YUAN Keyi, HAN Zandong, ZHONG Yuexian, CHEN Yifang
Journal of Tsinghua University(Science and Technology). 2015, 55(7): 739-743.
Stress-free, room temperature creep specimens are used in almost all ultrasonic creep testing experimental research. However, the ultrasonic testing parameters for this condition (stress-free and room temperature) will differ from those for realistic conditions with the creep stress and higher temperatures. These differences will influence the creep detection accuracy. Tests in more realistic conditions are conducted using pure lead for continuous creep experiments with real-time ultrasonic detection used during the creep process and then during the relaxation process. The real-time parameter variations are plotted versus creep time for some parameters such as the attenuation, acoustic velocity, and time attenuation. The results show that the detection sensitivities of the creep ultrasonic testing parameters for realistic conditions are higher than for stress-free conditions. Thus, if stress-free ultrasonic testing parameter measurements are used to assess the creep, the actual measured parameter values must be corrected to accurately assess the creep. In addition, the experiments show that the time-attenuation parameter has the same type of variations as the attenuation parameter with the increased creep time so the objective dimensions do not need to measure to calculate the time-attenuation parameter, which is much easier, especially in practical ultrasonic testing. This result shows that the time-attenuation parameter can be used in place of the attenuation parameter in metal creep ultrasonic testing.
