金属蠕变的实时超声检测实验研究

Experimental research on real-time ultrasonic detection of pure metal creep

目前绝大多数蠕变超声检测研究都是使用常温且无应力的蠕变试样进行检测实验,在该条件下测得的超声检测参数值与实时(维持蠕变温度和蠕变应力)测得的蠕变参数值有一定的差异,影响对检测对象蠕变程度的准确判断。该文使用纯铅进行连续蠕变实验,并在实验过程中进行实时超声检测,获得了蠕变过程和松弛过程中的超声实时检测信号,对此信号进行处理,得到了衰减、声速、时间衰减等参数随蠕变程度的实时变化曲线。实验结果表明:实时条件下测得的蠕变超声检测参数相对于无应力条件下测得的参数具有更高的检测灵敏度;如果以无应力检测参数值作为评定标准,则需对实时检测参数值作出修正才能准确评价被检测目标的蠕变程度;时间衰减参数与衰减参数具有相同的蠕变变化趋势,但时间衰减参数不需要对被检测目标进行几何尺寸的测量,因此时间衰减参数更适用于实际检测,可以作为金属蠕变检测中衰减参数的替代参数。

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.