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.

@en

The rheological properties of epoxy matrices and adhesives during cure are modelled in this work. Three epoxy-amine systems, designed for different applications with distinct curing behaviours, were investigated. Curing times ranged from a few seconds to upwards of 220 min depending on the cure temperature and formulation of the epoxy. The presented time-dependent model adds an exponential fit to Kiuna-Fontana's master curve of dimensionless viscosity, as well as a weighting function for the overall fit, aiming at creating a more accurate model. A major benefit of the approach is that time consuming determination of the cure kinetics using differential scanning calorimetry (DSC) is not required. The developed model was also used to predict the viscosity of a typical, non-isothermal curing cycle for composite manufacturing. It proved to correlate well with both isothermal and non-isothermal processes, demonstrating that it is particularly useful model to describe viscosity for flow modelling or process optimisation.

@en

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.@en