Measurement of Elastic Properties of Epoxy Molding Compound by Single Cylindrical Configuration with Embedded Fiber Bragg Grating Sensor

We propose a novel experimental method, based on a fiber Bragg grating (FBG) sensor, to measure the elastic properties of epoxy molding compound (EMC) from a single specimen configuration. The FBG sensor is embedded in the center of a cylindrical EMC specimen, and deforms together with the EMC. The Bragg wavelength (BW) shifts are documented during compressive and hydrostatic loadings. Young’s modulus and bulk modulus are determined from the BW shifts using the relationships between the elastic constants and the BW shift. Two major developments to accommodate the unique requirements of EMC testing include: (1) a large mechanical pressure to be applied during curing; and (2) a very high gas pressure required for hydrostatic testing. The shear modulus and Poisson’s ratio are calculated from the two measured constants to provide a complete set of elastic properties of EMC.     

Fiber Bragg Grating Strain Rosette

0Introduction OpticalFiberBraggGratings(FBGs)sensorshavefounddiverseapplicationsinvariousfields sincetheirdevelopmentinthelate1980s.FBGshaveanumberofsignificantadvantagesoverother fiberopticsensorssuchasmultiplexing,self referencing,optical,mechanicalandt…     

基于Bragg光纤光栅的位移-应变传感器分析

光纤光栅传感器技术应用于力学测试是国内外正在发展的一门新技术.本文基于光纤光栅传感的基本原理,介绍了一种用于位移测量的应变传感器,测得应变与位移变化具有良好的线性特点,重复性好;对该传感器的测量过程进行了有限元模拟,并与实验值进行了比较.     

Integrated Measurement Technique for Curing Process-Dependent Mechanical Properties of Polymeric Materials Using Fiber Bragg Grating

We propose an integrated technique to measure critical mechanical properties of polymeric materials. The method is based on a fiber Bragg grating (FBG) sensor. A polymer of interest is cured around a glass FBG and the Bragg wavelength (BW) shift is measured and documented while polymerization progresses at the curing temperature. After complete polymerization, the BW shift is monitored continuously as the temperature of the cured polymer changes. The desired material properties are then found inversely from the relationship between the Bragg wavelength shift and the deformation of the polymer caused by the changes in the material properties.     

Full-Spectral Interrogation of Fiber Bragg Grating Sensors Exposed to Steady-State Vibration

In this paper we measure for the first time the full-spectral response of a fiber Bragg grating (FBG) sensor subjected to vibration. We consider two cases: with and without an initial spectral distortion due to non-uniform strain along the length of the FBG. Previous work has measured only the dynamic response at a single wavelength which is valid when no spectral distortion is present. FBG sensors are mounted near the notch tip on a double edge notch specimen that is also subjected to harmonic vibration. We measure the full-spectral response of the FBG at 100 kHz applying an interrogator recently developed by the authors. The measurements of the FBG response with an initial spectral distortion clearly show the transient response and are verified through simulation. Finally, we demonstrate that the use of the high-speed, full-spectral interrogator permits the separation of the spectral distortion and the harmonic vibration from the FBG response signal through classical filtering and can therefore be applied to measure non-uniform strain fields in noisy environments.     

TiN薄膜掠射侧倾法应力测试

由于薄膜厚度很薄,使得在应用传统X射线法测试薄膜应力时,存在透入深度过深且衍射强度不够的缺点;而且一般气象沉积膜都存在择优取向的情况,应用常规法（或侧倾法）测试时易发生sin^2ψ曲线弯曲现象。准聚焦衍射几何也使得常规法在无应力情况下产生正、负ψ的sin^2ψ曲线发生分离现象。故与传统方法相比,掠射侧倾法具有透入深度浅、透入深度随ψ角变化不大以及对织构影响不敏感以及没有无应力试样的正、负ψ曲线分离等优点,所以掠射侧倾法是一种更适于薄膜应力测量的测试方法。本文应用掠射侧倾法测量了PVD和PCVD工艺的TiN薄膜的内应力情况,结果表明制备工艺对于气象沉积膜内的应力状态有较大影响,而且薄膜内的应力状态比较复杂,一般处于三向应力状态。     

Dual-Configuration Fiber Bragg Grating Sensor Technique to Measure Coefficients of Thermal Expansion and Hygroscopic Swelling

We propose a method based on the dual-configuration fiber Bragg grating (FBG) sensor to measure the coefficients of thermal expansion (CTE) and hygroscopic swelling (CHS) of polymeric materials. The Bragg wavelength shifts are documented in “two” small but different polymer-FBG assemblies while they are subjected to environmental loading conditions (temperature or moisture). The behavior of the infinite polymer/FBG assembly is reconstructed numerically from the data obtained from the two configurations. The coefficients, then, can be determined from the simple governing equation derived for the infinite assembly. The proposed method is implemented for an underfill material. The validity of measurements is corroborated by a commercially available tool, and the repeatability of measurements is verified by an experiment with a different configuration.     

