Nominal Stress Approach For Life Prediction Of Notched Members Under Vibration Loading

For engineering structures of aerospace and transportation which bear vibration loading, fatigue failure is one of the main failure types. The stress concentration at notch root is critical in anti-fatigue design of structure. Thus the study of vibration fatigue life for notch components has important theoretical significance and practical value.The frequency domain analysis of vibration fatigue has been reviewed systematically in this thesis. Two dynamic stress concentration factors were defined in this thesis. The static, modal, frequency response and random vibration analysis of notch components were accomplished. Then the definition and calculation formula of dynamic stress concentration factor were proposed according to the peak of power spectral density at the most dangerous point. The definition and calculation formula of the mean square stress concentration factor were proposed based on the root mean square of stress of hot point. Two examples were carried out and the results proved that these formulas could describe the stress concentration of notch components under vibration load conditions well.A nominal stress approach was presented to predict the vibration fatigue life of notched components in this thesis. Based on the basic mechanism of fatigue, the distribution characteristics of stress and stress mean square value around notch of groove and notched plates were studied. Considering distribution characteristics of stress mean square value in dangerous region around the notch, the formulas for notch fatigue factor under different distribution characteristics were given separately using mean stress model. Consequently the nominal stress approach for life prediction of notched components under vibration loading was obtained. Through two typical examples, it can be shown that the proposed method in this thesis was competent enough to predict the vibration fatigue life of notched components.