Advances in composites cracking principles
Professor Anthony Kinloch FREng FRS, Imperial College London, UK
Impact of CFRP composites
Professor John Dear, Imperial College London, UK
Experimental and theoretical modelling studies on the behaviour of continuous carbon-fibre/polymer matrix composites subjected to a relatively low velocity or high-velocity impact, using a rigid, metallic impactor. Drop-weight and gas-gun tests are employed to undertake the low-velocity and high-velocity impact experiments, respectively. The carbon fibre composites are based upon a thermoplastic poly (ether-ether ketone) matrix (termed CF/PEEK) or a thermoset toughened-epoxy matrix (termed CF/Epoxy). The results clearly reveal that the CF/PEEK composites exhibit the better impact performance. A three-dimensional (3-D) Finite Element Analysis (FEA) model incorporating an elastic-plastic (EP) damage model is developed to simulate the impact response of carbon-fibre reinforced-plastic (CFRP) composites. To validate the predictive capability of the model, experimental results are obtained from relatively low-velocity impact tests on CFRP plates employing either a matrix of a thermoplastic polymer, ie poly(ether-ether ketone), or a thermosetting epoxy polymer. The developed 3-D EP model is shown to model successfully the experimentally-measured impact behaviour of the CFRP composites.
Computational modelling of CFRP composites for crashworthiness assessment
Professor Brian Falzon, Queen’s University Belfast, UK
The airframes of the latest generation of wide-body passenger aircraft are primarily made from CFRP composites and estimated to be around 20% lighter than their aluminium counterpart, delivering a commensurate reduction in fuel consumption. As the industry transitions towards zero-emissions flight, further emphasis is being placed on reducing structural weight. A similar challenge faces the automotive industry where the comparatively heavier electric powertrain, compared to an internal combustion engine powertrain, is driving major lightweighting research and development programmes.
The aerospace and automotive industries have been at the forefront of incorporating computational modelling to reduce the cost of product development and certification. The use of composites has brought with it a new set of challenges in developing reliable and robust simulation tools. Modelling the energy absorbing capacity of composite structures undergoing crushing, is particularly challenging.
This paper provides an overview of recent developments in the computational modelling of composite crushing. Numerical strategies to enhance accuracy and robustness are presented. The fidelity of the numerical solution is highly dependent on the reliability of the material data generated from appropriate material characterisation tests. Not all such tests conform to an agreed standard and the testing at different strain rates presents additional complexity. Approaches for scaling up the computational models are also discussed.
Reinforcing polymers with low dimensional nanocarbons
Professor Ian Kinloch, University of Manchester, UK
Graphene, given its excellent intrinsic properties, should be an ideal reinforcement for stiffening, strengthening and toughening polymeric matrices. However, the reported performance of graphene reinforced elastomers, thermoplastics and thermosets is found to vary significantly in the literature. This talk will explore the challenge in realising the promise of graphene, and hence by extension other nanomaterials, through the characterisation and testing of model polymer composite systems, measuring interfacial micromechanics using Raman spectroscopy and analytical models. In particular, the roles of graphene morphology and dispersion and the nature of the graphene-polymer interface will be discussed.
Discussion contribution – Fracture and fatigue delamination propagation in DCB specimens: comparison of two material systems
Professor Leslie Banks-Sills, Tel Aviv University, Israel
Double cantilever beam (DCB) specimens composed of carbon fibre reinforced polymer laminate composites were tested. Two material systems were investigated. In the first, the specimens were fabricated from 15 plies of a plain woven prepreg (G0814/913) arranged in a multi-directional (MD) layup. The plies alternated with yarn in the 0°/90°- directions and +45°/-45°- directions with the delamination between these two ply types. For the second material type, the specimens were fabricated from 19 plies with the delamination between a unidirectional fabric and a woven ply with yarn in the +45°/-45°- directions. The remainder of the plies were woven, with yarn alternating between the 0°/90° and +45°/-45°- directions. This laminate was produced by means of a wet-layup.
Fracture toughness resistance curves, as well as fatigue delamination propagation properties were determined. A master curve based on the Hartman-Schijve approach to fatigue was found for each material system. It was seen that fatigue delamination propagation in the wet-layup is faster than that in the prepreg.
Discussion contribution – Viscoelastic matrix of natural composites
Professor Stanislav Gorb, Kiel University, Germany
Natural fibrous composites including wood, bone, skin, insect cuticle, etc are supplemented by the matrix composed (depending on particular biological material) of proteins, lipids, lignin. The matrix of biological composites is often hydrated and has tight bond to the fibres (and that is why it has strong adhesive properties) and viscoelastic behaviour. In this presentation, a short overview about matrices of different biological composites will be provided and more detailed information on propolis, which is a sticky substance used by bees to seal their hive and protect the colony against pathogens will be discussed.