Energy transmission efficiency and working bandwidth are the two major factors limiting the application of current acoustic diodes (ADs). This letter presents a design of high efficiency and broadband acoustic diodes composed of a nonlinear frequency converter and a linear wave filter. The converter consists of two masses connected by a bilinear spring with asymmetric tension and compression stiffness. The wave filter is a linear mass-spring lattice (sonic crystal). Both numerical simulation and experiment show that the energy transmission efficiency of the acoustic diode can be improved by as much as two orders of magnitude, reaching about 61%. Moreover, the primary working band width of the AD is about two times of the cut-off frequency of the sonic crystal filter. The cut-off frequency dependent working band of the AD implies that the developed AD can be scaled up or down from macro-scale to micro- and nano-scale.

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A new strain gauge-based triaxial extensometer (radial extensometers x, y and axial extensometer z) is presented to improve the volumetric strain measurement in a hydro-compression loading test for foam materials. By the triaxial extensometer, triaxial deformations of the foam specimen can be measured directly, from which the volumetric strain is determined. Sensitivities of the triaxial extensometer are predicted using a finite-element model, and verified through experimental calibrations. The axial extensometer is validated by conducting a uniaxial compression test in aluminium foam and comparing deformation measured by the axial extensometer to that by the advanced optical 3D deformation analysis system ARAMIS; the result from the axial extensometer agrees well with that from ARAMIS. A new modus of two-wire measurement and transmission in a hydrostatic environment is developed to avoid the punching and lead sealing techniques on the pressure vessel for the hydro-compression test. The effect of hydrostatic pressure on the triaxial extensometer is determined through an experimental test. An application in an aluminium foam hydrostatic compression test shows that the triaxial extensometer is effective for volumetric strain measurement in a hydro-compression loading test for foam materials.

Various acoustic and mechanical wave components have been developed. Most of them focused on the control of energy flow. However, these waves are not only energy flow but also wave signals with a frequency dependence. In this Letter, we propose a mechanical wave switch (MWS) capable of controlling energy flow and output frequency simultaneously. It consists of a difference frequency generation (DFG) unit and a wave filter. The DFG unit consists of two mass blocks and a tension/compression asymmetrical bilinear spring, and the wave filter is a one-dimensional mass-spring lattice. Systematical calculations were carried out to identify the critical condition for the design of MWSs. Both numerical and experimental results demonstrate the capability of the proposed MWS to tune the energy flow and the output frequency of acoustic waves via a small amplitude control wave signal. The scale-independent MWS can be implemented at micro- and nanoscales.

Austenitic stainless steel has been extensively used in nuclear power plants (NPP). The nondestructive Testing (NDT) of its mechanical damage at pre-crack state is very important for the safety assessment of a NPP. Aiming at to develop a new NDT method for inspecting mechanical damage before the initiation of macro cracks, the correlation between the natural magnetization and the mechanical damage is experimentally investigated for a typical austenitic stainless steel - SUS304. In the experiments, simple tensile loads were applied to lateral notch specimens to generate states of different plastic damages, and the corresponding natural magnetic field and residual strain distribution were measured after each loading cycle. The distribution of natural magnetization was analyzed based on the measured magnetic field signals in view of the principle of the metal magnetic memory phenomenon, and the dependence of the magnetization on the mechanical damage was discussed. The experimental results reveal that there is a good possibility to detect mechanical damages by measuring the natural magnetic field.