Prevention of thermal bending of multilayered beams and plates

A method is described to prevent bending in multilayered beams and plates of different isotropic materials with uniform and nonuniform temperature distribution through the thickness. The method involved the addition of an extra layer to the multilayered beams or plates. With the proper selection of the thermoelastic properties, the added layer would eliminate the curvature produced prior to this addition. A complete analysis for the determination of the various thermoelastic parameters of the extra layer was made. In addition, to ensure that the multilayered beams and plates actually remained straight, a thermoelastic analysis was performed for the solution of thermal stresses and strains in the laminate. The results gave assurance to the straightness of the laminate since the calculated strains have the same value throughout the thickness. The solutions are valid for any given uniform temperature change and for any given nonlinear temperature distribution through the thickness of the multilayered beams and plates. Several numerical examples are presented that illustrate the application of the method for various temperature distributions. A simple experiment was conducted that showed the validity of the analytical method. A brass strip was added to a bimetalic strip made of aluminum and steel at room temperature. The thickness of the brass strip was calculated from the theory to prevent bending. The trimetal strip was placed in a furnace and, as expected, it remained straight for varying temperatures.     

后张法预应力张拉常见问题分析及防治措施

在预应力张拉施工过程中,只有采取积极有效的预防措施,出现问题及时正确地解决,才能彻底清除预应力施工过程中的安全隐患,提高桥梁的工程质量,延长桥梁的使用寿命。     

Prevention of fog in a condenser by simultaneous heating and cooling

By partial condensation the vaporous component of a vapour–gas mixture can be separated. This process plays an important part, especially in the recovery of solvents when the solvent is a vapour and mixed with a gas. The only drawback is, however, the frequent occurrence of undesired fog formation. This fog consists of a large number of small solvent droplets and only by a large effort can it be separated again. Through good modelling of the processes of heat and mass transfer the causes for the formation of fog and a method for its prevention can be found. The solution seems to be paradoxical: to avoid the formation of fog the condenser has to be cooled and heated simultaneously. If fog can be prevented, the degree of separation of the vapour–gas mixture even increases. The heating of the condenser may be accomplished by internal energy recovery, thereby simplifying the apparatus concept and energy supply.     

钢筋砼薄壁桥台裂缝问题分析与防治

薄壁桥台的裂缝问题是一个很普遍又很难解决的工程实际问题,需从设计、施工和养护三方面综合考虑,要严格按照要求施工,保证养护合理,使薄壁桥台发挥其应有的作用。     

Thermographic detection of adhesive-bond and interlaminar flaws in composites

This paper reports the development of a liquid-crystal passive thermographic technique for the detection of adhesive-bond-line and interlaminar flaws in composite materials. The technique was successfully used for the detection of flaws in three composite systems: E-glass/epoxy, graphite/epoxy and HMC. Thermographic results are compared to ultrasonic C-scan results to assess the relative effectiveness of the new technique. A photomicrographic study was also used to verify the detected flaws and to characterize the type and extent of the actual damage.     

反应堆压力容器防断裂设计的规范法和分析法比较

针对AP1000反应堆压力容器的上封头部分,采用规范法计算了反应堆启动和停堆瞬态下表面椭圆形裂纹前沿的应力强度因子.计算结果表明在反应堆启动过程中,上封头外表面裂纹比内表面裂纹更加危险;而停堆过程中,内表面裂纹比外表面裂纹危险.对于远离结构不连续区,环向和径向裂纹前沿的应力强度因子相差不大.但是对于临近结构不连续处,反应堆启动过程中环向裂纹比径向裂纹危险;而停堆过程中,径向裂纹比环向裂纹危险.经评价表明该缺陷符合ASME安全设计的要求.同时建立含真实裂纹的三维有限元模型进行了防断裂分析评价.通过两种方法的对比表明,传统的规范法比有限元方法偏保守.     

材料的磨损失效及其预防研究现状与发展趋势

论述了材料磨损失效的主要模式和引起磨损失效的各种可能因素及材料磨损失效的研究现状与发展趋势,探讨了材料磨损失效研究所面临的课题和开展磨损失效研究的必要性。     

爆炸冲击波的提取和显示方法

在差分格式中引入人工粘性捕捉激波,处理压力、密度等物理量的间断,使间断得到平滑,在计算结果中,冲击波就表现为物理量具有很大梯度的一个狭窄过渡区。利用边缘检测算子从计算数据中检测出位于边缘上的点,通过处理压力数据可以在图像中清晰地显示冲击波的轮廓。     

Ultrasonic detection and measurement of fatigue cracks in notched specimens

An ultrasonic technique was developed and used to observe the formation and growth of fatigue cracks in notched cylindrical specimens subjected to reversed axial cyclic loading. Fatigue curves of life-to-initial detectable cracks as well as life-to-fracture were obtained for an aluminum-, a titanium- and a cobaltbase alloy, as well as a maraging steel. Depth of initially detectable cracks ranged between approximately 0.0005 and 0.004 in. (0.013 and 0.10 mm). Curves were also obtained relating ultrasonic system output voltage to crack depth up to 0.030 in. (0.76 mm) for three materials. These curves were used to demonstrate the capability of the device for monitoring crack growth.     

