Yuanwen Gao

Tunability of longitudinal wave band gaps in one dimensional phononic crystal with magnetostrictive material

Ways for controlling and adjusting the longitudinal wave band structures of one dimensional (1-D) rod phononic crystals with magnetostrictive material are theoretically investigated by the plane wave expansion method. Z-L model is adopted to accurately describe the constitutive relations of phononic crystal containing magnetostrictive material. Taking the magneto-mechanical coupling into account, the longitudinal wave band structures are calculated through the development of effective elastic constant, piezomagnetic constant, and magnetic permeability for magnetostrictive rod. Numerical results show that the longitudinal wave band gaps characteristics are significantly influenced by the applied static magnetic field and compressive pre-stress. Some new phenomena, such as the multi-peaks of the band gap widths corresponding to the varying filling fraction of the binary rod phononic crystal, are investigated.

The influence of material properties on the elastic band structures of one-dimensional functionally graded phononic crystals

We study the influence of material parameters on elastic band gaps of one-dimensional functionally graded phononic crystals (FGPCs). By using plane-wave expansion, we calculate the first four band structures of FGPCs consisting of functionally graded materials (FGMs). These structures vary exponentially. We systematically study the influence of material parameters for four different FGPC models. Compared with traditional phononic crystals (PCs), the FGPC band gaps are clearly changed by FGMs. We also consider the influence of material composition, material properties and geometrical parameters on band gaps. Results show that different FGM properties can change the band structures remarkably. Our work can facilitate the design of vibration filters and noise insulators and provide more design freedom in engineering.

Nonlinear magnetoelectric effect in PZT/Terfenol-D nanobilayer on a substrate with surface stress

Based on a linear piezoelectric constitutive relation and a nonlinear magnetostrictive constitutive relation, a nonlinear magnetoelectric (ME) effect model for lead zirconate titanate (PZT)/Terfenol-D nanobilayer on a substrate has been developed. In this study, the nonlinear ME coefficients at bending mode for two cases (without surface stress and with surface stress) are calculated by using Gurtin-Murdoch theory. The difference between two cases and the influence of residual surface tension are discussed. At the same time, the clamping effect of the substrate on ME effect is studied by altering the thickness ratio of the substrate and selecting different substrate materials. The influences of frequency of the magnetic field, PZT volume fraction on the ME effect are investigated, respectively. Finally, the dependence of ME effect on pre-stress is presented. The results show that for the nanobilayer, both the residual surface tension and surface stress have non-ignored effects on the ME effect. Besides, t...

Nonlinear magnetoelectric transient responses of a circular-shaped magnetoelectric layered structure

The nonlinear magnetoelectric (ME) transient responses and the frequency-multiplying behavior of a circular-shaped magnetoelectric layered structure are investigated by using a 2D nonlinear mechanical–magnetic coupling constitutive relation. The general analytical expressions for the ME coefficient in T–T and C–T modes have been obtained for circular-shaped magnetoelectric layered circular structures. The results indicate that the ME coefficient and the induced electric field exhibit a higher-order response mode for the nonlinear ME materials under strong applied magnetic fields. The amplitude of the applied magnetic field and the volume fraction of the piezoelectric layer have a significant influence on the ME coefficient. There exists an optimal piezoelectric layer volume fraction and an applied magnetic field at which the ME response coefficient is maximal. In addition, at high magnetic field frequencies, the ME voltage coefficient exhibits multiple peaks at different piezoelectric layer volume fractions.

A two-dimensional model for magnetic-field-direction dependent magnetoelectric effect in laminated composites

Experiments have shown that the direction of magnetic field plays an important role in magnetoelectric (ME) effect in laminated composites. In this paper, based on the average field method, a two-dimensional magnetic-field-direction dependent ME model is introduced. The numerical results were compared with previous experimental data with excellent correlation. Especially, the existence of an optimal angle is theoretically proved, which is changed with the value of DC magnetic field and can drive ME response to the best. Meanwhile, we found that the optimal magnetic field presents an obvious nonlinear variation with the angle. The prediction is closer to the experimental data than that given in previous work. Furthermore, the predictions show that the resonance magnetoelectric effect has the same trend with that at low frequency. ME coefficients are increased by about 100 times at resonance frequency.

