Abstract
Three-dimensional carbon fibre/epoxy resin composites were prepared, which had either three-axis or five-axis carbon fabrics (3D-3A and 3D-5A) in four weave gauges, and were embedded with PTFE film in the fabric structures to initiate various types of microcracks. The flexural fatigue properties of these 3-D composites were studied. The results show that the flexural properties and fatigue life of 3D-3A are higher than those of 3D-5A. Enlarging the weave gauge of 3D-3A and 3D-5A enhances the flexural properties, fatigue life and resistance to fatigue crack growth. The 3D-3A with a weave gauge of less than 5 mm or the 3D-5A with a fatigue stress lower than 140 MPa has a considerably higher ability to resist fatigue in presence of PTFE film. Under 120 MPa stress, both 3D-3A and 3D-5A retain more than 70% residual flexural breaking strength. However, with PTFE film embedding, their stiffness reduces significantly. A crack in 3D-3A grows along the Z-axial bundle, whereas a crack in 3D-5A grows in the X-Y plane. The 45°-axial bundle shows a pull-out phenomenon.
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