Fatigue Life Prediction And Reliability Analysis Of Notched Components Based On Field Intensity Approach

Due to the requirements of function or assembly of components in engineering practice,complex geometric discontinuities(such as holes,keys,grooves,etc.)are normally designed in engineering components,these geometric discontinuities are collectively called notches in fatigue analysis.When the notched component is subjected to cyclic loads,notches will raise local stress concentration and complex multiaxial stress state,which can easily cause cracks initiation and propagation until it fails.Moreover,the size effect and uncertainties also have shown a significant impact on the fatigue failure of notched structures.Therefore,valid methods considering the both notch and size effects and uncertainties in fatigue design and assessment are still lacking and highly desirable.Accordingly,this thesis surveys and sorts out the influencing factors in notch fatigue analysis and the existing approaches for predicting fatigue life of notch components.By combining with fatigue tests and elasto-plastic FE analysis,variety methods for notch fatigue analysis and life prediction are established.This thesis focuses on the follow works:(1)Proposed an effective damage zone determination method considering geometric size effect based on stress field intensity(SFI)method and improved the weight function.On this basis,a framework for notch fatigue analysis considering notch and geometric size effects is established,and the models are verified and compared by the fatigue data of En3 B and Al 2024-T351 notched components.The results indicated that the prediction of the model based on the proposed SFI method is the best.(2)Analyzed the problems existing in the application of the weakest-link theory to notched components.Through coupling the effective damage zone and weight function of the SFI approach,a generalized weakest-link model considering notch effect and statistical size effect is proposed.The model is verified and compared with the experimental data of GH4169,TC4 notched specimens and a turbine blade disk.Results showed that the median curve and probability scattering bands predicted by the new model are in good agreement with the experimental results.(3)The energy field intensity(EFI)approach modified by coupling the concept of characteristic total strain energy density and the notch radius.The effects of fatigue life and size effects on the effective damage zone are quantified.By combining the improved EFI model with Weibull distribution,a P-W-N curves based on two-dimensional Weibull distribution is proposed,and the transfer of fatigue life distribution between different sizes is established.