基于BOTDR的白泥井3号隧道拱圈变形监测

白泥井3号隧道是一条山岭隧道,隧道出口段位于滑坡等地质灾害多发的危险区域,为了确保隧道安全,应用国际上先进的BOTDR分布式应变测量技术,对隧道拱圈截面变形进行了分布式应变监测。本文着重介绍了BOTDR在隧道内安装布设以及监测数据的分析过程,监测成果显示,在将近1 a的监测时间里,隧道拱圈基本保持稳定,只是在个别区域,如K84+508.2处拱圈截面的衬砌表面发生张拉变形,变形量在雨季期间达到最大,据分析是由于雨水入渗山体造成围岩压力增大,致使拱圈截面受挤压变形。     

边坡变形的分布式光纤监测模拟试验研究

布里渊散射光时域反射测量技术(BOTDR)作为一项新型光电传感监测技术,因其具有良好的抗干扰、长距离、可植入性和分布式监测的特点而被广泛应用于结构工程健康监测中。而直接将光纤布设在土体中则存在变形协调性差、易折断及空间定位难等问题。本次研究通过室内小比例尺模型试验,分别将光纤植入土工布和土工格栅等柔性复合材料中并一起铺设在边坡模型不同深度处,利用BOTDR监测边坡在外荷作用下的变形特征。试验结果表明,布设在土工格栅中的光纤稳定性最好; 土工布中的光纤变形协调性和敏感性优于土工格栅; 通过合理布置光纤能够对异常应变进行较为准确的识别和定位。试验初步验证了该方法应用于土质边坡变形监测的可行性。     

分布式光纤传感测试系统(BOTDA)用于H型钢梁变形监测的实验研究

介绍了分布式光纤传感测试系统(BOTDA)的应变测量原理,并应用BOTDA技术对H型钢梁加载后的应变分布进行了测量。试验表明,BOTDA的应变测量结果与电阻应变片的测量结果及理论值具有良好的一致性。光纤测量的数据是连续的,因而更加适用于那些需要测试连续变形的结构。由BOTDA的实测应变分布推算出的H型钢梁的弯矩和挠度,与理论分析结果高度吻合。作为先进的监测技术手段,分布式光纤传感测试系统应用于SMW工法桩施工监测是完全可行的。     

分布式光纤传感器测量数据可靠性分析方法

分析了分布式光纤传感器测量结果的可靠性,提出从应变系数和温度系数标定到分布式光纤传感器物理量测量以及结果评价的方法,设计了分布式光纤传感器的应变系数和温度系数标定装置,同时分析了应变标定装置的不确定度来源,采用基于光频域反射技术的分布式光纤解调仪进行了实验验证。应变标定范围为-5000με~5000με,温度标定范围为20℃~50℃,第一次测量得到应变系数和温度系数分别为:-6.6775με/GHz和-0.5921℃/GHz。使用获得的应变系数和温度系数再次测量,得到在测量范围内,应变测量相对误差为1%,温度测量相对误差为2%,满足工程应用要求。上述结果表明,设计、发展的数据标定及分析方法可用于分布式光纤传感器应变系数和温度系数的标定。     

一种基于动态参考瑞利散射谱的分布式光纤大应变解调方法

基于光频域反射计(OFDR)的分布式光纤系统在结构健康监测领域得到广泛关注,通过对参考瑞利散射谱和测量瑞利散射谱进行互相关分析来确定谱偏移量,进而转化为结构应变。这种分布式光纤的应变解调方法具有较高的空间分辨率和测量精度,但在光纤受到较大应变时(超过3000με)会出现瑞利散射谱信号急剧衰减,从而导致互相关分析无法解调应变。本文提出了一种OFDR分布式光纤的大应变分步解调方法,采用动态参考瑞利散射谱取代固定参考瑞利散射谱的方法来突破大应变测量的限制。通过对复合材料层合板拉伸实验的大应变测量表明,本文所提出的光纤应变解调方法能稳定和可靠地测量10000με以上的大应变情况。     

