An incremental form of constitutive model is proposed for shape memory alloys using the modified strain based on experimental results and the finite element analysis, taking into account of the laminar microstructure, the thickness of martensite phase lamina and the interaction between the two phases. The pseudoelastisity of NiTi shape memory alloy micro-tube subjected to pure tension and pure torsion are analyzed and compared with the experimental results respectively. It can be seen that the pseudoelastic behavior, especially the stress drop during tension processes, can be well described with the proposed model.

Due to the complexity of service environment of thermal protection system on the aerocraft, the thermal shock resistance (TSR) of ultra-high-temperature ceramics (UHTCs), which are used as thermal protection materials, is no longer the material itself’s. Based on the restrictions of current experiments and the lack of theories, hafnium diboride (HfB2) is used to study the effects of the external constraint conditions and different thermal environment on the TSR of the UHTC in detail. The effects of different initial temperature, different external constraint conditions, and temperature rising rate on the TSR of the UHTCs through numerical simulation are discussed in detail in this study. This study can provide a more intuitively visual understanding of the evolution of the TSR of UHTCs during actual causative conditions.

In this paper, based on the study of effects of various physical mechanisms on the fracture strength of porous ceramic materials, a thermo-damage strength theoretical model applied to each stage of temperature is established. Using the model, the sensitivities of fracture strength to relevant parameters and their variation with temperature are studied in detail. The results show that under low temperature the strength is sensitive to the changes of porosity, pore size and pore shape factor, while under high temperature the effects of porosity, pore size and pore shape factor on the strength compared to the temperature are negligible, yet the strength is very sensitive to the Young’s modulus, thus the Young’s modulus is the dominant of strength under high temperature. This study will provide a theoretical basis and guidance to the design and application of porous ceramic materials.