Significance and Use 5.1 Controlled stimulation i.e. the
application of mechanical or thermal load, can generate AE from
flawed areas of the structure. Sources may include flaw growth,
oxide fracture, crack face stiction and release on load
application, and crack face rubbing. 5.2 The load range above
normal service (peak) load is used to propagate fatigue cracks
in the plastically strained region ahead of the crack tip. Crack
propagation may not be a reliable source of AE, depending on the
alloy and microstructure, the amount (rate) of crack extension,
and possibility of brittle fracture in a segment of crack
extension. 5.3 Load increases resulting in significant ductile
tearing may produce less emission than expected for the amount
of crack growth. Processes that result in more brittle cleavage
fractures are more detectable and produce more emission for
smaller amounts of flaw growth. These include corrosion fatigue
and stress corrosion cracking modes of flaw growth, and would
also be more likely in cast or