Damage mechanism of a carbon fiber ceramic composite during the step-loading indentation and its effect on the mechanical properties

Indentation damage to a carbon fiber silicon carbide composite (C/SiC) was introduced and then investigated using a step-loading method to understand the impact mechanism. Damages at different indentation energies were characterized by thermography, computed tomography, and microscopy. The indentation energy effects on the residual compressive and tensile strengths were compared. The indentation process indicates that below 0.96 J, the linear elastic behavior and the extensively cracking in the SiC matrix mainly take place in the C/SiC composite, above which it turns into the load-bearing, debonding, breaking and pulling out of the fibers. The C/SiC composites thus have dual damage resistances to the indentation loading, which are mean 1544.5 N from the matrix and 1839.8 N from the fibers respectively. It is evaluated that the fibers mainly absorbed more than 70% of the indentation energy, and the matrix, approximately 30%. Visible indentation damage is identified to initiate from around 0.48 J, behaving as the compressive shear failure of the matrix in the front side, and the tensile breaking of the fibers in the back side. Delaminlation occurs always along the interfaces of the compressive and tensile stress states, resulting accordingly in much larger real damage areas than the apparent ones. With increasing indentation energies, the decreasing rate of the compressive strength is nearly four times higher than that of the tensile ones, revealing that the former is more sensitive to the indentation damage than the latter. The indentation-failed composites still retain 77% residual compressive strength (212.5 MPa) and 89% residual tensile strength (169.5 MPa), respectively.