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Study Of Mechanical Behavior And Application Of Single Crystal Superalloy Base On Finite Deformation Crystallographic Theory

Posted on:2004-03-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:J S WanFull Text:PDF
GTID:1101360122961027Subject:Solid mechanics
Abstract/Summary:PDF Full Text Request
Development and application of Nickel-base single crystal superalloy are to improve the performance, durability and reliability of military, commercial aero-engines. In developed country, Nickel-base single crystal superalloy have been widely used as turbine blades and vanes of aero-engines and ground gas-turbine engines because their high-temperature properties are superior to those of polycrystalline nickel-base superalloy. In China, some aero-engines start to use single crystal turbine blades in practice. However, the anisotropic mechanical properties of the single crystal material makes a great deal of difficulties on the development and the application of the single crystal blade, which is a challenge for the engineering application of the single crystal superalloy, potential exploited and theoretic bases of the application.From the views of mechanics and metallurgy, the thesis studies the strength and life of single crystal blades taking into consideration of the anisotropic behavior, microstructure and macroscopic behavior by the theoretic analysis, numerical calculations and experiments. They are as follows:1. Based on finite deformation crystallographic constitutive model, Tangent stiffness type methods for rate dependent was employed, A rate-dependent constitutive model for single crystals was implemented into ABAQUS, a commercial finite element program that is capable of modeling large deformation and large strains. The correlation was established between resolved Shear Stress, strain and macroscopic stress, strain by orientation tensor.2. The equation between modulus and orientation was deduced. Systematic tensile experiments for DD3 single crystal alloy with different orientation under different temperatures and different tensile rates or under different temperatures and different stress levels were carried out. The effects of orientation, temperature, strain rate on Yield strength, ultimate tensile strength, elongation percentage, percentage reduction in area were revealed. The effects of strain rate on Yield strength, ultimate tensile strength was also showed. The tension/compression asymmetrical result of Nickel-base single crystal superalloy was discussed and the asymmetrical mechanism of asymmetrical flow behavior was investigated, a set of procedures for analyzing tension/compression flow was provided.3. The creep constitutive model of Nickel-base single crystal superalloy was presented, which based on finite deformation crystallographic constitutive model. The longitudinal and transverse orientation dependence of the rupture life was studied. The influence of orientation on rupture life was got. The lattice rotation equation was deduced result from continuum media method, and then the concept of rotation was used to explain orientation dependence. Based on the meso-and microstructure change and damage characteristic of Nickel-base single crystal superalloy, one parameter and two parameters creep damage constitutive equation and the life predictive model were suggested. In order to facilitate engineering application, a simple exponential form life predictive model was presented.4. The low cycle fatigue behavior of round bar and notch bar of [001]oriented single crystal of the Nickel-base single crystal superalloy DD3 was investigated at the temperature of 620℃. With the results of experimental data and FEM, The life predictive model of LCF for multiaxial stress states was presented. Based on test results, a unified life model was developed, in which the influence of mechanical fatigue, creep, thermal fatigue and theinteraction each other were considered. With the help of SEM, the failure mechanism of fatigue and creep was discussed.5. Three kinds of three-point-bend (TPB) were designed to studied fracture toughness and crack growth rate of single crystal DD3, Bicrystal 1, whose pre-crack is along the grain boundary and the applied load parallels to pre-crack direction, the other TPB specimen is named Bicrystal 2, whose the pre-crack is perpendicu...
Keywords/Search Tags:Nickel-base single crystal superalloy, turbine blade, finite deformation, crystallographic constitutive model, finite element, tensile experiment, tension/compression asymmetry, creep life, multiaxial stress states, low cycle life, unified model
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