Understanding Acoustic Emission Testing- Reading 1 Part B-A

Spooner and Dougill confirmed that this effect did not occur beyond the peak
of the stress-strain curve (i.e., in the descending portion of the stress-strain
curve), where acoustic emissions occurred again before the previous
maximum strain was reached. It has also been suggested that a form of the
Kaiser effect occurs as well for cyclic thermal stresses in concrete, and for
drying and wetting cycles. On the other hand, Nielsen and Griffin have
reported that the Kaiser effect is only a very temporary effect in concrete; with
only a few hours of rest between loading cycles, acoustic emissions are again
recorded during reloading to the previous maximum stress. They therefore
concluded “that the Kaiser effect is not a reliable indicator of the loading
history for plain concrete.” Thus, it is unlikely that the Kaiser effect could be
used in practice to determine the previous maximum stress that a structural
member has been subjected to.
Comments:
The continual curing of concrete matrix repair the previous loading induced
effects (microcracks, disbonding etc.) and return the concrete back to almost
preloading condition.
Charlie Chong/ Fion Zhang