Comparison of the mechanical hysteresis of carbon/ceramic-matrix composites with different fiber preforms

The mechanical hysteresis of four ceramic matrix composites with different carbon fiber preforms, i.e. needled C/SiC, 2D C/SiC, 2.5D C/SiC, and 3D C/SiC, was investigated and compared during cyclic reloading-unloading tests. An effective coefficient of the fiber volume fraction in the direction of loading (ECFL) was defined to characterize fiber architectures of the preforms. It is shown that an increase in permanent strain and a decrease in stiffness with the applied stress were strongly affected by the ECFL. The thermal residual stress (TRS) and ultimate tensile strength of the composites are predicted theoretically related to the ECFL, and then validated by experimental results and microstructural observations. The predicted results not only demonstrate good agreement with experimental measurements, but also explain why differences in the composite ECFL result in substantial variations in TRS. (C) 2008 Elsevier Ltd. All rights reserved.