基于光纤光栅传感器的复合材料层合板冲击能量研究

复合材料结构较容易产生结构表面无法探测到的低速冲击损伤。试验利用光纤复合材料结构中布拉格光纤光栅传感器受到低速冲击后光栅中心波长随应力变化这一特性,在恒温下用布拉格光纤光栅传感器对复合材料智能结构受到的低速冲击能量给出判别,并对通过光纤光栅解调仪采集下来的低速冲击信号进行频谱分析。在计算冲击信号所有能量等级的频谱峰值后,给出可以界定能量等级的频谱峰值临界值,利用其来判别低速冲击能量等级。试验表明布拉格光纤光栅传感器可以监测复合材料受到冲击的信号,能够对复合材料结构低速冲击进行能量等级判断研究     

基于光纤光栅传感器的飞机油箱表面复合材料板振动研究

飞机机翼油箱在飞行时容易受到各种振源影响,而油箱结构中的复合材料较容易受低频振动影响。试验利用布拉格光纤光栅传感器受到激励后光栅中心波长随应力变化这一特性,在恒温下用布拉格光纤光栅传感器对飞机油箱表面变截面碳纤维层合板受到的振动信号进行研究,并对通过光纤光栅解调仪采集下来的振动动态信号进行频谱分析。在计算出动态信号的频谱峰值后,分析得出变截面碳纤维层合板的振动信号受到截面厚度、激励点位置的共同影响。结果表明利用光纤Bragg光栅传感网络对飞机油箱表面变截面碳纤维层合板受到的振动影响进行监测。     

Low energy impact damage monitoring of composites using dynamic strain signals from FBG sensors - Part I: Impact detection and localization

Fiber reinforced composite materials risk to suffer from subsurface, barely visible, damage induced by transverse relatively low energy impacts. This two-paper series presents a method for the localization of an impact and identification of an eventual damage using dynamic strain signals from fiber Bragg grating (FBG) sensors. In this paper, the localization method allowing to predict the impact position based on interpolation of a reference data set is developed and validated. The data utilized in the method are the arrival times of the asymmetric zero order Lamb waves at the different sensors. A high rate interrogation method based on intensity modulation of the Bragg wavelength shift is used to acquire the FBG signals. The localization method allows to predict the impact position with a good accuracy and therefore the inspection of the laminate can be limited to this region.     

Intracore fiber bragg gratings for strain measurement in embedded composite structures

An intracore Bragg grating written on a photosensitive fiber core is used for strain measurement in composite specimens under load. The strain information is directly related to the absolute change in the Bragg-reflected wavelength. Fiber Bragg grating (FBG) sensors (fibers with intracore gratings) are thus sensitive to strain that is caused by changes in temperature as well as to load-induced changes. Thus these sensors can be made to be independent of source intensity variations and losses. FBG sensors used for load-induced strain sensing in composite structures and the effects of temperature on them are discussed. A detailed account of the use of such embedded structures as self-monitoring nondestructive testing devices is given.     

Simultaneous determination of curvature,plane of curvature,and temperature by use of a miniaturized sensing head based on fiber Bragg gratings

We present what we believe to be a novel miniaturized sensor configuration based on fiber Bragg gratings for simultaneous measurement of curvature and temperature in smart structures and composite materials. Because of the particular geometry of the sensing head, it is possible not only to measure the radius of curvature but also to determine the plane of curvature. We arrange three Bragg gratings in the vertices of the smallest equilateral triangle that can be defined by the cross sections of the fibers. The set is then inserted into a glue-filled capillary stainless-steel tube to provide both suitable protection for the Bragg sensors and rotational symmetry to the sensing head. This tube also ensures isolation from axial strain, allowing for the additional determination of temperature. The proposed sensing head is particularly well suited for applications in smart structures because it can be embedded along any layer of a composite material (including the neutral line) without special concern for the relative orientation of the Bragg gratings and the composite layers. We can also use this sensing configuration to implement more-sophisticated sensors dedicated, for example, to the measurement of multiaxial acceleration or flow and temperature.     

