MEMS高g加速度传感器高过载能力的优化研究

设计的MEMS高g加速度传感器抗高过载能力差,将导致在冲击等恶劣环境中应用时结构易破坏。本文通过分析传感器结构对其抗过载能力的影响,及在高冲击测试中传感器结构损坏情况的统计,提出了一种新颖的优化高g加速度传感器抗高过载能力的方法。该方法是在结构最易断裂的梁根部和端部添加倒角,以分散在冲击作用下传感器结构这些部位受到的应力,进而提高加速度传感器的高过载能力,并从理论仿真分析了该方法的可行性。最后利用Hopkinson杆测试方法对优化前后的加速度传感器进行冲击测试,测试结果表明,加速度计的抗高过载能力从180,000 g提高到240,000g,说明该优化方法显著,明显提高了该类加速度传感器的抗高过载能力,设计的加速度传感器达到了较理想的抗高过载能力。     

关于无晶振输出口通用计数器的晶振特性检定方法

本文针对无晶振输出口的通用计数器晶振特性无法由比对器直接获得的问题,由规程和相关知识总结出晶振特性各参数的检定方法,使它的晶振特性检定更加精确和完整。     

霍普金森压杆过载实验弥散分析

为准确获取霍普金森压杆高过载实验中试件加速度,用快速傅里叶弥散分析方法对入射波传播过程进行弥散修正,比较沿压杆轴向不同位置处加速度状态,分析弥散修正前后不同脉冲加载时试件加速度峰值及脉冲偏差。结果表明,弥散效应可导致压杆不同位置处加速度状态存在差异,火工品试件所受过载加速度峰值偏差在10%以上;脉冲宽度偏差因波形而异,绝对偏差均小于6μs;对含高频成分的弥散波,欲精确获得试件过载加速度需进行弥散修正。     

抗高过载防护结构的设计与性能测试

目的弹载记录仪在回收过程中,存在记录仪因硬着陆产生的高冲击力和高过载加速度使仪器损毁而致有效数据失效的现象。针对该问题设计新型双层壳体两级缓冲隔离的电路防护结构,并进行性能测试。方法结合Ansys/Workbench有限元数值模拟软件仿真分析该结构在冲击过程中的形变和受冲击过载特性,同时使用马歇特锤对使用该防护结构的记录仪模拟高冲击、高过载环境实验,由记录仪存储双层防护壳体内外嵌入的加速度传感器信号,并对多次试验信号数据进行处理和分析。结果在过载加速度小于25 000g时,该多层防护结构具有良好的缓冲效果,对记录仪保护效果良好;各层材料的声阻抗差别会影响整体保护效果,差别越大效果越好。结论该防护结构在高过载冲击环境下能有效衰减冲击效应,保护电子设备的安全。     

抗高过载电路的封装技术与封装材料

本文介绍了抗高过载电路的封装技术与封装材料,对抗高过载电路的封装工艺作了详尽的探讨。重点介绍了一种新型的封装材料—改性环氧树脂,并给出了它和其它封装材料在抗冲击实验中的性能指标比对情况。     

振动条件下的晶振稳健性机理研究

晶振在振动环境下产生严重的相位噪声恶化,由于其多学科交融的物理性质和在电子系统参考源中的应用价值而受到广泛关注。随着机电一体化设计理念的发展,研究振动环境下的信号调谐模式和探索它们独特的物理性质已经成为可能。该文从晶振的工作原理出发,分析了振动条件下相位噪声恶化的调谐原理,首次提出了一种新的晶振相位噪声振动恶化特征的物理表征方法。此外,搭建了晶振相位噪声测试系统,利用实验数据定量研究了各种输入条件对晶振电气性能的影响,并编制了相应的算法来进行求解,得出了非线性数学关系。最后,结合实验数据验证了机电一体化分析思路及物理表征方法的合理性,得到了晶振模块的振动稳健性矢量。     

机械振打除灰装置的纵向冲击特性

基于波动方程建立了机械振打器冲击过程的振动模型,并针对机械振打器撞击杆的特殊边界条件,推导了撞击杆在活塞杆纵向冲击下的位移、速度、应力分布以及冲击持续时间的解析表达式。结合机械振打器的实际工况,运用有限元软件ansys/ls-dyna模拟了撞击杆在活塞杆纵向冲击下的各种响应,结果表明解析解与理论解匹配良好。     

