UBC Theses and Dissertations
The effect of impactor mass and velocity on the structural response and damage modes of non-crimp and 2D braided CFRP panels Nesbitt, Scott Jonathan
The market demand for reduced operating costs and carbon emissions, together with competition and regulatory changes are primary drivers for improving vehicle efficiency. One method of improving efficiency is lightweighting, where composite materials can play a role due to their high specific stiffness and strength. Aircraft manufacturers have made use of these properties for many years, but they have the benefit of longer design programs (4-8 years) and production run lifetimes (20-30 years) to make extensive prototype testing feasible and economical. Automotive manufacturers do not have such long timescales or price-inelastic customers and must largely rely on computer simulation to design fit-for-purpose components in compressed timelines. Unfortunately, accurate structural simulation of composite materials is a challenge, owing to various path dependent failure modes and the influence of manufacturing processes on the material properties throughout the part, among other complexities. Consequently, new composite product design still relies heavily on physical testing. The aim of this thesis is to assist with improving modelling capabilities by providing insight into how damage develops in composite materials of interest to the automotive industry, through instrumented testing and damage characterization. These tests range from quasi-static deflection to high-velocity transverse impact. The materials investigated are non-crimp fabric (NCF) and 2D braid carbon fibre reinforced epoxy because they show promise for economical, high-rate manufacturing. It is found that the 2D braid does not show a delamination test rate sensitivity, owing to the stiffness mismatch being constrained within a single layer that can arrest cracks with its intra-ply fibres. The result is more localized fragmentation in the 2D braid material. Conversely, NCF materials delaminate substantially more under high-velocity impact conditions due to large shear stresses early on, combined with large stiffness mismatches between plies and the lack of crack arresting features. Damage resistance and permanent dent depth decrease substantially under high-velocity impact in both materials; making the damage easier to create and less detectable with surface-only inspection methods. A numerical model of an impacted NCF panel is also developed and compared to the experimental results, showing good agreement with the structural response (force-displacement), but under-prediction of delamination area.
Item Citations and Data
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