Acoustic emission during the low cycle fatigue of AISI 4340 steel

The effect of both the strain amplitude and the strain rate (by varying the cycling frequency) on the low cycle fatigue behaviour of as-received AISI 4340 steel was investigated. During the fatigue tests, acoustic emission was monitored. The total acoustic emission count was related to the cumulative damage due to low cycle fatigue. It was found that the extent of acoustic emission activity decreases with the strain amplitude Δϵt/2 when it is varied from 0.2% to 1% and then increases as Δϵt/2 is increased above 1%. Also, for a given strain amplitude Δϵt/2 of 1% the acoustic emission activity increases as the strain rate is increased. These findings are explained in terms of the microstructure of the AISI 4340 steel tested.