Research On Structural Damage Detection Method Based On Ultrasonic Lamb Wave

Both metal sheets and carbon fiber reinforced composite materials have been widely used in aerospace,marine warships,and pressure vessels.The usage of ultrasonic waves for damage detection in plate-like structures has always been a research hotspot and difficulty in the field of structural health testing.Ultrasonic Lamb waves are the most commonly used guided wave form in ultrasonic non-destructive testing.Compared with conventional point-to-point detection using ultrasonic body waves(transverse wave and longitudinal wave),ultrasonic Lamb waves excited at one point can spread widely,so ultrasonic damage detection methods based on Lamb waves are faster and more efficient.The change of wave velocity and amplitude caused by damage are usually used as the characteristic parameters to detect damage.In this paper,the amplitude variation of ultrasonic Lamb wave in thin plate was employed to study the ultrasonic imaging detection methods.The methods can locate and evaluate damage,which are effective techniques for visually determining damage through images.Firstly,the propagation mechanism of Lamb waves in various isotropic materials and anisotropic materials were introduced.By combining the wave equations in isotropic materials and the boundary conditions of plates,the Lamb wave dispersion equations for isotropic materials were solved,and Lamb wave phase velocity and group velocity dispersion curve on the aluminum plates were plotted.Based on wave division theory,the Lamb wave dispersion equations for anisotropic materials were solved.The concept of the wave energy flow image was introduced,and a damage evaluation method based on ultrasonic guided waves using Laser scanning scheme was put forward.Provide theoretical and technical basis for follow-up work.Secondly,Lamb wave propagation in the thin plate was simulated using finite element method,and the reliability of the damage evaluation method based on ultrasonic guided waves using Laser scanning scheme was validated.A three-dimensional finite element model of the aluminum plate containing damage was established.The propagation characteristics of Lamb waves in the aluminum plate were analyzed by the displacement deformation cloud image of the simulation results.The displacement historical output of nodes in the detection area was acquired,and the“wave energy flow” was plotted according to the change of the amplitude.The location and shape of the damage can be determined by using “wave energy flow”.The influenceof different frequency excitation signals on the damage detection effect was analyzed,and the damage detections under the complicated conditions of multiple damages and damages on the aluminum plate boundary were studied.A three-dimensional finite element finite element model of CFRP composite laminates with delamination damage was established to study the propagation characteristics of Lamb waves in different material layers of anisotropic materials,and collect the historical displacement output of nodes in the detection region.The “wave energy flow” was plotted to determine the location and shape of the damage.The effect of different sampling points on damage images and the complex conditions of multiple delamination damages were studied.Finally,an improved scheme two-level reconstruction method for tomographic images based on Lamb wave was proposed.Lamb wave signals that only capture at the boundaries of the detection region were used,which were much less than the ones using by the damage evaluation method based on ultrasonic guided waves using Laser scanning scheme.The image reconstruction was carried out in two steps.The first step was to roughly identify damage areas and locations by selecting the suspected ray paths,and the second step was to accurately reconstruct damage images using the least-square method.The effectiveness of the improved scheme was verified by experimentally examining the damage in aluminum plates containing non-penetrating notch and CFRP composite laminates containing internal delamination.This method is very suitable for scenarios that require rapid damage detection.