Hybrid composites based on polyethylene and carbon fibres Part IV Influence of hybrid design on impact strength

Abstract

Hybrid composites possess unique features that can be used to meet different design requirements with respect to strength, stiffness and impact resistance. A key parameter in hybrid composite structures is the arrangement of fibres within the hybrid, as demonstrated by studies on hybrid systems based on carbon, glass or aramid fibres. It was shown that the hybrid design strongly affects a variety of flexural properties such as the modulus [1], strength [2], fracture energy [3-6] and fatigue behaviour [7]. Hybridization of relatively brittle carbon fibres with tough, high-performance polyethylene (HP-PE) fibres has proven to be highly effective in improving the impact properties of carbon fibre-reinforced composites [8-10]. By varying the HP-PE/carbon fibre ratio, laminate design and adhesion level of the HP-PE fibres, impact properties of such hybrid composites can be tailored to a specific application requiring either improved energy absorption or damage tolerance. Previous studies on layered HPPE/carbon hybrids were directed towards optimizing impact properties with respect to improved elastic energy absorption and enhanced damage tolerance [8, 10]. Related studies showed that intermingled hybrids, incorporating HP-PE fibres possessing low levels of adhesion exhibited a strong positive hybrid effect, i.e. a positive deviation from the properties predicted by the rule of mixtures, with reference to the total energy absorption under Charpy impact conditions [9]. These type of hybrids, exhibiting synergistic effects with respect to energy absorption, are quite promising for applications requiring kinetic energy dissipation such as crash-impacts. In this letter the influence of the fibre arrangement within the hybrid on this positive synergistic effect is discussed.