Abstract
The effect of ply thickness on the notch sensitivity and bearing properties on carbon fibre reinforced polymer composites and their hybrid laminates with steel foils were studied. Laminates with ply thicknesses of 0.3 mm and 0.03 mm comprising of CFRP and hybrid laminates were manufactured and characterized using tension, open hole tension and double lap bearing tests. A 25% ply substitution was found to double the bearing load with extensive plastic deformation in the joint while maintaining high stress and maintaining constant cross-sectional thickness in the laminate. With a good agreement between the finite element predicted values and failure behaviour, the damage initiation and progression behaviour could be observed experimentally. We numerically captured (i) rapid failure of 0° plies in the thin ply CFRP hybrid and (ii) continuous delamination with significant plastic deformation for the thick ply CFRP hybrid. The numerical results significantly reduce future experimental work when designing hybrid laminates and could allow the laminate lay-up to be tailored for load cases. Both the experiments and numerical models underline the distinct size effects occurring with respect to the ply thicknesses when hybridising a very ductile metal with a brittle yet strong composite material.
Highlights
Aerospace structures are typically composed of carbon fibrereinforced thermosetting polymers (CFRP) to reduce weight and reduce emissions during operation [1]
Steel foils have become an attractive alternative because half of the metal volume is needed compared to titanium foils in order to achieve the same bearing strength at lower material cost
Steel foil hybridisation further increased the tensile strength to 994 MPa for the Thin_Hybrid and 942 MPa for the Thick_Hybrid, showing a significant improvement in comparison to the Thick_CFRP of 70%
Summary
Aerospace structures are typically composed of carbon fibrereinforced thermosetting polymers (CFRP) to reduce weight and reduce emissions during operation [1]. The high anisotropy of CFRP require diverse and complex layups, which are designed depending on the load case of the structure and usually exhibit a multi-directional fibre directions To achieve these orientations in a cost effective manner, automated manufacturing methods such as tape laying, pultrusion or resin transfer moulding (RTM) are used to build the laminates and to create sub-components that are joined together [2]. Studer et al showed that co-curing of doublers allow for an increase in the local bearing strength without the addition of substantial weight to the structure [3] The drawback of this method is the increased load path eccentricity, which requires longer bolts and larger metallic fittings and introduces secondary bending. Steel foil hybridisation has shown to improve the bearing strength of CFRP parts [6,7,8,9]
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