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.

The increasing use of carbon fibre reinforced polymer (CFRP) composites in aviation and automotive industries has led to the adoption of automated production methods such as pultrusion or resin transfer moulding (RTM) for cost reduction in the production lightweight structures. These processes however, offer limited freedom to locally reinforce structures. This paper describes an approach to utilise a basic geometry for several similar parts and add local reinforcement patches only in regions of load introduction or high local stress. The approach offers the benefit of being able to combine automated production methods with unprecedented design freedom. The specific bearing performance for three different local reinforcement using (1) add-on CFRP patches, (2) surface mounted steel foils and (3) steel foil interleaving in replacement of 90° plies with foils of the same thickness as the CFRP plies (0.125 mm) is compared by double lap bearing tests. The bearing strength improves with the addition of patches, for surface mounted steel foils, more so as CFRP co-cured patches, and most as an interleaved configuration. Quasi ductile failure of the bearing joints was maintained due to additional plasticity of the steel foils, producing a joint that fails safely while enhancing the bearing strength. When examining the hybrid laminates, all samples buckled and failed in bearing compression/shear. Brooming was evident on the compressive side of the hole where the bolt indented the laminate. Indentation led to shear kink bands along the washer supported region and appear as large compression/shear damage above the washer confined region of the laminate. When normalised by weight, the three approaches show similar bearing performance. However, each approach has specific advantages with regards to processing, electrolytic potential, or absolute bearing strength, depending on the design of the load introduction.

The objective was to study the bearing properties of steel foil and carbon fibre reinforced polymer composite (St-CFRP) laminates. Extremely thin carbon fibre plies offer an improved onset of damage and less accumulation of damage prior to ultimate failure; ply level hybridisation can enhance the bearing properties. Both effects were studied to better understand the progression of damage and effect of ply thickness. Both CFRP and Hybrid laminates of ply thicknesses 0.3 and 0.03 mm were manufactured and tested. The thin CFRP laminate has 31% higher tensile strength and a reduction in open hole strength of 28 % due to lack of delamination, critical load reached across the 0° plies more or less instantaneously. The lower delamination tendency of the thin ply composites was reflected in the open hole tensile measurements, where, the suppression of delamination resulted in higher notch sensitivity (2.26 versus 1.25). Hybridisation reduced the effects whilst increasing the open hole strength of the composite laminate further. When the bearing stress was studied, the thin CFRP laminate was observed to increase the bearing stress by 28 %. The hybrid laminates show small differences in the achieved maximum bearing stresses (circa 1,100 MPa - double that of the thick CFRP laminate), although the observed failure modes remain very different: delamination and buckling versus brittle failure. Optical analysis showed extensive plastic deformation in the joint, with evidence of good adhesion between the steel foils and thin CFRP plies. Plastic failure of the bearing joint was maintained due to the steel foils, producing a joint that may fail safely. A user subroutine was used to degrade the damaged material properties of the 3D solid model according to the Hashin failure criterion. The developed finite element models were able to recreate the observed experimental failure modes.