Phased Array Data Fusion Damage Imaging Method Based On Annular DE-IDT Array

Various types of plate-like structures,especially composite material plates,are widely used in many major engineering structures such as aerospace,high-speed rail,civil engineering,etc.Long term high-strength service is prone to fatigue cracks,corrosion,fracture and other damages.Ultrasonic guided waves are widely used in plate structures due to their advantages such as long propagation distance,fast propagation speed,small attenuation,and sensitivity to small damage.Among them,phased array detection is an important detection method.Ultrasonic testing is divided into contact testing and non-contact testing.Noncontact testing mainly receives plate displacement signals through Scanning Laser Doppler Vibrometer（SLDV）,but the collected signals are mainly off plane displacement（guided wave A₀ mode）,and the dispersion and multimodal characteristics of ultrasonic guided waves make it difficult to distinguish structural damage information.Contact detection refers to the detection of actuators and sensors through adhesive coupling or embedding structures.However,with the increasing application of curved panel structures and the increasing complexity of structures,the development of flexible sensors for signal front-end reception has become increasingly important.This article focuses on the above two issues.Firstly,a multi-modal data fusion damage imaging algorithm based on SLDV is studied to achieve the extraction of different modal damage information on orthotropic composite material plates and damage imaging in the frequency and frequency wavenumber（f-k）domains.At the same time,an annular broadband omnidirectional Interdigital Transducer（IDT）array based on flexible Dielectric Elastomer（DE）material and flexible piezoelectric material substrate composite was studied,achieving damage imaging detection of complex structures in the broadband range,and verifying the practicality of the flexible DE-IDT array.The main research content of this article is as follows:（1）The dispersion equation is derived and solved according to the propagation characteristics of ultrasonic guided waves in composite plates,the deflection angle caused by deflection effect is calculated,and the time/frequency domain imaging algorithm of narrow band and wide band for orthotropic composite plate structures is derived.A weighted amplitude plus multiplication combination data fusion method is given to improve the imaging contrast.（2）Establish a simulation model and damage detection experimental platform for an orthotropic composite plate actuated by a five peak narrowband modulated sinusoidal signal based on SLDV.A three-dimensional f-k domain window function is constructed for the separation of different modes of Lamb waves in anisotropic plate structures,and the data fusion of different modal damage results is achieved using the amplitude addition and multiplication method.The results show that the f-k domain imaging algorithm in which all frequency components in the frequency band participate in imaging is superior to the time domain imaging,and the damage imaging accuracy can be improved through the data fusion method.（3）In response to the shortcomings of the A₀ mode of guided wave,which is mainly received in SLDV detection,being insensitive to in-plate damage and difficult to meet the precise fixed-point scanning of curved panel structures,a circular DE-IDT phased array was optimized and designed,and a damage detection platform for isotropic curved aluminum plates and orthotropic composite material plates was built based on this circular array.The actuating signals were five peak narrowband modulated sine signals and linear frequency modulated Chirp signals.The band-pass filter is designed to filter the low-frequency noise interference in the experimental data,the time-frequency analysis is carried out using continuous wavelet changes,the time window function is designed to filter the incident wave,and the phased array data fusion algorithm is used to carry out damage imaging.The experimental results show that the chirp signal with linear frequency modulation contains more damage information due to its wideband characteristics,so its frequency domain imaging results are better than those actuated by the five peak narrowband modulated sine signal.Moreover,the accuracy of damage imaging can be improved through data fusion methods.The experiment also verifies the effectiveness of the application of the circular DE-IDT array.It provides theoretical and technical guidance for the application research of damage detection in curved panel structures and composite plate structures.