A comparison of fatigue damage detection in carbon and glass fibre/epoxy composite materials by acoustic emission

Ring specimens of four fibre composite materials, two containing carbon fibres (crfp) and two containing glass fibres (gfrp) have been monitored for acoustic emission (AE) during tension/ tension fatigue cycling.In cfrp continuous monitoring failed to provide warning of impending fatigue failure. The results are not consistent with the view that cessation of activity after initial shakedown guarantees stabilization and safe operation.In gfrp, if the activity is averaged over adequate periods, an underlying trend is revealed, short term deviations from which are attributed to the occurrence of a different damage process which determines final failure. It is shown that in the tests reported, the progressively increasing component of the activity can be related to the fatigue life. The distribution of events over the load cycle shows that a dominant part of this progressively increasing activity is associated with some stress independent process. Use of the appropriate part of the load cycle also offers the possibility of focussing on the events associated with the damage that leads to final failure.