Zhang Shuyi

Investigation of the surface qualities of laser shock-processed zones and the effect on fatigue life of aluminum alloy

Abstract The influence of surface qualities produced by laser shock-processing (LSP) on the fatigue life of aluminum alloy 2024T62 are investigated. The surface qualities of LSP zones can be divided into grades A, B, C and D. The harmful heat damage produced by LSP is completely avoided in grade A surface quality, but heat damage exists to some extent in the others. Therefore, the grade A surface quality reflects the LSP contribution to fatigue life, which increases greatly. The main feature of grade A surface quality is that the surface roughness of the LSP zone is less than or equal to the surface roughness of the un-shocked zone. A very dense bright shallow hollow is formed and the shot spot is well-defined. With 95% confidence, the mean fatigue life of LSP specimens with grade A surface qualities is 4.8–8.1 times larger than the un-shocked ones.

Transmission Characteristics in Tubular Acoustic Metamaterials Studied with Fluid Impedance Theory

Tubular acoustic metamaterials with negative densities composed of periodical membranes set up along pipes are studied with the fluid impedance theory. In addition to the conventional forbidden bands induced by the Bragg-scattering due to the periodic distributions of different acoustic impedances, the low-frequency forbidden band (LFB) with the low-frequency limit of zero Hertz is studied, in which the LFB is explained with acoustic impedance matching and the Bloch theory. Furthermore, the influences of the structural parameters of the tubular acoustic metamaterials on the transmission characteristics, such as the transmission coefficients, dispersion curves, widths of forbidden and pass bands, fluctuations in pass bands, etc., are evaluated, which can be used in the optimization of the acoustic insulation ability of the metamaterials.

Thermal Diffusivity of Film/Substrate Structures Characterized by Transient Thermal Grating Method

Transient thermal grating method is used to measure the thermal diffusivity of absorbing films deposited on transparent substrates. According to periodically modulated dielectric constant variations and thermoelastic deformations of the thin films caused by the transient thermal gratings, an improved optical diffraction theory is presented. In the experiment, the probing laser beam reflectively diffracted by the thermal grating is measured by a photomultiplier at different grating fringe spaces. The thermal diffusivity of the film can be evaluated by fitting the theoretical calculations of diffraction signals to the experimental measured data. The validity of the method is tested by measuring the thermal diffusivities of absorbing ZnO films deposited on glass substrates.

Thermal Depth Profiling Reconstruction by Multilayer Thermal Quadrupole Modeling and Particle Swarm Optimization

A new hybrid inversion method for depth profiling reconstruction of thermal conductivities of inhomogeneous solids is proposed based on multilayer quadrupole formalism of thermal waves, particle swarm optimization and sequential quadratic programming. The reconstruction simulations for several thermal conductivity profiles are performed to evaluate the applicability of the method. The numerical simulations demonstrate that the precision and insensitivity to noise of the inversion method are very satisfactory.

Finite element modeling of heating phenomena of cracks excited by high-intensity ultrasonic pulses

A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.

Photoacoustic spectra of complexes of phenylalanine with La3+, Nd3+, Sm3+ and Tb3+

Abstract Crystals of complexes Ln(Phe)Cl 3 ·5H 2 O (Phe: phenylalanine; Ln: La 3+ , Nd 3+ , Sm 3+ , and Tb 3+ ) were synthesized and their photoacoustic (PA) spectra in the UV–Vis region were recorded. PA intensities of central lanthanide ions are interpreted in terms of the probability of non-radiative transitions. It is found that PA intensity of the ligand phenylalanine bears a relation to the energy transfer processes. Different PA intensities of the ligand are interpreted by comparison with the fluorescence spectra. The relaxation process model is also studied based on their PA and fluorescence spectra. Co-fluorescence effect of co-precipitates Tb 0.8 Ln 0.2 (Phe)Cl 3 ·5H 2 O (Ln: La 3+ , and Nd 3+ ) are firstly reported. PA intensity of the ligand increases for Tb 0.8 La 0.2 (Phe)Cl 3 ·5H 2 O, Tb(Phe)Cl 3 ·5H 2 O and Tb 0.8 Nd 0.2 (Phe)Cl 3 ·5H 2 O, respectively. The changes of fluorescence spectra turn out to be complementary to the PA spectra. The intramolecular energy transfer and intermolecular energy transfer processes in the co-precipitates are discussed in depth from two aspects: radiative and non-radiative relaxations.

Photoacoustic Spectroscopy Measurement of C60 Thin Film

Photoacoustic spectroscopy of C60 thin film is presented. The optical band edge of solid C60 and the optical absorption coefficient at absorption edge are determined. A weak absorption shoulder at 1.70 eV is observed. While the thickness of C60 thin film is less than 1 μm, photoacoustic saturation at band edge is avoided.

Insulator–Metal Transition due to La Doping in Double Perovskite Sr2MnMoO6

Resistivity, thermal diffusivity, lattice and magnetic properties of double perovskite Sr2−xLaxMnMoO6 are investigated with systematic change of La doping concentration x from 0.0 to 0.4. The insulator to metal phase transition is observed with increasing x above 0.3, suggesting that the extra electrons via substitution of La3+ for Sr2+ ions occupy mainly the conduction Mo-4d band. According to the insulator to metal phase transition, the thermal diffusivity of Sr2−xLaxMnMoO6 enhances from 0.33 cm2/s at x = 0.0 to 0.49 cm2/s at x = 0.4. We further investigate the La doping effects on the lattice and magnetic properties.

Highly Sensitive Rayleigh Wave Hydrogen Sensors with WO3 Sensing Layers at Room Temperature

Rayleigh wave hydrogen sensors based on 128° YX-LiNbO3 substrates with WO3 sensing layers operating at room temperature are studied. The experimental results indicate that the WO3 layers obtained by a sol-gel method have much higher sensitivities because the sensing layers produced by the sol-gel method have small grains and high roughness and porosity. It is also confirmed that in the sol-gel method, keeping WO3 solutions at low temperature and/or decreasing the viscosity of the solutions can decrease the grain sizes and increase the hydrogen-absorbability of the sensing layer. Under the optimized preparation conditions, the high sensitivity of the hydrogen sensors at room temperature is obtained, in which 1% hydrogen in natural air induces the frequency shift of 72 kHz at the operating frequency of 124.2 MHz.

Influence of adhesive layer properties on laser-generated ultrasonic waves in thin bonded plates

This paper studies quantitatively the generation of Lamb waves in thin bonded plates subjected to laser illumination, after considering the viscoelasticity of the adhesive layer. The displacements of such plates have been calculated in the frequency domain by using the finite element method, and the time domain response has been reconstructed by applying an inverse fast Fourier transform. Numerical results are presented showing the normal surface displacement for several configurations: a single aluminum plate, a three-layer bonded plate, and a two-layer plate. The characteristics of the laser-generated Lamb waves for each particular case have been investigated. In addition, the sensitivity of the transient responses to variations of material properties (elastic modulus, viscoelastic modulus, and thickness) of the adhesive layer has been studied in detail.