Single edge notches (SEN) and double edge notches (DEN) of various depths were introduced at the centre of the gauge portion of the tensile specimens of this steel (solution annealed) by electro-discharge machining. Tensile tests were carried out at a nominal strain rate of 5 x 10^-4 s^-s at ambient temperature (298K). AE signals generated during the tensile tests were recorded using a piezoelectric transducer having resonant frequency at 175 kHz and analysed using an AE system (Model No. 204B) of M/s. AET Corpn. USA. A total system gain of 98 dB and a threshold of 0.7 V were maintained.

Higher amount of acoustic activity observed prior to and during yielding of the notched specimens as compared to the unnotched specimens is attributed to the localised deformation at the notch tip. Increased AE with increase in notch depth is attributed to the increase in the extent of localised deformation at the notch tip. Reduced AE from the notched specimens with increasing plastic strain is due to the blunting of the notch tip. The AE generated just before and during fracture is more for the notched specimens, than unnotched specimens. The reduced AE in the DEN specimens in comparison to the SEN specimens is attributed to the possible destructive interference of the AE signals generated simultaneously from the two notches in the DEN specimens. The variation of AE total count (N) with stress intensity factor (K) for the notched specimens, analysed in terms of the power law relationship N K^m, indicates that the acoustic emission generated during deformation of a flawed specimen is closely related to the stress intensity factor for that flaw. These results also suggest that an estimate of the flaw size, for an unknown flaw, could be determined by using acoustic emission technique. The onset of unstable fracture in the notched specimens can also be recognised by an abrupt increase in AE generated beyond ultimate tensile strength.