Influence of layup, stacking sequence and loading rate on energy absorption of tension-absorber joints
Jazib Hassan, Ronan M. O’Higgins, Thomas Feser, Matthias Waimer, C.T. McCarthy, Nathalie Toso, M.A. McCarthy
Abstract
“Tension-absorber” joints are bolted joints designed to absorb energy in a survivable crash landing, through an extended version of bearing failure. They have been proposed for use in future transport aircraft narrow-body composite fuselages. Herein, the influence of layup (percentage of each ply orientation), stacking sequence (exact location of each ply) and loading rate, on energy absorption is examined. Quasi-static and dynamic (3 m/s) tests are performed on pin-loaded IM7/8552 carbon-fibre/epoxy laminates. Seven layups and 11 stacking sequences are tested, with key variables being the percentage of 0° plies (from 12.5% to 62.5%), the position of the 0° plies, and the changes in orientation at ply interfaces. Performance measures include ultimate bearing strength (UBS), mass-specific energy absorption (SEA) and crush load efficiency (CLE). Computed tomography is used to examine damage progression in the quasi-static tests. It is found that the most important factor in maximising SEA is having small changes in orientation at ply interfaces. This is even more important than 0° content. A laminate with only 12.5% 0° plies, performed remarkably well due to its low changes in ply orientation. Laminates with a high SEA tend to have a low UBS. Highest UBS was for quasi-isotropic laminates. Increased loading rate results in increased UBS but decreased SEA. The results allow selection of a stacking sequence with a desired combination of UBS and SEA, and provide a valuable database for validation of composites damage models.