基于概率损伤算法的铝板电磁超声Lamb波扫描成像

Scanning Imaging of Aluminum Plate Using Electromagnetic Acoustic Lamb Waves Based on Probabilistic Damage Algorithm

A_0模态Lamb波具有波长短、检测灵敏度高等特点,可在板结构中实现大范围、高效率的损伤检测和监测。设计并制作了一种指向性的A_0模态电磁声传感器,其由印制于柔性电路板上的回折线圈和马蹄形磁铁组成。试验验证了所设计的传感器可在铝板中有效地激励出单一的A_0模态。为了实现铝板中缺陷的检测与重构,提出了一种基于EMAT(电磁声传感器)的Lamb波扫描成像技术,对铝板中不同形状的预制模拟缺陷进行扫描检测。对各扫描路径下检测信号的直达波进行虚拟时间反转计算,提取不同路径下的损伤指数,并结合损伤概率成像算法和数据融合方法,实现了预制模拟缺陷的定位和重构,成像结果与缺陷实际位置和形状非常吻合。

A0 mode of Lamb waves is widely used in defect detection and monitoring with large scale and high efficiency in plate-like structures due to its shorter wave length compared with other mode in the specified frequency range,which leads to high sensitivity to small damages.A unidirectional A0 mode electromagnetic acoustic transducer(EMAT)is developed and it consists of a meander coil on flexible printed coil(FPC),and a horseshoe magnet.The experimental results verify that the developed transducer can effectively produce the pure A0 mode in an aluminum plate.In order to realize flaw detection and reconstruction for the aluminum plate,a new electromagnetic ultrasonic scan imaging technology was developed.The damage index was defined by using virtual time reversal method.The combination of probabilistic damage algorithm and data fusion algorithm was used to deal with multiple sets of data.The location and imaging of simulated defects on the aluminum plate were well achieved accurately.