Bragg光栅式应变传感器的传感特性研究

光纤Bragg光栅是一种新型的传感元件,其原理是利用波长解调的方法将被测的信号转化为光栅反射波长的偏移量,同时反射波长不受入射光的功率波动或光路系统损耗的影响。光纤Bragg光栅应变式传感器因此具备良好的可靠性、不受电磁干扰、不易腐蚀,同时最大的优点是在一根光纤上将多个光纤光栅应变传感器串接组成构成阵列开展分布式测量等优点,在逐渐应用于各类力学检测领域。本文着重对光纤Bragg光栅温度和应变的传感特性简要介绍并进行试验分析.     

用于钢筋混凝土梁的光纤光栅应变传感器

在变形测定器中,光纤Bragg光栅被粘贴于内管的两端,这两端的距离确定了传感器的量规长度。为了测量拉应变和压应变,该光纤光栅必须保持处于与可能的最大压应变相等的永久性拉应变。将光纤Bragg光栅贴于H154梁的混凝土表面和H158梁的钢筋表面,以分别检测拉应变和压应变。当钢筋混凝土梁受到千斤顶的加载时,它的应变可由光纤Bragg光栅的反射Bragg波长的偏移量获得。实验表明,作为一种绝对检测器件,光纤Bragg光栅为钢筋混凝土梁提供了有效监测,其中,拉应变~1000me,而压应变~1500me。     

基于应变测量中光纤Bragg光栅温度补偿方案设计

设计两种温度分离和温度补偿方案来解决光纤Bragg光栅对温度、应变交叉敏感的问题,两种方案都采用Bragg光栅与长周期光栅相结合的方式,利用长周期光栅对温度具有高灵敏度的特性,且都避免在同一光纤、同一位置处写入两种光栅技术难,要求高的问题,并对两种方案的优点及不足之处进行分析说明。     

光纤Bragg光栅传感器化学镀铜研究

为了保护光纤Bragg光栅传感器并使其能与基体金属有良好的结合性,在光纤Bragg光栅表面进行了化学镀铜.阐述了光纤Bragg光栅的传感原理,通过去保护层、除油、粗化等一系列预处理过程,在光纤Bragg光栅表面采用化学镀的方法镀上一层铜膜,并对已镀光纤Bragg光栅进行了结合力、可焊性及导电性的检测,同时给出了光纤Bragg光栅化学镀铜的工艺配方,比较了化学镀前后的温度传感性能.镀层结合力好,可焊性高,导电性强.     

裸光纤Bragg光栅传感器工程特性试验研究

裸光纤Bragg光栅传感器结构纤巧,具有其它光纤光栅传感器无法比拟的结构优势。本文以等强度梁作为试验装置,通过对裸光纤Bragg光栅传感器的静态特性参数和动态响应特性进行的标定试验,验证了裸光纤光栅传感器在工程上直接应用的可能性。试验结果表明：裸光纤光栅传感器线性好,灵敏度较高,动态响应特性好,能够满足普通工程应用现场应力、应变的测量需求。     

光纤Bragg光栅用于三维编织复合材料结构的内应变测量

本文对应用光纤Bragg光栅传感器编入三维编织复合材料结构内部的测量进行了研究.首先简要介绍了光纤光栅的编入方法和传感原理.随后进行的实验结果显示由应变计及光纤光栅所得到的载荷-应变曲线都具有良好的线性关系,实验之间的结果符合得很好,表明光纤Bragg光栅传感器可以用来精确检测编织试件复杂载荷状态下的内应变.从而将会促进光纤光栅在3-D编织复合材料结构的内部结构检测和强度失效分析中的更广泛应用.     

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。     

光纤Bragg光栅应变传感器在霍普金森压杆上的冲击试验研究

利用复合材料封装光纤Bragg光栅(FBG)设计制作了用于测量高速碰撞或爆炸与冲击作用下混凝土内部动态应变的FBG应变传感器。在霍普金森压杆上对FBG在封装前的裸光栅和封装后的FBG传感器分别进行了高速冲击试验,试验表明：设计的FBG传感器的瞬态响应上升时间小于20μs,具有良好的动态响应特性,可以用于工程中混凝土结构内高速冲击下的动态应变测试     

基于单片机的光纤光栅解调仪

光纤光栅的解调技术是光纤光栅传感器的关键技术,该文提出了基于单片机的光纤光栅解调系统模型,研究了可调谐F-P滤波法解调原理以及解调系统的框架.经实践证明,系统测量精度达到5pm,是低成本、通用的解调系统,是Bragg光栅传感器实用化的关键.     

