摘要：
The objective of this paper is to investigate the effect of rapid thermal cycling on microstructure and optical property (luminous flux and luminous efficiency) of high power light emitting diode (LED) by thermal fatigue testing from -40 to 125. Under an application of thermal fatigue device as a heating source, the specimens that were being non-operating and thermal fatigue testing in the experiment were rapidly heated and cooled based on a control system that employs a fuzzy logic algorithm, respectively. The optical performances, including luminous flux, luminous efficiency, radiant power and color temperature (CCT) of LED specimens were tested and analyzed. It was found that the rapid thermal cycling have similar evident influence on them. The results showed that the color purity of LED was also descended, the correlated color temperature (CCT) was also risen, but their changing rate and extents are different. The high and low temperature distribution in LED chip was simulated by finite element modeling which is helpful for the failure analysis and design of the reliability of the LED packaging. The microstructures of LED chips are analyzed after different rapid thermal cycling time. The results are showed that rapid thermal cycling can affect greatly the LED properties and interface microstructures. All the results indicate that this approach to rapid thermal cycling by using rapid heating source is feasible to investigate the optical performance of high power LED, so it can also effectively verify the reliability of LED devices.
摘要：
A novel method for partial eigenstructure assignment of undamped vibration systems using acceleration and displacement output feedback is presented in this paper. It is based on modifications of mass and stiffness that preserve partial eigenstructure. A numerical algorithm for determining the required control gain matrices of acceleration and displacement output feedback, which assign the desired eigenstructure, is developed. This algorithm is easy to implement, and works directly on the second-order system model. More importantly, the algorithm allows the output matrix and the input matrix to be specified beforehand and also leads naturally to a small norm solution of the gain matrices. Finally, some numerical results are presented to demonstrate the effectiveness and accuracy of the proposed algorithm. (C) 2015 Elsevier Ltd. All rights reserved.
会议名称：
2016 International Symposium on Materials Application and Engineering (SMAE 2016)
会议时间：
2016-01-01
会议地点：
Chiang Mai, Thailand
会议主办单位：
[Wu, Yan] Wuhan Polytech Univ, Sch Mech Engn, Wuhan, Peoples R China.^[Xia, Si] China Aerosp Sci & Inoustry Corp, Acad 4, Special Vehicle Techol Ctr, Beijing, Peoples R China.
会议论文集名称：
MATEC Web of Conferences
摘要：
Nanometer scale and micron scale grain growth of polycrystalline AZ31 Magnesium alloy have been comparatively studied by phase field simulation, and the models are established under realistic spatial-temporal scales. The expression of local free energy density function is modified due to the different initial state of grain growth process at nano scale. The term of grain boundary range is to explain the physical backgrounds of the order parameter gradients at grain boundary and the diffusion grain boundary, and it is related to the correct gradient and coupling parameters. The simulated results are compared in nano scale and micron scale, they are also compared with experimental results in the literature, in order to find out the mechanisms for nano-structural evolution. It is shown that the grain boundary range will cover two adjacent grains in nano scale polycrystalline while the range should be a constant big value of about 1.2μm for grains in micron scale. It is found that the grain growth rate at nano scale is slower than that at the micron scale, and these simulated results can be proved by the experimental results in the literature. It is found that the grain size fluctuation is more intensely in nano-sized grains than that in micron-sized grains by the quantitative analysis of the mixed degree of grains size in nano-structure and micron-structure in the models.
关键词：
PLC;Small Platform;Level adjustment;Two-axis position adjustment
摘要：
Many engineering devices need a platform with high level and position accuracy. An automatic control system is proposed to adjust a small platform that is supported by four height-adjustable legs and two length-adjustable level screws. The control system scheme and working principle are analyzed, then the structure of the control system based on PLC is put forward and the hardware is designed. And then the direction decoupling control strategy is put forward and software of the control system is designed in detail. The device can adjust the levelness and position of the platform quickly, with the man-machine interface of electronic touch screen for status display and parameter setting, the functions of virtual leg detection and limit protection.
摘要：
Preparation of BGA micro-joint with single-double substrates used by SAC30S lead-free solder is fabricated by reflowing process based on substrate FR-4. The microstructure change and evolution law of the solder joints are studied through the method of rapid thermal fatigue. The single-base plate SAC30S/Cu solder joint was tested at extreme temperature 60-200 degrees C by rapid thermal cycle 24 hours and 36 hours respectively, it was found the IMC grow by the zigzag shape, and fatigue cracks appear at the interface of IMC/Cu, they are initiating and propagating along the boundary, and thread through the cross section of solder joint in the end, which lead to the failure of solder joint.
作者机构：
[Wu, Yan] School of Mechanical Engineering, Wuhan Polytechnic University, Wuhan, 430000, China;[Zong, Bernie Yaping] Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang, 110819, China;[Xia, Si] Special Vehicle Technology Center, The fourth Academy of China Aerospace Science and Industry Corp, Wuhan, 430000, China
