Investigation of geometrical and composite material parameters for tension-absorbing bolted joints

In the event of an aircraft crash landing, the fuselage cross-section tends to ovalise. This leads to tension loading of the passenger and cargo floor cross-beams. In past research activities, this has been identified as an opportunity to absorb energy, through a novel design of the frame to cross-beam attachments [1]. These specialised attachments are referred to as tension-absorbing joints. They are designed to protect the bolt from early failure and provide guidance for it to push through, and crush, the composite adherends over a considerable distance, leading to a substantial amount of energy absorption. In the present work, material and geometrical parameters of these joints are investigated experimentally to provide data for a design database. A simplified version of the joint is tested, in which a pin is pulled through a 2 mm thick composite laminate using a specialised experimental rig. The bearing strength and energy absorption capabilities are investigated under quasi-static loading, for 4 mm and 12 mm diameter pins and three different stacking sequences. Two different specimen widths are employed to determine the extent of damage progression towards the specimen edge. Digital Image Correlation (DIC) is used to measure the pin displacement. It is found that symmetric layups with a repeating unit of [45/ 45/90/0] inhibit off-axis pin movement, providing for a consistent test, and that the wider specimen is required to avoid the damage reaching all the way to the specimen edge. For both pin diameters, an interspersed stacking sequence results in higher values of peak load, mean crushing load and specific energy absorption than a blocked layup