Acoustic emission studies of filament wound carbon fibre reinforced rings and pressure ressels

Following earlier work on the use of acoustic emission techniques for studying fatigue and fracture in uni-directional plate samples o f carbon fibre reinforced plastic, experiments have been carried out on filament-wound rings and pressure vessels. The hydraulic expansion to failure of rings o f carbon/epoxy composites represents the fust step away from the earlier studies of model systems to more realistic structures, and it appears that the rings behave in exactly the same way as tensile samples. Of greater significance, however, is the fact that polar-wound pressure vessels in the form of oblate spheroids with aluminium screw-thread end connexions also show the same kind of acoustic emission patterns. If a vessel is pressurized and held at constant pressure the acoustic output is gradually reduced until it ceases. If the vessel is unloaded and reloaded, the pressure at which emission recommences (about 93 per cent of the previous maximum) can then be considered to be a safe working pressure. The response o f these vessels to monotonic loading, cyclic loading and stress relaxation is very similar to that of unidirectional tensile samples.