Research On Ultrasonic Testing Method For Internal Damage Of Concrete Structures

Concrete is widely used in the construction of public buildings,such as buildings,bridges,water conservancy and so on,because of its advantages of being stable,durable and low in price.But the highway,bridge collapse and other catastrophic events occur frequently in recent years,seriously endangering our personal and property safety.In order to ensure the safety of personal and property,non-destructive testing of concrete structure has become an urgent problem to be solved in our country.In this paper,the influence of the complex structure of concrete on the ultrasonic detection signal and the ultrasonic image is studied.The synthetic aperture imaging technology(SAFT)is proposed in concrete testing to solve the problem such as high structural noise and the defect signal difficult to be extracted effectively.The main research work of this paper is as follows:In this paper,an ultrasonic coupling system is used to measure the ultrasonic attenuation coefficient in concrete,in view of the problem that the acoustic characteristic parameters is difficult to measure,such as high acoustic attenuation and roughness surface.First,according to the attenuation of the sound pressure amplitude at different distances when the ultrasonic wave propagates in the air,the attenuation coefficient of the ultrasonic wave in the air is calculated.Then,according to the change of the amplitude of the sound pressure at the interface between the air and the concrete,the sound pressure reflectance of the ultrasonic wave at the air and concrete interface is calculated.And the attenuation coefficient of the ultrasonic wave in the concrete is obtained according to the attenuation of the sound pressure amplitude of the ultrasonic wave through the concrete structure.The finite difference simulation software was used to establish the numerical models of concrete structure.The concrete model with different depth and size defects was simulated numerically,and the experimental system were experimentally experimented to obtain the defect echo signal.By comparing the numerical simulation of the waveform with the experimental waveform,the simulation and experimental signal waveforms are in good agreement.According to the attenuation coefficient of the measurement,the corresponding attenuation coefficient is added to the numerical simulation,and the influence of different attenuation coefficient on the detection result is analyzed.The results show that the amplitude of the defect echo signal is significantly reduced with the increase of the attenuation coefficient,which brings great difficulties to the ultrasonic inspection of concrete.In view of the fact that the structure noise is large and the echo signal is difficult to be extracted,the synthetic aperture focusing imaging technique is applied to the ultrasonic concrete testing.The numerical simulation and experimental results show that the applied aperture imaging algorithm is applied to the ultrasonic inspection of concrete,the amplitude of the defect echo is obviously increased and the structural noise is suppressed.Compared with the ultrasonic B-scan image,the synthetic aperture-focusing image has higher signal-to-noise ratio and resolution,and it is more helpful to find the abnormal structure inside the concrete,which provides a solution for the effective detection of defects in concrete materials.