Energy absorption capability of composite bolted joints undergoing extended bearing failure

Innovative crashworthiness strategies are needed for future narrow-body composite fuselage aircraft due to limited crash energy absorption capability below the cargo floor. A recently-proposed approach is to use specially-designed “tension absorber” joints which absorb energy through an extended bearing failure process. To explore the design space, experimental tests are performed on pin-loaded joints in a widely-used carbon fibre/epoxy composite, with varying stacking sequence, pin diameter and laminate thickness. A bespoke rig is used to pull the pin completely through the laminate. Performance parameters include ultimate bearing strength, mean crushing stress and mass-specific energy absorption. Three-dimensional computed tomography (3D CT) and scanning electron microscopy are used to examine failure and damage. Diameter-to-thickness ratio is found to be an excellent predictor of energy absorption, with small values giving best results, provided the thickness is sufficient to avoid global bending of the specimen. The use of a well-characterised material and availability of 3D CT data enables the results to be used for validation of analysis tools.