Study On Elastic-Plastic Finite Element Analysis And Life Prediction For Smooth Specimens Under Variable Amplitude Multiaxial Loading

In this paper, the stress-strain state of nickel-based superalloy GH4169 under variable amplitude uniaxial / multiaxial nonproportional loading was investigated The stress and strain of smooth thin tubular specimens subjected to variable amplitude uniaxial / multiaxial nonproportional loading were analyzed by the elastic-plastic finite element method. The calculated results were compared and verified with the experimental results. On the basis of the finite element analysis, the finite element data were used to calculate multiaxial damage with accumulative damage theory ,and to predict multiaxial fatigue life by the critical plane approach. A modified multiaxial life prediction approach was proposed.Firstly, a series of variable amplitude fatigue experiments were carried out on MTS809 material test system for GH4169 smooth thin tubular specimens at high temperature. On the basis of the fatigue experiments, the hardening and softening characteristics of cyclic stress-strain response were studied under uniaxial / multiaxial cyclic loading. The fatigue fracture surfaces of the specimens subjected to variable amplitude loadings were observed and analyzed by the Hi-scope advanced KH-3000 microscope, and the fatigue crack initiation and propagation was studied.Then, the stress and strain of the smooth thin tubular specimens subjected to variable amplitude uniaxial / multiaxial nonproportional loading were analyzed by the 3D elastic-plastic finite element method. The results showed that the calculated stress-strain values by FEM have a good agreement with the experimental results. Therefore, it is suitable that the fatigue behavior for smooth thin tubular specimens subjected to variable amplitude uniaxial / multiaxial nonproportional loading was studied by the 3D elastic-plastic finite element method.Last, on the basis of the results of finite element analysis, the critical plane approach and accumulative damage theory were used to predict the fatigue life and a modified multiaxial fatigue life prediction approach was proposed in this paper. The predicted lives were compared with the experimental data. The results showed that the modified approach can predict preferably the fatigue life of the smooth thin tubular specimens subjected to variable amplitude uniaxial / multiaxial nonproportional loading.