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Emerging challenges to structural integrity technology for high-temperature applications
TU Shantung
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 375-387.
https://doi.org/10.1007/s11465-007-0066-y
Structural integrity technology has been widely used with great success for the design, manufacture and failure prevention of modern constructions such as chemical and petrochemical plants, power generation and energy conversion systems, as well as space and oceanic exploration. The modern needs of structural integrity technology are largely attributed to the increase of service temperature of the structures that results in the efficiency improvement in energy conversion and chemical processing technologies. Besides the needs arising from large-scale high-temperature plants, the high tech developments, such as micro chemo-mechanical systems and high-power electronics, provide new challenges to structural integrity technology. The present paper summarizes the recent technical progresses in large process plants and the aviation industry, micro chemo-mechanical systems, fuel cells, high-temperature electronics, and packaging and coating technologies. The state-of-the-art of structural integrity technology for high temperature applications is reviewed. Suggestions are provided for the improvement of current design and assessment methods.
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Error measurement and assemble error correction of a 3D-step-gauge
MAO Xinyong, LI Bin, SHI Hanmin, LIU Hongqi, LI Xi, LI Peigen
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 388-393.
https://doi.org/10.1007/s11465-007-0067-x
A new artifact called 3D-step-gauge consisting of a pyramid array and a compound, is proposed to calculate geometrical errors for machine tools. Only one point on each profile of the pyramid in the array is probed, and its center coordinate can be calculated. Then, the intervals of the pyramids can be transfered a length standard to measure errors. Considering the differences in the structural parameters and the location of the pyramids, a volumetric error measurement method of discrete points is presented. Furthermore, the location errors between the calibration state and the measurement state are studied and their influences on the accuracy of the position measurement are investigated on an actual machine tool. The 3D-step-gauge was tested on an actual machine tool and the measurement result shows quick assembly, convenient measurement, and high accuracy.
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Current research, key performances and future development of search and rescue robots
LIU Jinguo, WANG Yuechao, LI Bin, MA Shugen
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 404-416.
https://doi.org/10.1007/s11465-007-0070-2
Frequent natural disasters and man-made catastrophes have threatened the safety of citizens and have attracted much more attention. The rescue mission under disaster environment is very complicated and dangerous for a rescue team. Search and rescue (SAR) robots can not only improve the efficiency of rescue operations but also reduce the casualty of rescuers. Robots can help rescue teams and even replace rescuers to perform dangerous missions. Search and rescue robots will play a more and more important role in the rescue operations. A survey of the research status of search and rescue robots in Japan, USA, China and other countries has been provided. According to current research, experiences and the lessons learned from applications, the five key performances of a search and rescue robot are survivability, mobility, sensing, communicability and operability. Multi-technique fusion and multi-agent intelligent network are considered to be requirements for the future development of the search and rescue robot. Disaster prevention, disaster reduction and disaster rescue are the important parts of national public safety. They are also crucial for the safety of citizens and their estates. Search and rescue robotic technique is an urgent needed, strategic and core technique for national development. It will be important and strategic for national economy and safety.
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Dynamical research on spherical micro actuator with piezoelectric ceramic stacks drivers
ZHANG Ruihua, CHEN Haichu
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 433-438.
https://doi.org/10.1007/s11465-007-0074-y
This paper develops a 30 mm × 30 mm × 50 mm spherical micro actuator driven by piezoelectric ceramic stacks (PZT), and analyzes its dynamic performances. First, the space coordinate relationship of the spherical micro actuator and a dynamic model are set up. Second, The Runge-Kutta arithmetic is used to calculate the dynamical parameters of the micro actuator; the SIMULINK module of MATLAB is used to build the dynamical simulating model and then simulate it. Third, an experimental sample of the spherical micro actuator is developed, a micromanipulator is integrated with a micro-gripper based on the sample spherical micro actuator, and the experimental research on the micro assembly is conducted between a micro shaft of Φ180 μm and a micro spindle sleeve of Φ200 μm. Finally, the characteristics of the spherical micro actuator influenced by the mass of the metal sphere of the micro actuator, driving signal frequency, friction coefficient of the contact surface between the metal sphere and the friction block of the micro driving unit are analyzed. The experimental results indicate that the rotation resolution of the micro actuator reaches 0.000 1°, the rotation positioning precision reaches 0.000 5°, and the maximum working frequency is about 1200 Hz. The experimental results validate the back rotation vibration model of the spherical micro actuator. The micromanipulator integrated by the spherical micro actuator can meet the requirements of precise micro operation and assembly for micro electro mechanical systems (MEMS) or other microelements in micro degree fields.
