Measurement of the elastic moduli of dense layers of oriented carbon nanotubes by a scanning force microscope

A technique is developed for measuring the modulus of elasticity of a material with a Nanoscan scanning force microscope on the basis of measuring the dependence of probe vibration frequency on the penetration depth of the needle into the specimen. This technique makes it possible to study materials with elastic moduli from 50 to 1000 GPa. The Young moduli of dense films of carbon nanotubes oriented at angles of 45° and 90° to the quartz substrate are measured. From their ratio, the Young modulus in the direction perpendicular to the tubes and the anisotropy of the elastic moduli are determined. A comparison of these values with the corresponding values obtained for a nanotube film deposited on a silicon substrate is carried out. On the basis of this comparison, a conclusion is made concerning the interaction between single-layer nanotubes and between nanotubes in a mixture of single-layer and multilayer ones.     

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.     

Nondestructive evaluation of high‐temperature elastic modulus of 3C‐SiC using Raman scattering

A nondestructive method is reported to measure the high‐temperature modulus of 3C‐SiC coating and bulk samples using Raman scattering. Within the temperature range from 20 °C to 900 °C, both the longitudinal optical and transverse optical phonon frequencies decrease linearly as the temperature increases. The elastic moduli derived from the longitudinal optical phonon agree with previous results measured using other techniques. It is further shown that the grain size and impurity only have a negligible effect on the elastic modulus of 3C‐SiC. Copyright © 2011 John Wiley & Sons, Ltd.     

Porosity, mechanical properties, residual stresses of supersonic plasma-sprayed Ni-based alloy coatings prepared at different powder feed rates

The aim of this paper was to investigate the effect of powder feed rate (PFR) on the microstructure and mechanical properties of the supersonic plasma-sprayed Ni-Cr-B-Si-C coatings. The microstructure, porosity and mechanical properties of the coatings and the residual stresses at the coating surfaces were experimentally determined. Results showed that the variations of porosity, elastic moduli and micro-hardness of the coatings followed Weibull distribution. From the statistical trend, the porosity of the coating increased with increasing PFR. However, the elastic modulus and the micro-hardness of the coating decreased and reached local minima and then increased with increasing PFR. Elastic modulus could be generally considered to be an increasing function of micro-hardness. The mean value of the elastic modulus of the coating calculated from Weibull plot was almost proportional to the square root of the mean value of the micro-hardness of the coating. Moreover, with increasing PFR, the residual stress at the coating surface, which was mainly governed by the elastic modulus of the coating, decreased to a local minimum and then increased.     

Cavitation erosion mechanism of titanium alloy radiation rods in aluminum melt

Ultrasound radiation rods play a key role in introducing ultrasonic to the grain refinement of large-size cast aluminum ingots (with diameter over 800 mm), but the severe cavitation corrosion of radiation rods limit the wide application of ultrasonic in the metallurgy field. In this paper, the cavitation erosion of Ti alloy radiation rod (TARR) in the semi-continuous direct-chill casting of 7050 Al alloy was investigated using a 20 kHz ultrasonic vibrator. The macro/micro characterization of Ti alloy was performed using an optical digital microscopy and a scanning electron microscopy, respectively. The results indicated that the cavitation erosion and the chemical reaction play different roles throughout different corrosion periods. Meanwhile, the relationship between mass-loss and time during cavitation erosion was measured and analyzed. According to the rate of mass-loss to time, the whole cavitation erosion process was divided into four individual periods and the mechanism in each period was studied accordingly.     

基于弹性模量检测骨疲劳的超声导波方法研究

研究早期诊断骨疲劳的方法是当前骨质评价方面的研究热点之一. 本文对不同弹性模量下长骨中超声导波的传播特性进行了理论分析和仿真研究.首先, 通过数值计算得到导波在管状长骨中的理论解析解.然后对管状长骨进行了时域有限差分(FDTD) 仿真, 并验证了它与理论解析解的一致性, 同时得到长骨中不同模式导波群速度、 中心频率和衰减与弹性模量的关系.研究结果表明各个导波模式的群速度和中心频率均随弹性模量的增加而增加, 而衰减随弹性模量的增加而减小.说明超声导波的传播特性参量可以反映长骨弹性模量的变化, 从而为长骨的早期疲劳诊断提供理论依据.     