基于光纤光栅的直升机桨叶应变试飞研究

研制了基于光纤布拉格光栅(FBG)传感原理的光纤光栅应变机载测试系统,并应用于直升机旋翼桨叶的外场试飞测试,使直升机桨叶应变试飞实现了光学传感。首先基于等强度梁开展电学应变计与FBG应变计的对比测试,验证了两者测量应变的一致性;其次搭建桨叶运动姿态物理仿真平台,并开展基于模拟桨叶的FBG挥舞弯曲应变测试,初步验证了FBG应用于桨叶应变测试的可行性;最后在直升机飞行试验中,使用FBG网络动态测量桨叶多剖面的分布式挥舞弯曲应变,并分析和对比电学应变计与FBG传感器阵列的实测数据,验证了分布式FBG网络应用于直升机桨叶试飞的技术可行性。     

基于OFDR分布式光纤传感器的应变测试试验研究

利用光频域反射技术(OFDR)测试应变时在空间分辨率、灵敏度、传感精度、响应度和测量距离上的显著优势,以铝合金梁三点弯曲试验为载体,开展了基于OFDR分布式光纤传感器的应变测试,并通过与电阻式应变片测试结果、梁三点弯曲试验有限元模拟结果进行对比分析,论证了分布式光纤传感器应变测试的可行性和准确性.试验揭示了铝合金梁在三...     

薄钢板低周疲劳测试技术研究

汽车钢板材料由于厚度较薄,在低周应变疲劳性能测试中,试样容易发生屈曲,并且受限于试验段的标距,无法使用传统机械式引伸计进行应变的测量,在工程中,其低周疲劳性能的测试是一项技术难点。本文基于数字图像相关技术,提出了一种非接触式的光学引伸计,结合光学显微镜头和防屈曲装置,实现材料表面应变的实时监测。该动态应变测量系统使用普通的CCD相机,采用了优化的计算方法,应变测量的频率可以高达60Hz。该动态应变测试技术可以广泛地应用于各个工程领域的动态变形测量。     

基于双光纤光栅的冰压力传感器研究

冰压力是高纬度地区结构的重要荷载,然而传统的基于电阻应变计开发的冰压力传感装置在稳定性与耐久性上遇到难以跨越的难题。光纤光栅是目前在智能材料系统与结构健康监测研究与应用最为广泛的敏感材料之一,具有分布式绝对测量、抗腐蚀能力强等优点。本文基于双光纤光栅应变测量原理,考虑冰压力测试装置的环境条件,设计开发出冰压力传感装置,详细推导和试验验证了该装置的传感特性,并将试验与理论结果进行了对比。研究结果表明该装置具有温度自补偿、测量值与荷载作用点无关、线性度和重复性好、精度较高等优点,具有良好的应用前景。     

1981年日本实验应力和应变分析述评

1.概况NDI(无损检测协会)第4分科会的内容,已从过去的以测量技术为中心的狭义应变测量,向着谋求扩大应用领域,充实研究内容,提高技术水平这一广义应变分析的方向发展。在电阻应变测量方面,正在采取措施,以实现测量的系列化和数据处理的自动化;同时研究提高测量精度,以扩大测量的应用范围(包括在医学、工程等方面的应用)。在光弹性方面,进一步认识到把光弹法和有限元法同时并用,更能充分有效地发挥光弹法的优点。实      

Residual Strains using Integrated Continuous Fiber Optic Sensing in Thermoplastic Composites and Structural Health Monitoring

The evolution of spatially resolved internal strain/stress during the manufacturing of thermoplastic composites and subsequent relaxation from water intake are evaluated using an in-situ fiber optic sensor corresponding to a coated optical glass fiber with a nominal diameter of 160 μm. Unidirectional carbon fiber-polyamide 6 composites are produced using compression molding with an embedded fiber optic for strain measurement. The distributed fiber optic based strain sensor is placed in an arrangement to capture 0, 45, and 90° strains in the composite to resolve in-plane strain tensor. Strains are monitored in the direction of fiber optic sensor along its length at high resolution during the various stages of compression molding process. Results indicate considerable internal strains leading to residual stress at the end of processing step along the off-axis (45°) and transverse (90°) directions, and small strains in the carbon fiber pre-preg (0°) direction. At the end of compression molding process, an average of 7000 and 10,000 compressive micro-strains are obtained for residual state of strain in the off-axis and transverse direction. Since water/moisture infusion affects the mechanical properties of polyamide-6 matrix resin, these composite panels with embedded sensors targeted for marine applications are monitored in a water bath at 40 °C simulating accelerated testing conditions. Using the same fiber optic sensor based technique, the strain relaxation was observed during water uptake demonstrating in-situ strain monitoring during both manufacturing and subsequent composite implementation/application environment. The technique presented in this paper shows the potential of optimizing time-temperature-pressure protocols typically utilized in thermoplastic manufacturing, and continuous life-cycle monitoring of composite materials using a small diameter and inexpensive distributed fiber optic sensing.     

