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

Within the EUCLID project, 'Survivability, Durability and Performance of Naval Composite Structures', one task is to develop improved fibre 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 overlaminates of the same thickness as the skin laminates.

Various improved T-joints have been designed and investigated. Some with focus on improved strength (survivability), and others with focus on reduced weight. 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 60 mm thick PVC foam core and 4 rum thick glass fibre/vinyl ester skin laminates. The panels are joined by use of filler and two triangular PVC foam fillets (core triangles). A method for a finite element (FE) parameter study is developed and used for selection of a promising (strong) configuration of the T-joint.

Tensile (pull-out) tests are performed to load the core triangles and filler in tension and the strength and failure mode are compared both with the FE modelling and results from tests on the existing T-joint design. The numerical simulations are used to perform a comparison of stresses from different T-joint configurations along a pathway 0.5 mm from the border in the filler and 1 mm inside the remaining parts - core triangle, base panel core, etc.

This is found to be a comprehensive way to compare many different configurations. The base angle of the core triangle is the most important geometry parameter of the joint, and tensile tests show very good agreement with the numerical predictions. The lightweight T-joint has 20% higher strength than the existing design, and the weight is only about 40% of that of the existing design. (c) 2004 Elsevier Ltd.

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