Influence of layup, stacking sequence and loading rate on energy absorption of tension-absorber joints

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 mode