DELAYED FRACTURE KINETICS OF HIGH-TENSION STEEL BY THE SOURCE ANALYSIS OF AE BY USING THE EXPERIMENTAL TRANSFER-FUNCTION

We propose a new method for estimating the AE (or elastic wave) source wave in the delayed fracture of a finite specimen (NACE-TM0177) by us ing the experimental transfer functions of medium and for AE transduce r. A laser induced dielectric break-down of silicon grease was utilize d to examine the frequency resolution of the AE system employed. Due t o the limited frequency resolution of the system and the reflected wav es, the accurate source analysis of micro-fracture was limited to a re latively slower crack generation with the rise time longer than 0.5 mu s. Crack generation rate in the delayed fracture of QT-treated SCM 44 0 allay with tensile strength of 1323 and 1500 MPa was estimated to ch ange from 50 m/s ( effective rate :145 m/s) to 170 m/s (490 m/s), depe nding on both the strength of material and hydrogen concentration in f ront of notch.