The effect of electric charge on the mechanical properties of graphene

The effect of electric charge on the mechanical properties of graphene under tensile loading is investigated by using molecular dynamics method. A modified atomistic moment method based on the classical electrostatics theory is proposed to obtain the distribution of extra charges induced by an external electric field and net electric charges stored in graphene. The electrostatic interactions between charged atoms are calculated using the coulomb law. The results show that the Young’s modulus and the critical fracture stress under uniaxial tension decrease with the increase of electric potential and net charges on graphene. The failure of graphene induced by electric charges is found to be controlled by charge level. The results indicate that the carbon-carbon bonds at the edge of graphene will break first.

Electromagnetic behaviors of superconducting Nb3Sn wire under a time-dependent current injection

We build a 3D model to analyze the electromagnetic behaviors of Nb3Sn filamentary strand exposed to a time-varying current injection, under the consideration of n value and strain effect. Electromagnetic behaviors, performance degradation and AC loss are investigated. Results show that the filament bundles prevent a further field penetration from the outer shell into the interior matrix. Different current/field profiles occur in the strand and outside. Compared to the critical current, the average transport current keeps a high value with little change over a broader strain range, and has a larger magnitude by several orders of magnitude. Increasing the strain results in a suppression of the current transport capacity, and part of the current is expelled into the metal matrix causing larger AC loss. The larger twist pitch implies a longer current circuit and more magnetic flux enclosed, thus increasing the loss. More details are presented in the paper.

IEEE : Mechanical behavior of a 16-T FCC dipole magnet during a quench

Future accelerator magnets are pushed to their limits in terms of magnetic field, mechanical strength and from the quench protection point of view. These forces the magnet designers to rethink the quench modelling. One issue that has not so far been largely explored is the mechanical behavior of the superconducting coils during a quench. This can cause limitations to the design of high-field accelerator magnets. This paper focuses on mechanical behavior in the event of a quench of an Nb3Sn 16 T dipole magnet currently developed in the framework of the EuroCirCol project in view of the future circular collider conceptual design study. The thermo-mechanical analysis is performed through the finite element modeling. The analysis takes into account the Lorentz force and the thermal stress due to the nonuniform temperature distribution in the winding during a quench.

Anisotropic critical-state model of type-II superconducting slabs

We introduce a critical-state model incorporating the anisotropy of flux-line pinning to analyze the critical states developing in an anisotropic biaxial superconducting slab exposed to a uniform perpendicular magnetic field and to two crossed in-plane magnetic fields which are applied successively. The theory is an extension of the anisotropic collective pinning theory developed by Mikitik and Brandt. The anisotropic flux-line pinning enters into the critical states by generating the angular dependence of the critical current density and by deviating the direction of the electric field from the current in the plane perpendicular to the vortex line. We find that an enhanced in-plane anisotropy moderates the gradients of the magnitudes of the magnetic field and the electric field along the slab thickness, however increases the gradients of their rotations.

Effect of surfaces similarity on contact resistance of fractal rough surfaces under cyclic loading

Although numerous studies have shown that contact resistance depends significantly on roughness and fractal dimension, it remains elusive how they affect contact resistance between rough surfaces. The interface similarity index is first proposed to describe the similarity of the contact surfaces, which gives a good indication of the actual contact area between surfaces. We reveal that the surfaces’ similarity be an origin of contact resistance variation. The cyclic loading can increase the contact stiffness, and the contact stiffness increases with the increase of the interface similarity index. These findings explain the mechanism of surface roughness and fractal dimension on contact resistance, and also provide reference for the reliability design of the electrical connection.