Research On Non-destructive Testing System Of Composite Materials Based On Lamb Wave

Graphene composite materials are considered as functional materials with good prospects in strain measurement,insulation and corrosion protection,and electromagnetic wave absorption due to their lightweight,flexible,and conductive properties.Currently,they have been widely used in electronic equipment,aerospace,and military fields.However,external damage or internal defects in composite materials will seriously affect electrical performance and equipment safety.A Lamb wave based non-destructive testing system for composite materials was designed to address the above issues,and the damage localization algorithm was optimized to achieve real-time monitoring and localization of composite material damage defects.The main research content is as follows:(1)A non-destructive testing system for composite materials was designed based on the tunneling effect of graphene epoxy resin and the time-of-flight measurement method of Lamb waves.The system includes a flexible damage detection unit,a damage signal extraction circuit,and a damage cloud image display unit.The damage detection unit is composed of 4 piezoelectric ceramics and 32 pairs of electrodes.Combining the characteristics and parameters of graphene epoxy resin composite material,the parameter design of Lamb wave excitation source and detection electrode is optimized;Based on the method of time division multiplexing,a multi-channel acquisition circuit for the variation of array electrode resistance was designed using a multiplexer and a Wheatstone bridge;Based on the time-of-flight measurement method,analyze the time difference between Lamb wave response signal and damage scattering signal reaching the detection electrode,and combine the array electrode and multi ellipse imaging method to achieve damage location localization;The cloud image display of the damaged area was achieved using the MAT algorithm.The results indicate that the designed 300 mm × The 300 mm damage detection unit can achieve the detection and cloud image display of single or multiple defects with a geometric radius greater than 1mm inside the graphene epoxy resin composite material,and the system detection time is about 30 seconds.(2)To improve the accuracy of damage localization,the Lamb wave based damage detection algorithm was optimized.Using Kalman filtering to filter out boundary reflection signals and other noise in Lamb wave damage scattering signals;Ellipse reconstruction algorithm based on weight analysis to weaken the impact of edge ellipses on localization;Combined with the two-dimensional kernel density estimation algorithm,the density of the damage ellipse intersection set is judged,the shape of the damage location is modified,and the positioning accuracy is improved.The experimental results show that the algorithm has a positioning error of better than 4.0% for single damage with a geometric radius of 1mm,and a positioning error of better than 8.0% for double damage.Compared with damage probability imaging and circular algorithm,the position error is reduced by 50%.(3)Established a non-destructive testing system for graphene epoxy resin composite materials,completed 300 mm × 300 mm and 100 mm × 100 mm Design and physical preparation of two types of damage detection units;Completed the physical preparation of damage signal extraction and processing circuits;Completed the design of the upper computer UI interface and communication protocol,and achieved real-time display of damage cloud images.Using damage location simulation method for 300 mm × 300 mm composite material,using 4 × 8 electrode arrays were used to detect multiple circular damages with a radius of 2mm inside the material.The results showed that as the number of damages increased,the positioning error rapidly increased.When there were more than four damages,the positioning error increased from 6.62% to 35%;To improve the accuracy of multi damage localization,the number of electrode pairs can be increased,but it will significantly increase the detection time of the system.Therefore,it is necessary to further optimize the detection mode of flight time and the algorithm for damage localization.