BOTDR分布式检测技术在复杂地层钻孔灌注桩测试中的应用研究

分析了Kagome格栅的等效刚度和屈服面. 其屈服面奇异,由4段直线围成. 利用该屈服面, 估算了Kagome具有I型、II型半无限大裂纹的裂尖塑性区,有限元计算验证了解析预测的 准确性. 与奇异屈服面相比,由Mises光滑屈服面给出的塑性区误差较大. 因此只有弹性情 况,可以将Kagome等效为各向同性;若材料塑性,或应力场奇异性较强,Kagome的强度依 赖于主应力方向,不能用各向同性模型来描述.     

Live monitoring of the distributed strain field in impulsive events through fiber Bragg gratings

In this paper, we propose a measurement technique based on local strain measurements to perform real-time reconstruction of the overall structural deformation and the distributed stress field produced by the impact of a body on a water free surface. In particular, we seek establishing a measurement chain capable of acquiring and elaborating the signals at high frequency, so that it can be utilized to study rapidly varying strain fields, such as those occurring in impulsive events. Fiber Bragg gratings are utilized to sense the local structural deformation. Experiments are conducted on flexible plastic wedges with variable deadrise angles impacting on a quiescent fluid surface. The experimental tests are performed in free fall and we explore variations of the entry velocity by varying the drop height. The structural deformation is reconstructed from point-wise strain measurements utilizing a modal reconstruction methodology. The impact dynamics are analysed through accelerometers and linear position sensors. Results show that the impact behaviour of the flexible body is characterized by a main overall deformation where the structure is distorted in the direction of the loading, whereby marked vibrations, whose amplitude increase with the entry velocity, dominate the dynamic response. The influence of the mode shapes considered in the present analysis on the accuracy of the results is also observed. The proposed methodology allows for a fairly high acquisition frequency, which translates into a real-time structural reconstruction technique. Results show that the proposed methodology can be a valuable tool for the live monitoring of structures undergoing impact events.     

Evolution of bond fractures in a randomly distributed fiber network

Fracture in a planar randomly ordered fiber network subjected to approximately homogenous macroscopic stress and strain field is considered. A theory describing material degradation on a macroscopic scale is derived via Griffith’s energy balance for an internal fractured area in the network assuming the active fracture process on the microscopic level is fiber–fiber bond breakage. Attention is confined to a purely mechanical theory assuming isothermal processes and the theory relies on equations commonly used in theories of statistical physics. In the theory, a bond breaking driving force is stated to be equal to the elastic strain energy density of a non-fractured network. A debond fraction can be coupled to a linearly decrease of the network’s macroscopic stiffness. The rate of the fracture processes is determined by the network’s inherent properties (bond and fiber density, bond strength, etc.). During the loading process, until onset of localization, the bond breaks occur at randomly distributed locations spread over the fiber network and the theory estimate material degradation on a macroscopic level. When localization takes place, the fracture process changes from a two-dimensional randomly distributed process to a one-dimensional process and other theories have to be included to describe post-localization behavior. An approximately in-plane isotropic low-density paper is used in tensile experiments while monitoring acoustic emission activity to evaluate the theory. The experimentally obtained results support the theory surprisingly well.     

