Fatigue Characterization of Fabricated Ship Details. Phase 2
Final technical rept.
ILLINOIS UNIV AT URBANA DEPT OF CIVIL ENGINEERING
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The available analytical models for predicting the fatigue behavior of weldments under variable amplitude load histories were compared using test results for weldments subjected to the SAE bracket and transmission variable load amplitude histories. Models based on detail S-N diagrams such as the Munse Fatigue Design Procedure MFDP were found to perform well except when the history had a significant average mean stress. Models based on fatigue crack propagation alone were generally conservative, while a model based upon estimates of both fatigue crack initiation and propagation the I-P Model performed the best. An extensive series of fatigue test was carried out on welded structural details commonly encountered in ship construction using a variable load history which simulated the service history of a ship. The results from this study showed that linear cumulative damage concepts predicted the test results, but the importance of small stress range events was not studied because events smaller than 68 MPa 10 ksi stress range were deleted from the developed ship history to reduce the time required for testing. An appreciable effect of mean stress was observed, but the results did not verify the existence of a specimen-size effect. Baseline constant-amplitude S-N diagrams were developed for five complex ship details not commonly studied in the past.
- Marine Engineering