Tensile Creep Behavior Of A 3D-C/SiC Composite At Elevated Temperature

The tensile creep and rupture behavior of a Three-Dimensional C/SiC composite has been investigated in this thesis. The Three-dimensional C/SiC composite, containing 40 Vol% T300 carbon fiber, was fabricated by Chemical Vapor Infiltration. Tensile creep and rupture tests have been performed under vacuum for temperatures ranging from 1100ε to 1500ε and for stresses from 180MPa to 290MPa.The study of the macroscopic creep of the Three-Dimensional C/SiC has revealed a good creep resistance compared to other ceramic matrix composites with the steady-state strain rate in the 10-8~ 10-9s-1 range.Throughout the experiments, there is no accelerated creep regime, which is in accordance with most of the ceramic matrix composite. It has been discovered that the deformation in the primary creep regime can well described byeqution: ε -ε0 = Atm, Moreover, the eqution: ε = Aσn exp(-Q/RT) can be used tointerpret phenomenally the relationship between the steady-state creep rate and stress, temperature.The empirical relation, the Monkman-Grant relationship and the Larson-Miller parameter can be used for creep rupture life prediction for the Three-Dimensional C/SiC composite,The damage can be accumulated during the tensile creep tests at elevated temperature. A suitable damage parameter is needed to fully describe the process. The variation of fractional electrical resistance increase and the variation of elastic module were adopted as damage parameter to identify the tendency of damage evolution.The limits of classical creep mechanics were evidenced when it wan applied to analysis the mechanics of the Three-Dimensional C/SiC composite, which is seriously inhomogeneous and anisotropic.The rupture of ceramic matrix composite submitted to a constant load, at elevated temperature, generally results from the interaction of time-dependent damage mechanisms together with creep of the constituents (ie. Fiber, matrix and/orinterphase ). At the macroscopic scale, it can be considered that we are in presence of a damage accumulation via matrix microcracking coupled with interfacial sliding phenomenon which may be settled according to a slow crack growth mechanism. Once matrix microcracking has reached the saturation state, microcracking opening due to a time-dependent mechanism, which is encountered at the fiber/matrix interface, has been evidenced. Decohesion and sliding are enhanced thanks to the anisotropy if the graphite sheets at the interphase/matrix interface. It seemed that the fiber and the matrix did not creep themselves in the range of the testing stress and temperature, so the matrix microcracking and interfacial sliding will be the main contributer to the macroscopic deformation of the Three-Dimensional C/SiC composite.