The EPSRC-funded High Performance Ductile Composite Technologies (HiPerDuCT) programme grant (a collaboration between The Composites Centre at Imperial College London and the Advanced Composites Centre for Innovation and Science at the University of Bristol) aims to develop composite systems with a ductile or pseudo-ductile response, while maintaining good strength and stiffness.
One example of the work underway in the Department of Aeronautics is the development of a wavy ply sandwich panel consisting of composite skins and light crushable foam core. The aim is to achieve large extensions under tensile loading by straightening of the load-carrying skins as the core crushes. Following preliminary assessment of potential configurations using simple analytical equations, the tensile response of wavy-ply sandwich structures was in investigated using detailed Finite Element (FE) simulations.
One configuration was manufactured using machined foam cells and wavy metallic moulds. Tension testing demonstrated that a yielding-like stress strain response was achieved.
The measured stress-strain response showed good agreement with the FE predictions.
Multiple impact performance of composite fuselage panels
This research is investigating the post-impact behaviour of composite fuselage panels subjected to multi-site impacts. The research, being conducted within the EU-funded project SARISTU, involves both experimental exploration and finite element simulations.
Large curved stiffened panels (1.2 m x 0.8 m) are being subjected to sequential drop-weight impacts at two locations previously determined to be critical in FE simulations. After assessment of the impact damage each panel is subjected to a highly instrumented compression test to failure.
An existing damage model, developed in the Department of Aeronautics for laminated composites and implemented into Abaqus, is being used to simulate the impact and CAI performance of the composite panels. The modelling approach yields predictions which are in good agreement with both the impact damage and the subsequent compression performance.
Composites with stiffness control and shape memory capabilities
Two types of hybrid composites exhibiting controllable stiffness have been developed in research in the departments of Aeronautic and Chemical Engineering. One type consists of carbon fibre thermoset laminates containing thermoplastic interleaf layers and another consists of thermoplastic coated carbon fibres in a thermoset matrix. In both types, it is the loss in shear stiffness of the thermoplastic at elevated temperature which results in the loss in flexural stiffness of the composite. Experiments on a polystyrene-interleaved carbon fibre reinforced epoxy hybrid composite have shown that reductions of over 90% in flexural stiffness are possible when the hybrid is heated. The interleaved composite also exhibits a shape memory effect because the carbon epoxy layers remain elastic during the high temperature deformation. Research is being conducted to further develop and investigate these hybrid composites which may find applications in deployable and adaptive structures.
Video showing the deployment process of a simple assembly of cross ply interleaved laminates. View the video.