高应变速率下等径角挤压高纯粗晶铝中的形变孪晶与退火孪晶

在室温下对铸态高纯粗晶铝进行一道次高应变率动态等径角挤压(D-ECAP)变形,利用电子背散射衍射技术(EBSD)研究挤压过程中所形成的孪晶。结果表明:利用D-ECAP能够在粗晶铝中同时制备出形变孪晶和退火孪晶,但两者在形态、Kernel平均取向差(KAM)以及与相邻晶粒的取向差三个方面存在较大差异。D-ECAP高应变率和大剪切变形使高层错能铝中形成了百微米级的形变孪晶,形变孪晶的形态为透镜状,后续变形使得孪晶界偏离∑3 60°〈111〉取向关系且KAM值主要集中于0.6°~1.8°。高应变率剪切变形下形成的大量层错和复杂的位错组态以及高形变储存能在变形温升的作用下促进了退火孪晶的形成。退火孪晶的形态较不规则,但孪晶界的取向关系更接近于∑3 60°〈111〉且KAM值主要集中于0.2°~0.5°。     

抗高过载加速度计微结构的设计与分析

介绍一种抗高过载加速度计的结构,对其惯性结构、过载保护结构及气体阻尼结构进行了详细分析,其中惯性结构采用有较好过振保护的双端固支梁,其截面设计成一种具有应力集中特点的凹形截面.用有限元分析对微结构进行模拟计算,并通过试验验证.验证结果表明,该加速度计在经过20000gn冲击后,在±50gn的量程内非线性达到1%,灵敏度达到1mV/g.     

简易晶振驯服模块的研发与应用

介绍了一种利用高精度时间测量技术、Kalman滤波算法以及PID反馈控制原理,研制的一种简易恒温晶体振荡器(OCXO)驯服模块.该模块在不使用FPGA和复杂算法的前提下,可以将10-7量级的OCXO驯服到10-10级别,适用于初涉时频计量领域的研究人员进行装置研制和成果转化.课题组已经将该模块应用于机场送站车辆计时系统...     

Effects of strain rate on mechanical properties and failure mechanism of structural Al–Mg alloys

The effects of strain rate on the mechanical properties and failure mechanism of AA5754 and AA5182 sheets were investigated. Tensile tests were conducted at quasi-static (less than 10⁻¹ s⁻¹) and dynamic (600, 1100 and 1500 s⁻¹) strain rates at room and elevated temperature using an INSTRON machine and Tensile Split Hopkinson Bar (TSHB) apparatus, respectively. Shear band decoration, interrupted tensile tests, electron microscopy, and image analysis techniques were also utilized. The results obtained show that the studied alloys exhibit negative strain rate sensitivity at quasi-static rates, but mild positive sensitivity at dynamic rates. Different failure mechanisms were also observed. Strain localization and shear band formation was found to be a necessary pre-requisite for the development of damage and final failure under quasi-static conditions. In the dynamic strain rate regime however, less shear banding was observed. Void nucleation, growth and coalescence that is characteristic of dynamic tensile fracture appears to be the dominant mode for failure under dynamic conditions.     

用参量法通过LiNbO3晶体产生太赫兹的理论设计

按照参量振荡器的基本原理,从理论上设计了一个太赫兹参量振荡器。根据动量守恒、能量守恒条件以及相位匹配条件,应用铌酸锂(LiNbO3)晶体,给出了理论设计过程。画出了频率在太赫兹波段,波长与折射率的关系曲线,分析了太赫兹参量振荡器的非共线相位匹配条件,确定了晶体形状及其切割角、输出太赫兹波的可调谐范围,并画出了晶体为铌酸锂时相应的曲线,根据有效的输出功率,最后设计出最佳的太参量振荡器的结构。     

Failure mode analysis of lead-free solder joints under high speed impact testing

Using an Instron micro-impact system, this study investigates the failure characteristics of 96.5Sn–3Ag–0.5Cu lead-free solder joints aged at either room temperature or 125 °C, respectively, and then impacted at shear rates of up to 1 m/s. Four types of failure mode are identified, namely M1: interfacial fracture with no residual solder left on the pad; M2: interfacial fracture with residual solder left on the pad; M3: solder ball fracture; and M4: substrate fracture. The experimental results reveal that the solder specimens fail in different failure modes at the same impact speed. The transition from ductile to brittle failure occurs at an impact speed of around 0.5 m/s. At an impact speed of 0.7 (±0.05) m/s or more, over 70% of the specimens fail in the M1 or M2 modes under all of the testing conditions. The isothermal aging process is found to reduce the interfacial strength, and hence the percentage of M3 and M4 mode failures reduces significantly. Overall, the experimental results suggest that the failure mode distribution obtained in high speed impact tests performed at 0.5 m/s provides a feasible component-level quality assurance index.     

