Composites processing and characterisation

What is composites processing and characterisation?

Knowledge of material microstructures and processing characteristics enables enhanced and novel approaches to be developed for manufacturing composite components. Select from the options below for an overview of work undertaken in ACCIS under this theme.

Reinforcement deformation

Academic leads:Prof. Kevin Potter, Prof. Stephen Hallett, Dr Dmitry Ivanov

drape imageThe way in which reinforcements conform to a mould is critically important with regard to the costs of manufacture, the fibre orientations and ultimate performance of the composite structures and the development of a range of defect types. We are studying the detailed deformation characteristics of the various reinforcement materials we use with regard to both in-plane and out of plane deformations, and developing robust tools that can be utilised in design. The understanding of reinforcement deformations is also vitally important in the development of novel preforming processes such as dry tow placement and in studies of defects and how residual stresses develop during the manufacturing processes.

Find out more >>

Drape modelling

Academic leads: Prof. Kevin Potter, Prof. Stephen Hallett

Virtual Fabric Placement (VFP) is a kinematic drape modelling tool being developed to give designers of composite components the ability to lay-up a virtual ply or stack of plies onto a virtual tool before a tool is fabricated. By providing this ability, the designer will be able to design not only the component itself, but also the lay-up sequence required to produce that component. The virtual fabric placement tool can also be used to support the development of robotic lay-up of woven fabrics. For highly accurate and realistic modelling of the drape of fabric, new models are being developed for explicit finite element software. This is being applied to multi-layer fabric forming and a range of textile preforms including non-crimp fabrics and 3D woven material.

Find out more >>

Residual stresses and distortion

Academic leads: Prof. Kevin Potter, Prof. Martyn Pavier, Prof. Michael Wisnom

U channel imageResearch is investigating the distortions that arise during high temperature cure of composite structures due to different mechanisms such as material anisotropy, cure shrinkage, tool-part interaction and material variability. Our industrial partners are interested in distortions in components such as rotorblades, wing spars and engine nacelle structures. Work is also being undertaken to extend the deep hole drilling technique to composites. This has been successfully developed to allow the residual stresses in laminated plates up to 22mm thick to be evaluated.

Defects

Academic leads: Prof. Stephen Hallett, Prof. Kevin Potter, Dr Dmitry Ivanov

 Quality control is an essential part of any manufacturing operation. This includes the identification and sentencing of defects that are found to occur. Our work aims to better understand the origins of these defects through fundamental research into the mechanisms that lead to their formation. For example, consolidation of plies leads to a change in thickness, which in turn can lead to ply movement and formation of out-of-plane wrinkles. Tool-ply interaction can cause defects to form as pre-preg material moves across the surface. Novel constitutive models have been developed for pre-preg material in its uncured state, leading to accurate prediction of consolidation. When combined with cure kinetics models, these can be used to predict the full manufacturing cycle and the onset of defect formation.

Resin Transfer Molding process improvement

Academic lead: Prof. Kevin Potter

RTM Material and Process Improvement imageIn order to understand the Resin Transfer Molding (RTM) process as applied to real components we are studying the internal fibre architecture, the resin and binder distribution, the type and incidence of defects within the parts, the sources of defects in the manufacturing process, the likely effects on performance of those defects and approaches to improved processing and performance. Techniques such as CAT scanning can show the internal structure and the use of fluorescent resins (right hand image) can help identify near-surface effects.

Recycling

Academic lead: Prof. Kevin Potter

recycling imageCurrent composites manufacturing techniques lead to the production of significant amounts of waste prepreg material. This adds to the cost of production, and must be disposed of as active waste to special landfill sites. Processes are being identified by which the maximum value can be extracted from the waste prepreg, ideally by direct reprocessing into added value components. At the same time the overall economics and marketing issues are also under consideration.

Ultrasonic arrays for composite characterisation

Academic leads: Prof Robert SmithProf. Paul Wilcox, Prof. Bruce Drinkwater, Dr Anthony Croxford

ultrasonic arrays for composites characterisation imageUltrasonic array transducers are increasingly widely used in Non-Destructive Testing (NDT). They have obvious advantages when used simply to emulate inspections performed with conventional transducers such as increased inspection speed and flexibility. More importantly, an array enables the ultrasonic wavefield to be controlled in ways that could not be physically realised with a single-element transducer. The inherent anisotropy and multi-scale heterogeneity of composite materials presents acute challenges for conventional ultrasonic NDT. For this reason, current inspections are generally based on unfocused normal incidence ultrasound and are limited to detecting in-plane delaminations. However, an array enables the angle-dependent ultrasonic velocity in composite material to be accommodated hence opening up the possibility of higher-resolution focused images to detect more subtle defects, such as resin-rich regions, voids, ply-drops and fibre waviness.

Further information: Ultrasonics and Non-destructive Testing (NDT) Group

3D Non-destructive characterisation and NDT-based performance modelling

Academic leads: Prof Robert A Smith, Prof Stephen Hallett

‌‌‌Detailed 3D non-destructive characterisation of the material properties of composites will enable production-process verification and increase confidence in conformance to design, thereby underpinning more efficient design strategies. This team of 15 staff and students is developing methods for inverting data from ultrasonic, eddy-current and X-ray CT methods to produce 3D maps of ply-drops, fibre-tow orientation, out-of-plane wrinkling, in-plane waviness, and porosity. They are also using these maps to create 3D finite-element analysis models to determine the performance of the as-manufactured components including features such as deviations in fibre alignment. ‌

Further information: Ultrasonics and Non-destructive Testing (NDT) Group

Aligned short fibre composites

Academic leads: Prof. Kevin Potter, Prof. Michael Wisnom

aligned short fibre composites imageHigh performance composites normally fail suddenly and catastrophically, which is an undesirable characteristic for many structural applications. In order to overcome this issue and obtain ductility or pseudo-ductility of composites, as one of approaches, a lab-scale aligned discontinuous fibre prepregging rig with the HiPerDiF (High Performance Discontinuous Fibre) method has been developed. Since aligned discontinuous fibre composites with shorter length than the critical fibre length exhibit ductile properties as predicted in modelling work, the new rig allows a range of further interesting studies as a key technology to investigate new ductile composite materials.

Edit this page