Study On Temperature-dependent Elastic Modulus And Yield Strength Of Metallic Materials And Thermal Shock Resistance Of Single-phase Ceramics

With the rapid development of modern science and technology,the demand for expanding service conditions is increasingly strong,and the high temperature service performance of materials has become a core problem in various fields.A deep understanding of the mechanical properties of materials under high temperature environment is not only a basic research to explore the response and failure mechanism of materials in extreme environment,but also an urgent need for national strategic security and prevention of major disasters.In this paper,theoretical,experimental and numerical simulation methods were used to study the temperature-dependent elastic modulus of metallic material,the temperature-dependent surface tension coefficient of liquid materials,the temperature-dependent yield strength of solid solution strengthening materials,and the thermal shock resistance of single-phase ceramic materials.The main research work is shown as follows:（1）A new temperature-dependent elastic modulus model without arbitrary parameters for metallic bulk materials is developed.The model is capable of predicting the Young’s modulus,elastic stiffness,and shear modulus at different temperatures.The inherent relationships between temperature-dependent elastic modulus,coefficient of expansion,heat capacity（or Debye temperature）,and melting point of metallic material are uncovered by the model.The model also provides a new method to predict elastic moduli:the elastic moduli at extremely high and low temperatures,which are difficult to obtain through experiments,can be predicted by the model with reference of an easy-to-access elastic modulus.Furthermore,the method of studying the temperature-dependent elastic modulus is extended to the theoretical characterization of temperature-dependent surface tension.A temperature-dependent prediction model without arbitrary parameters for the coefficient of surface tension of homogeneous liquid is established and verified by the experimental results of all available fifteen kinds of pure liquids.The model uncovers the inherent relationship between the coefficient of surface tension,boiling point,heat of evaporation,heat capacity,and coefficient of linear expansion.In addition,it can help analyze the variation of coefficient of surface tension with increasing temperature.（2）This study reports new temperature-dependent yield strength models for solid solution strengthening binary and multi-component alloys.The models include the contributions of base metal,solid solution strengthening,and grain boundary strengthening at different temperatures and are verified by experimental results in a wide range of temperature.Based on the temperature-dependent yield strength model for solid solution strengthening binary alloys,the sensitivity of yield strength to lattice misfit are analyzed.It is found not suitable to cursorily estimate the lattice misfit by the atomic radius of solute and solvent.In addition,the variation with temperature of the contribution of each mechanism to the yield strength of solid solution strengthening binary and multi-component alloys are analyzed in this study.The study also provides some useful suggestion to improve the temperature-dependent yield strength of solid solution strengthening alloys in manufacturing.（3）The thermal shock resistance of ceramic materials is studied by means of experiment,theory and numerical simulation.It is found that the mechanical shock which often exists in the common thermal shock test methods has a significant influence on the experimental characterization results of thermal shock resistance of ceramic materials.In this study,a series of experiments are designed and developed to study the effects of mechanical shock on thermal shock behavior of ceramic materials,and the corresponding mechanisms are also analyzed.In addition,a numerical model has been established according to practical applications that ultra-high temperature ceramics are used as parts of the thermal protection system.Taking HfB₂ as an example,the effects of convective heat transfer coefficient,thermal shock initial temperature and external constraints on the thermal shock resistance of ultra-high temperature ceramics under active cooling condition have been studied.The model also considers about the temperature-dependent thermo-physical properties and failure criterion of ultra-high temperature ceramics.