In Situ CT Study of Mesoscale Failure onset in Textile Composite Material

The mesoscale failure behaviour of textile Carbon Fibre Reinforced Polymer (CFRP) is investigated using in-situ CT scan. The research focused on the potential of using CT acquired geometries, deformation, and failure information to validate traditional modelling techniques and improve the accuracy of future modelling. Carbon Fibre Reinforced Polymer (CFRP) has been widely used in aerospace, automobile, and sporting industry due to its high strength to weight ratio, high stiffness and resistance to fatigue or corrosion. Textile CFRP is a fabric weaved from fibre bundles. Compared to traditional unidirectional CFRP, textile CFRP is usually easier to handle and to form into complex shapes during manufacturing. Due to the yarn interlacing, textile CFRP is also more stable and damage tolerant. However, the interlacing fibre bundles (yarn) introduced additional layer of complexity when predicting the strength and failure of textile composite parts. The main approaches used in current modelling techniques, assume the textile fabric has a regular and repeating structure, failed to capture the irregularity in mesoscale structure introduced during the manufacturing process. As experimental observation shown, the irregularity in mesoscale structure initiates micro crack and failure and has a considerable influence on the properties and failure behaviour of textile CFRPs. The ability of capturing a textile CFRP meso-structure and reconstructing it for FE modelling improves the accuracy of numerical analyses and result in a more reliable and efficient CFRP structure. This research demonstrated the potential of using computer tomography (CT) to improve the understanding of CFRP mesoscale failure behaviour both numerically and experimentally. A more realistic numerical model was constructed using the geometry extracted from the CT image. The CT image volume was classified based on the tow direction and the material property was adjusted based on the fibre orientation. Irregularities in the specimen could be fully reflected in the finite element model. This improves the ability of predicating the onset and progression of failure of textile CFRP. In-situ CT scan was used to investigate the failure mode and crack propagation in several textile CFRP tensile specimens. An in-situ tensile testing rig was designed and manufactured to allow a reliable CT scan of textile CFRP specimens while under tension. One major challenge identified in mesoscale CFRP study is to have a specimen large enough to encompass complete meso-structures while have sufficient resolution. Tensile specimens with a gauge width of 10mm was found to be large enough while providing a good CT image result when scanned using the lowest voltage of 60 kV with 6 accumulations. This resulted in a CT image resolution of 3.2μm. The CT results showed cracks that were usually not visible under conventional scanning technique. Digital volume correlation (DVC) was used to calculate the 3D displacement field by comparing the pre and peri load CT images, providing a quantitative understanding on the failure process. Strain fields were calculated using the forward difference of the displacement field and were used to validate the result of numerical models. The original contribution of this project is the use of CT scan to improve the procedure of obtaining the numerical and experimental results, thus improve the understanding of textile CFRP failure behaviour. A novel in-situ testing rig and the corresponding specimens were manufactured to allow the observation of textile CFRP failure under load. The novel algorithm developed during the project provided a more detailed and accurate geometry of the specimen and allowed for a more accurate model. These contributes to the significant improvement in the understanding of textile composite failure behaviour, both experimentally and numerically