| The purpose of this thesis is to propose an extension of half-cycle theory for predicting fatigue life to include the crack closure effect. The 1 st goal of this study is to examine the convergence of the series expansion. Then, Fatigue life was calculated for the Inconel 718 alloy subject to a specific random fatigue flight environment by using the Ko's closed-form aging theory with and without consideration for crack closure effect. Subsequently, fatigue life was calculated to include crack closure effect over a range of values for the Inconel 718 alloy, from plane stress to plane strain cases. The fatigue prediction of cast AM50 alloy was calculated by using the Ko's closed-form aging theory including crack closure effect to demonstrate that the result of another material can also be accurately obtained. For the comparison purpose, the Wheeler model was applied over a range values for the material parameter of Inconel 718 alloy to prove the accuracy of fatigue life prediction by using the Ko's closed-form aging theory including crack closure effect. According to the results, both the Ko's closed-form theory by including the crack closure effect and the Wheeler model can improve the fatigue life predictions. |
