Application of Acoustic Emission Technique to Study of Weld Cracking (1st Report)

Abstract

Acoustic emission technique which has been used as a research tool to the deformation and fracture of materials or as a method of non-destructive inspection is tried to apply for detection of the delayed cracks in weldments. The acoustic emission measurements are carried out right after completion of slag removing to avoid the noise from the welding arc and the slag cracks.
No special problems due to interference from the transmitted mechanical noise or the electrical circumstances can be encountered and the acoustic emission data recorded in terms of count rate by an electric counter are attributed to the burst type emission from weld cracking.
Experiments reveal that the initiation and growth of delayed cracks in HT 80 weldments can be readily detected and discontinuous process of slow crack-growth can be characterized by means of this new system used. In y-groove restraint cracking test using MIG, the effect of various factors in practice, such as restraint intensity, preheating temperature and weld heat input, on the primary and secondary incubation periods of delayed cracking can be evaluated in details and accurately from the acoustic emission data. Both preheating and postheating treatment retard effectively the initiation and propagation of cracks, and these phenomena are well reflected upon the acoustic emission count.
The acoustic emission technique is concluded to be useful to detect weld defects and to understand a mechanism of the hydrogen cracking.