Strain field estimation based on digital image correlation and radial basis function

Two methods based on digital image correlation (DIC) and radial basis function (RBF) were proposed to obtain the accurate strain field in this paper. One is a combined method. RBF was applied to remove the noisy discrete displacement data first. After that, the strain was computed by a local least-squares algorithm. The other is a partial derivative of RBF (PD-RBF) based strain estimation method which integrated denoising with differential process. The effectiveness and accuracy of the proposed methods were verified through two numerical simulation experiments. A practical application on the normal strain measurement of an aluminum alloy beam under symmetric four-point bending via an outer loading frame was also presented. The measurement results are in good accordance with the data obtained by strain gauges. Furthermore, a shape parameter selection method based on rate of convergence was suggested. The new method simplifies the choice of the good shape parameter.     

基于应变片的自由活塞斯特林制冷机位移测试研究

压缩活塞与排出器的位移大小及相位差对自由活塞斯特林制冷机的制冷性能具有极其重要的影响。文中通过对目前各种位移测试方法优缺点分析,结合自由活塞式斯特林制冷机自身特点,提出了采用应变片响应涡旋柔性弹簧形变来测量活塞和排出器位移的新方法。通过分析、设计和标定,建立了一套基于应变片的自由活塞斯特林制冷机位移测量系统。实验测试结果表明,该位移测量系统是可靠的,具有体积小、投资省等优点,且不需要特别的安装空间。     

一种利用光反射原理测量小位移的新方法

提出一种利用光反射原理进行小位移量测量的设想 ,并对其进行了原理分析 ,同时给出了实际应用方法 ,最后结合实际应用对其进行了实验验证 ,证明了该原理的可行性和有效性。与机械位移放大法、电阻应变法、压电应变测量等传统小位移量测量方法相比较 ,该方法主要优点是 :对被测位移量干扰小 ,是一种非接触式测量方法 ;位移放大倍数高 ,且便于用户调节 ;测量精度高 ,实现容易 ,成本较低。该方法适合于众多测试场合     

Dynamic strain measurement using two wavelength-matched fiber Bragg grating sensors interrogated by a cascaded long-period fiber grating

In this work, we describe a fiber Bragg grating (FBG) sensing system using two wavelength-matched FBG sensors for static and dynamic strain measurement. A cascaded long-period fiber grating (CLPG)-based demodulation technique has been used to interrogate the two wavelength-matched FBG sensors. Experimental results of static strain measurement show that the proposed system has a strain resolution of 1 με. This system has also been used for dynamic strain measurement. An eddy current displacement meter-based system has been used as a comparison measurement. Experimental results of dynamic strain measurement have proved that the FBG sensing system has a good performance in the measurement of dynamic strain. The results of static and dynamic strain measurement indicate that the sensing system using two wavelength-matched FBG sensors is superior to the single FBG sensor system.     

Interrogation of fiber-Bragg-grating temperature and strain sensors with a temperature-stabilized VCSEL

The interrogation of fiber-Bragg-grating (FBG) sensors using a vertical-cavity surface-emitting laser (VCSEL) is discussed. A long-wavelength (1.54 μm) VCSEL was used as a wavelength-tunable source by variation in the current. Temperature stabilization was performed with a thermoelectric device. Characteristics of temperature and strain sensing were investigated. FBGs with different reflectivities were compared. For temperature sensing, the root-mean-square error in the measurement was reduced to 1/3 that without temperature stabilization. The dependence of the measurement error on the reflectivities of the FBGs was investigated. The measurement error was larger for FBGs with lower reflectivities in both temperature and strain sensing. Improvement on the sensing with low-reflectivity FBGs is discussed.     

基于光纤光栅绝对测量技术的高耐久智能钢拉杆

针对目前钢拉杆构件缺少施工荷载下的内力测试和服役期间的长期监测手段问题,采用玻璃钢封装技术研制开发出一种新型的基于光纤光栅绝对测量传感技术的高耐久性智能钢拉杆。在理论屈服荷载85%的拉伸荷载下,智能钢拉杆感知的应变具有很好的线性度和重复性,由其得到的测试杆力与实验张拉力吻合良好,误差在4%以内。该智能钢拉杆具有抗电磁干扰、传感距离长、成本低、耐腐蚀、绝对测量等优点,既可以方便给出任何阶段的受力状态,也可以作为一个大应变式荷载传感器对其相邻的结构进行荷载监测,适合用于恶劣服役环境下的钢拉杆工程结构。     

A novel temperature and strain sensing method based on high-birefringence fiber loop mirror

A novel temperature and strain sensor based on a fiber loop mirror (FLM) consisting of high-birefringence polarization-maintaining fibers is proposed. The output spectrum was theoretically deduced based on Jones matrix. Two equal-length high-birefringence fibers (HBFs) with different birefringence indices were inserted into the FLM. The temperature and strain sensing system was built. The sensitivity coefficients of temperature and strain were calibrated respectively. The double parameters measurement of temperature and strain was realized. High resolution of 2.38 μ? has been achieved for strain sensing. Meanwhile, the temperature resolution is 0.016 °C.     

