Understanding Acoustic Emission Testing- Reading 1 Part B-A

16.7.2 Type of Cracks
A number of attempts have been made to relate acoustic events of different
frequencies, or of different energies, to different types of cracking in concrete.
For instance, Saeki et al., by looking at the energy levels of the acoustic
emissions at different levels of loading, concluded that the first stage of
cracking, due to the development of bond cracks between the cement paste
and the aggregate, emitted high energy signals; the second stage, which they
termed “crack arrest,” emitted low energy signals; the final stage, in which
cracks extended through the mortar, was again associated with high energy
acoustic events. Similarly, Tanigawa and Kobayashi used acoustic energies
to distinguish the onset of “the proportional limit, the initiation stress and the
critical stress.” On the other hand, Tanigawa et al. tried to relate the fracture
type (pore closure, tensile cracking, and shear slip) to the power spectra and
frequency components of the acoustic events. The difficulty with these and
similar approaches is that they tried to relate differences in the recorded
acoustic events to preconceived notions 先 入 为 主 的 观 念 of the nature of
cracking in concrete; direct cause and effect relationships were never
observed.
Charlie Chong/ Fion Zhang