Research On Damage Detection Of Composite Based On Ultrasonic Lamb Wave

During the forming and service process of composite materials,various defects and damages will be caused by various factors.If they are not discovered and handled in time,the performance of the structure will be seriously affected.Ultrasonic Lamb wave nondestructive testing technology has the advantages of being sensitive to damage,long propagation distance,small attenuation,etc.It is currently the main method of composite structure health monitoring.However,at the same time,the composite material has a fast damage expansion speed,great hazards,and difficult monitoring.Compared with metal materials,the anisotropic characteristics of the composite material,the multimodality and dispersion characteristics of the Lamb wave propagation process also make the detection process and results more For the complex.In this paper,based on the study of the principle of Lamb wave propagation,combined with the probability damage reconstruction algorithm(RAPID),the effective signal method and the time reversal method are used to study the damage of the composite material structure crack and the circular hole,and the damage size,Location,shape detection and evaluation.The research content is as follows:First,the ultrasonic Lamb propagation theory and dispersion characteristics are analyzed.In order to reduce the influence of the boundary reflection signal on the measurement signal during the Lamb wave propagation process,the boundary of the ultrasonic Lamb wave propagating in the composite structure is improved by adding an absorption layer with increasing damping The effect of reflected wave absorption;and the effects of parameters such as the length of the absorption boundary,the maximum value of the damping coefficient,and the power index on the absorption effect are studied to obtain the optimal value of the absorption boundary parameter.On this basis,a composite damage detection model was established,and the application of absorption boundary in composite damage detection was explored.Secondly,according to the Lamb wave dispersion curve in the composite material,the Lamb wave propagation mechanism is analyzed.For the crack damage of the composite material structure,the effective signal method is used to extract the effective length of the damage signal and the damage coefficient(DI),Use RAPID algorithm to get the approximate damage area;use the absolute value difference method to scan the damage area,determine the crack direction,correct the crackdirection DI value and then damage the imaging again,so as to realize the monitoring of crack damage of the composite structure.After determining the crack direction,according to the relationship between the center angle of the receiving end and the DI value,re-evaluate the crack length to obtain the damage image.The crack damage method of this composite material was verified by finite element simulation and experiment respectively.The results show that this method can identify crack damage more accurately.Finally,for the circular hole damage of the composite material structure,it is monitored by the ultrasonic Lamb wave time reversal method.The damage coefficient DI is obtained by reconstructing the relationship between the inverted aggregate signal and the excitation signal,and the damage visualized image is obtained using the RAPID algorithm.In order to accurately assess the size,shape,and location of damage,the effectiveness of the shape factor calculation method in composite damage detection imaging was verified,and a method to obtain more accurate data based on the parameters such as damage location,size,and sensor distance was proposed.The calculation method of the shape factor value of the sensing path.Experimental results show that this method is more accurate than traditional imaging methods in detecting and evaluating the damage size,location,shape,and other information of the composite hole.