Study On Multiaxial Constitutive Model Of DD6 Alloy

DD6 alloy is a second-generation single-crystal superalloy independently developed by China.It has been gradually used in high-temperature parts of aerospace engines due to its high yield stress,high melting point and anti-fatigue at high temperature.In practical applications,the materials are often in complex load environment.Therefore,the mechanical behavior of DD6 alloy under different loading conditions and its related shaping constitutive model were studied.The main research work and conclusions are as follows:1.The uniaxial stretching of DD6 alloy at 600 °C and the high-temperature low-cycle fatigue test with strain levels of 0.75%,0.85% and 1% were carried out.The stress-strain curves,cyclic stress response curves and fatigue life were obtained.The analysis results show that DD6 alloy exhibits strain hardening characteristics under uniaxial tension;at low strain level,the material basically exhibits cyclic stability.As the strain level increases,the cyclic hardening characteristics of the material become more obvious;At each strain level,the cycle exhibits varying degrees of asymmetry.2.The experimental study on the different equivalent strain levels of multi-axis ratio of DD6 alloy at 600 °C was carried out,and the stress-strain curve and fatigue life of the material were obtained.The analysis results show that the mechanical properties of the material are more complicated under multi-axial loading.Under the same strain level,the torsion cycle hysteresis loop area of the material is larger than that of the tensile cycle,and the cyclic hysteresis characteristics are more obvious.3.The microstructures of alloy DD6 were observed by SEM.Based on the experimental results,three micro-geometric characteristic parameters were proposed and characterized.Micro-structure characteristics,statistical analysis of its distribution law to establish representative volume units for material constitutive model research4.Based on the crystal shape theory,the constitutive model is established from the two different scales of cell scale and RVE scale for numerical simulation.Using the crystal homogenization constitutive theory,the stress-strain relationship of DD6 alloy under uniaxial tension and circulation was simulated by using the original cell as the object;the microscopic two-phase structure and the dislocation evolution law of the material were introduced,and the RVE model was used to simulate the simulation.The uniaxial mechanical properties of the material were compared and the difference between the two simulation methods and the experimental values was compared.5.Based on B-P theory,a multi-axis proportional cyclic shaping constitutive model was established from the macroscopic scale,and ABAQUS numerical simulation technology was used to simulate the high temperature fatigue mechanical behavior of DD6 alloy under different load conditions at 600 °C.The prediction results and experiments were carried out.The results are in good agreement,verifying the validity of the constitutive model and numerical simulation techniques.