A novel delamination defects designed for understanding mechanical degradation in a laminated C/SiC composites

Delamination defects are especially easy to be formed in the processing of a C/SiC composites laminated layer by layer of carbon cloths (2D C/SiCs), causing a significant effect on the mechanical properties and failure modes. A novel method was presented, by embedding polytetrafluoroethylene paper into the 2D carbon fiber cloths and then automatically produce delamination defect once high temperature fabrication of SiC matrix, to tentatively understand mechanical degradation behaviors of laminated 2D C/SiC composites with different sizes of delamination defects (R-d, thus was defined as ratio of delamination defects width D to gauge length L). For tension, the tensile strength was first subjected to a sudden decrease with a slight reduction in elastic modulus when delamination defects occurred. With further increase of R-d, the tensile strength and elastic modulus do not decrease sharply but tend to be stable. For compression, the compressive strength had continuous and nearly linear decrease from original 345.41 MPa to final 275.72 MPa with relatively large variation in compressive modulus when the R-d increased. It can be also observed from the macro fractured sections that the failure modes of 2D C/SiC composites under tension and compression are completely different. The compression was bearded mainly by the matrix while the tension was bearded mainly by the fibers, leading to a result that the width of the delamination defects in laminated 2D C/SiC composites propagated more easily under the compression than under the tension. (C) 2018 Elsevier B.V. All rights reserved.