Experimental tire mechanics by moiré

Tires and their component parts are made from various low modulus rubbers and cord/rubber laminates. In service they typically undergo large deformations of about 1–30%. The accurate measurement of these deformations by either pointwise (strain gage) or full-field (optical) techniques is rendered difficult in these circumstances. Ordinary strain gages reinforce these soft structures and inhibit their deformation, whereas most optical methods are too sensitive to measure large motions. These difficulties can be overcome by the judicious use of various moiré methods: moiré interferometry, geometric moiré and shadow moiré.Several applications of moiré methods to tire mechanics problems are presented. The emphasis is on the range of problems that has been successfully approached and on the results obtained. Examples are drawn from work on belt-edge strains, tread groove strains, sidewall strains, dynamic sidewall deformations and material properties determination. Proprietary details of technique are not included.     

波长扫描极值解调法实现光纤光栅应变和温度传感的测量

本文用可编程调谐光纤光栅环行腔激光器作扫描光源,采用波长扫描极值传感解调法对光纤光栅应变及温度进行了测量。应变测量范围为±2440με,灵敏度为0.016step/με;温度测量范围达608℃,灵敏度为0.13step/℃。     

Applications of Fiber Optic Grating Technology to Multi-Parameter Measurement

Abstract

In this article, approaches reported in the literature for multi-parameter measurement relying on fiber grating technology are reviewed. Due to its importance, the particular case of temperature/strain simultaneous measurement is addressed in further detail, as well as the techniques and sensing heads for temperature-independent strain measurement. Specific criteria are also proposed for sensing head classification in the context of multi-parameter measurement.     

Brillouin fibre laser discrete sensor for simultaneous strain and temperature measurement

In this work, a Brillouin fibre laser sensor for strain and temperature discrimination is presented. The fibre laser sensor consists of a Fabry–Pérot cavity with 20 m of optical fibre between two Bragg gratings. For the strain measurement, the 20 m were split in half and in 10 m a pre-tension was applied originating two Brillouin peaks. For the temperature measurement all of the sensing head was heated. The resolutions achieved were ±1 με and ±1 °C for strain and temperature measurements, respectively. PACS 42.81.-I; 42.55.Wd; 42.65.Es     

Simultaneous strain and temperature measurement based on a photonic crystal fiber modal-interference interacting with a long period fiber grating

An alternative all-fiber sensor for simultaneous strain and temperature measurement based on a photonic crystal fiber (PCF) spliced between single-mode fibers cascaded with a long period grating (LPG) is proposed. By collapsing the air holes at two splicing regions along the PCF, a simple but effective modal-interference (MI) is occurred between the core and cladding modes of the PCF. Due to the different responses on the changes of strain and temperature on the MI and the cascaded LPG, the strain and temperature can be measured simultaneously. Experimental results show that the sensing resolution of 9.1 με in strain measurement is experimentally achieved over a range of 2640 με, while the temperature sensing resolution is 0.27 °C within a range of 30-100 °C.     

Simultaneous temperature and strain measurement with combined spontaneous Raman and Brillouin scattering

We report on a novel method for simultaneous distributed measurement of temperature and strain based on spatially resolving both spontaneous Raman and Brillouin backscattered anti-Stokes signals. The magnitude of the intensity of the anti-Stokes Raman signal permits the determination of the temperature. The Brillouin frequency shift is dependent on both the temperature and the strain of the fiber; once the temperature has been determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.     

Calibration and evaluation of optical systems for full-field strain measurement

The design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards.     

