Analysis of roll forming continuous fibre reinforced thermoplastic composite sheets

Abstract

Roll forming is a rapid, cost effective forming process that is suitable for exploiting many of the advantages inherent to continuous fibre-reinforced thermoplastic sheet materials. A limited understanding of the material behaviour, coupled with the complexity of the forming operation are two major obstacles that must be overcome if the process is to be commercially realised. The first part of this study looks at the shear deformation of continuous fibre-reinforced thermoplastic composites using a novel vee-bending device. The results of a set of experiments have been interpreted within the framework of a theoretical model which is based on an idealised fibre reinforced material. The material investigated, is found to behave in a non-linear fashion exhibiting behaviour typical of shear thinning polymers. This behaviour is determined for both the longitudinal and transverse viscosities and is studied over a variety of forming temperatures and shear rates.The computational framework for analysing continuous fibre reinforced thermoplastic sheets in a steady state deformation process has also been developed. The problem has been formulated using a Lagrangian approach where the governing equations of stress and strain are developed in terms of the undeformed sheet. The formulation leads to a unique description of strain rate which is independent of time but can be conveniently expressed in terms of higher order spatial derivatives. The governing equations have been implemented into a large strain finite element analysis program and used to analyse two steady state forming problems: roll bending and roll forming. Although a number of difficulties were encountered, the results of the analysis have gone some way towards demonstrating the suitability of the methods developed.Finally, an experimental analysis of roll forming continuous fibre reinforced thermoplastic sheets has also been undertaken in an attempt to understand the fundamental forming mechanisms and deformation characteristics of the process. The deformation has been characterised using a surface grid strain technique. The dominant mode of deformation is observed to be that of in-plane shear. The conformance of parts to their intended geometry has also been studied using experimental and numerical methods.