In situ characterization of the flexural behavior and failure mechanism of 2D needle-punched carbon/carbon composites by digital image correlation

摘要

Combining the load-displacement curve with the In situ strain field evolution obtained by the digital image correlation (DIC), the flexural behavior and failure mechanism of 2D needle-punched carbon/carbon composites under three-point flexural tests were investigated. The carbon/carbon composites showed a typical pseudoplastic mechanical behavior, and the average flexural strength was 137.0 +/- 15.5 MPa. The microstructures and fracture morphology of composites were examined by optical microscopy and scanning electron microscopy. The results indicated that the crack propagation process was significantly affected by the microstructures of composites, including needled fibers and lamination structures. The position of needled fiber became the strain concentration area, resulting in the initial matrix cracking. Massive fiber pullout and fiber bridging were found at the fracture surface along the crack propagation path, which were the main toughening mechanisms of composites. Considering the stress distribution of three-point flexural tests, the failure process of the needle-punched carbon/carbon composites was clearly distinguished. According to the relationship between the first principal strain (epsilon(1)) and the maximum strains (epsilon(xx), epsilon(yy) and epsilon(xy)) in a typical region of interest, the crack propagation process could be divided into four stages. The results showed the great potential of DIC in the In situ characterization of the composite failure mechanism.