50 research outputs found
Magnetostriction in the magneto-sensitive elastomers with inhomogeneously magnetized particles: pairwise interaction approximation
We analyze the magnetostriction effect occurring in the magneto-sensitive
elastomers (MSEs) containing inhomogeneously magnetized particles. As it was
shown before, the expression for the interaction potential between two magnetic
spheres, that accounts for their mutual inhomogeneous magnetization, can be
obtained from the Laplace equation. We use this potential in the approximation
formula form to construct magnetic energy of the sample in terms of the
pairwise interactions of the particles. We show that this form of magnetic
energy leads to the same demagnetizing factor as predicted by the continuum
mechanics, confirming that only dipole-dipole magnetic interactions are
important on a large scale. As the next step, we examine the role played by the
particles arrangement on the magnetostriction effect. We consider different
spatial distributions of the magnetic particles: a uniform one, as well as
several lattice-type distributions (SC, BCC, HCP and FCC arrangements). We show
that the particles arrangement affects significantly the magnetostriction
effect if the separation between them became comparable with the particles'
dimensions. We also show that, typically, this contribution to the
magnetostriction effect is of the opposite sign to the one related with the
initial elastomer shape. Finally, we calculate the magnetostriction effect
using the same interaction potential but expressed in a form of a series
expansion, qualitatively confirming the above findings
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Intrinsic modulus and strain coefficients in dilute composites with a Neo-Hookean elastic matrix
A finite element modelling of dilute elastomer composites based on a Neo-Hookean elastic matrix and rigid spherical particles embedded within the matrix was performed. In particular, the deformation field in vicinity of a sphere was simulated and numerical homogenization has been used to obtain the effective modulus of the composite μeff for different applied extension and compression ratios. At small deformations the well-known Smallwood result for the composite is reproduced: μeff=(1+[μ]φ)μ0 with the intrinsic modulus [μ]=2.500. Here φ is the volume fraction of particles and μ0 is the modulus of the matrix solid. However at larger deformations higher values of the intrinsic modulus [μ] are obtained, which increase quadratically with the applied true strain. The homogenization procedure allowed to extract the intrinsic strain coefficients which are mirrored around the undeformed state for principle extension and compression axes. Utilizing the simulation results, stress and strain modifications of the Neo-Hookean strain energy function for dilute composites are proposed
Mechanical properties of magneto-sensitive elastomers: unification of the continuummechanics and microscopic theoretical approaches
A new theoretical formalism is developed for the study of the mechanical behaviour of magneto-sensitive elastomers (MSEs) under a uniform external magnetic field. This formalism allows us to combine macroscopic continuum-mechanics and microscopic approaches for complex analysis of MSEs with different shapes and with different particle distributions. It is shown that starting from a model based on an explicit discrete particle distribution one can separate the magnetic field inside the MSE into two contributions: one which depends on the shape of the sample with finite size and the other, which depends on the local spatial particle distribution. The magneto-induced deformation and the change of elastic modulus are found to be either positive or negative, their dependences on the magnetic field being determined by a non-trivial interplay between these two contributions. Mechanical properties are studied for two opposite types of coupling between the particle distribution and the magneto-induced deformation: absence of elastic coupling and presence of strong affine coupling. Predictions of a new formalism are in a qualitative agreement with existing experimental data
Local and cluster critical dynamics of the 3d random-site Ising model
We present the results of Monte Carlo simulations for the critical dynamics
of the three-dimensional site-diluted quenched Ising model. Three different
dynamics are considered, these correspond to the local update Metropolis scheme
as well as to the Swendsen-Wang and Wolff cluster algorithms. The lattice sizes
of L=10-96 are analysed by a finite-size-scaling technique. The site dilution
concentration p=0.85 was chosen to minimize the correction-to-scaling effects.
We calculate numerical values of the dynamical critical exponents for the
integrated and exponential autocorrelation times for energy and magnetization.
As expected, cluster algorithms are characterized by lower values of dynamical
critical exponent than the local one: also in the case of dilution critical
slowing down is more pronounced for the Metropolis algorithm. However, the
striking feature of our estimates is that they suggest that dilution leads to
decrease of the dynamical critical exponent for the cluster algorithms. This
phenomenon is quite opposite to the local dynamics, where dilution enhances
critical slowing down.Comment: 24 pages, 16 figures, style file include
Fixed points in frustrated magnets revisited
We analyze the validity of perturbative renormalization group estimates
obtained within the fixed dimension approach of frustrated magnets. We
reconsider the resummed five-loop beta-functions obtained within the minimal
subtraction scheme without epsilon-expansion for both frustrated magnets and
the well-controlled ferromagnetic systems with a cubic anisotropy. Analyzing
the convergence properties of the critical exponents in these two cases we find
that the fixed point supposed to control the second order phase transition of
frustrated magnets is very likely an unphysical one. This is supported by its
non-Gaussian character at the upper critical dimension d=4. Our work confirms
the weak first order nature of the phase transition occuring at three
dimensions and provides elements towards a unified picture of all existing
theoretical approaches to frustrated magnets.Comment: 18 pages, 8 figures. This article is an extended version of
arXiv:cond-mat/060928