基于光纤智能夹层传感结构的应力测量研究

制作了一种模块化的光纤传感夹层,对夹层内的光纤传感器的应力特性进行了实验研究。分析了应变对传感系数的影响,对埋入到光纤智能夹层中的两种光纤传感器的输出特性进行了比较。实验结果表明:光纤Bragg光栅传感器的波长漂移与应变之间具有理想的线性关系,但应变灵敏度由1.2pm/με降至1.15pm/με;由于制作工艺的局限,对于非本征F-P光纤传感器,当应变达到350με后,应变与载荷具有较好的线性响应。与非本征F-P光纤传感器相比,光纤Bragg光栅传感器是光纤智能夹层首选的应变传感器。将埋入了Bragg光栅传感器的智能夹层粘贴于某型飞机的翼-身连接构件内部进行监测,实验结果为光纤智能夹层应用于复合材料结构的应变监测提供了参考。     

Nonstationary Plane Elastic Contact Problem for Matched Cylindrical Surfaces

An approach is proposed to study a collision of a long cylinder with the inside surface of a circular cylindrical cavity in an elastic medium. The problem is solved in plane formulation. A nonstationary mixed initial–boundary-value problem with unknown boundaries moving with a variable velocity is formulated and then reduced to an infinite system of Volterra integral equations of the second kind or, in a simplified formulation, to a sequence of Volterra integral equations. The penetration velocity is determined as a function of the cylinder mass and initial conditions. It is established that the reaction force peaks instantaneously and then dies out     

Plasticity Effects in the Hole-Drilling Residual Stress Measurement in Peened Surfaces

The incremental hole-drilling technique (IHD) is a widely established and accepted technique to determine residual stresses in peened surfaces. However, high residual stresses can lead to local yielding, due to the stress concentration around the drilled hole, affecting the standard residual stress evaluation, which is based on linear elastic equations. This so-called plasticity effect can be quantified by means of a plasticity factor, which measures the residual stress magnitude with respect to the approximate onset of plasticity. The observed resultant overestimation of IHD residual stresses depends on various factors, such as the residual stress state, the stress gradients and the material’s strain hardening. In peened surfaces, equibiaxial stresses are often found. For this case, the combined effect of the local yielding and stress gradients is numerically and experimentally analyzed in detail in this work. In addition, a new plasticity factor is proposed for the evaluation of the onset of yielding around drilled holes in peened surface layers. This new factor is able to explain the agreement and disagreement found between the IHD residual stresses and those determined by X-ray diffraction in shot-peened steel surfaces.     

物理气相沉积减摩与耐磨薄膜

在摩擦学研究的基础上，综合评述与探讨了物理气相沉积薄膜摩擦和磨损的机械－化学作用机理；根据这种机理分析讨论了对物理气相沉积润滑和耐磨薄膜的基本要求，提出了实现这些要求的物理气相沉积的技术基础。     

光纤光栅传感器在大体积混凝土基础温度监测中的应用

光纤光栅传感器具有体积小、质量轻、灵敏度高、耐腐蚀、抗电磁干扰、传输频带较宽、易于进行分布式测量等诸多其他传感器所不具备的优点,更适用于现场的长期健康监测。大体积混凝土在施工过程中的温度问题如处理不当将会引起混凝土开裂。利用温度计、热电耦等作为传感器的传统的检测手段已经大大的制约了数据的准确性与精度。寻求一种高精度温度检测手段已经成为用于现场结构监测的前提。本文结合具体的工程实例介绍了光纤光栅传感器在基础混凝土温度监测中的应用,介绍了监测系统的组成,传感器的构造和标定,并利用实测温度预测基础混凝土底板中温度应力,及时采取措施防止混凝土的开裂。     

Fiber Bragg grating sensor package for submicron level displacement measurements

Experimental Techniques - In this article, the design and development of a Fiber Bragg Grating (FBG) based displacement sensor package for submicron level displacement measurements are presented. A...     

基于界面端奇异性理论的单纤维拔出试验的试件设计

在单纤维拔出试验中，由于试件的界面端存在应力奇异性，这使试验所得到的界面剪切强度数据失去合理性[1]。但从文献[1]关于微珠脱粘试验研究的结论中可以发现当基体的楔形角小于某临界角度后，微珠试件界面端应力奇异性几乎消失。由此启发我们设计出一种楔形角小于该纤维／基体系统临界角的锥面的拔出试件，这样即可以防止出现传统拔出试件在界面端的强应力奇异性，又可以避免微珠脱粘试验自身的缺陷。界面端具有任意楔形角的轴对称模型被用于分析和确定纤维／基体系统的临界角，对方程进行渐近展开和分离变量处理，根据边界条件可以得到关于特征值λ的特征方程，针对确定的纤维／基体系统可以得到特征值和楔形角的关系曲线，我们把应力奇异性指数等于-0．005时所对应的楔形角定义为临界角，以及根据临界角设计锥面拔出试件的方法。     

