Research On Damage Imaging Of The Ultrasonic Lamb Wave For Plate-like Structure

Lamb wave is one of the ultrasonic guided waves in structural health monitoring and nondestructive testing.Because of its long propagation distance,point-to-point detection can carry integral structural information,it is widely used.In this paper,the methods of damage locating and imaging in aluminum plates are studied.The specific research work of this paper is as follows:(1)The principle of the basic theory of Lamb wave and damage detection method are introduced at first.Then,finite element simulation and experiment are used to study the transmission mechanism in the plate type structure and interaction with the damage of Lamb wave.The excitation parameters such as frequency,cycle and Lamb mode are determined based on this study.In addition,the relative error and experiment platform are introduced,being the foundation for the subsequent study.(2)To solve the problem that the probabilistic imaging algorithm has a large relative error in damage identification,an improving method was established,in which the distance coefficient and the time coefficient were proposed to select and intercept high signal noise ratio data from all experimental data.The experiment result revealed that the location imaging accuracy and efficiency were improved more than 50%and 30%respectively by using the improving method,which shown to offer significant performance advantages for SHM.In addition,the relative error analysis of experiment in square arrays with different areas and different damage sizes shows the sparse array with square area larger than 100×100mm is more favorable damage imaging,and when the damage diameter is less than 1mm,the commonly used linear ultrasonic Lamb wave will not be able to locate the image accurately.(3)In order to eliminate the influence of baseline signal on damage imaging.This paper presents a baseline-free imaging algorithm based on reciprocity damage index.Two reciprocity signals obtained after excitation and reception are exchanged through a set of piezoelectric transition,and then the reciprocity damage index is established according to the difference between these two signals,judging whether there is damage on the propagation path.The damage location is determined based on a plurality of every damage propagation paths.The distance coefficient and the time coefficient were further introduced in this part,and the relationship between them was studied to improve this reciprocity damage index.According to the proposed baseline-free damage localization method based on improved reciprocity damage index,the signals are filtered by the determined distance coefficient,and the damage imaging on the non-propagation path is realized.(4)This paper proposes a new baseline-free imaging algorithm.Four sensors are put in array of a rhombus.Every three piezoelectric transition can form a measurement group.A sensor is used as the actuator to excite the guided wave,and two signals are subsequently received by another two sensors who are equidistant to the actuator.The difference between the damage scattering distance of the two piezoelectric transitions can form a hyperbolic curve of the damage position,and finally the damage position can be determined by multiple intersection points of multiple hyperbolic curves.The other cases are also studied based on the location of damage.Finally,the effectiveness and efficiency of this method are verified by simulation and experiment.