The Influence Of Excitation On The Ultrasonic Response Of Defect In Engineering Layered Structure

Layered structure is an important engineering unit structure, and the quality of interfacial adhesion and the structure quality of each layer have the direct relation with the safety and durability of engineering structures, so the defect detection of engineering layered structure is very important. Ultrasonic testing is an important means for non-destructive testing and engineering evaluation. However, there is the low signal to noise ratio(SNR) and the difficulty of recognizing the prime time of response by the use of ultrasound to detect internal defects in engineering layered structure. The ultrasonic testing is based on the detection method of the excitation- the media- the response process. For improving the quality of response under the condition of unchanged medium, changing the means of excitation of ultrasonic testing is the only method should be adopted. The study of the influence that the means of excitation makes on the ultrasound response of layered structure defects contributes to a more rational design of a testing program for the engineering layered structure defects.The main contents and results of this paper are as follows:(1) The effects of excitation frequency on the ultrasound response to the ultrasonic testing of the layered structure defects were studied. Transient dynamic section of ANSYS was adopted, and the finite element model of double layered engineering structure with interface defects was established. The excitation frequency of defect detection for layered bonding structure commonly used in ultrasound testing is divided into 31 groups, and numerical simulation, velocity, amplitude, integral value of the nonlinear coefficient of response signal were analyzed. The results of the study mentioned above showed that: From50 KHz to 200 KHz, the transmission peak and integral value decreased with the increase of frequency, and the incident wave peak and integral value firstly drop then rise with the increase of frequency, and reached minimum in 165 KHz. The ratio of the reflected signal peaks to the incident is relatively large from 75 KHz to 130 KHz, and the integral value is relatively large from 80 KHz to 120 KHz.(2) The effects of excitation pulse width to the ultrasound response on the ultrasonic testing of the layered structure defects were studied. LS-DYNA section of ANSYS was adopted, and the finite element models of double engineering layered structure with inner media defects was established. The adoption of different excitation pulse time width were loaded and solved and analyzed, and the results showed that: Excitation pulse duration hasaffection on the response signal. When the pulse width is less than 40?s, the peak of response parameters increased with the increase of the width of the pulse. When the pulse duration exceeds 40?s, the peak of response parameters tend to be stabilized. The decrease of ultrasonic frequency exists in the process of ultrasonic wave propagation in the presence of the layered structure of the frequency attenuation. Pulse duration decreased with the increase of the offset. When pulse duration is 10?s, the apparent frequency shift has occurred.(3) Interface defects inspection of engineering layered structure with Chirp coded signal were studied. For the low SNR and the difficulty of recognizing the prime time of response,interface defects inspection by Chirp coded signal method is proposed. The basic method and principle of Chirp coding is introduced, and the matched filtering digital calculation method is designed, and receiving signal was processed by matching filtering, so the compressed output signal peak and high SNR is obtained. The finite element simulation was carried out for concrete with different size interface defect detection of the layered bonding structure. The results showed that the chirp coded signal detection concrete layered bonding structure can guarantee the defect resolution while improving the SNR.Through the study of this paper, the results of this paper has a certain reference value and guiding significance to the adoption of ultrasonic method to detect concrete quality layered bonding structure and engineering of ultrasonic testing equipment research and development.