Mechanical response and failure of 3D MWK carbon/epoxy composites at cryogenic temperature

Abstract

Static tensile and bending experiments are conducted on 3D MWK carbon/epoxy composites with two types of fiber architecture at room and cryogenic temperature (low as −196 ℃). Macro-Fracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that tensile stress vs. strain curves have linear elastic feature up to failure; while the load-deflection curves for composites with large fiber orientation angle have pronounced nonlinear and failure in steps. Meanwhile, tensile and bending properties at liquid nitrogen temperature have been improved significantly. Moreover, the properties can be affected greatly by the fiber architecture and these decrease with increasing fiber orientation angle at room and cryogenic temperatures. The results also show the damage and failure patterns of composites vary with the fiber architecture and temperature. The main failure for material A is 0 ° fibers fracture and matrix cracking. The failure mechanism for material B is the delamination, 90 °/+45 °/−45 ° fiber/matrix interface debonding and fibers tearing, as well as 0 ° fibers’ breakage. At cryogenic temperature, the matrix is solidified and the interfacial adhesion between fibers and matrix is enhanced significantly. However, the brittle failure becomes more obvious, more microcracks propagate and interpenetrate.