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

本研究的目的是开发一种结构健康监测系统，以检测和抑制加载初期产生的90度层横向裂缝。将小直径（涂层直径为40 μm，涂层直径为52 μm）光纤光栅（FBG）传感器嵌入到与90度层相邻的CFRP片层中，进行横向裂纹检测。光纤光栅传感器测量截面上产生的横向裂纹会导致同一截面内应变分布不均匀，传感器反射光谱发生变化。这种现象可用于横向裂纹的检测。成功地对交叉层合板和准各向同性层合板进行了横向裂纹检测实验。通过对非均匀应变分布的理论分析和光纤理论对实验结果进行了合理的解释。采用40 μn厚的预应变形状记忆合金（SMA）箔嵌入层间区进行横向裂纹抑制。当预应变SMA受热时，SMA收缩并产生恢复应力，从而延缓了裂纹萌生的应变水平，降低了裂纹增殖速率。对不同温度下的交叉层合板进行了横向裂纹抑制实验。基于修正Brinson模型的SMA本构方程和剪切滞后分析的理论分析也合理解释了这些实验结果。确定了SMA位置、预应变水平和施加温度的最佳条件。然后，在同一碳纤维复合材料层合板上实现了检测和抑制系统，以演示同时检测和抑制系统。损伤检测系统检测到90度层的横向裂纹后，损伤抑制系统运行成功。

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.