Study On Elastic-Plastic Finite Element Analysis And Life Prediction For Notched Specimens Under Multiaxial Loading At High Temperature

In this paper, the stress-strain state of GH4169 superalloy under multiaxial proportional loading with constant amplitude was studied. The stress and strain of tubular specimens subjected to proportional loading were analyzed by the elastic-plastic finite element method. The calculated results were verified by the multiaxial proportional loading tests. On the basis of elastic-plastic finite element analysis for tubular specimen, the stress-strain state in the critical position for notched specimen was analyzed and calculated by the proposed finite element model, and then the obtained results were used to predict the multiaxial fatigue life of notched specimens. First, a series of multiaxial fatigue tests were carried out on MTS809 material test system for GH4169 tubular specimens and notched specimens at 650℃. On the basis of the multiaxial fatigue experiments, the characteristics of cyclic stress-strain response and the behaviors of cyclic hardening and softening were studied under multiaxial cyclic loading. The fatigue fracture surfaces of notched specimens subjected to proportional and non-proportional multiaxial loadings were observed and analyzed by the scan electron microscope. According to the observed results of the fatigue fracture surfaces, the mechanisms of fatigue crack initiation and propagation was studied. The results showed that the fractographic behavior of the combined modeⅠ-modelⅡwas mainly shown under multiaxial loading. Then, the stress and strain for tubular specimen subjected to proportional loading were analyzed by 3D elastic-plastic finite element method. The results showed that the calculated stress-strain values by FEM have good agreement with the experimental results, and then the stress-strain state for notched specimen was analyzed and calculated by the proposed finite element model. Last, on the basis of the results of finite element analysis, some multiaxial fatigue models were used to multiaxial fatigue life. The predicted lives were compared with the experimental data. The results of fatigue life prediction showed that a good agreement was demonstrated with experimental data.