冲击荷载下基于埋入式光纤光栅传感器的混凝土动态应变测试

为实现冲击荷载下混凝土材料内动态应变的直接测量,研制了基于光纤Bragg光栅的混凝土光纤光栅应变传感器。将光纤光栅传感器埋入混凝土试件在SHPB装置上进行了冲击试验,由光纤传感器和粘贴于试件表面的电阻应变计分别测量了试件内和表面的动态应变。利用测量结果分析了混凝土在冲击荷载下的动态应力应变响应。对测量结果的分析和比较表明,采用埋入光纤传感器来实现混凝土结构内应变直接测量的方法可行、合理,研制的光纤光栅传感器适合于混凝土内动态应变测量,可更广泛地应用于混凝土、岩石等介质的动态性能试验及结构的动态响应测试中。     

大幅面高速重载模切机动平台传动肘杆分析及设计

目的 利用Ansys有限元软件，对模切机肘杆进行分析及优化设计，实现高速重载模切机动平台高精度、高可靠性、高速平稳运行。方法 采用Adams动力学分析方法，对传动肘杆运动的位移、速度和加速度进行分析，得到其曲线，分析其是否满足重载高速运动工况下模切机的运动规律；利用牛顿-欧拉方法求解复杂多刚体运动系统动力学问题，求出下肘杆受力的数值解，利用有限元分析软件对动平台传动肘杆进行有限元分析，得到在加载一定压力下的应力、应变的云图，并与数值解进行对比分析，判断下肘杆机构是否满足重载的需求。结果 得到了肘杆部件的应力云图和变形云图，及其各个零件的最大应力，应力最大值为469.1 MPa。结论 利用有限元分析的手段，从理论上指导模切压力试验平台的结构优化设计，提高了设计的准确性，缩短了产品的试制周期。     

高速重载模切机动平台运动分析及结构优化设计

目的 利用Ansys有限元分析软件,对模切机动平台进行分析及优化设计,实现高速重载模切机动平台高精度、高可靠性、高速平稳运行。方法 采用有限元分析软件对现有的动平台进行有限元分析,在加载一定压力情况下,得到平台的应力、应变以及位移云图,判断现有动平台是否满足重载的需求,同时得到可以进行优化的位置及空间;对优化后的动平台进行有限元分析,将得到的应力、应变以及位移结果与优化前的进行对比。结果 优化后的动平台整体质量减小了157kg,加载相同载荷的情况下,优化后的动平台最大变形量减小。结论 利用有限元分析的手段,可以从理论方面指导模切压力试验平台的结构优化设计,提高设计的准确性,缩短产品的试制周期。     

基于TRIZ理论的纸盒成型机主轴结构的优化设计

目的运用TRIZ理论对纸盒成型机主轴结构进行优化设计。方法利用TRIZ理论的冲突解决原理对纸盒成型机主轴结构进行分析归纳,得到相应的创新设计原理和优化方向,通过分析对比选择最佳的创新原理,以解决设计中的矛盾,并利用TRIZ理论提供的优化方向对主轴结构进行有限元分析。结果通过TRIZ理论得到了纸盒成型机主轴结构的优化方案和方向,利用有限元仿真软件进一步分析得到了纸盒成型机主轴结构的的最大变形为0.1796 mm,通过对纸盒成型机主轴结构最终优化方案的实验验证,得到主轴结构的最大变形为0.18 mm,满足使用要求。结论利用TRIZ理论和有限元相结合的方式为纸盒成型机主轴结构的优化设计提供了一种新的思路,同时也为纸盒成型机主轴结构的进一步优化设计提供了依据。     

Response of fiber Bragg gratings to longitudinal ultrasonic waves

In the last years, fiber optic sensors have been widely exploited for several sensing applications, including static and dynamic strain measurements up to acoustic detection. Among these, fiber Bragg grating sensors have been indicated as the ideal candidate for practical structural health monitoring in light of their unique advantages over conventional sensing devices. Although this class of sensors has been successfully tested for static and low-frequency measurements, the identification of sensor performances for high-frequency detection, including acoustic emission and ultrasonic investigations, is required. To this aim, the analysis of feasibilty on the use of fiber Bragg grating sensors as ultrasonic detectors has been carried out. In particular, the response of fiber Bragg gratings subjected to the longitudinal ultrasonic (US) field has been theoretically and numerically investigated. Ultrasonic field interaction has been modeled, taking into account the direct deformation of the grating pitch combined with changes in local refractive index due to the elasto-optic effect. Numerical results, obtained for both uniform and Gaussian-apodized fiber Bragg gratings, show that the grating spectrum is strongly influenced by the US field in terms of shape and central wavelength. In particular, a key parameter affecting the grating response is the ratio between the US wavelength and the grating length. Normal operation characterized by changes in wavelength of undistorted Bragg peak is possible only for US wavelengths longer than the grating length. For US wavelengths approaching the grating length, the wavelength change is accompanied by subpeaks formation and main peak amplitude modulation. This effect can be attributed to the nonuniformity of the US perturbation along the grating length. At very high US frequencies, the grating is not sensitive any longer. The results of this analysis provide useful tools for the design of grating-based ultrasound sensors for meeting specific requirements in terms of field intensity and frequencies.     

