Detection of Damage in Model Structure under Thermal Transient Loading by Ultrasonic Detection Method

摘要

Creep-fatigue is one of the main damages of the structural material on FBR plant. In order to extend the life of the plant, the remaining life assessment based on the creep-fatigue damage is desirable to he developed. In this study, the ultrasonic detection method which are as the nondestructive detection technology to evaluate the damage mechanics, are applied to detect the creep-fatigue damage for the vessel model on the cyclic thermal transient loading in sodium. The obtained ultrasonic echo waveform was analyzed, and was evaluated for some parameters. Fourier analysis is one of the methods to obtain the frequency properties. However, if the echo waveform is evaluated by the time-frequency analysis, it becomes possible to analyze the micro damage in detail. In this study, the wavelet transform method for the time-frequency analysis was applied to measure the micro damages before micro crack appearance. The analysis of ultrasonic echo by Gabor wavelet showed drop of the sound velocity at higher frequency than the peak frequency because of attenuation in the high frequency component. Then the amount of damage could he estimated by the sound velocity of ultrasonic echo on the time-frequency plane. The difference of the peak frequency #DELTA# f #rho# between Bi and B2 echoes increased with the amount of damage, and #DELTA# f #rho# was available as a parameter for the micro damage detection. The correlation between the sound velocity and the micro hardness for the amount of damage was also found. Furthermore, the exhaust life of vessel model by damage could be predicted from the exhaust life of creep-fatigue damaged specimen by the material test.