3D Characterizations of Pores and Damages in C/SiC Composites by Using X-Ray Computed Tomography

Pores and damages in the bulk of a two-dimensional plain woven C/SiC composite formed by chemical-vapor infiltration process are characterized in 3D by using X-ray Computed Tomography in order to validate the effectivity of X-ray Computed Tomography to establish the relations between pores and damage mechanisms in the following in-situ tests. An undamaged specimen is examined in order to characterize the pores, and a damaged specimen after a bending fatigue test under 500 degrees C is examined for the purpose of the characterization of damages. The morphologies of pores and damages are visualized in 3D through a series of 3D digital image processing and analysis. The pores in the undamaged specimen form a highly interconnected plain networks inside SiC matrix between laminates and even connect through several laminates to form a 3D interconnected network architecture. The SiC matrix enclosing the networks of pores could obstruct the contact between the air in the networks of pores and the fiber tows. However, once they are broken under mechanical loadings, the 3D interconnected network architecture may help the contact of air with fiber tows and thus accelerate the oxidations at high temperature. Fiber breaks and matrix breaks are both identified in the fractured area in the damaged specimen. Delaminations and matrix breaks are also observed in the bulk outside the fracture area. Oxidations of carbon fiber tows are not observed obviously under the current test temperature, i.e. 500 degrees C.