三种结构光纤光栅应变传感器应变灵敏度分析研究

基于光纤光栅应变传感器的应变传感理论以及封装技术,针对"矩、工、回"三种结构的基片式光纤光栅应变传感器进行了有限元仿真分析,在相同载荷作用下三种结构传感器的应变灵敏度差别较大,其中"回"型结构传感器具有更高的灵敏度和适用性。     

基于FBG传感技术的复合材料T型加筋板低速冲击在线监测研究

将布拉格光纤光栅(Fiber Bragg Grating,简称"FBG")埋植在复合材料加筋板结构三角填充区,在线监测复合材料加筋板冲击过程及压缩过程的应变信号。研究了冲击点位置、冲击能量对FBG传感器应变监测性能的影响,分析了FBG传感器对复合材料T型加筋板冲击及压缩过程监测的精确性。结果表明:在相同冲击能量条件下,随着冲击点位置与FBG传感器距离的增加,FBG传感器测得的复合材料T型加筋板应变值呈下降趋势;当复合材料T型加筋板出现较为明显的损伤时,FBG传感器未发生断裂失效。将FBG传感器埋植于加筋板的三角填充区内,在压缩过程中,FBG传感器反射波谱保持单个波峰且形状未发生变化,初步实现了对复合材料T型加筋板冲击及冲击后压缩过程应变信号的在线监测。     

光纤光栅传感器在道路测试及工程应用的研究进展

路面结构内部温度、湿度、应力和应变等参数的测试一直是道路测试领域的重点和难点,随着光纤光栅传感技术的发展,为道路测试领域提供了新方法;为了论证光纤光栅传感技术在道路测试领域的可行性,介绍了光纤光栅传感系统的基本结构,从温度和应变传感器基本原理出发,综述了光纤光栅传感器的室内探索性研究和在实际路面温度和应变测试的成果.最后介绍了光纤光栅传感器在其他工程,包括桥梁、隧道及机场跑道中的应用情况,并分析了光纤光栅在道路测试工程中推广使用所面临的困难和发展方向.     

光纤传感器在监测RTM固化过程及复合材料健康状况中的应用

本文论述了应用光纤传感器对RTM的固化过程及制品疲劳损伤进行监测的技术方法。研究中，采用的增强材料的玻璃布，环氧树脂作基体。应用两种光纤应变传感器进行应变测定，一种是Bragg光栅（FBG）传感器；另一种是外置式Fabry-perot干涉型（EFPI）传感器。传感器埋入方向与树脂流动方向垂直或平行。研究结果表明：垂直埋入的FBG传感器在被固化树脂约束前，复观性差。另外，还发现FBG和EFPI传感器在冷态下具有良好的准确性。平行埋入的FBG传感器在模塑工艺中表现出良好的复观性。标距为1mm和4mm的传感器的应变现象不同。上述结果说明，将光纤传感器埋入FRP中，光纤传感器的埋入结构和标距对应变测量的精度有影响。利用埋入的光纤传感器进行固化监测，然后再循环加载试验，测定其内应变。循环加载试验的结果是用FBG传感器测得的应变与粘贴应变片测得的应变具有良好的一致性。本项研究得出的结论是：通过埋入FBG应变传感器可对RTM成型FRP工艺过程和使用过程中的内应变进行有效地监测。     

光纤传感器在复合材料研究中的应用

本文介绍了光纤传感器的性能及其在复合材料应变、温度等测量过程中的应用.     

一种基于内置FBG的复合材料模具型面应力-应变监测模块设计方法及性能分析

介绍了一种自主开发的复合材料模具的内置光纤光栅传感器(FBG)模块,首先在垂直集中静压力作用下标定传感器模块的线性应变敏感度,通过分析该传感器模块的模态屈曲,判定其在内置条件下的使用稳定性。之后将模块应用至大型风电叶片模具型面监测过程,在调节模具型面的过程中通过对照激光跟踪仪收集到的挠度位移矢量与传感器模块得到垂直分量应变,最后验证该模块性能满足实际应用可行性。     

光纤光栅在先进复合材料固化成型研究中的应用

先进树脂基复合材料被广泛应用于航空航天领域。热压罐成型工艺是复合材料结构件首选成型工艺之一,但存在效率低、成本高等问题,并且在成型过程中产生的固化应变会影响制件成型质量,通过光纤光栅传感器在线监测应变/应力参数对于制定合理工艺规程、提高制件品质具有重要作用。本文详细介绍了热压罐成型中光纤光栅传感器应变和温度交叉敏感解决方案,综述了近年来基于光纤光栅传感器在线监测的复合材料固化成型研究进展。并结合国内外研究现状,对光纤光栅在线监测的应用前景及亟待解决的问题提出了几点思考。     