Elastic behavior of amorphous-crystalline silicon nanocomposite: An atomistic view

In the context of mechanical properties, nanocomposites with homogeneous chemical composition throughout the matrix and the dispersed phase are of particular interest. In this study, the elastic moduli of amorphous-crystalline silicon nanocomposite have been estimated using atomistic simulations. A comparison with the theoretical model reveals that the elastic behavior is significantly influenced by the crystal-amorphous interphase. On observing the effect of volume-fraction of the crystalline phase, an anomalous trend for the bulk modulus is obtained. This phenomenon is attributed to the relaxation displacements of the amorphous atoms.     

Drag reduction by compliant coatings made of a homogeneous material

The possibility of drag reduction due to compliant coatings of viscoelastic silicone rubbers has been tested experimentally. For this purpose, a series of single-layer coatings of various thicknesses was made of a homogeneous material. The experiments were carried out in a high-speed cavitation tunnel of Pusan National University. Dynamic viscoelastic properties of coating materials were carefully measured. The range of flow rates and coating thicknesses was calculated assuming that the coatings can interact intensively with the dynamic structures of the turbulent boundary layer only in the region of frequencies of their maximum compliance. The predicted range of coating parameters and flow velocities, in which the coatings reduce drag, is compared with experimental data.     

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.     

Relation between the parameters of the elasticity theory and averaged bulk modulus of solids

A relation between the elastic moduli and Poisson’s ratio of crystalline and vitreous solids is considered. The feasibility of introducing the averaged bulk modulus, which has the same attributes as other elastic moduli, is substantiated. A relationship between the Grüneisen parameter and Poisson’s ratio is discussed.     

Nanoindentation Experimental Approach and Numerical Simulation of Al/Cr Bilayer Films

The Al/Cr double-layer film structure samples (thickness, 1200 nm) were prepared by the magnetron sputtering method. To investigate the mechanical properties, the samples were measured by using a nanoindentation instrument. The test results showed the nonlinearity and different modes of the main mechanical properties by comparing the macro-scale structure samples with other samples of similar materials. Based on the test, the elastic modulus and hardness of thin film structures can be calculated by considering different loads to conduct multi-point indentations. Meanwhile, the relationships between the mechanical parameters can be investigated based on these Al/Cr double-layer film structure samples. To validate the test, numerical analysis was developed using a finite element method to simulate the loading and unloading process of indentation. The simulation results were compared with the results of experiments to illustrate the validity of both the test and simulation to a certain extent. The investigation builds not only an experimental basis for practical applications for future study, but also supplies a complementary means of verification for theoretical analysis.     

On a simple impact test method for accurate measurement of material properties

A simple impact test method is presented to accurately measure the elastic and shear moduli and Poisson's ratio of a uniform Aluminum 6061-T651 cylindrical specimen with free boundary conditions. The elastic modulus is determined from the longitudinal vibration of the specimen and the shear modulus is determined from its torsional vibration. A new technique is developed to mount an accelerometer on the specimen to measure its torsional vibration. The Poisson's ratio determined for the specimen matches exactly with its known value.     

Synergistic effect of ultrasonic cavitation erosion and corrosion of WC–CoCr and FeCrSiBMn coatings prepared by HVOF spraying

The high-velocity oxygen-fuel (HVOF) spraying process was used to fabricate conventional WC–10Co–4Cr coatings and FeCrSiBMn amorphous/nanocrystalline coatings. The synergistic effect of cavitation erosion and corrosion of both coatings was investigated. The results showed that the WC–10Co–4Cr coating had better cavitation erosion–corrosion resistance than the FeCrSiBMn coating in 3.5 wt.% NaCl solution. After eroded for 30 h, the volume loss rate of the WC–10Co–4Cr coating was about 2/5 that of the FeCrSiBMn coating. In the total cumulative volume loss rate under cavitation erosion–corrosion condition, the pure cavitation erosion played a key role for both coatings, and the total contribution of pure corrosion and erosion-induced corrosion of the WC–10Co–4Cr coating was larger than that of the FeCrSiBMn coating. Mechanical effect was the main factor for cavitation erosion–corrosion behavior of both coatings.     

Surface functionalization by nanosecond-laser texturing for controlling hydrodynamic cavitation dynamics

The interaction between liquid flow and solid boundary can result in cavitation formation when the local pressure drops below vaporization threshold. The cavitation dynamics does not depend only on basic geometry, but also on surface roughness, chemistry and wettability. From application point of view, controlling cavitation in fluid flows by surface functionalization is of great importance to avoid the unwanted effects of hydrodynamic cavitation (erosion, noise and vibrations). However, it could be also used for intensification of various physical and chemical processes. In this work, the surfaces of 10-mm stainless steel cylinders are laser textured in order to demonstrate how hydrodynamic cavitation behavior can be controlled by surface modification. The surface properties are modified by using a nanosecond (10–28 ns) fiber laser (wavelength of 1060 nm). In such a way, surfaces with different topographies and wettability were produced and tested in a cavitation tunnel at different cavitation numbers (1.0–2.6). Cavitation characteristics behind functionalized cylindrical surfaces were monitored simultaneously by high-speed visualization (20,000 fps) and high frequency pressure transducers. The results clearly show that cavitation characteristics differ significantly between different micro-structured surfaces. On some surfaces incipient cavitation is delayed and cavitation extent decreased in comparison with the reference – a highly polished cylinder. It is also shown that the increased surface wettability (i.e., hydrophilicity) delays the incipient cavitation.     

