FBG应变传感器的疲劳性能研究

将光纤布拉格光栅(FBG)应变传感器埋入树脂基复合材料内部,采用试验的方法研究了传感器的疲劳性能.FBG应变监测曲线变化规律符合复合材料层合板疲劳理论,经历106次循环载荷作用过程后,最大应变测量相对误差为1.11％,保持了良好的应变测试能力和较高的测量精度.实验证明:FBG能够实现对交变应变、应力的监测,具有良好的抗疲劳能力,为重要结构服役过程中的在线损伤监测、剩余寿命预报以及材料破坏失效的预警奠定了重要基础.     

非增强式原型封装光纤Bragg光栅钢筋应变计

为了适应量大面广的重大土木工程结构的长期健康监测,特别是克服恶劣的施工与服役环境(如,腐蚀、疲劳等),封装的光纤Bragg光栅(FBG)应变计不仅必须要有很好的测试精度、布设可靠等特性,还必须具有优越的性价比。针对这一实际应用要求,提出了一种非增强式原型封装光纤光栅钢筋应变计,并通过静载试验对其传感特性进行了研究。研究结果表明:试验结果与理论分析基本吻合,光纤光栅的波长变化与应变存在很好的线性关系,其相关系数均达到0.999以上,并具有很好的重复性;通过管内外应变对比试验说明:此钢筋应变计对钢筋几乎没有加强作用,能如实地反映钢筋应变。     

桥梁疲劳监测传感器设计

设计了一种桥梁疲劳监测传感器,它通过电阻不可逆变化的疲劳载荷响应机理拾取结构损伤信号。所设计的独特应变倍增器可将微弱的交变应变信号进行机械放大,使敏感元件在桥梁高周疲劳载荷作用下仍工作在敏感区。解决了疲劳敏感元件存在的较高动应变响应门槛值与结构较低动应变损伤间的矛盾,采用弓形弹性元件与硅橡胶预应力组合结构,得到了可靠性好、刚度低、放大率高及使用方便的理想结构,从而满足了桥梁结构长寿命、低应力工作特点的寿命检测要求。静载和疲劳试验说明:所设计的传感器具有很高的疲劳灵敏度、长期稳定性,完全适用于桥梁结构的高周疲劳检测。     

海洋平台安全性评估集成软件的设计与实现

中国船舶科学研究中心对海洋平台安全性评估方法集成软件进行了开发。该集成系统前台是以Orient.CAE平台为基础,根据专业分析需要定制界面,后台集成专业人员研制的求解程序。包含基于中国近海海况下,海洋平台非线性波浪诱导载荷预报系统;高阶水动力快速预报计算程序;基于半潜式钻井平台结构的疲劳失效概率、强度和稳定性失效概率计算方法的平台结构安全载荷能力系数预报系统;典型半潜式钻井平台结构全寿期安全性评估系统。形成了自主知识产权的海洋平台结构安全评估软件。     

B/S模式的FBG信号远程监控系统设计

采用B/S结构作为监控系统的基本架构,开发了光纤Bragg光栅(FBG)远程监测系统.通过访问Web网络可以在浏览器界面查看FBG解调系统检测的FBG传感器数据.研究结果表明:通过查询2014年11月28日～2014年12月27日期间应变桩FBG应变传感器应变变化的时序曲线图与边坡上表面FBG位移传感器位移变化的时序曲线图,能够及时了解到不同监测对象的物理变化量.通过远程实时观察传感器数据信息,为工程的安全监测提供了依据.     

基于光纤光栅的组合结构界面脱空变形检测

利用光纤B ragg光栅(FBG)传感器检测钢砼组合桥面板模型界面的脱空(掀起)损伤。模型试验经历了静载、300万次循环疲劳加载和破坏3个阶段。测试结果表明:在静载和疲劳试验阶段,FBG传感器布设点并未发生脱空,传感器测得相应位置的应变值;破坏阶段,在FBG传感器布设点相继出现脱空损伤。利用FBG传感器测得经历300万次循环加载疲劳试验后,钢砼组合模型发生脱空变形的临界应变值,并追踪其发展的全过程,为组合结构界面脱空变形检测提供了一种全新的、可靠的检测方法。     

基片式FBG在飞机蒙皮测试中的对称补偿研究

基片式FBG传感器封装结构在应变测试中受到广泛关注,尤其是在航空航天领域,其粘贴方式对监测飞机蒙皮应变具有重要意义。为了提高基片式封装结构的FBG测量飞机蒙皮应变精度,对薄板试验件粘贴基片式FBG传感器进行力学性能研究,实验结果表明传统粘结基片式FBG传感器方式会引起被测薄板材在拉伸过程中产生非线性变形。据此,通过ANSYS有限元分析软件仿真粘贴1 mm传感单元的1.5 mm薄板静态加载过程,并进行静力学有限元优化分析,力学分析及理论推导结果显示,对称粘贴基片式FBG传感单元能够解决应变与波长非线性关系,且能够有效补偿温度对测量的影响。搭建FBG解调系统与MTS力学测试实验系统,实验结果表明,在对称补偿的布点方式下,应变测试线性度为0.998,传感单元应变灵敏度为0.946 pm/με,提高了应变测试精度,可以有效的应用到飞机蒙皮应变测试。     

