超声激励-光纤光栅传感的板结构损伤识别

Plate structural damage identification based on ultrasonic excitation and fiber Bragg grating sensing

为实现利用光纤光栅代替压电陶瓷进行固体中超声波信号的检测和结构损伤的识别,搭建了超声激励-光纤光栅检测系统。系统采用超声波探伤仪激励超声探头从而在薄板中产生超声波,利用粘贴型光纤光栅对超声波进行测量,用基于可调激光光源的解调系统实现光纤光栅中心波长的解调。分析了该检测系统的工作原理,理论推导了其输出电压与所测超声应变的关系式。在此基础上,首先,将该装置用于5052铝合金板中超声波声轴线声强分布特征的研究,验证了该装置用于板中超声波信号测量的可行性;然后,利用该装置分别进行5052铝合金板中2处直径为6 mm的孔缺陷的检测,实验证明,当板中出现孔缺陷时,光纤光栅所测波形中将出现新的波包,可通过损伤前后新增波包到来的时刻确定孔的位置,两孔的缺陷定位偏差分别为3.3 mm和0.8 mm。

In order to measure ultrasonic waves propagating in solids and identify the structural damage with fiber Bragg gratings （FBG） instead of piezoelectric ceramics, a detection system based on ultrasonic excitation and fiber Bragg grating sensing was established. The ultrasonic fault detector is employed to stimulate the ultrasonic probe and generate ultrasonic waves in the thin plate. The adhesive FBG is used to measure the ultrasonic waves and the demodulating system based on tunable laser source is applied to achieve the center wavelength demodulation of FGB. The working principle of this detection system is analyzed, and the expression between the output voltage and measured ultrasonic strain is derived in theory. On these bases, the detection system was used to study the characteristics of acoustic intensity distribution along the acoustic axis in the aluminum alloy （5052） plate and verify the feasibility of detecting acoustic waves with the system. Then, the experiment system was used to detect the defect of the two holes with diameters of 6 mm in the aluminum alloy （5052） plate. Experiment results prove that new wave packet will appear in the FGB measured ultrasonic waveform when there is hole damage in the plate, and the arriving time of the new wave packet before and after the damage can be used to determine the damage location. The positioning errors of the two holes are 3.3 mm and 0. 8 mm, respectively.