Design of new composite crash absorbers stitched by natural fibres to improve effective crack growth

Advance Composite Materials have found various applications due to their unique properties over the past years. Properties such as high specific strength and stiffness, corrosion resistance and fatigue resistance that can be adjusted to specific requirements have made these materials as one of the main candidate considered during design process. The high energy absorbing capabilities of FRP composite materials is one of the main factors in their application in automotive and aerospace structures. They also provide other functional and economic benefits such as enhanced strength, durability, weight reduction and hence lower fuel consumption. The brittle nature of most composites accompanying other forms of energy absorption mechanisms such as fibre breakage, matrix cracking, deboning at the fibre-matrix interface and especially plies delaminations which play important roles on progressive failure mode and energy absorption capability of composite structures. Delamination which is known as principle mode of failure of layered composites due to separation along the interfaces of layers is one of the main concerns in designing of composite structures. This factor plays an important role on progressive failure mode and energy absorption capability of composite structures. Delamination can occur due to various reasons such as impact, imperfection in manufacturing, high stress concentration, environmental effects and post-processing. In this project an advanced manufacturing methods will be applied to stitch carbon-fibre composite testing specimens using sustainable natural flax fibres. The natural fibres running through the thickness of laminated composite structures will increase the resistance to crack propagation and consequently the energy absorption capability of composite absorbers. Natural flax fibres have the main advantage over the synthetic fibres (e.g. carbon and glass) of providing both resistance and progressive failure (effective crack growth resistance) in the wall of composite box absorbers. Progressive failure can provide high energy absorption in a controllable behaviour which reduces the main injuries and death during a crash event