film using a scanning probe microscopy system. The
piezoresponse force microscopy and magnetic force microscopy responses suggest
that both the ferroelectric domains and the magnetic domains in Bi0.9La0.1FeO3
film could be switched by mechanical force as well as electric field. High
strain gradient created by mechanical force is demonstrated as able to induce
ferroelastic switching and thus induce both ferroelectric dipole and magnetic
spin flipping in our thin film, as a consequence of electro-elastic coupling
and magneto-electric coupling. The demonstration of mechanical force control of
both the ferroelectric and the magnetic domains at room temperature provides a
new freedom for manipulation of multiferroics and could result in devices with
novel functionalities
Hydro-micromechanical modeling of wave propagation in saturated granular media
Biot's theory predicts the wave velocities of a saturated poroelastic
granular medium from the elastic properties, density and geometry of its dry
solid matrix and the pore fluid, neglecting the interaction between constituent
particles and local flow. However, when the frequencies become high and the
wavelengths comparable with particle size, the details of the microstructure
start to play an important role. Here, a novel hydro-micromechanical numerical
model is proposed by coupling the lattice Boltzmann method (LBM) with the
discrete element method (DEM. The model allows to investigate the details of
the particle-fluid interaction during propagation of elastic waves While the
DEM is tracking the translational and rotational motion of each solid particle,
the LBM can resolve the pore-scale hydrodynamics. Solid and fluid phases are
two-way coupled through momentum exchange. The coupling scheme is benchmarked
with the terminal velocity of a single sphere settling in a fluid. To mimic a
pressure wave entering a saturated granular medium, an oscillating pressure
boundary condition on the fluid is implemented and benchmarked with
one-dimensional wave equations. Using a face centered cubic structure, the
effects of input waveforms and frequencies on the dispersion relations are
investigated. Finally, the wave velocities at various effective confining
pressures predicted by the numerical model are compared with with Biot's
analytical solution, and a very good agreement is found. In addition to the
pressure and shear waves, slow compressional waves are observed in the
simulations, as predicted by Biot's theory.Comment: Manuscript submitted to International Journal for Numerical and
Analytical Methods in Geomechanic
マルチスケール手法によるジオテキスタイル補強地盤の特性評価
広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora
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