The Study on the Fracture Characteristic for the Nuclear Structural Material using Acoustic Emission

In order to evaluate the nuclear structural integrity, non-destructive test methods such as radiographic test, ultrasonic test and eddy current are generally used in the industrial field. However, these methods have restrictions that defect detection is possible after the crack growth. For this reason, Acoustic Emission Testing (AET) could be one of powerful inspection methods to verify the structural integrity of pressure vessels, high temperature reactors and pipes, and a number of other equipment because AET has an advantage that it is able to monitor the structure continuously. Acoustic emission is defined in the ASTM standards as 'the class of phenomena whereby transient elastic wave(s) so generated'. These waves propagate through the material and cause surface displacements, which can be converted to electrical signals using a suitable transducer. AE signals can be basically characterized as burst and continuous type. Burst signals refer to acoustic emission events that are of short duration are well separated in time. The signal amplitudes are much larger than the background noise. On the other hand continuous signals refer to AE event, which have the form of a random oscillatory appearance devoid of distinguishing features. The AE events are closely spaced in time and form a single waveform. The signal amplitudes are only slightly higher than the background noise. In this study, acoustic emission signal was collected from stainless steel 304 specimens and test was performed through tensile tests to verify the acoustic signal characteristic. And the fracture characteristic of specimen was studied using parameters relation analysis