Off-axis damage tolerance of fiber-reinforced composites for aerospace systems

Off-axis strength retention of continuous carbon fiber-reinforced dense ZrB2-based ceramics (C-f/ZrB2) after thermal or indentation damage was evaluated. Thermal damage was in-situ induced and characterized by cyclic dilatometric analysis. Indentation damage was induced through Vickers indentation and then characterized by digital microscopy. The investigation of Vickers imprints suggested that residual stresses promoted the material pileup onto the fibers' plane and the appearance of out-of-plane freed fibers (OFF). On the other hand, thermal damage reduced the residual stresses and left inner freed fibers (IFF) that enhanced the elastic response. Finally, the flexural tests on damaged specimens unexpectedly revealed that C-f/ZrB2 kept its load bearing capability either after thermal or indentation damage (in both cases) and showed damage insensitivity although tested in fully matrix-dominated loading configuration (off-axis configuration).