Experimental and numerical analysis of mechanical properties and failure mechanisms of a non-crimp basalt fibre reinforced epoxy composite

Non-crimp fabric (NCF) based composites manufactured using conventional fibres such as E-glass are widely used in structural applications such as turbine rotor blades. However, the anthropogenic environmental effects of utilising these fibres have motivated researchers to look at sustainable alternatives. Basalt being a mineral fibre and having better mechanical properties than E-glass is considered a potential alternative. However, lack of data is still preventing the industry from considering Basalt as a potential competitor for E-glass in structural applications. Additionally, the majority of studies in the literature have focused on analysing mechanical properties of plain-woven fabric-based basalt fibre reinforced composites. Whereas NCF is the most commonly used fabric architecture for fibre reinforced composites used to manufacture structural applications such as wind and tidal turbine blades. There is also a significant gap in literature with regard to analysing the failure mechanisms of NCF basalt epoxy composites subjected to different loading conditions. Therefore, this thesis aims to provide detailed insight regarding the mechanical properties and associated damage mechanisms of a non-crimp basalt fibre reinforced epoxy composite under different loading conditions (ex-situ and in-situ flexure, interlaminar shear and in-plane shear). Novel testing methodologies such as, performing interrupted tests ex-situ have been utilised to provide detailed information regarding the evolution of different failure mechanisms in NCF basalt epoxy composites. Composites are tested both in dry condition and following moisture ageing in seawater and deionised water to investigate the effect of different environments on the material properties, which is relevant to their application in off-shore wind and tidal turbine blades. Finite element models of NCF basalt epoxy composite have been developed for flexural and interlaminar shear loading conditions. Numerical modelling using Abaqus has been carried out, in conjunction with the experiments to determine the dominant failure mechanism as well as to investigate the damage initiating stresses. The study reveals that under flexural and shear loading, fibre/matrix debonding, leading to matrix cracking in the 90° sub-plies is the damage initiating failure mode. Final failure in flexure tests occur due to fibre kinking in 0° sub-plies at the top ply on the compression side. Numerical modelling reveals that matrix cracking in 90° sub-plies is controlled by shear stresses ranging between 35-45 MPa. It is also observed that moisture ageing significantly affects the strength of the composite with failure initiating at a much lower stress level (approx. 20% lower compared to when tested in the dry condition). In-plane shear stiffness of the composite is also significantly affected (approx. 10% lower compared to when tested in dry condition), but no significant effect on the flexural stiffness of the composite is observed.