Study On Temperature/Pressure-dependent Yield Strength And Shear Modulus And Theoretical Characterization Methods Of Metallic Materials

With the rapid development of high-tech fields such as aviation,aerospace,national defense,energy,the application of metallic materials in extreme environments of high temperature and high pressure has become more and more extensive.In order to ensure the safety and reliability of metallic materials in actual engineering application,it is necessary to fully understand the yield strength and shear modulus of metallic materials,both of which are very sensitive to temperature and pressure.The research on the yield strength and shear modulus of metallic materials under different temperatures/pressures has become one of the current active research fields.Therefore,to study the control mechanisms of the temperature/pressure-dependent yield strength and shear modulus of metallic materials and their evolution with temperature/pressure,and to establish theoretical characterization models of temperature/pressure-dependent yield strength and shear modulus can provide technical support for the development of traditional metallic materials and the search for new high-performance and high temperature/high pressure resistant materials,which has important scientific significance and engineering application value.This thesis establishes a temperature-dependent yield strength theoretical model for high-strength steel materials that consider the effect of grain boundary sliding.Besides,considering the coupling effects of temperature and pressure,temperature and pressure dependence of shear modulus and yield strength theoretical characterization models are also developed.The specific research work is shown as follows:(1)Based on the Force-Heat Equivalence Energy Density Principle,a temperature dependent grain boundary sliding energy model is established for high-strength steel.And then on the basis of this model,a temperature-dependent yield strength model considering the effect of grain boundary sliding is developed.The model predicted results are compared with the available experimental data of 18 kinds of high-strength steels and these prediction results of the steel structure design standards including fitting parameters,such as American Society of Civil Engineering(ASCE),Australian Standard(AS4100),American Institute of Steel Construction(AISC)and Eurocode 3(EC3).It shows that the predictions by our model are in better agreement with the experimental results.The established temperature-dependent yield strength model provides theoretical support for the safe application of high-strength steel at different temperatures.(2)Based on the Force-Heat Equivalence Energy Density Principle,these models of shear modulus and yield strength that can characterize the coupling effect of temperature and pressure are established by modifying the linear temperature term of the classic Steinberg Cochran Guinan(SCG)model.The predicted results are in good agreement with the available experimental data.By comparison with the SCG model and the SCG models modified by Li and Yang which all contain fitting parameters.Our model without any fitting parameters,making it more convenient for engineering applications.Our models provide a simple,convenient and effective method to forecast temperature and pressure dependence of shear modulus and yield strength at different pressure,avoiding a great deal of high-temperature and high-pressure tests.