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Study of mechanism of activating flux increasing weld penetration of AC A-TIG welding for aluminum alloy
HUANG Yong, FAN Ding, FAN Qinghua
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 442-447.
https://doi.org/10.1007/s11465-007-0076-9
When multi-component flux AF305 is used as surface activating flux for an aluminum alloy, the weld pene tration of activating flux-tungsten inert-gas (A-TIG) welding is over two times more than that of conventional TIG welding. Using A-TIG welding with the modes of alternating current (AC), direct current electrode negative (DCEN) and direct current electrode positive (DCEP), respectively, the flux differently affects weld penetration when the polarity is different. After studied the effect of compelled arc con striction on weld penetration of AC welding, it is believed that the constriction of the whole arc root is not the main mechanism that flux AF305 dramatically improves weld penetration. The penetration has a relationship with the separate distribution of slag on the weld surface. Then, an observation of scanning electron microscopy (SEM) and an electronic data systems (EDS) analysis of slag were performed respectively. The separate distribution of slag on the weld pool during welding and the great constriction of arc spots were confirmed by TIG welding with helium shielding gas. The relationship between slag distribution and weld penetration was studied by adding aluminum powder into flux AF305 to change the distribution of slag. During welding, the separate distribution of slag on the weld pool results in the great constriction of arc spots, an increase in arc spot force, and an increase in Lorentz force within the arc and weld pool. Finally, the weld penetration is increased.
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Knife-edge technique for laser cooling
WANG Zhanshan, MA Shanshan, MA Yan, ZHAO Min, LIU Hengbiao
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 468-473.
https://doi.org/10.1007/s11465-007-0081-z
The transfer characteristics of an atomic beam and the effect of laser were investigated in this paper. In the application of knife-edge technique, the temperature of atoms through laser cooling was measured. Results indicate that, after atoms are emitted from an atomic oven, the longer the atoms move, the worse the distribution of the atomic beam shows, regardless the laser cooling is taken or not. Laser cooling can reduce the transverse velocity of the atomic beam to several orders of magnitude and also increase the uniformity of an atomic beam. Knife-edge technique can measure the temperature of an atomic beam through laser cooling. The measurement accuracy depends on the pixel size of the charge coupled device (CCD), which is used for the fluorescent imaging of the atomic beam. The results are very important for the future experiments of laser cooling.
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Effects on mechanical properties in electron beam welding of TC4 alloy by laser shock processing
LU Jinzhong, ZHANG Yongkang, KONG Dejun, REN Xudong, GE Tao, ZOU Shikun
Frontiers of Mechanical Engineering in China. 2007, 2 (4): 478-482.
https://doi.org/10.1007/s11465-007-0083-x
The surface of TC4 titanium alloy welding line by electron beam welding (EBW) was processed by high power Q-switched and repetition-rate Nd: glass laser. Effects of laser power and spot diameter on residual stress and micro-hardness of the TC4 alloy welding line by laser shock processing (LSP) have been analyzed. Results show that residual stresses almost do not change as laser power is 45.9 J, spot diameter is φ9 mm; While laser power is 45.9 J, spot diameter less than φ3 mm, the distribution of residual stress in welding line occurs obvious variation, which residual stress increase obviously with spot diameter decrease. When power density is bigger than 1.8×1010 W/cm2, residual stresses of electron beam welding line occur change by LSP, which improve obviously residual stress distribution; while laser power is bigger than 1.2×1010 W/cm2, the surface micro-hardness of electron beam welding line occurs change by LSP, which improve obviously micro-hardness distribution. Mechanical properties of TC4 titanium alloy welding line will be improved by LSP, which provides experimental foundation for further controlling the distributions of residual stress and micro-hardness during laser shock processing.
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