Abstract
Acoustic emission generated during the fracture of materials contains potential information about the fracture mechanisms. A methodology has been developed for the analysis of acoustic emission signals. Based on this, the amplitude distribution and hence the steps by which the fracture proceeds can be characterized by the average counts per event data. This methodology was used to study the hydrogen-assisted cracking of AISI 4340 steel heat treated to produce average grain sizes of 25, 125 and 250 μm. The fracture toughness varied from 50 to 85 klbf in − 3 2 and the yield strength was maintained at about 215 klbf in −2. The cumulative counts, events and the amplitude distribution were monitored as a function of crack length and stress intensity factor. A relationship combining stress intensity K, grain diameter d i and the amplitude of emission V i has been derived as V i α Kd i From this relationship and assuming a lognormal grain size distribution, combined with the fact that the fracture was predominantly intergranular, it is possible to correlate the observed acoustic emission behaviour with the material characteristics. The observations also confirm the discontinuous crack jumps that are characteristic of hydrogen-assisted cracking.
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