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991.
Mechanical properties of silicon nanobeams with undercut evaluated by combining dynamic resonance test and finite element analysis 下载免费PDF全文
Mechanical properties of silicon nanobeams are of prime importance in nanoelectromechanical system applications. A numerical experimental method of determining resonant frequencies and Young's modulus of nanobeams by combining finite element analysis and frequency response tests based on an electrostatic excitation and visual detection by laser Doppler vibrometer is presented in this paper. Silicon nanobeams test structures are fabricated from silicon-on-insulator wafers by using a standard lithography and anisotropic wet etching release process, which inevitably generates the undercut of the nanobeam clamping. In conjunction with three-dimensional finite element numerical simulations incorporating the geometric undercut, dynamic resonance tests reveal that the undercut significantly reduces resonant frequencies of nanobeams due to the fact that it effectively increases the nanobeam length by a correct value Δ L, which is a key parameter that is correlated with deviations in the resonant frequencies predicted from the ideal Euler-Bernoulli beam theory and experimentally measured data. By using a least-square fit expression including Δ L, we finally extract Young's modulus from the measured resonance frequency versus effective length dependency and find that Young's modulus of silicon nanobeam with 200-nm thickness is close to that of bulk silicon. This result supports that the finite size effect due to surface effect does not play a role in mechanical elastic behaviour of silicon nanobeams with the thickness larger than 200 nm. 相似文献
992.
航天器在研制过程中要经过一系列地面力学验证试验, 但在传统加速度控制振动试验中, 受试航天器或其部组件和试验台的连接机械阻抗与真实飞行状态存在很大差异, 如果仅采用加速度条件进行控制可能产生严重的"过试验" 现象. 美国早在20 世纪60 年代就已认识到这一问题, 但直到最近十几年才通过力限振动试验的办法加以解决. 力限振动试验技术分为力限振动试验条件设计技术和力限振动试验控制技术, 其中试验条件设计是开展振动试验的基础和依据. 本文对国内外力限振动试验技术的发展历程和重要成果进行了简述, 并结合我国力限振动试验技术的现状, 对力限振动试验技术在我国的应用和发展, 以及有待进一步研究的问题进行了展望. 相似文献
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通过四种不同双向加载规则的钢筋混凝土高墩拟静力试验,初步研究了双向拟静力加载规则对其滞回特性的影响规律。本文主要介绍钢筋混凝土高墩的试验构件设计,加载装置、测试方法和加载规则,着重比较了对角线加载、正方形加载、菱形加载和圆形加载等四种加载规则的钢筋混凝土高墩的滞回性能,包括荷载-位移滞回曲线、荷载-位移骨架曲线、荷载退化、刚度退化以及累积滞回耗能的特点,并分析这些特点与双向加载规则之间的关系。结论认为:对角线加载模式加载效率高且能较好反映高墩双向抗震滞回性能,适合于高墩的双向拟静力试验研究。 相似文献
994.
Kazuhisa Sato Ken Suzuki Keiji Yashiro Tatsuya Kawada Hiroo Yugami Toshiyuki Hashida Alan Atkinson Junichiro Mizusaki 《Solid State Ionics》2009,180(20-22):1220-1225
The conductivity and elastic modulus of (CeO2)1 − x(YO1.5)x for x values of 0.10, 0.15, 0.20, 0.30, and 0.40 were investigated by experiments and molecular dynamics simulations. The calculated conductivity exhibited a maximum value at approximately 15 mol% Y2O3; this trend agreed with that of the experimental results. In order to clarify the reason for the occurrence of the maximum conductivity, the paths for the transfer of oxygen vacancies were counted. The numerical result revealed that as the content of Y2O3 dopant increases, the number of paths for the transfer of oxygen vacancies decreases, whereas the number of oxygen vacancies for conductivity increases. Thus, the trade-off between the increase in the number of vacancy sites and the decrease in the vacancy transfer was considered to be the reason for the maximum conductivity occurring at the Y2O3 dopant content of approximately 15 mol%. The calculated elastic modulus also exhibited a minimum value at approximately 20 mol% Y2O3, which also agreed with the experimental results. It was shown that the Y–O–Y bonding energy increased with the increasing content of Y2O3 dopant. Thus, the trade-off between the increase in the number of vacancy sites and that in the Y–O–Y bonding energy was considered to be the reason for the minimum elastic modulus occurring at the Y2O3 dopant content of approximately 20 mol%. 相似文献
995.
N. A. Khilo P. I. Ropot N. S. Kazak V. N. Belyi A. G. Mashchenko 《Journal of Applied Spectroscopy》2009,76(3):434-439
We present an optical method for determining the hardness of metals, based on the correlation between the thermal diffusion
coefficient and the hardness of the material. Spatial and temporal modulation localized in the nonstationary thermal wave
profiles is transferred to the surface of the metal, where the time evolution of the speckle images produced by a probing
laser beam is recorded by a CCD camera. A special algorithm for processing the speckle images allows us to determine the thermal
diffusion coefficient. Experimental studies on steel samples confirmed the workability of the proposed method.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 3, pp. 460–465, May–June, 2009. 相似文献
996.
应用电磁波的反射与折射理论建立了多层导电结构电涡流检测探头阻抗解析模型.电涡流检测中空间电磁场可看作线圈激励场与涡流场的叠加,而涡流场是线圈激励场的反射与折射效应,因此应用线圈激励场的级数型解析解和电磁波的反射与折射理论推导了级数型探头阻抗解析解.最后,比较了推导的级数型与传统的积分型探头阻抗解析解的计算结果,并进行了实验验证.计算结果与实验结果基本吻合,表明推导的级数型探头阻抗解析解是正确的,且与积分解析解相比具有不需要确定积分上限、耗时少、计算精度容易控制等优点.
关键词:
电涡流检测
多层导电结构
反射与折射理论
探头阻抗 相似文献
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