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Heterogeneous fibre microstructures and their influence on failure
Author(s) -
ZYWICZ E.,
KINNEY J. H.,
SATTLER M. L.,
BREUNIG T. M.,
NICHOLS M. C.
Publication year - 1993
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1993.tb03301.x
Subject(s) - materials science , composite material , silicon carbide , microstructure , core (optical fiber) , fracture (geology) , composite number , radius , planar , phase (matter) , fiber , chemistry , computer graphics (images) , computer security , organic chemistry , computer science
SUMMARY A detailed microscopic, experimental and micromechanical evaluation of fibre damage initiation in a unidirectional aluminium matrix‐silicon carbide fibre (SCS‐8 TM ) composite has been performed for a monotonic load sequence. The salient fibre features include a 33‐μm‐diameter monofilament turbostratic carbon (C) core, a ∼ 1·5‐μm pyrolytic C layer, an interior sheath of β‐phase silicon carbide (SiC) crystallites imbedded in an amorphous C matrix, and an exterior sheath of radially orientated β‐SiC. Quantitative microscopy shows that the interior sheath's surplus C varies smoothly from ∼ 35% by volume near the core to zero at the mid‐radius. The multi‐phase structure of the fibre produces an internal mechanical stiffness that increases with distance from the core, and thus peak stresses result in the exterior sheath. X‐ray tomographic microscopy (XTM) reveals that cores fracture randomly, without failure of the surrounding SiC, at stress levels above half the ultimate strength of the composite. Three‐dimensional XTM reconstructions show planar, non‐planar and spiral cracks in the failed fibre, suggesting multiple and competing initiation mechanisms. Qualitative fracture assessments suggest that flaws near the C core grow outward in a curved manner through the SiC–C and planar beyond the mid‐radius, whereas cracks originating near the fibre–matrix interface favour planar trajectories inward across the whole fibre.