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Recent development of vibration
utilization engineering
WEN Bangchun
Front. Mech. Eng.. 2008, 3 (1): 1-9.
https://doi.org/10.1007/s11465-008-0017-2
The utilization of vibration and wave, which was developed during the latter half of the 20th century, is one of the most valueable technology applications and has been rapidly developing recently 1&8211;10. Because the technique is closely associated with industry and agriculture, it can create huge social and economical benefits and provide excellent services for society. Thus, due to its necessity in industry and daily life, extensive research has been devoted to vibration utillization engineering. In this paper, vibration utilization is classified into linear or non-linear vibrations, waves, and electric-magnetic oscillations. Their phenomena, patterns, and applications in nature and society are introduced. Some research results about vibration utilization engineering are described.
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Wear mechanism of disc-brake block
material for new type of drilling rig
WANG Xinhua, WANG Simin, ZHANG Siwei, WANG Deguo
Front. Mech. Eng.. 2008, 3 (1): 10-16.
https://doi.org/10.1007/s11465-008-0009-2
To improve friction and wear performance and service life of the disc-brake pair material of a drilling rig, a new type of asbestos-free frictional material with better performance for disc-brake blocks is developed, and its wear mechanism is investigated by friction and wear experiments. Topography and elementary components of the brake block’s wear surface are analyzed by employing SEM and EDAX patterns, revealing its tribological behaviour and wear mechanism. When the frictional temperature is lower, the surface film of the brake block is thinner, dense, smooth with plasticity, and divided into the mixture area, Fe-abundant area, carbon-abundant area and spalling area. The mixture area consists of various constituents of frictional pairs without ploughing and rolling trace. The Fe-abundant area mainly consists of iron and other constituents. The carbon-abundant area is the zone where graphite and organic fibre are comparatively gathered, while the spalling area is the zone where the surface film is spalled and its surface is rough and uneven, with a loose and denuded state. During the period of high frictional temperature, the frictional surface is also divided into the mixture area, Fe-abundant area and spalling area. In this case, the mixture area consists of abrasive dust from friction pairs, and the surface film is distributed with crumby hard granules, exiguous oxide, carbide granules and sheared slender fibre. The Fe-abundant area is mostly an oxide layer of iron with a flaky distribution. Fracture and spalling traces as well as an overlapping structure of multilayer surface films can be easily found on the surface film. The components of the spalling area are basically the same as that of the matrix. At the beginning of wear, the hard peaks from the friction surface of the disc-brake plough on the surface of the brake block. With increasing frictional temperature, the friction surface begins to soften and expand, and oxidized wear occurs at the same time. During the high-temperature wear period, severely influenced by friction heat, obvious softening and plastic flow can be found on the friction surface of the brake block, its anti-shearing ability is weakened, and adhesive wear is intensified. Thermal decomposition of cohesive material in the brake block is simultaneously strengthened, so that constituents shed due to loss of adhesion. Organic fibre is in a flowing state and obviously generates drawing, shearing, carbonization and oxidization. In addition, thermal cracking, thermal oxidization, carbonization and cyclization of organic substances on the surface of brake block can make the friction surface produce pores or cracks, thus fatigue wear occurs.
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Shape reconstruction of parallelogram
flaw
ZHENG Gangfeng, WU Bin, HE Cunfu
Front. Mech. Eng.. 2008, 3 (1): 17-22.
https://doi.org/10.1007/s11465-008-0015-4
To reconstruct the shape of the scatterer in elastic media, the authors deduce the Born approximation solution of the two-dimensional scattering problem, which includes the shape factor that embodies all information about the shape of the scatterer. Accordingly, the change in the shape of the scatterer only necessitates the number of the corresponding new shape factors. For a parallelogram void in a long Al rod, its shape factor can be obtained. In view of the definition of a characteristic function, the shape factor has a corresponding integral representation. Obviously, the shape factor can be considered as a Fourier transform of the characteristic function, which is reconstructed from the inverse Fourier transform. The integral equation is considered as the basic equation to reconstruct the shape of the scatterer. The identification of the geometrical character of a flaw is then given by the two dimensional inverse Born approximation in a low-frequency range. For the parallelogram void, a theoretical calculating identification is performed. At the same time, the numerical results are obtained by the finite element method.