A testing technique for concrete under confinement at high rates of strain

A testing device is presented for the experimental study of dynamic compaction of concrete under high strain rates. The specimen is confined in a metallic ring and loaded by means of a hard-steel Hopkinson pressure bar (80 mm diameter, 6 m long) allowing for the testing of specimens large enough regarding the aggregate size. The constitutive law for the metal of the ring being known, transverse gauges glued on its lateral surface allow for the measurement of the confining pressure. The hydrostatic and deviatoric responses of the specimen can then be computed. The proposed method is validated by several numerical simulations of tests involving a set of four different concrete-like behaviours and different friction coefficients between the cell and the specimen. Finally, three tests performed with the MB50 concrete at three different strain rates are processed with the method and are compared with literature results for the same material under quasi-static loadings.     

Modeling the response,strength and degradation of 3D woven composites subjected to high rate loading

Experimental results which were obtained using a split Hopkinson pressure bar (SHPB) apparatus to determine rate dependent effects, and reported by the authors in [1] are used as the basis to perform dynamic simulations of 3D woven composites (3DWCs) using representative unit cells (RUCs). The input material properties for the RUC simulations were determined from the concentric cylinder model (CCM) in conjunction with the geometry of the textile architecture, mechanical properties of pure epoxy samples and fiber mechanical properties. The RUC model incorporates rate dependent plasticity. Additionally, linear-eigen perturbations that correspond to buckling modes are used to seed imperfections in the RUC model to capture buckling and subsequent failure that was observed in experiments. The RUC model results showed good agreement with experiment and correctly captured the observed modes of failure while pointing to transitions in failure modes.     

A mathematical model of a crystal oscillator and clock in the form of an augmented system of state equations

An analysis of a mathematical model of a crystal oscillator and clock and disturbances in the form of an augmented system of state equations is performed. By means of such a model, it is possible to synthesize an optimal frequency-time stabilization system for the GLONASS/GPS synchronizing reference receiver. __________ Translated from Izmeritel’naya Tekhnika, No. 4, pp. 35–38, April, 2007.     

The strengthening mechanism of a nickel-based alloy after laser shock processing at high temperatures

Abstract

We investigated the strengthening mechanism of laser shock processing (LSP) at high temperatures in the K417 nickel-based alloy. Using a laser-induced shock wave, residual compressive stresses and nanocrystals with a length of 30–200 nm and a thickness of 1 μm are produced on the surface of the nickel-based alloy K417. When the K417 alloy is subjected to heat treatment at 900 °C after LSP, most of the residual compressive stress relaxes while the microhardness retains good thermal stability; the nanocrystalline surface has not obviously grown after the 900 °C per 10 h heat treatment, which shows a comparatively good thermal stability. There are several reasons for the good thermal stability of the nanocrystalline surface, such as the low value of cold hardening of LSP, extreme high-density defects and the grain boundary pinning of an impure element. The results of the vibration fatigue experiments show that the fatigue strength of K417 alloy is enhanced and improved from 110 to 285 MPa after LSP. After the 900 °C per 10 h heat treatment, the fatigue strength is 225 MPa; the heat treatment has not significantly reduced the reinforcement effect. The feature of the LSP strengthening mechanism of nickel-based alloy at a high temperature is the co-working effect of the nanocrystalline surface and the residual compressive stress after thermal relaxation.     

高g值微加速度计在冲击环境下的可靠性

详细分析了高g微加速度计在冲击环境下的失效模式和失效机理,对0～150 000g 4端全固支的压阻式梁-岛结构微加速度计进行霍普金森杆(Hopkinson bar)激光干涉冲击试验.由试验结果可知,该结构的微加速度计抗冲击过载能力达100 000 g以上,微加速度计的失效模式表现为梁的裂纹和断裂.微加速度计在冲击环境下的可靠性采用应力-强度干涉模型进行评估.     

Using split Hopkinson pressure bars to perform large strain compression tests on polyurea at low,intermediate and high strain rates

The strain rate sensitivity of polyurea is characterized using a modified split Hopkinson pressure bar (SHPB) system. The device is composed of a hydraulic piston along with nylon input and output bars. In combination with an advanced wave deconvolution method, the modified SHPB system provides an unlimited measurement time and thus can be used to perform experiments at low, intermediate and high strain rates. A series of compression tests of polyurea is performed using the modified SHPB system. In addition, conventional SHPB systems as well as a universal hydraulic testing machine are employed to confirm the validity of the modified SHBP technique at low and high strain rates. The analysis of the data at intermediate strain rates shows that the strain rate is not constant due to multiple wave reflections within the input and output bars. It is demonstrated that intermediate strain rate SHPB experiments require either very long bars (>20 m) or very short bars (<0.5 m) in order to achieve an approximately constant strain rate throughout the entire experiment.