新型疲劳传感器设计与性能研究

基于经过特殊退火处理的康铜材料具有不可逆电阻疲劳载荷响应,用其作为疲劳敏感元件材料,但因制成的疲劳寿命计工作响应应变门槛值太高,设计了结构独特的弹性放大元件,两者组合构成的疲劳传感器灵敏度得到很大提高,满足了大型工程结构循环应力低、工作寿命长的寿命检测要求,从而达到对大型结构长期健康监测目的。通过试验,研究了该新型疲劳传感器的热输出特性和不同受力情况的放大系数变化,得到了传感器热输出和放大系数修正公式。所设计的疲劳传感器性能满足各种大型工程结构疲劳损伤监测要求,与其他疲劳检测方法相比,其测试精度、经济性和效率均具有明显优势。     

沥青混凝土路面光栅应变传感器的试验研究

疲劳是沥青路面设计标准之一,沥青混凝土的疲劳失效与沥青层底拉应变值的大小相关.为了准确测得在实际车辆荷载作用下沥青层底的应变响应,采用光栅应变传感器代替传统的电信号传感器进行路面应变测量的试验研究,结果表明光栅传感器在抗振动、抗电磁干扰等方面性能较好,试验结果与路面结构和材料类型相符,能够满足路面应变测量的要求.     

无封装FBG应变传感器在桩基试验中的标定研究

针对海上风电桩基的沉桩模型试验,采用无封装分布式光纤光栅(Fiber Bragg Grating, FBG)应变传感器对模型桩的沉桩过程进行应变监测,为提高FBG应变传感器的测量精度,通过采用自主设计并研制出的标定装置,提出了一种用于桩基试验的无封装FBG应变传感器灵敏度系数的标定方法,并将标定结果与理论值进行对比。随后,在模型桩的桩顶、桩中和桩底位置安装电阻式应变片进行加载试验,将FBG应变传感器的测量应变数据与电阻应变片测量数据进行对比分析。研究结果表明：标定后的FBG应变传感器的灵敏度系数与理论值相比存在较大差异,最大误差为6.76%,这是由于标定后的FBG应变传感器测量结果更为准确,并且FBG传感器的测量精度要高于应变片。该标定试验为后续沉桩试验模型桩应变、应力及桩侧阻力的监测提供了可靠的数据支撑。     

Evaluation of thermo-mechanical damage and fatigue life of solar cell solder interconnections

The soldering process of interconnecting crystalline silicon solar cells to form photovoltaic (PV) module is a key manufacturing process. However, during the soldering process, stress is induced in the solar cell solder joints and remains in the joint as residual stress after soldering. Furthermore, during the module service life time, thermo-mechanical degradation of the solder joints occurs due to thermal cycling of the joints which induce stress, creep strain and strain energy. The resultant effect of damage on the solder joint is premature failure, hence shortened fatigue life. This study seeks to determine accumulated thermo-mechanical damage and fatigue life of solder interconnection in solar cell assembly under thermo-mechanical cycling conditions. In this investigation, finite element modelling (FEM) and simulations are carried out in order to determine nonlinear degradation of SnAgCu solder joints. The degradation of the solder material is simulated using Garofalo-Arrhenius creep model. A three dimensional (3D) geometric model is subjected to six accelerated thermal cycles (ATCs) utilising IEC 61215 standard for photovoltaic panels. The results demonstrate that induced stress, strain and strain energy impacts the solder joints during operations. Furthermore, the larger the accumulated creep strain and creep strain energy in the joints, the shorter the fatigue life. This indicates that creep strain and creep strain energy in the solder joints significantly impacts the thermo-mechanical reliability of the assembly joints. Regions of solder joint with critical stress, strain and strain energy values including their distribution are determined. Analysis of results demonstrates that creep energy density is a better parameter than creep strain in predicting interconnection fatigue life. The use of six ATCs yields significant data which enable better understanding of the response of the solder joints to the induced loads. Moreover, information obtained from this study can be used for improved design and better-quality fabrication of solder interconnections in solar cell assembly for enhanced thermo-mechanical reliability.     

