An Evaluation of Threshold Stress-intensity Factor, K_ISCC Using AE Technique

Abstract

In this paper, a new method to evaluate the threshold stress-intensity factor K_ISCC by the use of acoustic emission (AE) signal analysis is proposed using the material of type 4340 steel, of which hydrogen content was controlled by the cathodic electrolytic method. In the subcritical crack growth due to hydrogen embrittlement, a linear correlation was observed between stress-intensity factor K and emission event counts N. From this relation K_ISCC was defined as a stress-intensity factor K_AE corresponding to the generation of AE events. The effects of K and threshold voltage of AE measurement on the K_ISCC were discussed in detail, and with the results of fractography it was concluded that the obtained K_ISCC corresponded to the nucleation of hydrogen induced intergranular microcrack in the maximum triaxial stress field ahead of the crack tip.