弹性体结构光纤光栅应变传感器的设计与性能研究

为提高光纤光栅传感器的精度和长期使用稳定度,在分析其应变响应机理和研究现状的基础上,设计基于应变弹性体封装的光纤光栅应变传感器,封装材料采用305不锈钢。力学传递原理和Ansys力学分析结果都表明:该传感器能够有效地通过弹性结构将应变传递到光纤光栅上。利用激光切割技术制作不锈钢光纤光栅传感器封装壳体,在-2 000~2 000με的测量范围内,实验测得其应变灵敏度为1.21pm/με、线性度达0.999 6、检测精度不大于1με、稳定度不大于±3με。     

基于FBG传感器的碳纤维复合材料内部热应变监测

将光纤布拉格光栅(Fiber Bragg Grating,简称"FBG")传感器分别埋入单向板和平纹机织层压复合材料中,采用Sm125型光纤光栅解调仪测试两种复合材料在20~100℃温度范围内的内部热应变,分析单向板和平纹机织层压复合材料在仅受温度作用下内部热应变变化特征。结果表明,FBG传感器可以准确测量复合材料内部热应变变化;单向板和平纹机织层压复合材料的内部热应变均随温度升高而增大;织物结构影响复合材料内部热应变,且同一温度点,平纹机织层压复合材料内部热应变较单向板大。     

光纤光栅用于混凝土结构应变模态检测的研究

光纤Bragg光栅传感技术是一种先进的技术，具有传统技术无可比拟的优势。损伤检测研究是一个跨学科的前沿研究领域，传感技术的发展必将推动混凝土结构损伤检测新技术的研究与应用。本文介绍了光纤Bragg光栅传感技术原理，阐述了基于光纤Bragg光栅传感技术和应变模态理论的损伤自诊断的基本原理，并进行了相关的混凝土结构的可行性实验研究。结果表明光纤Bragg光栅传感器抗干扰能力强，具有高灵敏度和长期稳定性，其作为应变测量的工具用于应变模态，进行混凝土结构损伤识别是可行的。     

Evaluation of embedded optical fiber sensors in composites: EFPI sensor fabrication and quasi‐static evaluation

This article reports on the fabrication and evaluation of extrinsic Fabry–Perot interferometric (EFPI) sensors when embedded in fiber‐reinforced composites and tested under quasi‐static tensile and compressive mechanical loading. The EFPI strain sensors were embedded in carbon fiber composite test specimens, and their performance was compared against a surface‐mounted extensometer and electrical resistance strain gauges. When the composite was subjected to quasi‐static tensile loading, the sensors failed around a strain level of 0.5%; under compressive loading, the sensors survived until the failure of the composite at 1.1% strain. The EFPI sensors used in this study were fabricated in‐house and the issues relating to fabrication are discussed in the context of their performance when embedded in composites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Health monitoring of structural composites with embedded carbon nanotube coated glass fiber sensors

Structural health monitoring (SHM) seeks to provide ongoing monitoring of a structure’s integrity. Current SHM approaches include embedding some type of sensor within the composite or applying a sensor to the outside surface of the structure. These sensors react to strain or other changes in order to detect damage. In this study, a novel, multi-modal, nanomaterial based sensor technology that can provide wide area detection of damage was used. The efforts presented here serve as a feasibility study into the incorporation of carbon nanomaterials into structural composites as sensors. The carbon nanotube (CNT) covered fiber (fuzzy fiber) sensors exhibit similar sensitivity to conventional strain gages and are more easily integrated into composite structures as the sensor itself is a composite. The fuzzy fiber strain gages can be used to sense strain within composite structures and can be readily integrated into the structural laminate to provide sensing over large sections and in previously inaccessible locations. The unique properties of the fuzzy fiber lends itself to application in a wide range of sensing tasks within a structural composite including strain, temperature, degradation, etc. The fuzzy fiber may be tailored so that the same basic sensor can be used for a multitude of sensing applications.     

Strain Profile Measurement for Structural Health Monitoring of Woven Carbon-fiber Reinforced Polymer Composite Bonded joints by Fiber Optic Sensing Using an Optical Backscatter Reflectometer

In order to monitor crack initiation and propagation under static and fatigue loading in adhesively bonded joints, strain profile measurement such as backface strain (BFS) is a very efficient technique. In single lap (SL) joints, crack initiation and propagation in the glue line can be monitored by detecting the negative peak of the strain profile. Therefore, the accuracy of the monitoring system greatly depends on detecting the strain profile correctly and accurately. Previously, an array of electrical strain gages as well as fiber Bragg grating (FBG) sensors had been used successfully to capture the profile of BFS of a SL joint by applying sensors on the backface of an adherend, near the overlap zone. In this work, the backface technique is improved by replacing an array of strain sensors by an ordinary optical fiber (without FBG sensors) connected to an optical backscatter reflectometer. The great advantage of this system over the more conventional arrays of FBG is that the entire length of the fiber can be used for sensing strains, and hence it provides a better spatial resolution. The experimental results are compared with finite element analyses, which were further validated by two-dimensional digital image correlation measurements.     