基于FBG传感技术的复合材料T型加筋板低速冲击损伤监测

针对碳纤维增强树脂复合材料低速冲击损伤的实时监测,设计将布拉格光纤光栅（FBG）传感器埋植在复合材料T型加筋板结构的三角填充区,在线监测复合材料T型加筋板冲击损伤过程。分别将FBG传感器埋植于复合材料层合板内部和复合材料T型加筋板的三角填充区,对比FBG传感器的埋入对复合材料层合板和复合材料T型加筋板力学性能的影响。结果表明,内埋FBG传感器的复合材料层合板试样的拉伸强度比未埋植传感器的层合板试样降低了约5%,但在FBG传感器的破坏应变范围内,FBG传感器可以准确、实时地监测复合材料的应变信号。将FBG传感器埋入复合材料T型加筋板的三角填充区,内埋FBG传感器的T型加筋板样件压缩破坏载荷与未埋植的样件基本一致。通过对比T型加筋板蒙皮上冲击位置、冲击能量对FBG传感器测得的冲击过程持续时间和最大应变值的影响,表明冲击过程持续时间随着冲击能量增大而延长,最大应变值随着冲击距离的增加呈下降趋势,而最大应变值随着冲击能量的增大呈上升趋势。利用FBG传感器测得的应变信号可初步实现对复合材料T型加筋板蒙皮冲击损伤位置及冲击能量的实时监测。      

光纤Bragg光栅传感检测组合结构的断裂损伤

采用光纤Bragg光栅(FBG)传感器对钢-混凝土组合桥面板模型由加载产生的滑移、掀起(脱空)和裂缝三类损伤进行检测。试验经历了静载、300万次循环疲劳加载和破坏三个阶段。结果表明在静载和疲劳试验阶段未出现滑移、掀起和纵向裂缝,传感器测得FBG布控处的混凝土应变值。破坏阶段中,组合结构相继出现裂缝、滑移和掀起损坏,利用FBG传感器测到发生此三种损坏的临界应变值并追踪其发展。结果表明:光纤Bragg光栅(FBG)传感器能够检测组合结构的断裂损伤,并追踪其发生发展的全过程。该技术对组合结构的健康检测和优化设计是很有用的。     

Crack tip identification with long FBG sensors in mixed-mode delamination

The uncertainty of the crack tip position inside composite coupons during a delamination test under variable fracture mode conditions reduces the accuracy of the experimental results. In this work a method is presented where the crack tip position is located using long embedded Fibre Bragg Grating (FBG) sensors together with the Optical Low Coherence Reflectometry (OLCR) technique. With this technique the local Bragg wavelength is measured which then enables to calculate the axial strain profile within the grating. Carbon/epoxy samples are tested under different mode ratios through the standard Mixed-Mode Bending (MMB) test. Embedded long FBG sensors are used to measure the axial strain profile along the whole grating at different stages of the test. The crack tip can be precisely identified with the long embedded FBGs and then checked by means of a visual inspection after complete delamination of the sample. The data indicate that the long FBG sensor detects the crack tip inside the sample at least as precisely as the traditionally performed visual inspections carried out during the test by means of the lateral markings. Numerical simulations using cohesive elements are in good agreement with the experimental data.     

智能材料工艺与结构中的先进传感器的发展

建立复合材料成型过程的智能化在线监控系统,有效地调整生产工艺,科学设计和优化生产工艺,可以有效地提高生产质量,降低生产成本。除生产工艺智能化外,还需建立材料结构的智能化体系,从复合材料固化成型、材料生产到材料应用整个过程均实现智能化,将开辟材料科学研究的新途径。建立智能材料工艺与结构体系需要先进的性能优良的传感器,本文以智能材料体系为背景阐述了各种传感器技术性能及发展方向。     

光纤机敏复合材料与结构

介绍了光纤机敏复合材料与结构的概念,发展历史,应用领域以及可用于光纤机敏复合材料与结构的常见的光纤传感器及传感阵列。     

Sensitivity of embedded fibre optic Bragg grating sensors to disbonds in bonded composite ship joints