DAMAGE DETECTION STRATEGY FOR RETICULATED STRUCTURES BASED ON INCOMPLETE STRAIN MODE

Damage detection based on strain responses of vibration is highly attractive for monitoring long-span reticulated structures.However,there are a lot of structure members in reticulated structures and it is impossible to install strain sensors in each member.Therefore,how to locate and quantify damages with the incomplete mode shapes obtained from few strain sensors is a challenge topic.A new strategy,named incomplete strain mode damage detection(ISMDD) strategy,is proposed in this paper.In the strategy,the distribution of the strain sensors in the reticulated structures can be optimized through sensitive analysis on strain mode perturbation matrix,which can be obtained by perturbation theory.Mode assurance criterion(MAC) value is applied in damage location,and the members with relative large MAC values are defined as damage members.In addition,damage index obtained by solving the perturbation equation is used for damage quantification.Numerical analysis on a long-span reticulated structure,including damage location and quantification for single-and multi-member damages,detection for different damage quantity,the effect analysis of sensor quantity,are performed to verify the effectiveness of the proposed ISMDD strategy.It can be shown from the analysis that the ISMDD strategy is effective in damage location and quantification for both single-and multi-member damages.And the quantity of strain sensors has effect on damage location,but has no obvious influence on damage quantification.Additionally,the anti-noise pollution ability analysis of the ISMDD strategy is carried out,which shows that the ISMDD strategy has excellent anti-noise pollution ability for both single-and multi-damaged members.     

线起爆膨胀柱壳实验加载及诊断技术

基于电爆炸丝引爆炸药、继而驱动尼龙对金属柱壳进行碰撞加载的方式,在金属柱壳中部、半柱高范围内实现了一维柱面膨胀加载。同时,基于沿轴向的加载（或径向速度）一致性和沿环向的加载（或径向速度）轴对称性,提出了一维柱面加载的有效性判据。相比于滑移爆轰加载,一维柱面加载方式具有应力状态相对简单、易简化为二维轴对称问题分析的优点。在柱壳断裂诊断方面,建立了分布式表面速度诊断方法来监测柱壳圆周范围内的初始断裂。其原理为:均匀承载壳体断裂引起的局部承载失效将导致均匀速度曲线簇出现分叉（或演化趋势变化）。与高速分幅照相诊断方法相比,分布式表面速度诊断方法可准确获取柱壳圆周范围内的初始断裂信息（含断裂时刻和断裂位置）。利用建立的线起爆膨胀柱壳实验加载和诊断技术,获得了304钢和45钢柱壳的一维柱面动态拉伸初始断裂性能数据（含断裂应变、平均应变率）,其中,45钢柱壳的断裂应变（或延展性）低于304钢柱壳的。     

A strain-energy criterion for recognition of identified modes of continuous structural models

In structural modal analysis and modal testing, an important but difficult task is to match the identified natural frequencies and the corresponding modal deflections. This process is called the modal recognition in this paper. There were some treatments towards this problem for the lumped parameter structural models. For the distributed parameter models, however, little research has been reported on the modal recognition problem. In this paper, a strain-energy criterion for modal recognition has been developed. As an example, a distributed parameter model for a two-beam structural system has been formulated, which is expected to simulate the dynamics of a two-arm manipulating system fixed on a shuttle. Transfer matrix method has been used to set up the dynamic equation of the system. The natural frequencies are obtained from the solution of the characteristics equation. Consequently, the mode shape functions are found out analytically.

Strain energy can be viewed as a measure of the structural deformation. When performing modal analysis, we always assume that the structural system is vibrating at a particular natural frequency. The strain energy is, therefore, stored in the deflection caused by such a harmonic motion. The vibration at a particular natural frequency will not produce any strain energy in the other modal components. On the other hand, if a particular mode shape is contributed mostly by the deformation of a specific component of the global structural system, then the great percentage of the total strain energy will be stored in the deformation of that component. Based upon the calculation of the strain energy in the structural components we can find out which component is deformed most and in what motion it is deformed, thereby, the mode shape can be detected. The computer simulation demonstrated that the strain energy indicated an essentially perfect recognition of the identified natural frequencies with the corresponding mode shapes. The creation of the strain-energy criterion consummates the procedure of the distributed parameter modeling, modal identification and parameter estimation.