Analysis of pull-out and failure of unidirectional bundles in a laminated carbon/carbon composite

The carbon/carbon composites for braking applications, processed by Messier Bugatti, Division Carbone Industrie (Villeurbanne) are laminates of [0/60/−60]n stacking, needled in the through-thickness direction. The unidirectional plies are made of adjacent meshes of square cross-section which exhibit some porosity between them because of the CVI processing route. The goal of the present paper is the study of the fracture behaviour of an individual mesh, and the analysis of the interfacial properties between the mesh and its surroundings. Tensile tests have been performed on special specimens where the mesh, embedded in the composite bulk over a given embedded length, can be loaded. For a long embedded length (d > 3.6 mm), the mesh is broken and the ultimate stress is 260±80 MPa. For a shorter embedded length, the mesh debonds first with a mean interfacial shear stress of 18±8 MPa. The post-debonding extraction is controlled by friction, starting with an interfacial shear stress of 8±3 MPa. The pull-out curves are analysed and modelled by using the Amontons–Coulomb law.