The effect of specimen geometry upon the parameters that govern the stress transfer (transfer length, interfacial shear strength, positively affected length and stress concentration factor) in a carbon fibre/epoxy composite was examined in detail. Five frequently employed composite geometries were considered: single fibre composite coupons incorporating discontinuous and continuous carbon fibres, multi-fibre composite tapes with a controlled inter-fibre separation, four-ply unidirectional coupons, and, finally, impregnated fibre tows. The chemistry and the curing characteristics of the matrix were kept unaltered regardless of specimen geometry. All fibre stress measurements were conducted by means of Raman microscopy.The experimental results showed that the transfer length, positively affected length (PAL) and the interfacial shear stress obtained at the location of a fibre fracture are not considerably affected by specimen geometry. In contrast, the residual fibre stress of the unloaded specimens and the stress concentration factors obtained in fibres adjacent to a fibre fracture site were found to be significantly dependent upon fibre volume fraction and specimen geometry. Figure 2. Schematic of the single (a) continuous and (b) discontinuous fibre coupon geometries.

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