Development of smart composite structures with small-diameter fiber Bragg grating sensors for damage detection: Quantitative evaluation of delamination length in CFRP laminates using Lamb wave sensing

The authors and Hitachi Cable, Ltd. have recently developed small-diameter optical fiber and its fiber Bragg grating (FBG) sensor for embedment inside a lamina of composite laminates without strength reduction. The outside diameters of the cladding and polyimide coating are 40 and 52 μm, respectively. First, a brief summary is presented for applications of small-diameter FBG sensors to damage monitoring in composite structures. Then, we propose a new damage detection system for quantitative evaluation of delamination length in CFRP laminates using Lamb wave sensing. In this system, a piezo-ceramic actuator generates Lamb waves in a CFRP laminate. After the waves propagate in the laminate, transmitted waves are received by an FBG sensor attached on or embedded in the laminate using a newly developed high-speed optical wavelength interrogation system. This system was applied to detect interlaminar delamination in CFRP cross-ply laminates. When the Lamb waves passed through the delamination, the amplitude decreased and a new wave mode appeared. These phenomena could be well simulated using a finite element analysis. From the changes in the amplitude ratio and the arrival time of the new mode depending on the delamination length, it was found that this system could evaluate the delamination length quantitatively. Furthermore, small-diameter FBG sensors were embedded in a double-lap type coupon specimen, and the debonding progress could be evaluated using the wavelet transform.     

智能型电动葫芦下滑量检测仪

在总结和分析了现有电动葫芦制动下滑量测试方法的基础上 ,提出了采用AT89C5 2单片机设计的智能测试系统 ,该系统使测试的精度、劳动效率显著提高 ,而且减少了劳动量。实际运行正常、可靠性良好。     

无励磁分接开关故障对电力变压器安全运行的危害及预防措施

介绍了两起由于无励磁分接开关故障引发的变压器事故，分析了事故原因，并根据近几年类似故障情况提出了预防措施。     

锌含量对铅锌合金电化学行为影响的研究

采用循环伏安(CV)、线性电位扫描(LSV)、交流阻抗(EIS)等方法研究了不同锌含量的铅锌合金电极在硫酸溶液中氧化膜的生成情况。由电位区间0.9~1.7 V循环伏安曲线、恒电位1.5 V,1 h后的线性电位扫描伏安曲线中PbO2还原峰电流和还原电量可知,PbO2膜生成量随锌含量增加而增长;恒电位0.9 V,1 h后的线性电位扫描伏安曲线中PbO PbO.PbSO4和PbSO4还原峰电流和还原电量显示,随锌含量增加,铅(Ⅱ)氧化膜生成量减小,电阻与电位的关系曲线表明,随锌含量增加,氧化膜电阻减小,电导增强。     

Oscillation and convergence behaviours exhibited in an ‘unstable’ second‐order digital filter with saturation‐type non‐linearity

This letter explains the oscillatory behaviours exhibited in a second‐order digital filter with saturation‐type non‐linearity via the Hopf bifurcation theorem. It is shown that depending on the bifurcation parameter, the state variables may converge to zero even when the eigenvalues of the system matrix are outside the unit circle. Copyright © 2004 John Wiley & Sons, Ltd. abstract     

Three dimensional cutting force analysis in end milling

The analysis of cutting forces plays an important part in the design of machine tool systems as well as in the planning, optimization, and control of machining processes. This paper presents a three-dimensional model of cutting forces in peripheral end milling in terms of material properties, cutting parameters, machining configuration, and tool/work geometry. Based on the relationship of the local cutting force and the chip load, the total cutting force model is established via the angle domain convolution integration of the local forces in the feed, cross feed, and axial directions. The integration is taken along the cutter axis and summarized across the cutting flutes. The convolution integral leads to a periodic function of cutting forces in the angle domain and an explicit expression of the dynamic cutting force components in the frequency domain. The closed-form nature of the expressions allows the prediction and optimization of cutting forces to be performed without the need of numerical iterations. To assess the fidelity of the analytical model, experimental data from end milling tests are presented in the context of three dimensional time waveforms, power spectra, and phase angles, in comparison to the values predicted by the model.     

多波长线性回归——导数分光光度法同时测定油品中的铁和钒

用5-Br-PADAP 作显色剂,采用多波长线性回归一阶导数分光光度法同时测定油品中铁和钒,灵敏度高,ε铁=5.08×10~5L.mol~(-1)cm~(-1),ε铁=2.65×10~5Lmol~(-1)cm~(-1).铁和钒的最低检出限分别是0.005μgmL~(-1)和0.003μgmL.合成样品分析,加标实验及对照实验结果表明,该法简单、灵敏、准确。     

安全停输时间的数值计算

输油系统出现故障,进行抢修或是输油设备进行定期维修都要求停输。停输可作为输油管道运行管理的一种手段,但停输引起的一些问题也应特别注意,尤其是如何确定安全停输时间成为停输工艺的关键。热油管道停输后,管内存油的温度下降,粘度上升。当存油温度降到一定程度时,管道再启动工作就会变得十分困难,甚至发生凝管事故。输油管道安全停输时间计算的准确与否直接影响到管线安全运行及效益,该项计算极其复杂,需要综合考虑整个输油系统各方面的因素。根据热油管道的流动特征,建立了热油管道停输数学模型,并用追赶法计算安全停输时间,从而为指导生产防止凝管事故发生提供了科学的依据。计算结果与实测数据基本相符     

一种新的基于图论的图像分割算法

传统的基于图论的图像分割方法计算复杂度大,对图像亮度变化比较敏感,且分割效果有待提高.针对传统算法的不足,提出一种新的基于人眼视觉特征的图像阈值分割算法.该算法基于图论和归一化划分准则,并把对数图像处理模型(LIP模型)应用到图像处理中.同时,该算法综合考虑像素的灰度信息和空间位置信息,具有全局性,使分割目标比现有方法更为准确,且时间复杂度适中.实验结果表明,该算法不仅有效地分割出目标来,而且在图像亮度小幅度变化时,效果稳定可靠.     

电能质量单项指标和综合指标评估的研究

从电力用户对电能质量需求的多样性出发,论述了电能质量单项评估和综合评估的重要性与必要性。基于我国电能质量相关标准或规定的限值,对电压偏差、频率偏差、电压闪变、三相不平衡、谐波以及电压暂降与中断,定义了6个归并后的单项指标和1个综合指标。指标量化的结果能体现监测中电能质量存在的问题及其严峻程度,便于调度和规划部门发现警戒点及时控制和解决问题,也可以作为用户选择供电服务的参考依据。