Lu Guan, Zhou Yuchen, Xu Yiming
School of Mechanical Engineering, Nantong University, Nantong 226000, China.
School of Electrical Engineering, Nantong University, Nantong 226000, China.
Sensors (Basel). 2021 Sep 12;21(18):6103. doi: 10.3390/s21186103.
Variable thickness composite laminates (VTCL) are susceptible to impact during use and may result in irreparable internal damage. In order to locate the internal impact damage of complex composite structures and monitor the impact signals of VTCL at the same time, a low velocity impact (LVI) monitoring system based on an optical fiber sensing network was constructed. Fiber Bragg grating (FBG) sensors are suitable for monitoring strain characteristics. By arranging FBG sensors on the laminate, we studied the spectrum analysis and localization of the impact signal collected by a FBG demodulator at constant temperature. The prior knowledge of variable thickness composite structures is difficult to obtain, and the multi-sensor dynamic monitoring is complex and difficult to realize. In order to locate the LVI of composite structures without prior knowledge, based on empirical mode decomposition (EMD), we proposed an impact localization method with zero-mean normalized cross-correlation (ZNCC) and thickness correction. The experimental results of LVI localization verification show that the ZNCC algorithm can effectively remove the temperature cross-sensitivity and impact energy influencing factors, and the thickness correction can reduce the interference of variable thickness characteristics on localization performance. The maximum localization error is 24.41 mm and the average error is 15.67 mm, which meets engineering application requirements. The method of variable-thickness normalization significantly improves impact localization performance for VTCL.
变厚度复合材料层合板（VTCL）在使用过程中易受冲击，可能导致无法修复的内部损伤。为了定位复杂复合材料结构的内部冲击损伤并同时监测VTCL的冲击信号，构建了一种基于光纤传感网络的低速冲击（LVI）监测系统。光纤布拉格光栅（FBG）传感器适用于监测应变特性。通过在层合板上布置FBG传感器，研究了恒温下FBG解调器采集的冲击信号的频谱分析和定位。变厚度复合材料结构的先验知识难以获取，多传感器动态监测复杂且难以实现。为了在无先验知识的情况下定位复合材料结构的LVI，基于经验模态分解（EMD），提出了一种具有零均值归一化互相关（ZNCC）和厚度校正的冲击定位方法。LVI定位验证实验结果表明，ZNCC算法能有效消除温度交叉敏感性和冲击能量影响因素，厚度校正可降低变厚度特性对定位性能的干扰。最大定位误差为24.41 mm，平均误差为15.67 mm，满足工程应用要求。变厚度归一化方法显著提高了VTCL的冲击定位性能。
