基于布拉格光纤光栅的铝合金应力腐蚀裂纹扩展监测技术

Monitoring Technology for Stress Corrosion Crack Propagation of Al-alloy Based on Optical Fiber Bragg Grating

为监测装备服役过程中应力腐蚀裂纹扩展,以预制裂纹的高强度铝合金双悬臂试样为研究对象,对应力腐蚀裂纹扩展开展研究。首先,阐述了应力腐蚀裂纹扩展机理,通过Matlab仿真确定了试样应力腐蚀裂纹扩展尖端x方向、y方向应变与裂纹长度关系为线性关系;采用Abaqus有限元仿真进一步确定了裂纹扩展尖端应力集中区域,确定出布置光纤距裂纹尖端为10和15 mm;针对布拉格光纤光栅应力腐蚀裂纹扩展感知技术进行研究,确定出光栅温度补偿模型;最后,对腐蚀裂纹扩展中布拉格光纤光栅传感器进行标定裂纹长度与布拉格光纤光栅传感器波长变化量之间的关联关系,结果表明裂纹长度与波长变化量相关性分别为R^(2)=0.9893、R^(2)=0.9870;在海南万宁搭建了户外暴露试验系统,通过组网实现铝合金应力腐蚀裂纹扩展原位监测,监测数据表明在采用温度补偿后,靠近裂纹尖端10 mm布置的传感器测量误差仅2.61%,监测结果可为装备的服役提供数据支撑。

In order to understand and monitor the process of stress corrosion crack propagation of engineering equipment in service,the study focuses on the propagation of stress corrosion cracks of a designed double cantilever specimen of high-strength Al-alloy with prefabricated crack.Firstly,the mecha-nism of stress corrosion crack propagation was described,and the linear relationship of the crack length with the variation of the strain in the x-and y-directions of the stress corrosion crack propagation tip was determined through Matlab simulation;The stress concentration area at the crack tip was further determined by Abaqus finite element simulation,afterwards,the distance between the position of optical fiber sensing probe and the crack tip was selected to be 10 and 15 mm respectively;The relevant sensing technology of stress corrosion crack propagation in fiber Bragg gratings was also studied,and then a grating temperature compensation model was proposed;Finally,the correlation between the crack length and the wavelength change of the fiber Bragg grating sensor during corrosion crack propagation was calibrated.The results showed that the correlation of the crack length and the wavelength change was R^(2)=0.9893 and R^(2)=0.9870,respectively;Afterwards,an outdoor exposure test set was constructed in Wanning of Hainan Province,to achieve in-situ monitoring of stress corrosion crack propagation of Alalloys through networking.The monitoring data showed that after adopting the suitable temperature compensation,the measurement error is only 2.61%for sensor positioned 10 mm near the crack tip,and the monitoring results can provide data support for the real operation of engineering equipment.