The effect of heat setting on the elastic and viscoelastic properties of nylon-6 films

The elastic and viscoelastic properties of nylon-6 films with different structural forms and different degrees of crystallinity, obtained by heat setting nylon-6 films at various temperatures, without constraint, have been investigated. The elastic modulus increases with increasing degree of crystallinity. The values of the transverse elastic moduli for completely amorphous and completely crystalline samples have been calculated on the basis of these results. The measurements of dynamic mechanical properties were carried out at two different frequencies, viz., 11 Hz and 110 Hz, over a range of temperature from room temperature to 150°C under ambient conditions of humidity. It is observed that the moisture content increases whereas the glass transition temperature decreases with increasing temperature of pretreatment. The activation energy of the α transition has also been calculated.     

双涂层光纤应变传感器的理论与实验研究

对带有聚合物涂敷层和缓冲层的光纤应变传感器的力学特性进行了研究，建立了双涂层光纤与基体材料相互作用的线弹性理论模型.理论研究表明：在小半径近似条件下，双涂层光纤的力学传递特性决定于涂覆层和缓冲层的弹性模量的相对值；当缓冲层的弹性模量远大于涂覆层时，其作用可忽略.实验中，将光纤传感器埋入基体材料内部，利用白光干涉应变测量方法，对平均应变传递系数进行了实验研究.实验结果与理论仿真具有较好的一致性.     

Theoretical study of the dependences of the young’s and torsion moduli of thin single-layer carbon zigzag and armchair nanotubes on the geometric parameters

The Young’s and torsion moduli of single-layer carbon (m, 0) and (m, m) nanotubes are studied. It is demonstrated that both moduli depend on the chirality, diameter, and length of the nanotube. It is found for the first time that the torsion modulus increases with the nanotube diameter and diminishes with an increase in its length. By considering nanotubes with various values of the diameter-to-length ratio, it is shown that the Young’s and torsion moduli of the nanotubes saturate at a diameter-to-length ratio of ～0.3. The values of the torsion modulus as calculated from the Young’s modulus we obtained and from the deformation energy do not coincide, which can be attributed to the effect of dangling bonds at the open ends of the nanotubes. Energy calculations are performed using the Goodwin modification of the semiempirical Harrison tight-binding method.     

黏弹性吸声材料复弹性模量优化研究

针对黏弹性材料吸声效率问题,利用分层介质声传播理论和数值算法优化了不同物理条件下材料的复弹性模量。采用参数等效的方法分析了含气泡黏弹性材料的声学特性,并给出了此种材料优化后的弹性模量曲线。根据物理模型计算了一定边界条件下材料复弹性模量等吸声系数曲线,得到了几种背衬条件下黏弹性材料吸声系数大于0.8的弹性模量和损耗因子范围。研究表明调节黏弹性材料的复弹性模量可以有效提高材料的吸声性能,吸声系数大于0.8时其弹性模量和损耗因子范围在不同背衬条件下差异较大,发现一定厚度的钢背衬会降低调控复弹性模量的难度,对含气泡黏弹性材料的计算也可得到类似结果。      

Influence of alloying elements on the elastic properties of ternary and quaternary nickel-base superalloys

Using new supercells, the influence of the alloying elements Co, Cr, Ta, Re, and Ru on the elastic properties of ternary and quaternary nickel-base superalloys are systematically studied by the first-principles pseudopotential method. The calculated results of the five ternary and three quaternary superalloys suggest that the alloying elements can increase the elastic moduli. Re is found to be most effective in increasing the moduli of ternary alloys. Among the quaternary alloys, the Ni-Al-Re-Ru system has the largest moduli. Our calculated values of the elastic moduli agree very well with the experimental results. The charge density redistribution and partial density of states are calculated for the quaternary system including both Re and Ru. Covalent-like bonding between Re and its nearest neighbor is observed. The hybridization between the Re-d orbital and the host Ni-p, d orbitals are the origin of the modulus strengthening effect.