Steel Foil Reinforced Thin Ply Composites: Experimental and Numerical Study of Strength, Plasticity and Ply Size Effects

Abstract

Steel foil carbon fibre reinforced polymer composite (CFK) laminates, (St-CFK) were studied for improvement of the bearing properties. The bearing load was found to double with 25 % ply substitution in the St-CFK composite and optical analysis shows extensive plastic deformation in the joint, hence producing a structural joining method that may fail in a safe and predictable manner. Moreover, extremely thin carbon fibre plies are known to offer an improved onset of damage and less accumulation of damage prior to the ultimate failure. The hybridisation of composite materials with steel foils proved to be a convenient solution to significantly increase the structural load transfer in bolted joints, without the drawback of a higher laminate thickness. In this work, the effects of ply thickness in St-CFK hybrid composite joints are studied in order to better understand the progression of damage. Both CFK and Hybrid laminates of ply thicknesses 0.3 or 0.03 mm were manufactured and tested using tension, open hole tension (Fig. 1) and bearing strength. The different ply thicknesses show significantly different damage progression and maximum loads. A finite element model was also generated in Abaqus 6.10-1 (Fig. 2). A user subroutine is used to degrade the damaged material properties of the 3D solid model, according to the Hashin failure criterion. Cohesive contacts are used to model the delamination between plies, as well as the in-plane inter-fibre failure provided efficient and relatively realistic recreation of the joint behaviour that was observed experimentally (Fig.3).