The potential application of embedded fibre optic Bragg grating strain sensors for the health monitoring of adhesively bonded composite ship joints is investigated in this paper. Bragg grating sensors were embedded at various locations along the interface of adhesively bonded glass-reinforced plastic composite joints with artificially introduced disbonds to assess their capability to detect bond-line damage under in-plane shear and through-thickness tension. Finite element (FE) models indicated that the presence of the disbond significantly altered the bond-line strain distribution under such loads. The embedded sensors successfully detected this effect, and the sensor measurements compared well to FE predictions. However, the experimental measurements of the magnitude of the strain at the tips of the disbonds showed significant variations, presumably due to its high sensitivity to defect edge conditions which could not be experimentally controlled with a high degree of repeatability. Both the FE models and the experimental results showed that the effect of disbond damage was localised, more so under in-plane shear than through-thickness tension. This would necessitate the use of an optimised sensor array and pattern recognition algorithm for the reliable detection of an arbitrary disbond.     

智能复合材料中FBG智能夹层的研究

光纤自诊断系统是智能复合材料结构的重要组成部分，但将光纤埋入复合材料中还存在着诸多问题．解决这些问题最有潜力的技术途径是将光纤传感器集成在一起形成一个模块化的便于埋入复合材料中的光纤智能夹层。基于FBG传感器的优点，对FBG智能夹层进行了研究。研究结果表明，智能夹层的埋入对复合材料结构的强度性能影响较小，智能夹层中FBG传感器波长偏移与应变具有良好的线性关系，可以将智能夹层埋入复合材料结构内部，利用FBG传感器网络和先进信息处理技术，建立结构损伤主动、在线和实时监测系统。     

Inverse scattering algorithm for reconstructing lossy fiber Bragg gratings

We demonstrate an inverse scattering algorithm for reconstructing the structure of lossy fiber Bragg gratings. The algorithm enables us to extract the profiles of the refractive index and the loss coefficient along the grating from the grating transmission spectrum and from the reflection spectra, measured from both sides of the grating. Such an algorithm can be used to develop novel distributed evanescent-wave fiber Bragg sensors that measure the change in both the refractive index and the attenuation coefficient of the medium surrounding the grating. The algorithm can also be used to analyze and to design fiber Bragg gratings written in fiber amplifiers. A novel method to overcome instability problems in extracting the parameters of the lossy grating is introduced. The new method also makes it possible to reduce the spectral resolution needed to accurately extract the grating parameters.     

Impact localisation with FBG for a self-healing carbon fibre composite structure

We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.     

Impact localisation with FBG for a self-healing carbon fibre composite structure

We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.     

热残余应力对内埋光纤光栅传感器性能的影响

将布拉格光纤光栅(FBG)埋植于复合材料T型加筋板结构非干涉区—三角填充区作为应变传感器对复合材料加筋板在固化过程及冲击后压缩过程中的应变变化进行监测。对比了光纤刻栅区采用UV光固化树脂涂层保护和未保护的两种FBG传感器的波谱信号变化; 分析了复合材料在固化成型过程中产生的非轴对称热残余应力对FBG传感性能的影响。结果表明, 刻栅区采用聚合物涂层保护的FBG传感器的半峰宽(FWHM)在固化过程中未发生变化, 并且聚合物涂层可以有效地消除非轴对称热残余应力对光纤光栅反射波谱的影响。在冲击后压缩过程中, 采用聚合物涂层保护的FBG传感器测得的应变与贴于试样表面的应变片测得的应变数据一致性较好。本文对埋植于复合材料加筋板三角填充区的FBG传感器在复合材料固化过程及冲击后压缩过程中应变监测的有效性及可靠性进行了有益的探索。     

