| Summary: | 博士 === 國立清華大學 === 動力機械學系 === 83 === The fatigue lives for notched specimens under multiaxial
loading were investigated in this study. Three topics were
included: crack initiation life prediction for notched
specimens under fully-reversed biaxial loading, the crack
initiation life prediction for notched specimens under biaxial
non-proportional loading paths with mean strain effect, and two-
level cumulative fatigue behavior for notched specimens under
different biaxial loading mode sequences. In the correlation
the crack initiation lives, local strain approach was used to
find the local stress/strain states. In using local strain
approach, Neuber''s estimation and elastic- plastic finite
element method were employed. After obtaining the local stress/
strain state, the prediction models for multiaxial fatigue
lives were used to correlate the experimental results with
reference data for smooth specimens. Lohr-Ellison model was
shown to give correlation between the fatigue lives with
reference fatigue data for smooth specimens. In the study of
mean strain effect, the prediction models were extended by
considering the stress effect. The predicted results by using
these models were also compared and discussed. It was found
that the critical planemodel proposed by fatemi and Socie
correlated experimental results for notched specimens under
both proportional loading and non-proportional loading within
reasonable deviation bands. In the study of two-level
cumulative fatigue lives, several predicted models were
extended to evaluate the cumulative lives. Double linear damage
rulewas found to evaluate the remaining cycle ratio of the
second level within the reasonable deviation bands, and the
majority of the predicted results were conservative.
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