Ultrasonic signal characteristics by pulse-echo technique and mechanical strength of graphite materials with porous structure

摘要

Ultrasonic testing (UT) is an important non-destructive method to detect internal flaws and is widely applied to product control in industrial fields. In an investigation on ultrasonic signal characteristics in porous ceramics. the present authors developed an ultrasonic wave propagation model for the pulse-echo technique by improving an existing one for the transmission technique. A wave-pore reflection process was taken into account in the improvement. In the developed model, both diffusion and scattering losses can be treated as important factors of ultrasonic wave attenuation. The model was demonstrated by experimental data on ultrasonic signal characteristics of nuclear grade graphite. As an application of the model, the authors proposed a new approach combined UT signal with fracture mechanics to evaluate the mechanical strength of porous ceramics from UT signal. The combined approach was tried to apply to the acceptance test and the in-service inspection conditions of graphite components in the High Temperature Engineering Test Reactor (HTTR) as an example. This paper presents the developed propagation model for the pulse-echo technique as well as the combined approach. Moreover, both acceptance test and in-service inspection techniques of graphite components in high temperature gas-cooled reactors (HTGRs) using the combined approach was also proposed in this paper.