Improved strain sensing performance of glass fiber polymer composites with embedded pre-stretched polyvinyl alcohol–carbon nanotube fibers

Polyvinyl alcohol–carbon nanotube (PVA–CNT) fibers differing on their pre-stretching condition were embedded in glass fiber reinforced plastic (GFRP) composites and used as strain sensors for damage monitoring of the composite. Strain sensing of the composite was made by the in situ measurement of the embedded fiber’s electrical resistance change during the mechanical tests. Four glass fiber composite plates were manufactured; each one had embedded a different type of produced PVA–CNT fibers. The multi-functional materials were tested in monotonic tensile tests as well as in progressive damage accumulation tests. The electrical resistance readings of the PVA–CNT fibers were correlated with axial strain values, taking into account the induced damage of the composite. It has been demonstrated that increasing the fiber’s pre-stretching ratio, its electrical resistance response increases due to higher degree of the CNTs alignment in the PVA matrix. Higher fiber pre-stretching degree enables the better strain monitoring of the composite due to higher measured electrical resistance change values noticed for the same applied axial strain values. To this end, it enables for the better monitoring of the progressive damage accumulation inside the composite.     

Enhanced Strain Sensing Performance of Polymer/Carbon Nanotube‐Coated Spandex Fibers via Noncovalent Interactions

Over the past decade, flexible strain sensors have been of tremendous interest due to their wide application in robotics, medical diagnostics, human motion detection, and healthcare. Herein, a fiber strain sensor is fabricated by continuously coating a layer of ultrathin multi‐walled carbon nanotube (MWCNT)/thermoplastic polyurethane (TPU) nanocomposites onto the surface of commercial spandex fiber. The effect of noncovalent functionalization of MWCNTs using 1‐pyrenecarboxylic acid (PCA) on the electrical conductivity as well as the sensing performance of the fiber sensor is investigated. The low‐cost strain sensor possesses a large workable strain (up to 200% strain), high sensitivity (gauge factor is 14 191.5 under 170–200% strain), and excellent stability (up to 1000 cycles), and regular signal responses within a wide measuring frequency range of 0.01–1 Hz are achieved with the introduction of PCA via enhanced nanotube dispersion and polymer–nanofiller interactions. Additionally, the resistance response to strain is fitted with a model based on tunneling theory to understand the sensing mechanism, and to prove that the fitted results are in agreement with the experimental results. Furthermore, the developed sensor is successfully applied in human motion detection, such as joint movement, facial microexpressions, and speech recognition.     

Highly Stretchable and Sensitive SBS/Graphene Composite Fiber for Strain Sensors

Flexible strain sensors have attracted tremendous interests due to the emergence of intelligent wearable technology. Electrically conductive fibers are desirable candidates for flexible strain sensors, but up til now, there still exist enormous challenges to obtain conductive fibers exhibiting simultaneously high stretchability and high strain sensitivity. This paper introduces a poly (styrene‐butadiene‐styrene) (SBS)/graphene (Gr) composite fiber‐based flexible strain sensor fabricated by a facile and highly scalable wet spinning method. The results demonstrate that the graphene content has significant influence on the morphology, mechanical properties, and electromechanical properties of the composite fibers. The fibers with 5 wt% graphene have a wide response range of up to 100% strain, a high electrical sensitivity with the gauge factor of 10083.98 at 100% strain, and meanwhile, a high level of stability for 2100 stretching–releasing cycles under an applied strain of 20%. Furthermore, the SBS‐5%Gr composite fibers display excellent sensing performance in detecting human upper limb movements at different joints including hand joints, wrist joints, elbow joints, and shoulder joints.     

周边约束状态下板式混凝土早期开裂及收缩应变的分布

改进型的板式试件法可用于实验室或施工现场快速测试混凝土的早期抗裂性能。大量实验的统计结果表明这种板式混凝土的早期收缩裂缝的分布主要集中在两个区域：每边中点处相连形成的“十”字形区域和4个边角区域附近。通过埋置光纤光栅传感器法对这种混凝土板在早期处于风吹加速干燥条件下内部收缩应变的分布进行测量,结果表明：混凝土收缩应变与离干燥表面的距离成指数函数关系;在距离模具边框越近的位置,混凝土表现出的收缩应变值越小。     

Design and development of low‐cost optical‐fiber sensors for temperature metrology: Process monitoring of an epoxy resin system

This article reports the design and deployment of two optical‐fiber temperature sensors based on the fiber Fabry–Perot etalon. The first involved the use of an extrinsic fiber Fabry–Perot sensor, but in this instance, the coefficient of thermal expansion of the reflector and/or capillary was chosen to offer a mismatch. Hence, the cavity length could increase or decrease according to the coefficient of thermal expansion of the fiber and/or capillary. For comparison, single‐mode and multimode optical‐fiber Bragg gratings were also used as temperature sensors. The Fabry–Perot sensors operated from ?50 to 410°C. The accuracy of the measurements was up to ±0.5°C with a low‐cost charged‐coupling‐device spectrometer. The sensors also worked effectively in a microwave oven and in a composite panel in an autoclave. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 83–95, 2004