Structural response of a hybrid composite-to-metal bolted connection under uniform pressure loading

This paper presents an experimental investigation of the structural response of a hybrid composite-to-metal bolted joint panel assembly, under uniform pressure loading. The overall objective was to implement a watertight, hybrid joint concept into an existing large-scale four-panel assembly, and test the assembly to failure. The hybrid joint was used to connect the composite panels to steel I-beam members. A description of the panel configuration, the details of the joint, the test system and the testing method are presented. The panels were loaded to a peak pressure of 248 kPa. Strain gages and displacement sensors were mounted on the panels to monitor strains and vertical displacements, respectively. Photogrammetry targets were used to monitor the displacement field. Test results indicated a stable and linear response of the system during the first two loading cycle sets, up to a design pressure of 82.74 kPa. Non-linear behavior of the structure was observed in the load–displacement and load–strain curves during the third cycle set, when loaded to a pressure of 124 kPa. The panel assembly withstood a peak pressure of 248 kPa and watertight integrity of the joint was maintained. Failure initiated at 117 kPa, as delamination at the stiffener/panel interface. This study serves as proof of joint concept, panel design, and demonstration of the fabrication techniques and hydrostatic test method.