Damage Detection And Evaluation For Metallic Plates Based On Frequency-wavenumber Analysis

Plate-type structure prone to corrosion, fatigue and other damage under the influence of flaw caused by design and production and the external loads and environment corrosion. The increasing damage will become invalid and destructive, even cause serious engineering accident. Structural damage detection method based on ultrasonic guided wave has the advantages with large detection range and sensitive to all kinds of minor damage compared to conventional detection methods.However, it is difficult to evaluate the characteristics of damage limited to contact transducer array drive or sensing mode. This paper adopts Doppler laser vibrometer for noncontact automatic scanning of array structure to extract the ultrasonic Lamb wave field signals with damage characteristics.It can makes accurate positioning and evaluation with the analysis method of space wave number domain.The non-contact structural damage detection method in this paper is applied to the practical detection of the plate structure. So it provides the reliability of security for various types of equipments to work safely and stably long term. The main work of this paper is as follows:Firstly, it introduces conventional nondestructive testing methods and general methods of ultrasonic testing in plate structures.And then describes the basic theory and signal processing technology of Lamb wave.And discusses the adding-windows analysis which provides the basic theory for subsequent structural damage detection and imaging of plate structures.Secondly, it uses COMSOL Multiphysics simulation platform to simulate the propagation of Lamb wave in plate structure.And grid scan for 3D model, single row point scanning for 2D model.Then makes the adding-windows analysis, multidimensional Fourier transform, imaging algorithm based on frequency wave number domain.At last analysises the damage location and damage size,also compared with the damage parameters set by the model in order to validate the efficiency of way of damage detection of ultrasonic guided wave field in frequency wave number domain.Finally, scaning for structure non-contactly and automatically with scanning laser Doppler vibrometer by constructing the experimental platform for the damage detection of plate structures.And damage detection is adopted according to the method based on the high resolution ultrasonic guided wave field which is obtained by instrument. Then compare with the numerical results to make sure the feasibility and accuracy of the method.And discuss the application prospect of the method in the real engineering structure damage detection.