Affordable Discontinuous Carbon Composites for Structural Automotive Applications

Carbon fibre composites offer the potential to significantly reduce vehicle weight, and thereby reduce emissions and fuel consumption. However, current manufacturing processes for these advanced materials are labour intensive, costly and produce high levels of waste. Aston Martin has pioneered a highly automated preforming process which has demonstrated high performance levels in semi-structural applications in its DBS models. During the course of the project, Aston Martin and the University of Nottingham will develop a holistic system of design, process modelling and manufacturing tools to increase the performance levels of these materials such that they can be exploited in structural applications to reduce vehicle mass and increase safety.
The mechanical properties of carbon fibre composite materials produced by the Aston Martin process are strongly dependent on fibre architecture and orientation, fibre volume fraction and matrix properties. In the project an extensive test programme will characterise this range of material properties to give a data library to facilitate efficient design. The mechanical properties of discontinuous carbon fibre preforming (DCFP) based parts will be investigated. The processing properties (compaction and permeability) of the preforms will be examined, to enable reliable process models to be derived. The effect of a toughened resin on the mechanical performance will also be assessed. Two candidate fibre architectures will be tested using both resin transfer moulding (RTM) and vacuum infusion (VI). Aligned fibre versions will be characterised and a new alignment process investigated to potentially double the mechanical properties in a direction of interest without negatively affecting the fibre deposition rate. The project will study the applicability of this unique fibre architecture on advanced design and computational analysis techniques used to optimise structural composites. A design procedure, based on an existing approach will be developed to suit discontinuous meso-scale materials.
The performance of the fibre chopping and placement system will be characterised using a laboratory–scale system at the University of Nottingham, based on the study of the primary variables of Tool Centre Point (TCP) height above preform screen, fibre feed velocity, tow size and fibre length. The influence of these factors on spray cone size and shape, position of spray cone relative to projected TCP and the orientation of fibres will be investigated. A process model will be developed to use this data and to capture the kinematics of the fibre as it is chopped, sprayed and deposited on the tool, coupled to the robot trajectory control program, to accurately predict the location of fibre tows in a finished preform.
An extensive study of adhesive bonding will be undertaken. Two-part (2K) adhesives will be characterised for use with carbon composite / carbon composite bonding and carbon composite / aluminium bonding. Factors such as tow size, fibre length, substrate thickness and bond dimensions (bond width, overlap and gap) will be investigated. Factors affecting bond strength in fibre architectures with varying properties through the thickness and stress concentrations on the surface will be investigated and fracture mechanics employed to study joint failure characteristics for improved FEA of the adhesive and substrate as a system.
A new composite manufacturing process will be developed to address the long manufacturing times encountered with conventional structural composite processes. The process is particularly suited to the use of C2F3P (Carbon Fibre Ford Programmable Preform Process) preforms. A comprehensive plaque moulding programme will be used to assess different fibre packages and preform process parameters to optimise the final moulded properties. Surrogate parts will be used to demonstrate process feasibility with real part geometries.
A composite-intensive body concept will be developed, based around the package and structural load case requirements of an existing Aston Martin VH platform vehicle. Carry-over elements will include wheel envelopes, powertrain, electrical and chassis components as well as occupant package space and interior hardware. This concept will then be developed further using Finite Element Analysis techniques, including topographical and topological optimisation, in order to optimise stiffness and crash performance while minimising weight. Combining the understanding gained in preforming, moulding and joining with that gained in the original body concept design, a further body concept study will be carried out which will include component manufacturing feasibility, assembly and sub-assembly feasibility and joint feasibility.
Various aspects of the new moulding process will be studied using existing process models and Computer Aided Engineering (CAE) techniques.