|
Time reversal method for guided wave inspection
in pipes
DENG Fei, WU Bin, HE Cunfu
Front. Mech. Eng.. 2008, 3 (3): 251-260.
https://doi.org/10.1007/s11465-008-0050-1
The application of the time reversal method in pipe-like structures based on finite element method (FEM) is investigated. A steel pipe model measuring 70 mm × 3.5 mm is used to analyze the reflection coefficient of the L(0,2) mode with the time reversal process. Simulation results show that the time reversal array method is beneficial to the improvement of the signal-to-noise ratio of a guided wave inspection system. As the intercepting window is widened, more energy is included in re-emitted signals, which leads to a large reflection coefficient of the L(0,2) mode. In parallel, a circumferential locating method based on the time reversal method is described. The time reversal process used for guided wave inspection leads to the temporal and spatial focusing. When the time reversal signals are re-emitted, the angular profile obtained at the axial location of the defect can be used to determine the circumferential location of the defect. Except for a pipe with one defect, the circumferential locating method has been verified on another pipe model with two defects. Meanwhile, the elements number of the time reversal array has been discussed for enhancing the discrimination of the defect circumferential location.
References |
Related Articles |
Metrics
|
|
Growth and properties analysis of metal-organic
chemical vapor deposited MgZnO films on -AlO substrates
SHI Zengliang, LIU Dali, YAN Xiaolong, GAO Zhongmin, BAI Shiying
Front. Mech. Eng.. 2008, 3 (3): 261-264.
https://doi.org/10.1007/s11465-008-0036-z
MgxZn1-xO (0 < x ? 0.12) thin films with the wurtzite structure have been successfully grown on c-Al2O3 substrates by metal-organic chemical vapor deposition (MOCVD). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), photoluminescence (PL) spectrometry, and transmission measurements are performed to study the characteristics of MgxZn1-xO thin films. Results show that with increasing Mg content, the diffraction peak of MgxZn1-xO thin films shifts towards a higher diffraction angle (the biggest shift is 0.22°), and the full width at half maximum (FWHM) of the diffraction peak is broadened. Meanwhile, a blue-shift occurs at the near-band-edge (NBE) emission peak and the largest blue-shift of the band gap of the MgxZn1-xO films is 113 meV with Mg content x = 0.12. Therefore, the energy band gap of the MgxZn1-xO films is determined by Mg content in the thin films and the energy band gap increases with an increase of Mg content.
References |
Related Articles |
Metrics
|
|
Piezoelectric film-actuated motion platform with
high resolution
HUA Shunming, ZHANG Hongzhuang, CHENG Guangming, FAN Zunqiang, LIU Jianfang
Front. Mech. Eng.. 2008, 3 (3): 265-269.
https://doi.org/10.1007/s11465-008-0041-2
A piezoelectric film-actuated motion platform with high resolution, which can run in two directions within a horizontal plane, is presented. On the basis of the analysis of the working principle of a stick-slip mechanism, a mathematical model describing its dynamic behavior is set up and simulated. Experiments of the motion performance and carrying ability on the prototype are conducted. Results show that this type of platform has advantages including a simple structure, small volume, light weight, stable step length, and large traveling range. When the driving voltage is less than 30 V, step error is less than 0.5 ?m. The carrying ability of the platform is terrific and about 7–8 times its weight.
References |
Related Articles |
Metrics
|
|
Design of composite flywheel rotor
BAI Yue, GAO Qingjia, LI Haiwen, WU Yihui, XUAN Ming
Front. Mech. Eng.. 2008, 3 (3): 288-292.
https://doi.org/10.1007/s11465-008-0045-y
A design method for a flywheel rotor composed of a composite rim and a metal hub is proposed by studying the connection between the rotor and the driving machine. The influence of some factors such as the rotor material, configuration, connection, and fracture techniques on energy density is analyzed. The results show that the ratio of the inner radius to outer radius of the rim is the key factor, and is determined by the rim material. Optimizing the hub can further efficiently improve energy density. The composite flywheel rotor is produced and its rotation stress has been tested at the speed of 20 krpm. The emulation results are consistent with testing results, which proves that the introduced design method is useful.
References |
Related Articles |
Metrics
|
|
Geometrical nonlinear deformation model and its
experimental study on bimorph giant magnetostrictive thin film
LIU Wei, JIA Zhenyuan, WANG Fuji, ZHANG Yongshun, GUO Dongming
Front. Mech. Eng.. 2008, 3 (3): 313-317.
https://doi.org/10.1007/s11465-008-0048-8
The geometrical nonlinearity of a giant magnetostrictive thin film (GMF) can be clearly detected under the magnetostriction effect. Thus, using geometrical linear elastic theory to describe the strain, stress, and constitutive relationship of GMF is inaccurate. According to nonlinear elastic theory, a nonlinear deformation model of the bimorph GMF is established based on assumptions that the magnetostriction effect is equivalent to the effect of body force loaded on the GMF. With Taylor series method, the numerical solution is deduced. Experiments on TbDyFe/Polyimide (PI)/SmFe and TbDyFe/Cu/SmFe are then conducted to verify the proposed model, respectively. Results indicate that the nonlinear deflection curve model is in good conformity with the experimental data.
References |
Related Articles |
Metrics
|
|
Recognition of diamond grains on surface of fine
diamond grinding wheel
HUO Fengwei, JIN Zhuji, KANG Renke, GUO Dongming, YANG Chun
Front. Mech. Eng.. 2008, 3 (3): 325-331.
https://doi.org/10.1007/s11465-008-0071-9
The accurate evaluation of grinding wheel surface topography, which is necessary for the investigation of the grinding principle, optimism, modeling, and simulation of a grinding process, significantly depends on the accurate recognition of abrasive grains from the measured wheel surface. A detailed analysis of the grain size distribution characteristics and grain profile wavelength of the fine diamond grinding wheel used for ultra-precision grinding is presented. The requirements of the spatial sampling interval and sampling area for instruments to measure the surface topography of a diamond grinding wheel are discussed. To recognize diamond grains, digital filtering is used to eliminate the high frequency disturbance from the measured 3D digital surface of the grinding wheel, the geometric features of diamond grains are then extracted from the filtered 3D digital surface, and a method based on the grain profile frequency characteristics, diamond grain curvature, and distance between two adjacent diamond grains is proposed. A 3D surface profiler based on scanning white light interferometry is used to measure the 3D surface topography of a #3000 mesh resin bonded diamond grinding wheel, and the diamond grains are then recognized from the 3D digital surface. The experimental result shows that the proposed method is reasonable and effective.
References |
Related Articles |
Metrics
|
18 articles
|