Comparison of nondestructive microfailure evaluation of fiber-optic Bragg grating and acoustic emission piezoelectric sensors using fragmentation test

Nondestructive evaluation of microfailure mechanisms in two-diameter SiC fibers/epoxy composites is investigated using a directly embedded fiber-optic sensor attached with an acoustic emission piezoelectric (AE-PZT) sensor. Interfacial shear strength by fragmentation test, and optical failure observation inside microcomposite can contribute to analyze two sensors quantitatively. Although fiber Bragg grating (FBG) sensor exhibits sudden wavelength shift due to plastic deformation by larger diameter SiC fiber breakage, AE-PZT monitors much more precise microfailure process, such as the fiber break or matrix cracking. Since the FBG sensor can measure the strain at only a single point, whether it can detect a fiber break in single-fiber composite specimen depends on its proximity to the failure location. In addition, micro-strain measurement at one single point may not provide enough information on the whole microfailure process including multiple fiber breakage and matrix crack. It can be considered that FBG sensor can be somewhat effective in measuring the continuous micro-strain change due to the internal disturbance such as resin curing, whereas AE-PZT sensor can be effective in detecting the microfailure by elastic wave propagation through the composite materials.     

High Pressure Sensor Based on Fiber Bragg Grating and Carbon Fiber Laminated Composite

A simple anisotropic structure made by carbon fiber laminated composite for fabricating a high pressure sensor is reported. A pressure sensor with good sensitivity over a broad measurement range is fabricated by using fiber Bragg grating and the anisotropic carbon fiber laminated composite structure. The characteristic responses of pressure and temperature of the new pressure sensor are analyzed. Experimental data show that when the pressure changes from 0 to 70 MPa, the wavelength shift of the fiber Bragg grating pressure sensor is up to 7 nm, corresponding to a sensitivity of 10 kPa/pm.      

A Novel Fiber-Optic Tapered Long-Period Grating Sensor for Pressure Monitoring

The method and the required installations for fabricating tapered long-period fiber gratings can be simpler than that of standard fiber Bragg gratings, and the fabrication process is faster. To our knowledge, the tapered long-period fiber grating pressure sensor is presented here for the first time. In this paper, the fabrication method for tapered long-period fiber gratings, the sensing principle, the sensor structure, the measurement setup, and the preliminary results are presented and discussed. The pressure sensitivity of the sensor is as high as 5.1 pm/bar.     

Fiber Bragg grating flow sensors powered by in-fiber light

This paper presents an active fiber Bragg grating temperature and flow sensor based on self-heated optical hot wire anemometry. The grating sensors are directly powered by optical energy carried by optical fibers. In-fiber diode laser light at 910 nm was leaked out from the fiber and absorbed by the surrounding metallic coating to raise the temperature and change the background refractive index distribution of the gratings. When the diode laser is turned off, the grating is used as a temperature sensor. When the diode laser is turned on, the resonance wavelength and spectral width change of the self-heated grating sensor is used to measure the gas flow velocity. The grating flow sensors have been experimentally evaluated for different grating length and input laser power. The grating flow sensors have demonstrated a 0.35- m/s sensitivity for nitrogen flow at atmosphere pressure.     

Characteristics of short-period blazed fiber Bragg gratings for use as macro-bending sensors

The characteristics of short-period blazed fiber Bragg gratings for use as macro-bending sensors are discussed. This sensor is able to detect macro bending with the transmitted power variation of the first side mode in the blazed fiber Bragg grating. Since an incident ray experiences different variations of tilt angles with respect to bending direction, the blazed fiber Bragg grating has different coupling efficiencies of the first side mode, which can be reduced considerably in the case of twisted blazed fiber Bragg gratings.     

基于相移光纤光栅传感器的碳纤维增强树脂复合材料基体裂纹超声探伤

复合材料内部的微小裂纹常会引起后续严重的破坏,因此需要对其进行检测。然而超声探伤复合材料基体裂纹非常困难。本文搭建了一个具有高灵敏度、大带宽的相移光纤光栅超声传感系统,利用此系统探测了在正交铺层碳纤维增强树脂复合材料板中传播的Lamb波。对Lamb波进行数据处理发现,随着三点弯曲实验产生的基体裂纹个数增加,Lamb波的幅值和频谱峰值线性减少。通过和传统压电传感器比较表明,相移光纤光栅传感器测得的Lamb波信号随复合材料基体裂纹数的增加其幅值具有更高的下降速率,表明相移光纤光栅传感器更适合于复合材料基体裂纹的超声探伤。研究表明,新开发的传感系统能够探测到中心频率为300 kHz的微弱超声信号,并能够对碳纤维增强树脂复合材料板中微小基体裂纹个数进行精确评估。