A neutron diffraction study of load partitioning in continuous Ti/SiC composites

Neutron diffraction measurements are described of the internal strain response of Ti-6Al-4V/ 35 vol.% SiC continuous fibre composites to loading axial and transverse to the fibre alignment direction. In the as-fabricated condition large thermal residual strCTains are observed, being equivalent to average axial fibre and matrix stresses of -840 and 450 MPa, respectively. As one might expect, upon loading there are marked differences in load sharing according to whether the fibres are parallel or perpendicular to the loading direction. In the former case, load is transferred towards the fibres; a process which is accelerated when the matrix deforms plastically, while in the latter case, load is transferred to the fibres only at very low loads. At higher loads, the process reverses with the reinforcement shedding load back into the matrix. The measurements suggest that this is caused by matrix/fibre interface failure at transverse loads of around 300 MPa. Simple calculations suggest that this would require a non-zero matrix/fibre normal interface strength of around 100 MPa. The measured thermal and load-induced strains are interpreted in the light of Eshelby-based models throughout. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.