Research On Imaging A Crack In A Thin Plate Based On Reverse Time Migration Method With Flexural Wave

The detection and imaging of cracks and other defects in a thin plate are of critical importance for structural health monitoring of high-pressure vessels,aircrafts,reactors and other plate-like structures.The fundamental flexural wave,as one of the modes that propagate in a plate,is the main tool for detecting defects in a plate.In the modified reverse time migration(RTM)method with flexural wave,two time reversal(TR)operations are conducted to compress the stretched waveform due to dispersion and realize the backward propagation of the scattered wave.Then,the cross-correlation imaging condition of RTM is carried out for the backward wave and forward wave that comes from the original source in the same host plate,and the image of the crack in the plate is obtained.Based on the above theory,this paper presents further researches in numerical simulations and experiments for the detection and imaging of the crack in a thin plate.For a horizontal crack in a thin plate,the influences of the number of transmitting and receiving array elements as well as the shapes of transducer array on imaging quality of crack are investigated systematically through the numerical simulations,which provides theoretical basis for the following experiments.In the experiment,a PZT piezoelectric transducer is used as the emitter,and the flexure wave can be effectively excited in the aluminum plate;a laser vibrometer is adopted as the receiver,and the transmitting waveform at emitter and scattering flexure wave at receiver can be recorded with high fidelity.For the experimental aluminum plate without crack and other defects,the dispersion curve of flexure wave is derived by using F-K method to process the experimental data obtained by single transmitting and multiple receiving and incremental distance measurements,which is basically consistent with the theoretical curve.For the aluminum plate with a horizontal crack or anti-Z-shaped crack,the high quality and in-situ images of cracks are firstly reconstructed by using the modified RTM method to process the experimental data obtained by multiple transmitting and multiple receiving measurements.