Damage and toughening mechanisms of carbon fibers reinforced carbon matrix composites

Static mechanical responses of two-dimensionally and three-dimensionally reinforced Carbon/Carbon composites, 2D- and 3D-C/Cs, were compared. Mechanical properties were examined in the present study include tensile, compressive, shear stress-strain, S-S, relations and fracture behavior on the basis of compact tension tests. Compared with 2D-C/Cs, the 3D-C/Cs were shown to possess similar tensile S-S relation, intensively nonlinear shear S-S curves and far notch insensitivity and higher fracture resistance. The shear and fracture resistance differences suggested to be derived from weak fiber/matrix interface, intra-bundle damage through the rich matrix regions and weak interfacial bonding between fiber bundles in 3D-C/Cs. These weak interface characteristics are brought by high value of plane residual stresses caused by three-dimensional fiber constraint of 3D-C/Cs due the mismatch of thermal expansion during the processing.