Forming simulations of aligned discontinuous fibre thermoplastic prepreg

: Towards right-first-time sustainable composite manufacturing.

Abstract

This thesis presents the development of a simulation tool for the forming of aligned discontinuous fibre-reinforced composites (ADFRCs), with the aim of eliminating defects and reducing reliance on trial-and-error methods during mould design. The objective is to enable right-first-time, sustainable composite manufacturing. To achieve this, three key directional properties—tensile, shear, and bending—were characterised for a composite comprising poly(L-lactic acid) (PLA) as the matrix and 3 mm long aligned discontinuous carbon fibres. The study focuses on the temperature range between the glass transition temperature (𝑇𝑔) and the melting point (𝑇𝑚), also accounting for the degree of crystallisation of the PLA. To understand the crystallisation behaviour, as well as the 𝑇𝑔 and 𝑇𝑚 of PLA, differential scanning calorimetry (DSC) experiments were conducted. These were complemented by rheological analysis, which investigated the viscosity and storage modulus of the PLA. A micromechanical model was developed to predict the tensile stress response of the composite tape as a function of strain rate, incorporating the viscoelastic behaviour of the PLA matrix and the microstructural features of the tape. A similar modelling approach was applied to shear characterisation, assuming rigid fibres and shear deformation transferred through the matrix under equivalent assumptions. The bending behaviour was primarily derived from the tensile characterisation, with additional optimisation for compressive responses. These characterisations were integrated into a user-defined material subroutine (Vumat) for implementation in Abaqus/Explicit. The simulation framework was validated against experimental data for tensile performance and forming and later refined to incorporate shear and bending responses. The final simulation tool, experimentally validated, is capable of predicting defects, strain distribution, fibre overlap lengths, and thickness variations. It has been successfully employed to manufacture defect-free ADFRC components through right-first time forming experimentally.

Date of Award	30 Sept 2025
Original language	English
Awarding Institution	University of Bristol
Sponsors	The Republic of Turkey Ministry of National Education
Supervisor	Jonathan P Belnoue (Supervisor), Marco L Longana (Supervisor) & Ian Hamerton (Supervisor)