硅微陀螺正交误差及其对信号检测的影响

分析了硅微陀螺正交误差在运动方程中的表现,利用Simulink仿真研究了正交误差对信号检测的影响。文中先推导了不等弹性存在的情况下正交误差等效角速度的表达式,随后分析了某型硅微陀螺在角速度输入为0（°）/s和80（°）/s时敏感振动的频谱图,最后仿真分析了正交误差对模拟和数字检测电路的影响。经分析,对于模拟解调电路,正交误差会导致陀螺的零偏和温漂;对于数字解调电路,由于正交误差大大减小了敏感振动的电压幅值对角速度的标度因数,在AD量化噪声及其它电路噪声一定的情况下,会使陀螺零偏稳定性变差,从而限制了数字解调的优势。     

Ultrasonic detection of high-temperature fatigue-crack growth

An ultrasonic technique is described for continuously monitoring fatigue-crack growth at temperatures up to 300°C in wedge-opening-load type fracture-toughness specimens. The sound-wave energies reflected from the leading edge of the fatigue crack and from the bottom surface of the specimen are electronically compared and used to control the crack-measurement system.     

LIF based detection of low-speed streaks

An automated method for detecting low-speed streaks in laser-induced fluorescence (LIF) images of turbulent boundary layers is described. The method, based on the identification and characterization of local maxima in intensity educes all the low-speed streaks that can be visually identified in the LIF images. The proposed algorithm seems robust and can yield reliable information on the statistical characteristics of the streaks.     

Chaotic motions and fault detection in a cracked rotor

Applying the theory of Lyapunov exponents for nonsmooth dynamical systems, chaotic motions and strange attractors are found in the case of a cracked rotor. To detect the crack and establish a clear relation between shaft cracks in turbo rotors and induced phenomena in vibrations measured in bearings, a model-based method is applied. Based on a fictitious model of the time behaviour of the nonlinearities, a state observer of an extended dynamical system is designed resulting in estimates of the nonlinear effects.     

CORS基站周跳探测与修复方法

针对在CORS系统初始化后,周跳的出现将严重影响移动用户定位精度,CORS网中基站坐标已知,可精确预报对流层、电离层等系统误差,以及整周模糊度确定的特点,分析了周跳对双差模型的影响,通过分析普通卫星产生的周跳仅对一个双差观测方程产生影响,可以作为粗差,参考卫星的周跳会引入所有观测方程,从而对模型产生系统性误差,进而提出了使用附有系统参数的抗差估计方法,对CORS基站中的载波观测值进行整体平差,根据改正数V判断普通卫星的周跳,根据系统参数x2判断参考卫星的周跳。实验表明,该方法能将所有可见卫星进行整体的周跳探测,并且能实现高度角低于10°时的周跳探测和修复。     

Intelligent detection of rail corrugation using ACMP-based energy entropy and LSSVM

In this paper, an intelligent method to diagnose rail corrugation based on signal decomposition and entropy theory is proposed. The axle box acceleration signals are first decomposed into several components with different frequency bands by ACMP, EEMD and MODWT. By comparison, ACMP is able to successfully extract rail corrugation component from original signal without mode mixing. Energy entropy is then introduced here to quantify the degree of the rate of energy concentration. The analysis results show that the energy will change when rail corrugation occurs and the entropy will become small. It has been also proved that the entropy difference of rail corrugation and normal signal based on ACMP is the most significant. In addition, to intelligently diagnose rail corrugation, we combine energy entropy with energy index and the first mode energy, regarded as the input feature vector of LSSVM, to distinguish rail corrugation from mass data sets. It is obvious that the accuracy of ACMP-based technique is the highest.

     

用隐Markov模型的陀螺电机故障诊断方法（英文）

为满足机电陀螺仪高可靠性的要求,准确地检测和诊断陀螺仪核心部件——陀螺电机的各类故障是十分必要的。提出了一种陀螺电机检测和诊断的新方法,即基于隐Markov模型的模式识别方法。该方法从母线电流时域信号提取特征并作为电机状态的监测指标,通过顺序后推法选择最佳信号特征建立特征空间,并用于隐Markov模型的参数训练,进而使用隐Markov模型作为分类器对陀螺电机进行故障检测和诊断。为验证方法的有效性,用一台无刷直流陀螺电机作为样本进行了实验,构造了轴承故障和定子故障,并在不同的温度条件下进行了测试。实验结果表明:该方法对于陀螺电机故障检测和诊断的正确率达到96.8%。     

A new device for in-situ movement detection and measurement

A new device for movement detection in joints is designed using the moiré technique. Archimedean spiral grids are used. A space displacement may be evaluated in two planes by vectors of known magnitudes and directions. An extremely simple design is proposed to provide stability for the system being installedin situ over long periods of time.     

New concept for crack detection

The purpose of this paper is to describe the development, application techniques and the mechanical properties of a new and unique crack-detection coating. The coating consists of a base-layer matrix of epoxy resin and specially formulated, very delicate microcapsules, 250–500 μm in size, which contain black conductive liquid. A second layer of a thin, conductive silver coating then is added on the top of the base layer. Whenever a structure using this coating develops a fatigue crack, the base matrix over the fatigue crack also cracks, rupturing the microcapsules and releasing the conductive liquid into the crack. An electrical circuit is thus completed between the structure and the top conductive silver layer. A change in electrical resistance from 50 K megohms to one-tenth (0.1) of a megohm occurs and the conductive liquid, containing carbon black, will show a visual fine-hairline crack on the upper conductive silver coat (Figs. 1,2). The crack-detection coating is so formulated that the mechanical characteristics and fatigue-crack resistance are greater than the metal structure.