高灵敏度光纤应变传感器

提出一种基于锥形光纤和光纤F-P腔组合结构的光纤应变传感器。该传感器包含单模光纤拉锥形成的锥区和石英毛细管构建的F-P腔2个应变敏感区域。理论分析了光波在该传感器中的传播过程,获得了该传感器的光强传输函数。由于锥形光纤中激发出的包层高阶模参与干涉,导致传感器干涉光谱具有调制特性。实验获得了该传感器的干涉光谱,通过分析谐振波长偏移或消光比变化对应变实现独立测量,在0~500 με的测量范围内,该传感器的应变灵敏度为14.6 pm/με。利用锥形光纤引发的模式干涉和F-P腔的双光束干涉效应共同作用形成受调制的干涉谱型进行应变传感,应变灵敏度高,同时具备2种独立的应变检测手段(谐振波长和消光比检测)。     

HT-7U超导模型线圈电阻应变测量

针对 HT- 7U超导模型线圈实验中应变测量的特点 ,介绍了低温强磁场特殊条件下电阻应变测量方法 ,从测量电路、应变片粘贴布置方案、应变计算公式、测量结果等方面进行了具体分析。     

Two-dimensional strain measurement with ESPI

Optical techniques have been applied to the measurement of solid deformations in many instances. Practical difficulties with a particular technique can be overcome, in some circumstances, with attention to experimental detail. However, a common problem is the quantitative interpretation of the optical data thus obtained: this can be a time-consuming process and depends on the operator's skill. This paper describes an electronic speckle pattern interferometer that measures two in-plane displacement components simultaneously. The (phase-stepping) procedures implemented for automated displacement and strain analysis are described. Simultaneous measurement of the two displacement components is particularly important for shear strain measurement, because data from the two in-plane views must be combined. The accuracies of displacement and strain measurements are shown to be ±0·03 μm and ±6 μstrain, respectively. Results are presented for a compact tension specimen.     

Ni50.5Mn24.5G25单晶的预马氏体相变特性

通过交流磁化率、电阻、有无磁场下的预相变应变、磁致伸缩和磁化强度测量，系统研究了近正配分比Ni505Mn245Ga25单晶的预马氏体相变特性.在自由样品中观察到预马氏体相变应变.在预相变点，沿[010]方向施加大小约为80kA/m的磁场，在晶体母相的[001]方向上获得了高达505ppm的磁致伸缩，该值是相同条件下晶体母相磁致伸缩量的5倍多.同时，报道了不同方向磁场对预相变应变干预的结果.利用软模凝结的概念和依据单晶生长的特点，分析了预相变应变产生的机理.而磁场干预预相变应变的机理是磁场增大的磁弹耦合导致的晶格形变与材料内禀形变的竞争.利用磁性测量结果证实和解释了预相变过程中[001]和[010]轴方向间进一步增大的各向异性.进而对磁场沿[001]和[010]两个晶体学方向所导致的应变特性的差别，包括最大磁致伸缩、饱和预相变应变、饱和场等，进行了分析和讨论. 关键词： 预马氏体相变 应变 磁致伸缩 磁弹耦合     

Experimental study of the Raman strain rosette based on the carbon nanotube strain sensor

This work presents a new technique named Raman strain rosette for the micro‐strain measurement of both Raman active and Raman inactive materials. The technique is based on the theoretical model of the carbon nanotube (CNT) strain sensor that applies the resonance and polarization Raman properties of CNTs and calculates the synthetic contributions of uniformly dispersed CNTs to the entire Raman spectrum. In our work, the proposed technique is applied in different experiments on the Raman inactive materials, such as step‐by‐step uniaxial tensile and Raman mapping around a circular hole. The experimental results reached by the Raman strain rosette are consistent with the actual values as a whole. This study verifies that the Raman strain rosette is applicable to quantitative measurement of all the in‐plane components of the strain tensor (including both normal and shear strains) by three polarized Raman detections for each sampling spot on a microscale. The technique is further applicable to achieving the strain fields through Raman mapping. Copyright © 2010 John Wiley & Sons, Ltd.     

光纤光栅传感器交叉敏感问题研究

交叉敏感问题是光纤光栅传感器在实际应用中需面对的一个关键问题。从光纤Bragg光栅的传感理论出发，分析了光纤光栅在同时测量应变和温度时引起交叉敏感的物理机理，建立了带有温度-应变交叉灵敏度系数的光纤Bragg光栅反射波长方程。利用双波长矩阵算法针对上述建立的光纤光栅方程进行了误差分析，获取了在交叉敏感情况下温度和应变的相对误差曲线图。结合相对误差表达式和曲线图分析讨论了交叉敏感对测量带来的影响。结果表明在温度和应力测量中随着测量温度或者应变变化量的增大，忽略交叉敏感项而带来的测量误差越来越明显。