Pre-stressed advanced fibre reinforced composites fabrication and mechanical performance

摘要

Advanced composite materials have high strength-to-weight ratios, corrosionresistance and durability and are extensively used in aerospace, energy and defenceindustries. This research concentrates on minimising the process-induced residualstresses, and improving the fibre alignment of composites by employing a fibre prestressmethodology. A novel flat-bed fibre prestress methodology for autoclave processing of composites was developed. This research investigates the effect of fibre prestress on 1)residual stresses, 2) fibre alignment, 3) static tensile and compression properties and 4)fatigue behaviour of composites.Experimental results show that this prestress methodology, on a 16-ply unidirectional E-glass/913 epoxy composite, reduces the residual strain of the composite from –600 µε toapproximately zero for a prestress of 108 MPa. The strains measured from optical fibresensors were in close agreement with those obtained using strain gauge. The results fromfibre alignment studies showed that fibre prestressing improved the fibre alignment from20% of fibres aligned to 0 ° degree in non-prestressed composites to 75% of fibres alignedto 0 ° degree in 108 MPa prestressed composites.Findings have shown that prestressing is beneficial to the static compressive and tensile performance of composites. The results show that fibre prestressing improves the fatiguelife and resistance to stiffness degradation in the low stress level fatigue region. Also a change in static and fatigue damage mechanism was observed. The improvement in the static and fatigue properties is due to the reduction in residual stresses and fibre waviness.Overall the fibre prestressing methodology enhances the performance of composites byincreasing the resistance to static and fatigue loading. The thesis also suggests that there is an existence of prestress limits to retain optimal material performance.