“Predicting Failure in Carbon/Epoxy Specimens with Nol Ring Test and Acoustic EMISSION Analysis”

The rapid growth of filament winding techniques for fabricating plastic composite structures has not been matched by advancements in testing and evaluation methods. The Naval Ordnance Laboratory (NOL) ring test has emerged as a valuable technique for assessing filament wound composites, proving useful for material comparison in research and development, as well as quality control. Internal pressure is applied to ring-shaped specimens in a manner similar to burst testing used for pressure vessels. This method allows direct observation of fracture behavior within FRP layers, which is not possible with actual pressure vessels. This paper standardizes ring fabrication and testing methods for determining ring tensile strength and demonstrates the benefits of ring burst tests. Fracture analysis of carbon/epoxy NOL rings, under both defect-free and adverse conditions, was conducted using acoustic emission (AE) measurements to understand strength degradation. A mathematical method was also created to predict the failure load of carbon/epoxy NOL rings with a reasonable margin of error. The simplicity and cost-effectiveness of this method make it a practical alternative to burst tests of pressure vessels.