Damage propagation in carbon/silicon carbide composites during tensile tests under the SEM
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A study has been made of the evolution of damage during monotonic and cyclic tensile tests conducted in situ in a scanning electron microscope on a 2.5D carbon fibre/silicon carbide matrix composite. Tests were carried out on composite specimens and the damage evolution was observed in the lateral section, using a gold square mesh deposited on the surface. Owing to the mismatch of the thermal expansion coefficients of the constituents, the initial composite already contains matrix microcracks. Cracking was observed in the transverse and longitudinal directions according to the load. This cracking consists of the growth of the pre-existing cracks, due to the thermal misfit, and the initiation of cracks in previously undamaged zones. The complex architecture, and specifically the yarn weave, induce rotation of individual fibres or bundles, which leads also to a large opening of the longitudinal cracks. Moreover, sliding at the fibre/matrix interface or at the interfaces with adjacent fibres has been pointed out, from the opening of the transverse cracks and with the help of the mesh. These mechanisms, as in other composites, could be the main origin of tensile cyclic behaviour due to a wear phenomenon in the interfacial regions.
KeywordsCarbide Tensile Test Damage Evolution Composite Specimen Transverse Crack
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