Sound transmission across orthotropic laminates with a 3D model

This investigation examines the propagation of elastic waves in orthotropic materials to explain the sound insulation of FRP (Fiber Reinforced Plastics). The mechanical characteristics of an orthotropic material generally require nine independent parameters: three Young’s moduli, three shear moduli and three Poisson’s ratios. Three-dimensional analysis is performed with the elastic wave equations of an orthotropic material. The transfer matrix method which expresses the relationship between stress and velocity is adopted to calculate the sound transmission loss across an orthotropic material. Further, the transfer matrix method can only be calculated under the continuous boundary condition in the interface of each FRP layer. The boundary conditions which are indicated above are velocity and stress. The numerical results are compared with the experimental results. Additionally, along with varying material properties such as Young’s modulus, the acoustical properties of the orthotropic material are explained and discussed later.     

Band parameters of α-LiBeN semiconductor from density functional calculations

The structural, elastic, electronic, optical and thermal properties of α phase in LiBeN semiconductor have been studied using pseudo-potential plane wave method based on the density functional theory. The computed lattice parameter agrees well with previous theoretical work. The elastic constants and their pressure dependence are predicted using the static finite strain technique. A set of isotropic elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, average sound velocity and Debye temperature are numerically estimated in the frame work of the Voigt–Reuss–Hill approximation for α-LiBeN polycrystalline aggregate. The assignments of the structures in the optical spectra and band structure transitions have been examined and discussed. The thermal effect on heat capacities is investigated by the quasi-harmonic Debye model. To the best of our knowledge, most of the studied properties of the material of interest are reported for the first time.     

Effect of rare earth (Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3 and Er2O3 ) on the acoustic properties of glass belonging to bismuth-borate system

Bismuth-borate glasses doped with some rare earth ions were studied with respect to the density, molar volume and the elastic moduli, Poisson’s ratio, Debye temperature, microhardness, softening temperature, acoustic impedance, diffusion constant and latent heat of melting. Ultrasonic velocities were measured by the pulse echo overlap technique at a frequency of 10 MHz and at room temperature. From these velocities and density values, various elastic moduli were calculated. The correlation of elastic stiffness, the cross link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of shear modulus, bulk modulus, Young’s modulus, and Poisson’s ratio for our glasses are compared with the theoretically calculated values in terms of the bond compression model and Makishima-Mackenize theory.     

Ab initio investigation into the structural, electronic and elastic properties of AlCu2TM (TM = Ti, Zr and Hf) ternary compounds

The Al-Cu-TM (TM = transition metal) alloy system has attracted great attention for both excellent glass-forming ability and its interesting physical properties. In this work, an investigation into the crystal, electrical and elastic properties of the AlCu₂TM (TM = Ti, Zr, and Hf) compounds has been conducted by first-principles calculations based on density-functional theory. The fully relaxed structure parameters of the AlCu₂TM compounds are in good agreement with previous experimental and other theoretical results. Besides, the cohesive energies of all the AlCu₂TM compounds have been evaluated. The energy band and densities of state of these compounds are also obtained. According to the calculated single crystal elastic constants, all the compounds are mechanically stable. The polycrystalline bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio have been deduced by using Voigt-Reuss-Hill (VRH) approximations. The calculated negative Cauchy pressure and ratio of bulk modulus to shear modulus indicated that the AlCu₂TM compounds are ductile materials. The Debye temperatures of the AlCu₂TM compounds decrease with increasing the TM (Ti, Zr, and Hf) atomic number.     

Elastic properties of mono- and poly-crystalline PbO-type FeSe1−xTex (x = 0–1.0): A first-principles study

The structural parameters of the alloys are obtained as non-magnetic cases for which justification is provided. The elastic coefficients and various moduli of the monocrystalline FeSe_1−xTe_x system as a function of doping are predicted for the first time using density functional method. The bulk moduli, shear moduli, Young’s moduli, Poisson’s ratios, velocities of sound and Debye temperature of the corresponding poly-crystalline aggregates have been calculated and the results discussed.     

