Study On Structural Damage Detection And Identification Method Based On Acoustic Emission And Ultrasonic Waves/Phased Array

Structural health monitoring(SHM)is an effective method and the forefront of the research field in civil engineering which reveals the structural behavior at service,identifies and diagnoses the damaged and healthy status,assesses and predicts the safety level of the structures.Extensive researches and cases indicate that SHM can effectively obtain the whole status of the structures,however,it is difficult to identify the structural local minor damages.Damage detection techniques can get better structural local information.Therefore,combining the structural damage detection technique and SHM system together can comprehensively assess the health and safety status of the structures,which is the important developing trend of SHM.In this paper,the local structural damage detection based on acoustic emission damage detection technique,ultrasonic computed tomography,guided waves and phased array damage detection and identification method have important theoretical significance and practical value.The main contents of the paper are as follows:Firstly,the basalt fiber reinforced polymer(BFRP)specimens and carbon fiber reinforced polymer(CFRP)-steel hybrid cable will be studied based on acoustic emission(AE)technique.The AE signals are analyzed based on the time-frequency features,amplitude and energy features to reveal the damaged patterns and the principles of the two typical structures.Secondly,considering the acoustic emission detection technology can not detect the existing damage structure,based on the sparse features of the structural damages,the ultrasonic computed tomography(CT)damaged detection technique and identification method based on compressive sampling(CS)mathematical method has been studied and improved.The effectiveness of the identification method has been verified via both the simulation results and experimental tests.Furthermore,the damage detection and identification method in the structures has also been studied based on compressive sampling and guided waves.This paper proposes a method of structural damage localization based on dictionary matrix and a damaged severity identification method based on the Euler-Bernoulli beam theory.At last,based on the application of conventional ultrasonic phased array damage detection,the damaged detection theories of Lamb waves and shear horizontal(SH)waves phased array systems have been studied.Both the Lamb waves phased array and SH waves phased array are designed and established.Via individually controlling the time delays of excitation signals to each element in the phased array,a directional guided wave beam of Lamb waves or SH waves can be launched and focused on a special focal point for damage detection.By using the GPU parallelized Local Interaction Simulation Approach(LISA)method,the wave field emitted by the phased array in the plate-like structure can be simulated accurately.Both laser Doppler vibrometer(LDV)instrument and the developed phased array are used in the experimental testing,which realizes the effective identification and reconstruction of the location and size of the damage.