Why does the Mechanical Fatigue Tool sometimes produce alternating stresses that are unrealistically large compared to the calculated stress in Mechanical, and in turn, predict zero life?
April 13, 2023 at 7:33 amSolutionParticipant
It might be caused by a high mean stress. For the Goodman and Gerber mean stress theories to be valid, the mean stress must be less than the ultimate stress. For the Soderberg mean stress theory to be valid, the mean stress must be less than the yield stress. If the mean stress exceeds these limits, the Fatigue Tool will issue a warning message, but the solution will proceed and calculate meaningless effective alternating stresses (essentially a divide by zero situation). The reported alternating stress values (1e25 range) just indicate that calculation exceeded an internal code limit and was set to that value. These large effective alternating stresses will produce essentially zero life. To produce meaningful alternating stress, you must ensure that the mean stress does not exceed the allowable limit; ultimate for Goodman and Gerber and yield for Soderberg. You can use the attached simple model to test this behavior.
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