Structural Health Monitoring of CFRP Laminates : Development of 90-degree Crack Detection and Suppression System

研究目的是开发一种结构健康监测系统，用于检测和抑制90度层在加载初期产生的横向裂纹。横向裂纹检测是将小直径(涂层直径40μm，涂层直径52μm)光纤布拉格光栅传感器埋入与90度层相邻的CFRP层中进行检测。光纤布拉格光纤陀螺传感器测量截面上产生的横向裂纹会引起同一截面应变分布不均匀，使传感器的反射光谱发生变化。这一现象可用于横向裂纹的检测。成功地对正交层合板和准各向同性层合板进行了横向裂纹检测实验。实验结果还得到了应变分布不均匀的理论分析和光纤理论的合理解释。在层间区域嵌入40μn厚的预应变形状记忆合金薄片进行了横向裂纹抑制。当预应变形状记忆合金受热时，形状记忆合金收缩并产生回复应力，从而延缓了裂纹萌生的应变水平，降低了裂纹扩展速率。对不同温度下的正交层合板进行了横向裂纹抑制实验。这些实验结果也得到了基于SMA本构方程修正Brinson模型的理论分析和剪滞分析的合理解释。然后确定了形状记忆合金的位置、预应变水平和施加温度的最佳条件；然后，在同一个CFRP层合板上实现了两个检测和抑制系统，以演示同时进行损伤检测和抑制的系统。在损伤检测系统检测到90度铺装层出现横向裂纹后，损伤抑制系统成功运行。

The purpose of the present study is to develop a structural health monitoring system to detect and suppress transverse cracks in a90-degree layer which generate at the early stage of loading.Transverse crack detection was made with a small-diameter (40 μm in coating diameter, 52 μm in coating diameter) Fiber Bragg Grating (FBG) sensor embedded in the CFRP lamina neighboring to the 90-degree layer. Transverse cracks generated in the gage section of the FBG sensor induce non-uniform strain distribution in the same section and change in the reflection spectrum of the sensor. This phenomenon can be used for the detection of transverse cracks. The experiments for the transverse crack detection were successfully conducted for cross-ply laminates as well as quasi-isotropic laminates. The experimental results were also reasonably explained by the theoretical analysis of the non-uniform strain distribution and the fiber optic theory.Transverse crack suppression was made with a 40-μn thick pre-strained shape memory alloy (SMA) foil embedded in the interlaminar region. When the pre-strained SMA is heated, the SMA shrinks and the recovery stress is generated, which retards the strain level of crack initiation and reduces the crack multiplication rate. The experiments for the transverse crack suppression were successfully conducted for cross-ply laminates at different temperatures. These experimental results were also reasonably explained by the theoretical analysis based on both the modified Brinson model for SMA constitutive equation and the shear-lag analysis. Then the optimum condition was determined for the SMA location, pre-strain level and applied temperature.Then, both detection and suppression systems were implemented in the same CFRP laminate to demonstrate the simultaneous damage detection and suppression system. The damage suppression system was successfully operated after the damage detection system detected the transverse cracks in the 90-degree ply.