A Study of Friction in Composite Materials Forming

The composite materials industry is rapidly growing in response to the need to conserve energy and reduce emissions by reducing weight - particularly in transport sectors such as automotive and aerospace. Many composite parts are produced using a forming process (especially those with irregular shapes). In such processes, it is essential that the final component meets the design specifications and is free from wrinkles, voids and unwanted thickness variations. At present, however, the only way to ensure success is to carry out costly trial and error type testing in advance. Since the component geometries can change on a regular basis, the forming industry would like to have a predictive tool which can predict outcomes and can therefore be used to set up the process optimally to produce the required part. A crucial job of any predictive model is to predict the forming forces. One of the important forces acting during the forming process is friction. To correctly predict friction forces in forming, an underlying physical understanding of the frictional behaviour must be developed and the frictional response using relevant fabric and resin types must be characterised. Some friction tests have been carried out previously, but these have often been idealised or on small contact areas which are not representative. This project will design experiments to give representative friction force measurements for different fabric and resin systems under a wide range of boundary conditions. A database of results will be established giving the friction response to changes in the various variables affecting friction such as resin type, fabric type, temperature, normal load and shear rate etc. Both tool-ply and ply-ply friction will be investigated. An ABAQUS user subroutine based on the experimental database will then be developed to model the contact behaviour. This predictive capability for friction in the forming process will then be added to presently available forming models within our group to improve their forming predictions. Finally, the model will be validated by comparing predictions with test results for some case-study type forming examples. The project will produce a valuable physical description of friction in forming, a database of relevant results and a predictive subroutine which can be added to existing models to increase their accuracy. The result will be a significant step in the direction of accurate predictive forming models which have the potential to reduce costs considerably and to optimise products. A final aspect of the project will be to look at viable approaches to reducing friction during the forming process.