Fracture of aluminium-coated carbon fibres

Abstract

A degradation in the ultimate tensile strength (UTS) of aluminium-coated carbon fibres was associated with the formation of a reaction layer of aluminium carbide during annealing treatments ⩾ 475° C for high tensile fibres (HT) and ⩾ 550° C for high modulus fibres (HM). It was established that for a given annealing treatment, the UTS depended on the square root of the original coating thickness and proposed that fracture was controlled by cracks in the aluminium carbide, with a specific surface energy (γ) and intrinsic crack length (c ₀) of 2.33 J m⁻² and ∼ 30 nm for HT fibres, and of 0.64 to 0.77 J m⁻² and ∼ 20 nm for HM fibres.