纤维复合材料层合板内埋光纤光栅传感器的保护技术

内埋的光纤Bragg光栅（FBG）传感器的存活率及测试精度是其在线监测纤维增强树脂基复合材料制备和服役状态的重要前提。采用[90₁₁/0₁₁]的碳纤维预浸料铺层方式,在层合板0°和45°方向的典型位置埋入FBG温度和应变传感器,采用模压成型工艺制备复合材料层合板。在异向铺排（光纤光栅方向与碳纤维方向不同）的45°方向光纤光栅传感器内埋于碳纤维预浸料层间的过程中,对其采用4种不同的保护方式。通过对比实验结果发现:当对异向铺排的FBG传感器不采取保护措施时,在加热加压复合材料时光纤光栅容易失活;整层铺设同向预浸料以保护异向铺排的FBG传感器的方式改变了具有特定铺层参数复合材料的力学性能;采用窄长条同向预浸料上下包埋保护FBG传感器的方式增大了应变光栅测量结果的系统误差;采用窄长条同向预浸料上下包埋并在邻近铺层开凹槽的保护方式能明显提高内埋光纤光栅的存活率及测试精度。      

Assessment of the strain monitoring reliability of fiber Bragg grating sensor (FBGs) in advanced composite structures

Fiberoptic Bragg grating sensors were embedded in composite structures in order to be used as the detection system for structural health monitoring purposes. Firstly, optical fibers had been embedded in several locations in between the layers of composite material and for the typical tensile testing coupon configuration. It has been shown experimentally and with finite element analysis that embedding the optical fiber out of the neutral axis of the coupon, downgrades significantly the composite’s ultimate tensile strength. Secondly, a composite patch with embedded FBG has been used to restore a typical damage case on aluminum structure currently applied on advanced ‘aging’ vehicles. Data values taken from the FBG system during the experimental tension tests of the composite structures were calculated to axial strain values with the aid of an interrogator. Theoretical axial strain values of the composite patch had been calculated by exploiting a newly-developed finite element model. Discussion has been made on the correlation between experimental and theoretical results for the verification of sensing sensitivity and accuracy.     

FBG光纤的飞秒激光刻蚀特性及传感应用

在布拉格光栅（FBG）光纤的包层中制作微槽,结合敏感材料提高了FBG光纤传感器的灵敏度,拓宽了其传感应用领域。利用飞秒（fs）激光对I型布拉格光栅光纤进行刻蚀,通过调节激光功率和辐照时间,分析光纤折射率变化以及光纤表面和内部结构的刻蚀特性,并探讨fs激光对光纤光栅微沟槽形貌和反射光谱的影响。实验结果表明,微槽表面由于碎屑的凝固而产生许多柱状结构,且随着激光能量的增加,柱状结构不断长大,槽深和形状服从高斯能量分布;随着激光功率和辐照时间的增加,反射率谱永久红移,带宽增加。利用微结构光纤增敏性能,有效提高微结构光纤光栅磁场探头和氢气探头的传感性能。     

Strain monitoring in composite-strengthened concrete structures using optical fibre sensors

In this paper, the mechanical behaviour of the composite-strengthened concrete structures is addressed. Optical fibre sensor presents a great deal of potential in monitoring the structural health condition of civil infrastructure elements after strengthening by externally bonded composite materials. The use of embedded optical fibre sensor for strain and temperature monitoring enables to reveal the status of the composite-strengthened structure in real-time remotely. In this paper, an experimental investigation on the composite-strengthened concrete structures with the embedment of fibre-optic Bragg grating (FBG) sensors is presented. Single- and multiplexed-point strain measuring techniques were used to measure strains of the structures. Frequency modulated continuous wave (FMCW) method was used to measure strains in different points of the structure with using only one single optical fibre. All strains measured from the sensors were compared to conventional surface mounted strain gauges. Experimental results show that the use of the embedded FBG sensor can measure strain accurately and provide information to the operator that the structure is subjected to debond or micro-crack failure. Multiplexed FBG strain sensors enable to measure strain in different locations by occupying only one tiny optical fibre. Reduction of strength in composite laminate is resulted if the embedded optical fibre is aligned perpendicular to the load-bearing direction of the structure.