In the paper, a phononic crystal plate composed of a magnetorheological elastomer with adjustable band gaps in the low frequency range is constructed. The dispersion relations of Lamb waves are studied by the supercell plane wave expansion method. The transmission responses as well as the displacement fields of Lamb waves are calculated by the finite element method. The influence of geometric parameters on the band gaps, the regulation effect of the volume ratio of Fe particles and the bias magnetic field on the band gaps are analyzed. Based on the numerical results, we find that the volume ratio of Fe particles and the magnetic field affect the band gap effectively. The location and width of the band gaps can be adjusted within a broad frequency range by varying the geometric parameters and magnetic field. We can control the band gap, achieve an appropriate and wide low band gap by selecting proper geometric parameters and applying an external contactless magnetic field to deal with complicated and changeable engineering environment. The results are useful for understanding and optimizing the design of composite vibration isolation plates.

The paper investigates the in-plane elastic wave propagation in hierarchical lattices. The hierarchical organization is obtained by removing a certain amount of cells successively from a general hexagonal lattice that involves the re-entrant configuration with negative Poisson's ratio. The symmetry reduction caused by the alteration of the internal angle and the formed vertexes with stacking hexagons gives rise to a significant effect on the dispersion properties of the structure materials. Results show that the lattices with different hierarchy levels possess a stable behavior of the band gap in the position near the resonant frequency of the cell walls, and the gap width has an evident increase in the re-entrant hierarchical structures. In addition, band structure in the low frequency range has an unchanged performance for the varying parameters of cell walls, and the reason is owing to the steady of the structure vibration pattern for the Bloch modes. The authors' findings of the dispersion behaviors in the hierarchical lattices provide a broad design space for the lightweight materials in the wave manipulation and vibration control.

Dual-phase nanoscale lamellar microstructures containing alternating regions of soft phase and hard phase are known to produce alloys with an exceptional combination of strength and plasticity. Here, the effect of layer thickness on the mechanical properties and deformation mechanism of the fcc/bcc dual-phase CoNiFeAlxCu1−x high-entropy alloys multilayers are investigated by the molecular dynamics simulation method. The results show that the deformation behavior of the multilayers is strongly related to the layer thickness. At the yield point, the deformation behavior of the small thickness multilayer is caused by the dislocation slip in the fcc phase, while the plastic deformation of the large thickness multilayer is initiated by the bcc → hcp phase transformation in the bcc phase. During the subsequent plastic deformation, the phase transformation of bcc → fcc also occurred in the bcc phase of the multilayer, which depended on the relative size of the bcc phase in the multilayer. Especially for the multilayer with the layer thickness of 2 nm, the bcc → fcc phase transformation promotes the formation of twins, and the fcc/bcc phase interface transforms into a perfect twin boundary. The twin formation mechanism and phase transformation mechanism are also discussed in detail.

Abstract. This paper investigates the shear horizontal surface acoustic wave (SH-SAWs) propagating in layered piezomagnetic/piezoelectric structures covered a microbeam array, which involves a thin piezomagnetic layer bonded perfectly to an unbounded piezoelectric substrate. The beams are modeled by the Euler-Bernoulli theories when they are bending during the piezomagnetic/piezoelectric structures in shear motion. The explicit formulations of SH-SAWs dispersion relations in such layered structure with consideration of magnetoelectrically open and shorted cases are derived. The effects of the microbeam array on the phase velocity are analyzed. The numerical results are presented and discussed. From the results, we can find that the effects of microbeams on the properties of the SH-SAWs are remarkable. The phase velocity decrease with the non-dimensional wave number and increase with the number of microbeams and the thickness of piezomagnetic layer. The analytical method and the results in the paper could be useful to the design of the chemical sensors of magnetoelectric materials. IntroductionIt is well known that the composite materials consisting of piezoelectric (PE) and piezomagnetic (PM) have the ability to convert energy between magnetic and electric fields which is not present in single-phase piezoelectric or piezomagnetic materials [1][2]. For this reason, PM-PE composites are potential candidates for magnetic sensors, transducers and microwave devices, e.g. delay lines, magnetic field probes, damage detectors, medical ultrasonic imaging, and resonators, etc. These applications are done with wave propagations and vibrations in PM-PE composites, and so their dynamic behavior is the first concern in design as well as in performance. A number of investigations have been reported about the wave propagation problems in such composites [3][4].We all known a large number micro-or nano-scale beam arrays have been made by using different techniques due to the extensive effort on micro-and nano-technologies [5][6]. These new structures have great potentials for new devices such as efficient microneedles, dynamic tuning of surface wetting, microelectromechanical systems (MEMS) actuators and resonators, etc. There are strong needs to study the effects of microbeams on vibrations of structures or wave propagation in structures due to the design of resonators, sensors and actuators. Li et al discussed the collective buckling of nonuniform nanobeams interacting through an elastic substrate [7]. Lin et al considered the effects of surface deformation on the collective buckling of an array of rigid beams on an elastic substrate [8]. Liu et al investigated shear vibration of a rotated Y-cut quartz crystal plate carrying an array of microbeams with their bottoms fixed to the top surface of the plate [9]. From the paper, we can find that the plate was modeled by the theory of anisotropic elasticity and the beams were modeled by the Euler-Bernoulli theory for beam bending, and a frequency equation that determines the resonan...

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