基于白光干涉原理的光纤传感技术——V.光纤传感器和基体材料的相互作用

White light interfereometric fiber optic sensing technology——V. Interaction between optical fiber sensors and matrix materials

建立并测试了一个简单的模型,利用该模型可将光纤传感器测得的数值来解释结构的实际应变。光纤传感器测得的应变并不能完全表征试件或结构的应变,因此由理论分析所得的结果非常重要。所采用的光纤及其保护涂敷层的机械特性可改变传感器的应变传递能力。很多前提假设可通过系统的表达式对数学的严格性进行简化,光纤的应变传递特性取决于与承受应变的材料相接触的玻璃纤芯、保护涂敷层和光纤传感长度。数学公式导出了同样数量级的应变。有效长度长的传感器中的界面切应变效应弱于有效长度较短的传感器,理论结果可通过包括白光干涉仪在内的一系列实验进行验证。由此研究得到的最重要的结果就是提出了描述α(L,k)的理论表达式,α(L,k)为可用光纤感知到的应变(珋εg)确定实际引入到材料中的应变(εm)的比例系数。这一关系使得在将光纤传感器应用到结构传感应用之前不必对应变数据进行标定和回归分析,通过反复实验,验证了理论分析的有效性。由此可知,对于带有涂敷层的光纤,可在应变仪与光纤传感器测得数值之间得到一一对应的关系。对于裸纤可得α=1.0,这种情况下无需利用本研究所得的结果。然而,裸纤非常脆弱因此很难应用到实际测量中。

A simple model has been proposed and tested through which it is possible to interpret the actual level of structural strains from the values measured by an optical fiber sensor. Results from the theoretical analysis introduced here are important due to the fact that the strain measured by optical fibers are not entirely representative of strain levels in a test specimen or a structural element. Mechanical properties of the protective coatings employed in conjunction with optical fibers alter the strain transfer capabilities of the sensor. A number of realistic assumptions were introduced to simplify the development of the mathematical rigor through systematic expressions. It was determined that the strain transfer characteristics of optical fibers depend on the mechanical properties of the glass fiber, the protective coating, and the gauge length of the optical fiber in contact with the material subjected to the strain. Mathematical formulations led to the same levels of strain. The effect of interface shear strain loss in longer gauge length sensors is less pronounced than in shorter sensors. The theoretical findings were verified through a series of experiments involving white light interferometry. The most significant result acquired from the study reported herein is the development of a theoretical expression describing a （L, k）, which is the constant of proportionality that can be used for determining the actual strain induced in the material （e.,） from the strain sensed by the optical fiber （~）. This relationship will eliminate the need for calibration tests and regression analysis of strain data prior to employment of the optical fiber in structural sensing applications. The validity of the theoretical analysis was examined through repeated experiments. It was determined that for coated optical fibers it is possible to achieve a one-to-one correspondence between the strain gauge and the optical fiber measured values. It is possible to achieve a=l. 0 by using bare fibers and thus eliminate the need for using the results of the study reported here. However, bare fibers are very fragile, and it is very difficult to use them in real applications.