一种求解层合圆柱壳的杂交应力单元

根据修正的余能原理，推导出一种求解复合材料层合圆柱壳的杂交应力单元。取用六面体等参单元，此单元反映了各层材料性质不同及应力分布沿整个厚度不连续现象，同时计入横向剪切变形和法向挤压变形，适用于厚层壳体。文章通过实例说明此单元能准确求出各层内的应力值，实用价值高。     

Out-of-Plane CTE Measurement Method for Freestanding Thin Films

An out-of-plane linear coefficient of thermal expansion (CTE) measurement method was developed to overcome the difficulty in measuring the in-plane deformation of freestanding thin films with a thickness of less than 1 μm. The out-of-plane profile measurement was relatively easy with the added advantage of simplicity, easy specimen preparation, and a simple test setup. White light interferometry was used for determining the out-of-plane thermal deformation as a function of temperature. Two types of supporting substrates, silicon and ZERODUR®, were used to account for the substrate effect on the CTE measurement. Attempts were made to fit the measured profiles using several peak functions and then find the optimal one. The test procedures were demonstrated using a freestanding 530-nm-thick aluminum film that was used in a previous in-plane measurement method. The calculated CTE value of this aluminum film was 23.7 ppm/°C, which was in good agreement with the in-plane measurement result. The out-of-plane CTE measurement method incorporating a zero CTE substrate was shown to be the most convenient and straightforward method.     

<Emphasis Type="Italic">Ex Vivo</Emphasis> Intervertebral Disc Bulging Measurement Using a Fibre Bragg Grating Sensor

Advances using optical fibres as sensors may represent an important contribution for development of minimally invasive techniques in biomedical and biomechanical applications. Concerning spine injuries, intervertebral disc (IVD) degeneration is a major clinical issue since it represents gross structural disruption and it is irreversible. Measuring biomechanical parameters of the IVD should contribute for better understanding on its mechanical response to external applied forces. The purpose of this study was to explore the potential of a Fibre Bragg Grating (FBG) sensor to measure strain caused by bulging of the intervertebral disc under axial compression. Disc bulging is a consequence of IVD compression and a technique to register this behaviour is addressed in this study. Needle-mounted sensors were already used to measure IVD pressure in cadaveric material. In this study we also explored the possibility of using needles only for sensor guiding and positioning leaving sensor directly in contact with the IVD material. An ex vivo porcine dorsal functional spinal unit was instrumented with a FBG sensor and submitted to axial compression. Results suggest the sensor’s ability to measure strain response to load. Bulging of the annulus fibrosus as a consequence of axial compression was confirmed using the FBG sensor. Hysteresis and viscoelastic behaviour were observable suggesting that energy is dissipated by the deformation of the annulus and that unloading time was insufficient for disc recovery. Nevertheless the relatively low strain sensitivity of the sensor as well as signal artefacts caused by transverse loading may constitute a problem in the analysis and interpretation of strain data. The technique may not be suitable for measurement of physiologic bulging being more indicative of the radial force exerted by the annulus.     

圆柱空腔内涡破裂的LDA三维流动测量

针对旋转圆柱空腔内旋转流场泡状涡破裂现象,设计了实验装置,分析了实验系统中光路设置、折射率补偿、示踪粒子选择等关键问题的处理方法,采用激光多谱勒速度测量技术ＬＤＡ（ＬａｓｅｒＤｏｐｐｌｅｒＡｎｅｍｏｍ ｅｔｒｙ）进行测量,给出了圆柱空腔内子午面上二维速度全场和涡破裂区域的内部三维流动测量结果． 同时给出的数值计算模拟结果和实验测量结果非常吻合．     

基于DIC方法的残余应力快速测量系统

结合数字图像相关(Digital Image Correlation,DIC)方法与钻孔法,开发了残余应力快速测量系统。该系统可分为两部分:适用于现场测量的便携式机械系统与针对残余应力测量而改进的基于DIC算法的程序。在四点弯曲加载平台上对工件进行载荷释放前后的残余应力测量试验,通过与应变片测量结果进行对比,该残余应力测量系统的精度达到了应变片测量的同等精度。同时,该测量系统解决了传统应变片测量系统对心误差大、操作繁琐、效率低和测量结果稳定性差等问题,具有较高的工程应用价值。     

傅里叶变换投影栅线法测量大物体的变形

本文利用傅里叶变换投影栅线技术对大物体的离面变形进行了测量，分析了大物体的尺寸给测量过程带来的主要矛盾，讨论了方法的灵敏度和精度，用计算机数值模拟技术给出了大尺寸引起的频率变化所带来的误差。结果表明，傅里叶变换投影栅线技术可以用于大尺寸物体离面变形的精确测量。