Design and test of a sandwich T-joint for naval ships

Within the EUCLID project, 'Survivability, Durability and Performance of Naval Composite Structures', one task is to develop improved fiber composite joints for naval ship super structures. One type of joint in such a super structure is a T-joint between sandwich panels. An existing design consists of panels joined by filler and over-laminates of the same thickness as the skin laminates. In a superstructure a T joint may be loaded in tension if an internal blast occurs in two adjacent compartments or by an underwater explosion if two adjacent rooms have no support underneath the separating wall. Improved T-joints have been designed and investigated with focus on improved strength (survivability) and limiting delamination progress in over-laminates. This paper describes the design and test of a sandwich T-joint with reduced weight but with the same or higher strength than the existing design. The lightweight T-joint is designed for sandwich panels with 38 mm thick balsa foam core and 4 mm thick glass fiber/vinylester skin laminates. The panels are joined by filler forming a smooth transition (radius 35 mm) from the T-panel to the base panel, and over-laminated with laminates of 6mm thickness. Tensile (pull-out) tests are performed to load the structures in tension and the strength and failure mode are compared with results from tests on the existing T-joint base design. For the geometries in the present study, an increase of the over-laminate plies resulted in a 13% increase in the failure load.