Characterization of Mechanical Properties under Shear Load of a Short-Carbon-Fiber-Reinforced C/SiC Ceramic

The main objective of this work is the evaluation of the mechanical shear properties of a short-carbon-fiber-reinforced ceramic, which shows strong non-homogeneity in its microstructure and anisotropy through different fiber orientations. In this work, the shear modulus (G-modulus) and shear strength of this material were determined with the Iosipescu shear test and the Asymmetric-Four-Point-Bend shear test (AFPB test) at room temperature. Both test methods provide a nearly pure shear stress state in the shear plane and are therefore suitable for determination of the mechanical properties under shear load. Different notch opening angles with θ = 0° or θ = 110° and sample sizes for both methods are discussed. For strain measurement, strain gauge rosettes are applied on two sides of the test specimens. Because of the limited size of basic material, for the Iosipescu test small specimens were bonded onto aluminum tabs, which induced different failure mechanisms. Therefore the Iosipescu results are only valid for determination of shear modulus but not for evaluation of shear strength

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Evaluation of mechanical properties of a dense SiC/SiCN composite produced via PIP process

The material behavior of Polymer Infiltration and Pyrolysis based SiC/SiCN composites is studied and the characteristic thermal and mechanical properties in on- (0/90°) and off-axis (±45°) direction are summarized. The tensile properties are determined at room temperature and 1300 °C. Based on the ratio of Young’s modulus and strength between on- and off-axis loading, a new approach for the classification of Weak Matrix Composites (WMC) and Weak Interface Composites (WIC) is proposed, which seems to be reasonable for various CMCs. Even without fibre coating mechanical behavior of SiC/SiCN is similar to that of WIC. In order to explain this, a microstructure model is developed and confirmed by analysis of fracture surface. The effect of temperature on the tensile properties is investigated through analysis of residual thermal stresses. Even though at 1300 °C the strength is slightly lower, the fracture strain increased significantly from RT to 1300 °C

Characterization and modeling of tensile properties of continuous fiber reinforced C/C-SiC composite at high temperatures

In order to study the effects of temperature on the material behavior of Liquid Silicon Infiltration (LSI) based continuous carbon fiber reinforced silicon carbide (C/C-SiC), the mechanical properties at room temperature (RT) in in-plane and out-of-plane directions are summarized and the tensile properties of C/C-SiC were then determined at high temperature (HT) 1200 °C and 1400 °C under quasi static and compliance loading. The stressstrain response of both HT tests is similar and almost no permanent strain can be observed compared to the RT, which can be explained through the relaxation of residual thermal stresses and the crack distribution under various states. The different fracture mechanisms are confirmed by the analysis of fracture surface. Furthermore, based on the analysis of hysteresis measurements at RT, a modeling approach for the prediction of material behavior at HT has been developed and a good agreement between test and modeling results can be observed