Understanding Acoustic Emission Testing- Reading 1 Part B-A

Activity of AE Sources in Structural Loading
AE signals generated under different loading patterns can provide valuable
information concerning the structural integrity of a material. Load levels that
have been previously exerted on a material do not produce AE activity. In
other words, discontinuities created in a material do not expand or move until
that former stress is exceeded. This phenomenon, known as the Kaiser Effect,
can be seen in the load versus AE plot to the right. As the object is loaded,
acoustic emission events accumulate (segment AB). When the load is
removed and reapplied (segment BCB), AE events do not occur again until
the load at point B is exceeded. As the load exerted on the material is
increased again (BD), AE’s are generated and stop when the load is removed.
However, at point F, the applied load is high enough to cause significant
emissions even though the previous maximum load (D) was not reached.
This phenomenon is known as the Felicity Effect. This effect can be
quantified using the Felicity Ratio, which is the load where considerable AE
resumes, divided by the maximum applied load (F/D).
Charlie Chong/ Fion Zhang