Electromagnetically conducting elastic plates in a magnetic field: modeling and dynamic implications

The basic field equations and boundary conditions necessary for the dynamic approach of electromagnetically conducting flat plates subjected to an external magnetic field are derived.Whereas the structural equations include the geometrical non-linearities of elastic isotropic plates, the electromagnetic equations are used in a linearized form that is obtained from their non-linear counterpart by applying the small disturbance concept. In this context, it was shown that the governing equations involve the bending-stretching coupling arising from both the geometrical non-linear approach of the problem and the inclusion of the Lorentz ponderomotive forces that are reduced to a 2-D plate counterpart.A number of special cases are considered, implications of the external magnetic field on non-linear/linear eigenfrequencies are highlighted, and pertinent conclusions are outlined.     

Electric‐field tuning of magnetoelectric properties in Metglas/piezofiber composites

The tunability of magnetoelectric (ME) properties by applied dc electric field (E) was systematically investigated for a laminate composite consisting of Metglas, Pb(Zr_x Ti_1–x)O₃ fiber, and interdigitated electrodes. The ME coefficients and equivalent magnetic noise were found to be dependent on E. This dependence is attributed to variations in the magnetic properties. The dielectric properties and noise charge density were relatively invariant to E. A 1.3× improvement in the ME coefficient was obtained at the Villari point under E = 300 V/mm relative to E = 0 V/mm. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Magnetoelastic interactions in a soft ferromagnetic body with a nonlinear law of magnetization: Some applications

Linearized equations and boundary conditions of a magnetoelastic ferromagnetic body are obtained with the nonlinear law of magnetization. Magnetoelastic interactions in a multi-domain ferromagnetic materials are considered for magneto soft materials, i.e. the case when the magnetic field intensity vector and magnetization vector are parallel. As a special case, the following two problems are considered: (1) the magnetoelastic stability of a ferromagnetic plate-strip in a homogeneous transverse magnetic field; (2) the stress–strain state of a ferromagnetic plane with a moving crack in a transverse magnetic field. It is shown that the modeling of magnetoelastic equations with a nonlinear law of magnetization provides qualitative and quantitative predictions on physical quantities including critical loads and stresses. In particular, it is shown that the critical magnetic field in plate stability problems found with the nonlinear law of magnetization is in better agreement with the experimental finding than the one found with a linear law. Furthermore, it is also shown that the stress concentration factor around a crack predicted with the nonlinear law of magnetization is more accurate than the one obtained with a linear counterpart. Numerical results are presented for above mentioned two problems and for various forms of nonlinear laws of magnetization.     

Incident flow effects on the performance of piezoelectric energy harvesters from galloping vibrations

In this paper, we investigate experimentally the concept of energy harvesting from galloping oscillations with a focus on wake and turbulence effects. The harvester is composed of a unimorph piezoelectric cantilever beam with a square cross-section tip mass. In one case, the harvester is placed in the wake of another galloping harvester with the objective of determining the wake effects on the response of the harvester. In the second case, meshes were placed upstream of the harvester with the objective of investigating the effects of upstream turbulence on the response of the harvester. The results show that both wake effects and upstream turbulence significantly affect the response of the harvester. Depending on the spacing between the two squares and the opening size of the mesh, wake and upstream turbulence can positively enhance the level of the harvested power.     

Cracked elastic layer under compressive mechanical loads

We consider boundary value problem in which an elastic layer containing a finite length crack is under compressive loading. The crack is parallel to the layer surfaces and the contact between crack surfaces are either frictionless or with adhesive friction or Coulomb friction.Based on fourier integral transformation techniques the solution of the formulated problems is reduced to the solution of a singular integral equation, then, using Chebyshev’s orthogonal polynomials, to an infinite system of linear algebraic equations. The regularity of these equations is established. The expressions for stress and displacement components in the elastic layer are presented. Based on the developed analytical algorithm, extensive numerical investigations have been conducted.The results of these investigations are illustrated graphically, exposing some novel qualitative and quantitative knowledge about the stress field in the cracked layer and their dependence on geometric and applied loading parameters. It can be seen from this study that the crack tip stress field has a mode II type singularity.     

Antiplane Shear Waves in Two Contacting Ferromagnetic Half Spaces

The problem of reflection and refraction of antiplane shear (or magneto-elastic) waves at the interface between two ferromagnetic half-spaces with slipping contact (vacuum gap) is studied for waves propagating normal to the direction of the applied external magnetic field which is assumed to be parallel to the interface. We show the existence of new waves that are localized near the interface between the two ferromagnetic media and accompany the reflected and the transmitted waves. We call the new waves as accompanying surface magneto-elastic (ASME) waves; their amplitudes depend upon values of magnetoelastic parameters of the two media and the intensity of the applied magnetic field. We derive closed-form expressions for magnitudes (coefficients) of the reflected, the refracted (transmitted) and the ASME waves. We show that for a range of values of the applied magnetic field the coefficient of the reflected wave increases and that of the transmitted wave decreases with an increase in the magnitude of the applied magnetic field; these coefficients eventually approach 1 and 0, respectively. That is, the applied external magnetic field can totally eliminate the transmitted wave, and can control energies of the reflected, the refracted and the ASME waves.     

Some dynamic problems for elastic materials with functional inhomogeneities: anti-plane deformations

The paper considers two dynamical problems for an isotropic elastic media with spatially varying functional inhomogeneity, the propagation of surface anti-plane shear SH waves, and the stress deformation state of an anti-plane vibrating medium with a semi-infinite crack. These problems are considered for five different types of inhomogeneity. It is shown that the propagation of surface anti-plane shear waves is possible in all these cases. The existence conditions and the speed of propagation of surface waves have been found. In the section devoted to the investigation of the stress deformation state of a vibrating medium with a semi-infinite crack, Fourier transforms along with the Wiener Hopf technique are employed to solve the equations of motion. The asymptotic expression for the stress near the crack tip is analyzed, which leads to a closed form solution of the dynamic stress intensity factor (DSIF). Here also the problem is considered for five different functional inhomogeneities. From the formulae for DSIF thus obtained one can see that the inhomogeneity can have both a quantitative and qualitative impact on the character of the stress distribution near the crack.Received: 25 July 2002, Accepted: 3 April 2003, Published online: 27 June 2003PACS: 83.20.Lr, 83.50.Tq, 83.50.Vr, 46.30.Nz