A Thermodynamic Strength Theoretical Model to Explain and Predict Pseudo-Ductility Behavior of SiC_f/SiC Composite Material

In order to explain and predict the pseudo-ductility behavior and mechanical properties of SiCf/SiC composite material, a thermodynamic strength theoretical model based on fracture mechanics and thermodynamic method has been established. Compared with other theoretical models, the model proposed in this investigation unifies different cracks and defects based on energy method. Meanwhile, the stress-strain behavior of materials can be obtained with as few parameters as possible. Compared with previous experimental data, the correctness of this theoretical model has been verified. Some key material properties, such as elastic modulus, proportional limit stress (PLS) and yield stress (YS), have been investigated by calculating based on the theoretical model. The effect of the initial matrix porosity and the material properties of the matrix and fiber have been investigated. Results show that PLS and YS are almost not influenced by initial matrix porosity and can be seen as intrinsic parameters. Elastic modulus of the SiC reinforced fiber and the matrix can also affect material properties. Compared with the SiC matrix, PLS of the SiCf/SiC composite material is more sensitive to changes in elastic modulus of the SiC reinforced fiber. However, the improvement of elastic modulus and shear modulus of the SiCf/SiC composite material is much more difficult. For this purpose, the elastic modulus of both the SiC reinforced fiber and the matrix need to be enhanced. Results and conclusions in this investigation can provide guidance for predicting material properties of SiCf/SiC composite material and preparation in industry.