Health monitoring of composite materials using dual sensing fiber Bragg grating systems

这些天来，用内置传感器监测结构状况的智能结构引起了人们的注意。在智能结构中，包括使用传统技术检测冲击载荷和损伤，将安装应变计和压电式传感器。然而，这些电子传感器存在严重的缺点，它们受到电磁干扰，不能在爆炸性环境中使用。此外，它们还需要单独的电缆。因此，应用于大型结构物多点传感的监测系统不可避免地会包含复杂的电缆网络。为了克服这些技术难题，具有多功能、多样性和抗电磁干扰的光纤布拉格光栅(FBG)有望成为结构健康监测的传感器。本研究的目的是开发一种简单的能够测量应变和检测超声…的光纤布拉格光栅传感系统更多用于结构健康监测。基于波长-光强转换技术，利用光纤布拉格光栅构建了一种应变测量和超声检测的光纤系统。该光纤布拉格光栅传感系统由宽带光源、用于应变测量的宽带滤光片和用于超声检测的窄带可调谐滤光片组成。将该系统应用于碳纤维增强塑料冲击载荷下的应变测量和后续的冲击损伤检测，实验结果表明，光纤光栅和常规应变片的最小可检测应变分别为1.2με和8.1με，信噪比分别为40d B和8d B。由于FBG传感器具有自参考性和抗电磁干扰能力，在长期应变测量中具有很高的可靠性。此外，使用可调滤光器最大化超声波灵敏度的超声波检测可以检测到6.3×9 mm^2的撞击损伤。这些实验结果证实了FBG传感系统可以作为监测复合材料应变和损伤的有用工具。较少

Smart structures in which structural conditions are monitored with built-in sensors have drawn attention in these days. In smart structures including detection of both impact loading and damage using conventional technique, strain gauges and piezoelectric sensors would be installed. However, these electric sensors have serious drawbacks that they suffer from electromagnetic interference and cannot be used in explosive environment. Moreover, they need individual cables. Therefore, the monitoring system applied to large-scale structures where multi-point sensing is performed would inevitably include complex cable network. In order to overcome these technical difficulties, fiber Bragg gratings (FBGs) featuring multifunction, multiplexibility as well as immunity to electromagnetic interference have been expected to be promising sensors for structural health monitoring.The objective of the present study is to develop a simple FBG sensing system which can measure strain and detect ultrasound … More for structural health monitoring. A fiber-optic system featuring strain measurement and ultrasonic detection was constructed with fiber Bragg gratings based on wavelength-light intensity conversion technique. This fiber Bragg grating sensing system consists of a broadband light source, a broadband optical filter for strain measurement and a narrowband tunable filter for ultrasonic detection. The system was applied to strain measurement in impact loading to carbon fiber-reinforced plastics and the subsequent impact damage detection.Experimental results proved that the minimum detectable strain for FBG and conventional strain gauge are estimated to be 1.2με and 8.1.με, and signal-to-noise ratios are evaluated to be 40dB and 8dB, respectively. FBG sensors would be highly reliable in long-term strain measurement because of its self-referencing and immunity to electromagnetic interference. Furthermore, ultrasonic inspection in which ultrasonic sensitivity was maximized using the tunable filter could detect a 6.3X9mm^2 impact damage. These experimental results have confirmed that the FBG sensing system can be useful tools to monitor strain and damage in composite materials. Less