High Temperature Metal Material Mechanics Behavior Research

The development of human society is based on material as the main indicatorand the metal material always play an important role in this process. With thecontinuous development and innovation of science technology, the property ofmetal materials is required to getting better and better. The mechanicalproperties of metal materials under high temperature is significantly differentfrom those under normal temperature, then how to effectively use this feature orto avoid high-temperature defects makes the study of mechanical behavior ofmetallic materials under high temperature become particularly important.Generally, the structures of engineering are requested to be safe within theelastic range of material. So, the research of thermal stress constitutive relationin elastic stage of metal materials under high temperature is very meaningful.Based on the polynomial representation of tensor function, a completepolynomial thermal stress constitutive equation and strain energy function ofnonlinear isotropic elastic material is proposed with considering the temperaturefactor. It can be widely applied to most of the metal material. As an applicationexample, results are compared with known experimental data for high-temperature metal materials under uniaxial tension and compression of theelastic stage by use of MATLAB software, which shows a good agreement withthe results of the proposed theoretical model.At present, an elastoplastic thermal stress constitutive equation of tensor formhas also didn’t appear. The tensile test and numerical simulation inelastic-plastic range under high temperature are carried out in order to furtherstudy the plastic behavior and performance of metal materials under hightemperature condition,45steel as an example in this text.The high temperature tensile tests of45steel performance study in thetemperature range of600℃~750℃and0.5,0.7,0.8and0.9times the yield loadare carried out. We obtain the stress-strain curve, yield strength and tensilestrength in the case of loading under constant temperature, also the relationship between temperature and strain in the case of heating under constant load. Theresults show that there is a small variation in the mechanical properties of45steel for different test temperature of loading under constant temperature case,which have the same trend with the rising temperature. However, in the case ofheating under constant load, the strain changes quite gently before300℃andincreases gradually over a temperature range from300℃to500℃, then sharplyto necking around550℃.Finally, a thermal-structural coupling numerical simulation has carried out on45steel high temperature tensile tests using the excellent nonlinear analysiscapabilities of ANSYS software. The elastic-plastic stress-strain relations aredefined by using multi-linear isotropic hardening model. Different referencetemperatures of thermal stress analysis are used to calculate, for example, the610℃,660℃and710℃respectively. The temperature and stress field resultsare obtained and they intuitively display the thermal stress distribution andchanges in the stretching process.