Research On The Detection Technology Of Plate Structure Based On Non-contact Air-coupled Ultrasonic

Plate structure is a common structural form,the dead weight of slab is about 1/2~1/3 of that of reinforced concrete slab under the same condition,which is widely used in various engineering fields.Because the production of the plate is formed by the multi-pass rolling process and the large amount of deformation,in the period of the structure in service,a variety of factors will make the plate surface fatigue crack,resulting in the degradation of the overall performance of the structure,or even the occurrence of damage to cause an accident.Therefore,it is necessary to study the damage detection,defect location,damage degree assessment,structural service life prediction and automatic repair of structural damage of the plate,which has important theoretical and practical application value for ensuring the safe operation of the engineering structure.In this paper,non-contact air-coupled ultrasonic detection technology is used to detect plate structure.Comparing with conventional detection techniques,such as contact,such as water immersion,the greatest characteristic of non-contact air-coupled ultrasonic testing technology is no contact,no immersion,is free to transform distance,angle,frequency,ultrasonic inspire a variety of patterns.It is easier to form focused ultrasound,based on this technology can establish intelligent integration system to test the engineering structures in service.In the theoretical analysis module,the sound propagation model is established and the mathematical deduction is made for the penetration and V-through type of air-coupled technology,the influencing factors of energy transmission are sorted out,and the quantitative parameters are obtained.In the numerical simulation module,a new signal loading method,the element group surface load excitation method is proposed.In the study of V-through type,a modeling method based on gradient load method and surface effect element method was proposed in the simulation of incident Angle.Visual simulation of angle was realized for the first time and the validity of the detection method was verified by drawing visual images.Then,by simulating the influence of the incident angle on the propagation energy,the incident angle close to the theoretical analysis is found,and the detection distance is determined by the acoustic field characteristics of the ultrasonic transducer based on the radar sound source location,which provides parameters for the experiment.In the experimental research module,a one-side scanning scaffold was made and a non-contact air-coupled ultrasonic detection system was established.The curve of energy amplitude-scanning position of sound pressure signal was obtained through the v-mode experiment.The VMD decomposition technology is proposed in the data processing module,because of its low frequency noise resistance,fidelity to the original signal and high computing efficiency,it is very convenient for the processing of a large number of scanned data.By extracting the kurtosis characteristic values of received signals and drawing the distribution of plate surface characteristic values based on scanning coordinates,the imaging of signals in all directions was realized,and the image fusion technology of MATLAB was applied to the multi-direction signals to realize the imaging positioning of cracks and defects.Finally,based on the visualization simulation of ultrasonic wave propagation in the plate,the phenomenon of energy collapse was found.According to the characteristics of the excitation signal and the distribution of steel plate crack defects,it was believed that the standing wave caused the energy collapse.Through the extraction of time-domain signals at both ends of the crack,it was confirmed that the standing wave was the cause of the energy collapse.The detection of energy sink and the introduction of standing wave theory can detect the surface micro-defects of plate structure more effectively.