Elastic moduli of nc-TiN/a-Si3N4 nanocomposites: Compressible, yet superhard

Earlier measurements of elastic moduli of nc-TiN/a-Si₃N₄ nanocomposites of different composition and hardness by means of vibrating reed and surface Brillouing scattering, that yield Young’s and shear modulus, as well as the Poisson’s ratio, have been confirmed by high-pressure X-ray diffraction measurements, that yield bulk modulus. It is found that elastic moduli of all measured samples are essentially the same within relatively small error of measurements, and only slightly lower than that of pure TiN. The nanocomposites are superhard thanks to their unique nanostructure with strengthened SiN_x interface.     

Comparative first-principles calculations of electronic, optical and elastic anisotropy properties of CsXBr3 (X=Ca,Ge,Sn ) crystals

Detailed ab initio calculations of the structural, electronic, optical and elastic properties of CsCaBr₃, CsGeBr₃ and CsSnBr₃ crystals are presented in this paper. Based on the obtained results, CsCaBr₃ is characterized as a dielectric with an indirect band gap, whereas CsGeBr₃ and CsSnBr₃ are semiconductors with very narrow direct band gaps. The first theoretical estimations of the refractive indexes for all compounds are reported. Variations of the electron density difference distribution induced by changes of the second cation were analyzed and related to the type of chemical bonding between atoms. In addition, the complete set of elastic parameters (which includes the elastic constants, elastic compliance constants, bulk and Young’s moduli, elastic anisotropy) was obtained. Directional anisotropy of elastic properties was visualized; the directions in the crystal lattices, along which the maximal and minimal values of the Young’s moduli are realized, were identified.     

Study of elastic properties of CeO2 by statistical moment method

The purpose of the present paper is to investigate the temperature and pressure dependences of the elastic properties of cerium dioxide using the statistical moment method (SMM). The equation of states of bulk CeO₂ is derived from the Helmholtz free energy, and the pressure dependences of the elastic moduli like the bulk modulus, B_T, shear modulus, G, Young’s modulus, E, and elastic constants (C11, C12, and C44) are presented taking into account the anharmonicity effects of the thermal lattice vibrations. In the present study, the influence of temperature and pressure on the elastic moduli and elastic constants of CeO₂ has also been studied, using three different interatomic potentials. We compare the results of the present calculations with those of the previous theoretical calculations as well as with the available experiments.     

The structural stability, elastic constants and electronic structure of Al-Sr intermetallics by first-principles calculations

The lattice constants, enthalpies of formation, elastic constants and electronic structures of Al-Sr intermetallics have been calculated by first-principles method within generalized gradient approximation. The calculated lattice constants and enthalpies of formation are in good agreement with experimental and other theoretical results. The polycrystalline bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also estimated from the calculated single crystalline elastic constants. The total and partial electronic densities of state for the intermetallics were obtained, and the results indicated that Al₂Sr-oI is more stable than Al₂Sr-cF. Finally, longitudinal, transverse and average sound velocities and Debye temperature are estimated.     

TC4、16Mn合金及Al2O3陶瓷的高温弹性模量

 用脉冲回波法测量了TC4、16Mn、Al₂O₃陶瓷从室温到1 000 ℃的纵波与横波声速，由声速得到绝热弹性模量。给出了E、G随温度变化的回归方程。对材料熔点做了估算。     

Elastic moduli and internal friction of nanocrystalline Pd and PdSi as a function of temperature

Resonant ultrasound spectroscopy was used to study the elastic constants and internal friction of two nanocrystalline palladium samples over the temperature range 3–300 K. The first material, nc-Pd, had a grain size of 80–100 nm and a density 93% of that of single-crystal bulk palladium. The second material, nc-PdSi containing 0.5 at.% Si, had a grain size of 15–22 nm and a density 97% of the single-crystal value. The bulk and shear moduli were significantly reduced in the nc-Pd material from that expected based on single-crystal data, the effect being greater for the bulk modulus. The moduli of nc-PdSi were reduced 4–5% from that based on crystalline Pd. As compared to previous reports of the elastic moduli of nanocrystalline palladium (grain size 5–15 nm) the present values for the larger-grained nc-Pd are comparable, but the present values for the smaller-grained nc-PdSi are considerably higher. An internal friction peak and a modulus defect were found in the nc-Pd material, but not in the nc-PdSi material. These effects are attributed to a relaxation process at the grain boundaries. The temperature dependence of the moduli is similar to that of crystalline palladium and is strongly influenced by electronic effects.     