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Micro-spectrophotometer based on micro electro-mechanical
systems technology
ZHOU Lianqun, LI Zhenggang, WU Yihui, ZHANG Ping, XUAN Ming, JIA Hongguang
Front. Mech. Eng.. 2008, 3 (1): 37-43.
https://doi.org/10.1007/s11465-008-0001-x
A new mini-spectrophotometer is developed by adopting micro-silicon-slit and micro-silicon-fixer, which are based on micro electro-mechanical systems (MEMS) technology. Both the micro-silicon-slit and the micro-silicon-fixer have their own features, such as small volume and high precision, which are laid out and analyzed later. Meantime, through the analysis of the sample cell’s optical characteristics that have some impacts on the linearity of the spectrophotometer, a relationship equation, which is about the impact of the refractive index of the sample cell and the tested medium on the variety of the transmitted light intensity and the absorbency, is put forward. When the water and the air are taken as the referenced medium, the experiments demonstrate that the difference of the refractive index of the references does not influence the correlation coefficient r and the slope of the absorbency-concentration curve. The final results show that the new mini-spectrophotometer with micro-silicon-slit and micro-silicon-fixer is worked out, its correlation coefficient r > 0.999, and its refractive index resolving power is better than 0.01.
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Development of meso-scale milling
machine tool and its performance analysis
LI Hongtao, LAI Xinmin, LI Chengfeng, LIN Zhongqin, MIAO Jiancheng, NI Jun
Front. Mech. Eng.. 2008, 3 (1): 59-65.
https://doi.org/10.1007/s11465-008-0005-6
To overcome the shortcomings of current technologies for meso-scale manufacturing such as MEMS and ultra precision machining, this paper focuses on the investigations on the meso milling process with a miniaturized machine tool. First, the related technologies for the process mechanism studies are investigated based on the analysis of the characteristics of the meso milling process. An overview of the key issues is presented and research approaches are also proposed. Then, a meso-scale milling machine tool system is developed. The subsystems and their specifications are described in detail. Finally, some tests are conducted to evaluate the performance of the system. These tests consist of precision measurement of the positioning subsystem, the test for machining precision evaluation, and the experiments for machining mechanical parts with complex features. Through test analysis, the meso milling process with a miniaturized machine tool is proved to be feasible and applicable for meso manufacturing.
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Impact drive rotary precision actuator
with piezoelectric bimorphs
ZHANG Hongzhuang, ZENG Ping, HUA Shunming, CHENG Guangming, YANG Zhigang
Front. Mech. Eng.. 2008, 3 (1): 71-75.
https://doi.org/10.1007/s11465-008-0008-3
An impact drive rotary precision actuator with end-loaded piezoelectric cantilever bimorphs is proposed. According to finite element analysis and experiments of the dynamic characteristics of end-loaded piezoelectric cantilever bimorphs, a specific fixed-frequency and adjustable-amplitude is confirmed to control the actuator. The results show that an actuator excited by fixed-frequency and the adjustable-amplitude ramp voltage waveform works with a large travel range (180°), high resolution (1 ?rad), speed (0.2 rad/min) and heavy-load ability (0.02 Nm). With advantages of high-precision positioning ability, simple structure and only one percent the cost of traditional impact drive mechanisms, the actuator is expected to be widely used in precision industries.
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Method of internal 3D flow field
numerical simulation for hydrodynamic torque converter
SHANG Tao, ZHAO Dingxuan, ZHANG Yuankun, GUO Xiangen, SHI Xiangzhong
Front. Mech. Eng.. 2008, 3 (1): 86-90.
https://doi.org/10.1007/s11465-008-0012-7
To enhance the performance of a hydrodynamic torque converter and thoroughly understand the trait of inside flow, a numerical simulation method of internal 3D flow for the three-element centrifugal hydrodynamic torque converter was systematically researched and expatiated in this paper. First, the internal flow field of each impeller was calculated. The curves that illustrate the relationships between the pressure differences of the inlet and outlet versus flux were drawn. Second, the concurrent working point of each impeller was approximately estimated. Finally, a calculation was performed considering the influence on each impeller. The flow field of a working point was solved by multiple calculations and the actual working condition was gradually determined. The pressure and velocity distributions of the flow field were proposed. The performance parameters of the hydrodynamic torque converter were predicted. The calculation method, and the proposed pressure and velocity distribution of the flow field, have practical significance for the design and improvement of a hydrodynamic torque converter.
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Generation of closed-form inverse
kinematics for reconfigurable robots
ZHAO Jie, WANG Weizhong, GAO Yongsheng, CAI Hegao
Front. Mech. Eng.. 2008, 3 (1): 91-96.
https://doi.org/10.1007/s11465-008-0013-6
For reconfigurable robots, the automatic generation of inverse kinematics is a key problem, because such robots may assume various configurations. In this paper, the screw and product-of-exponentials (POE) formula are used to model the kinematics of reconfigurable robots. The POE formula can be converted to canonical subproblems through decomposition and adjoint transformation. Three classes and 28 types of subproblems containing geometric or algebraic solutions are identified and solved, which can be reused in different configurations. A generalized, decomposable, and reusable approach for close-form inverse kinematics of reconfigurable robots is developed based on POE and subproblems. The effectiveness of this method is shown in an example.
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