Characterisation of fibre hybrid thermosetting composites for automotive applications

Abstract

The objective of the research presented in this PhD thesis is to improve the understanding of the failure modes and numerical modelling techniques associated with both interlayer and intralayer fibre hybrid composites and their monolithic constituent composite counterparts, with the overall objective of using the fibre hybrid composites for automotive components. The materials tested, as specified by the funding body Composites Innovation Cluster (Datacomp), were: a plain weave spread tow T700 carbon composite, a non-crimp 0°/90° S2-glass composite, an interlayer fibre hybrid of the two aforementioned monolithic composites, and an intralayer fibre hybrid 2x2 twill weave T700 carbon/Vectran composite, all within an MTM57 epoxy matrix and manufactured by Resin Film Infusion (RFI). Standardised and non-standardised testing was employed to determine the in-plane material properties of each material in tension, compression, and shear, as well as interlaminar fracture toughness in Mode I and Mode II. Subsequently, a novel Compact Tension (CT) specimen geometry was developed to alleviate premature out-of-plane buckling and premature compressive failure. This was imperative in capturing the materials translaminar fracture toughnesses since the monolithic S2-glass composite and the intralayer fibre hybrid T700 carbon/Vectran failed prematurely when utilising typical standard CT test geometries. Once the in-plane material properties, and interlaminar and translaminar fracture toughnesses were measured, an existing energy-based bilinear plane stress traction-separation numerical modelling approach was used to provide insight into the complex failure processes associated with low velocity impacts. The fibre hybrid composites as well as their monolithic glass and carbon fibre composite counterparts were subjected to two discrete impact energy levels and their experimental load response curves and failure modes showed good agreement with the numerical modelling. Finally, a 1:5 reduced scale car bonnet made from the interlayer and intralayer fibre hybrid composites was subjected to low velocity impacts at two discrete energy levels and compared to the same numerical modelling strategy as used with the plate impact study. A novel experimental test rig was developed which allowed for quantifiable boundary conditions to be numerically modelled, presenting good comparison to the impactor tup experimental load response curves as well as two experimental independent strain gauge readings.