Complete mode identification for resonance ultrasound spectroscopy

This study is devoted to deducing exact elastic constants of an anisotropic solid material without using any advance information on the elastic constants by incorporating a displacement-distribution measurement into resonant ultrasound spectroscopy (RUS). The usual RUS method measures free-vibration resonance frequencies of a solid and compares them with calculations to find the most suitable set of elastic constants by an inverse calculation. This comparison requires mode identification for the measured resonance frequencies, which has been difficult and never been free from ambiguity. This study then adopts a laser-Doppler interferometer to measure the displacement-distribution patterns on a surface of the vibrating specimen mounted on pinducers; comparison of the measured displacement distributions with those computed permits us to correctly identify the measured resonance frequencies, leading to unmistakable determination of elastic constants. Because the displacement patterns are hardly affected by the elastic constants, an exact answer is surely obtained even when unreasonable elastic constants are used as initial guesses at the beginning of the inverse calculation. The usefulness of the present technique is demonstrated with an aluminum alloy and a langasite crystal.     

密度泛函理论研究高温高压下UO2弹性与热力学性能

采用第一性原理与准谐德拜模型研究UO2在高温高压条件下的弹性与热力学性能。UO2在高温高压下仍属离子型晶体,并且弹性性能计算表明,四角方向剪切常数在高温与高压下均保持稳定。高温下弹性常数C44没有明显变化,而高压下C44迅速增大。体积模量、剪切模量与杨氏模量均随压强增加而增大;高温条件下,体积模量、剪切模量与杨氏模量也未出现明显的降低,表明UO2在高温度高压下均可保持良好的力学性能。不同压强下,UO2定容热容均随温度迅速增大,并在1000 K 附近趋近于杜隆-佩蒂特极限。德拜温度则随温度降低,随压强升高。在低于室温条件下,热膨胀系数随温度急剧增加;温度继续增加,系数的增加趋势则逐渐变缓。计算结果还表明,UO2的热膨胀系数在相同条件下,远小于其他核材料。     

Dynamical measurements on viscoelastic behaviors of spiders in electro-dynamic loudspeakers

Spiders in electro-dynamic loudspeakers are most commonly concentrically corrugated fabric disks, and their viscoelastic behaviors affect the loudspeaker reproductions. A noncontact dynamic measuring technology is presented by a subwoofer closed box to excite the tested spiders pneumatically with a Laser Doppler Vibrometer (LDV) to measure the velocity of the moving spiders. Correlation techniques were employed to get an accurate and reliable acoustical transfer function between the measured velocity and sound pressure. The Young’s moduli of the tested spider composite materials were derived from the measured vibration modes. The creep effect and the level dependent behaviors of tested spiders were investigated. The results indicate that, the Young’s moduli of the tested spiders are frequency dependent. The mechanical stiffness increases with a small slope in low frequency range while a large slope in high frequency range. The loss factor exhibits the maximum around the resonance frequency, and after that it decreases with increasing frequency. The effective stiffness has a monotonic decrease with input voltage levels and the harder the spider, the less stiffness changes with input levels.     

Determination of elastic modulus of a beam by using electronic speckle pattern interferometry

This paper proposes a sonic resonance test for an elastic modulus measurement which is based on the electronic speckle pattern interferometry. Previous measurement technique of elastic constant has the limitation of application for thin film or polymer material because contact to specimen affects the result. It has been developed as a non-contact optical measurement technique which can visualize resonance vibration mode shapes with whole field. The maximum vibration amplitude at each vibration mode shape is a clue to find the resonance frequencies. The dynamic elastic constant of test material can be easily determined from vibration of a beam equation using the measured resonance frequencies. The proposed technique is able to give high accurate elastic modulus of materials through a simple experimental set-up and analysis. The experimental result also compared to the theoretical result.     