Elastoplastic analysis of tubular joints of offshore platforms

The subject of this paper is the analysis and design of complex tubular joints, eventually including internal and external gussets and stiffener rings, corresponding to fixed and mobile offshore structures.Two different joints are analysed. In the first case an X joint is studied for elastic and elastoplastic behaviour, loading up to collapse in order to determine ultimate strength and safety factor. Finite elements which can reproduce the elastic and plastic singularities of the stress and the strain fields in the crack tip, are then used for the analysis of a T joint. Both direction and rate are considered in the crack propagation, and an elastoplastic analysis is carried out, to determine the crack opening displacement (COD).Finally, the consideration of fatigue effects in tubular joints is discussed, and techniques for evaluating fatigue life are outlined.     

FBG传感器在复合材料固化监测中的应用

FBG传感器广泛应用于复合材料结构健康监测中,将双光栅的FBG传感器埋入到玻璃纤维/环氧树脂预浸层合板结构中,监测热压固化过程中温度、内应力变化以及固化残余应变,分析了残余应变对FBG传感器性能的影响。实验表明FBG传感器可以有效监测复合材料结构固化过程的温度和内应力,以及由温度计算的粘度变化,为智能固化控制提供依据,且固化于复合材料结构内的传感器可用于结构的全服役周期健康监测。     

缆索内置光纤光栅传感器胶接植入试验研究

为实现光纤光栅传感器胶接固定于桥梁缆索钢丝以监测缆索索力,利用胶接结构的剪切测试、钢丝疲劳测试和循环加卸载测试分别对光纤光栅传感器支座与钢丝间胶接结构的剪切性能、疲劳可靠性以及胶接光纤光栅传感器的测试性能进行评估.试验发现:光纤光栅传感器支座与桥梁缆索钢丝间的胶接结构具有较大的剪切载荷,且200万次疲劳载荷对其胶接结性能影响较小;胶接固定于钢丝上的光纤光栅传感器可测出钢丝加卸载的滞回效应,并每个循环加、卸载的波长和钢丝承载载荷关系呈线性且分别重合.结果表明:内置光纤光栅传感器的胶接固定结构具有良好的剪切力学性能和疲劳可靠性,可保证其光纤光栅传感器的测试具有良好的准确、稳定、可靠性.     

光纤和电阻应变片在结构变形测试中的对比试验研究

在测量结构应变和变形时,传统的电阻应变片测试技术和新型的光栅布拉格光纤传感技术（FBG）、布里渊光时域反射技术（BOTDR）三者均具有不同的监测原理。设计并进行了基于这三种监测技术的简支梁弯曲试验,测试结构应变,对比结构挠曲变形,分析了三种监测技术在应变测量中的精度、灵敏度、布设工艺和适用性等,评价了两种光纤传感技术用于结构挠曲变形测试的特性。为选择土木工程结构监测手段提供参考依据,对进一步研究、开发新型应变传感器和监测仪具有参考价值。     

Investigation on packages of fiber Bragg grating for use as embeddable strain sensor in concrete structure

The paper covers detailed investigation on encapsulation and packaging of fiber Bragg grating (FBG) for strain sensing of concrete structures in embeddable form. Non-uniform strain distribution due to imperfect curing of the epoxy and its effect on the FBG spectrum has been studied experimentally and correlated with theoretical simulation. For a specific package, an optimal curing condition has been found and shown to have good repeatability. The successfully packaged sensor has been embedded in a concrete structure and the response has been found to be linear. Response of the sensor under static loading condition is compared with surface mountable electrical resistance strain gauge (ERSG) and embeddable type EFPI (extrinsic Fabry Perot interferometer) fiber optic sensor. The sensor has also been tested under dynamic loading of the structure.     

Fibre Bragg gratings in structural health monitoring—Present status and applications

In-service structural health monitoring (SHM) of engineering structures has assumed a significant role in assessing their safety and integrity. Fibre Bragg grating (FBG) sensors have emerged as a reliable, in situ, non-destructive tool for monitoring, diagnostics and control in civil structures. The versatility of FBG sensors represents a key advantage over other technologies in the structural sensing field. In this article, the recent research and development activities in structural health monitoring using FBG sensors have been critically reviewed, highlighting the areas where further work is needed. A few packaging schemes for FBG strain sensors are also discussed. Finally a few limitations and market barriers associated with the use of these sensors have been addressed.     

基于光纤光栅应变传感器的监测系统设计

通过在桥梁、建筑等重大工程结构的具体实施应用中，对光纤光栅工程结构应变长期监测系统的设计方法、基本构成、传感网络的优化、系统的温度补偿、现场传感器的布设、保护工艺等诸多重要问题进行了分析和研究，并加以解决。应用此系统对大型重量级工作制钢吊车梁的加固进行了监测，通过与理论的对比表明采用光纤光栅应变传感网络对大型构件实现应变检测是可行的。