Acoustic emission characteristics of damage accumulation in Kevlar® 49 composites

Acoustic emission (AE) data attained during tensile testing of epoxy impregnated Kevlar® 49 (K/Ep) composite strands were reduced and analyzed to monitor progressive damage accumulation during the approach to tensile failure. The K/Ep material tested in this study was chosen due to its similarity to the material-of-construction used in composite overwrapped pressure vessels (COPVs) used on the NASA Space Shuttle Orbiter. Insight into the progressive microstructural degradation of K/Ep strands was gained by monitoring AE event rate and energy. Source location based on energy attenuation and arrival time data was used to differentiate between significant AE attributable to microstructural damage accumulation, and spurious AE attributable to grip and background noise. One of the more notable features observed in the AE data was increasing violation of the Kaiser effect (Felicity ratio \u3c 1.0). The effectiveness of three different stress schedules that allowed the Felicity ratio to be analytically determined is discussed in detail. Potential use of such stress schedules for qualification testing and structural health monitoring of COPV composite materials-of-construction, including carbon-epoxy (C/Ep), is discussed. Future work whereby additional information about progressive damage accumulation is extracted using the modal AE signatures, specifically AE event frequency and velocity information, is also discussed, along with the relevance of anticipated findings