Manufacturing, testing, modelling and fractography of thermoplastic composites for the automotive industry

Abstract

Considerable advances in mechanical properties have been achieved in thermoplastic composites in the aerospace industry and several high-performance vehicles in the auto-motive industry. However today, original equipment manufacturers (OEMs) are seeking to implement this technology on a wider scale. By establishing a materials database, with the help of computer-aided engineering (CAE), virtual prototyping will be optimised. In this way, processing times could be shortened, and production volume could be increased. The study aims to characterise high-performance non-crimp fabric (NCF) of carbon fibre rein-forced thermoplastic (CFRTP) composites for the UK automotive industry. This work presents the characterisation of a range of in-plane and out-of-plane mechan-ical properties of two NCF CFRTP systems, (i) T700 carbon/polyamide 6.6 (PA6.6) and (ii) T700 carbon/polyphenylene sulphide (PPS), discusses their behaviour in those loading conditions and compares them with equivalent thermosetting counterparts. This includes original experimental observations which is complemented by novel numerical and ana-lytical work. In this way, the automotive industry would receive invaluable information re-garding the basic mechanical properties of thermoplastic composites and be able to make informed decision on whether these two CFRTP systems could provide alternative material solutions to their ongoing design and manufacturing process. The mechanical properties measured through experimental observations comprised of tensile, compressive, in-plane shear, mode I and mode II interlaminar fracture toughness and translaminar fracture toughness. Further laboratory work includes the characterisation of the materials’ dynamic behaviour under tension using Split Hopkinson bar, low-velocity impact (LVI) and high-velocity impact (HVI). ii Numerical models using energy-based finite element formulation have been developed for predicting the mechanical response of the thermoplastic systems under; (i) compact ten-sion (CT), (ii) low-velocity impact (LVI) and (iii) high-velocity impact (HVI). The finite element (FE) models developed using LS-DYNA® have been calibrated and validated against the experimental data gathered throughout the study. In summary, the thesis discusses the potential of two CFRTP material systems being used for automotive applications with respect to their performance and behaviour in a range of loading conditions described above. Additionally, the work also reports on the effects of through-thickness stitching in NCF composites as well as the influence of the stitching material. In short, the novelty of this thesis with respect to the two biaxial NCF CFRTP material sys-tems includes; the measurement of their mode I and mode II interlaminar fracture tough-ness, the development of a bespoke compact tension (CT) sample and the measurement of their intralaminar/translaminar fracture toughness, the analysis of their dynamic tensile behaviour using split pressure Hopkinson bar (at varying strain rates) and experimental and numerical analysis of their LVI and HVI behaviour.