Understanding Acoustic Emission Testing- Reading 1 Part B-A

16.7.6 Fiber Reinforced Cements and Concretes
A number of acoustic emission studies have been carried out on fiber
reinforced cements and concretes. Lenain and Bunsell, in a study of asbestos
cement, found that acoustic emissions resulted both from cracking of the
matrix and fiber pullout.
They noted that the Kaiser effect was not found for this type of fiberreinforced
composite, since on unloading of a specimen the partially pulled
out fibers were damaged, and particles of cement attached to them were
crushed, giving rise to acoustic emissions on unloading. Because these
damaged fibers were then less able to resist crack growth, on subsequent
reloading cracks started to propagate at lower stress levels than on the
previous cycle, thus, giving off acoustic emissions below the previously
achieved maximum load.
Akers and Garrett also studied asbestos cement; they found that acoustic
emission monitoring could be used to detect the onset and development of
prefailure cracking.
Charlie Chong/ Fion Zhang