Broad-band transient recording and characterization of acoustic emission events in composite laminates

Acoustic emission (AE) transients due to different kinds of microdamage, such as matrix cracking, fiber breakage and local delaminations, have been recorded in glass/epoxy composite laminates. Different stacking sequences, [0 degrees, 90(2)degrees](S), [90(2)degrees, 0 degrees](S), [+45 degrees, -45 degrees](S) and [0(4)degrees], were used in order to trigger different crack mechanisms during tensile testing. The AE transients were recorded as functions of time by the use of broad-band AE transducers. In the experiments, it was observed that different types of cracks generated acoustic emission signals varying in amplitude, duration time and frequency content. It was also seen that the same type of crack produced signals with different characteristics depending on the layer in which the crack appeared and its orientation compared to the location of the transducer. The majority of signals from the tests could be divided into a few main groups. Typical signals and characteristics representing these groups are presented in the paper. The observations show that there is a potential in future development of quantitative methods for identification of damage development in composite laminates. (C) 2000 Elsevier Science Ltd. All rights reserved.