Controlled deposition of density defects for understanding mechanical reduction on 2D C/SiC composites

Continuous carbon fiber reinforced silicon carbide matrix composites (C/SiCs) have been widely used in aeronautic and astronautic fields because of their more attractive high temperature properties with less structural weight. However, density defects (DD) with randomness and unpredictability will have a serious impact on the mechanical properties of the laminated C/SiC composites (2D C/SiCs). A novel method was presented, by masking graphite-papers with different sizes on the surface of the ground C/SiC composite plates and then automatically produced various size low density region to tentatively imitate the DD once high temperature fabrication of SiC matrix. The mechanical reduction on 2D C/SiCs with different size DD (R_dd, thus was defined as ratio of DD width D to whole sample length L) was investigated subsequently. Results show that, tensile strength of the C/SiCs continuously decreased from original 241.7 MPa to final 212.2 MPa when the R_dd below 30%. There trended to stable tendency above 88.8% of original strength with further increase of the R_dd. Meanwhile, compressive strength was subjected to a larger decrease from original 280.3 MPa to final 232.2 MPa and then tended to be constant at 82.2% of original strength when the R_dd further increased. The compressive strength decreased to a greater extent and tended to stabilize earlier as the R_dd increased. It pointed out that the DD caused higher sensitivity to the compressive strength of the C/SiCs than to the tensile strength. In addition, as the R_dd increased, both tensile and compressive elastic modulus decreased to the nearly same extent, eventually falling to 83.25% of the initial value, indicating that the increased DD fewly further reduced the stiffness.