Abstract
Based on the S-H cavity model theory and the thermodynamic diffusion equation, the high temperature fatigue lifetime equation is deduced, and the influence of stress amplitude and mean stress on fatigue lifetime is quantitatively analyzed. At high temperature of 650°C, according to the test data of fatigue lifetime of GH4133B superalloy under different stress ratios or alternatively at various maximum stress levels, the nonlinear regression analysis method is applied to identify the material parameters in the fatigue lifetime equation, and a 3D Nf-σm-σa curve surface is plotted. The comparison between theoretic fatigue lifetime Nfp and test one Nft indicates that the fatigue lifetime equation derived from the microstructure evolution of metallic materials can accurately predict the fatigue lifetime of GH4133B superalloy under different cyclic loading parameters. Finally, a parameter γ is introduced to characterize the effect of mean stress σm and stress amplitude σa on fatigue lifetime Nf of GH4133B superalloy. It is suggested that the effect of mean stress σm on Nf is larger than that of stress amplitude σa on Nf under the condition of tensile-tensile fatigue loading.
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