Structural, elastic and electronic properties of transition metal carbides TMC (TM=Ti, Zr, Hf and Ta) from first-principles calculations

The structural, elastic and electronic properties of TiC, ZrC, HfC and TaC have been investigated by first-principles calculations using the plane-wave pseudopotential method. Different exchange-correlation functionals regarding the local density approximation and the PBE, RPBE and PW91 forms of generalized gradient approximation are taken into account. The NaCl-type cubic structures of TMC (TM=Ti, Zr, Hf and Ta) are optimized and confirmed to be mechanically stable. The elastic properties such as the elastic constants, bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of TMC are investigated, and the performances of LDA and GGA are discussed. The electronic density of state, electron charge density and Mulliken population analysis have been explored to discuss the electronic properties and bonding behaviors of TMC. The present calculation results compare satisfactorily with the experimental data and previous theoretical calculations.     

Elastic properties of mono- and polycrystalline ( and Lu) under pressure effect

The structural and elastic properties of perovskite-type RCRh₃, with R=Sc, Y, La and Lu, under pressure effects have been investigated using the pseudo-potential plane-wave method based on the density functional theory within the generalized gradient approximation. For monocrystalline RCRh₃, the optimized lattice constants, elastic constants and directional elastic wave velocities are calculated and analyzed in comparison with the available experimental and theoretical data. An increase in the lattice constant has been found with increasing atomic size of the R element and a corresponding decrease in the hardness. The anisotropic elastic constants and directional elastic wave velocities increase linearly with increasing pressure. A set of elastic parameters and related properties, namely bulk and shear moduli, Young’s modulus, Poisson’s ratio, Lamé’s coefficients, average sound velocity and Debye temperature are predicted in the framework of the Voigt–Reuss–Hill approximation for polycrystalline RCRh₃. We have found that the toughness of RCRh₃ compounds can be improved at high pressure.     

Influence of valence electron concentration on elastic, electronic and optical properties of the alkaline-earth tin oxides A3SnO (A=Ca, Sr and Ba): A comparative study with ASnO3 compounds

By employing first principles method of the plane wave pseudo potential calculations (PP-PW), based on the density functional theory (DFT), within the local density approximation (LDA), the correlation between valence electron concentration and structural, elastic, electronic as well as optical properties of A₃SnO and ASnO₃ compounds where A=Ca, Sr and Ba are investigated. The elastic constants and their pressure dependence are calculated using the static finite strain technique. We derived the bulk, shear and Young's moduli for ideal monocrystalline and for polycrystalline A₃SnO and ASnO₃ aggregates. Band structures reveal that alkaline-earth tin oxides A₃SnO are direct energy band gap (G-G) materials.The hardness of these compounds was explained using chemical bonding properties and Milliken charges transfer. The optical constants, including the dielectric function, optical reflectivity, refractive index and electron energy loss, are calculated for radiation up to 20 eV. We have found that the static dielectric constants of all these compounds are in good agreement with Penn model.     

Monocrystal elastic constants in the ultrasonic study of welds

For studying welds ultrasonically, the importance of knowing the material's single-crystal elastic constants, the C_ijs, is explained. Where these constants are not known, some guidelines are given for estimating them from polycrystalline elastic constants such as Young's modulus and the shear modulus.The important case of [001] fibre texture is considered. Being transversely isotropic, this case exhibits five macroscopic elastic constants, which are related to the three cubic elastic constants: C₁₁, C₁₂, C₄₄. From these five constants the angular variations of Young's modulus, the torsional modulus, and the sound velocities can be computed. For the same [001] fibre texture, results are given for a standard well-characterized material — copper, where the C_ijs are well known.