Gerber & ASME Elliptic Fatigue Failure Criteria | Torsional Fatigue | First Cycle Yielding

LECTURE 24:
Here the Gerber and ASME Elliptic fatigue failure criteria are presented and discussed in light of experimental data. A problem is completed in which a torsion rod is used to provide spring force to a roller, which induces a fluctuating torque in the rod as the roller goes over bumps. This fluctuating torque is examined to determine midrange and alternating torsional stress components, including a torsional fatigue stress concentration factor. A fully corrected endurance limit is found by evaluating surface, size, loading, and reliability Marin factors. The factor of safety formulations given in Shigley for the Gerber and ASME Elliptic criteria are transformed to make them appropriate for shearing stresses and strengths, and these factors of safety are then computed. The factor of safety against first-cycle yielding is also computed. The load line and fatigue and yielding failure lines for this example problem are plotted on midrange-alternating stress axes and discussed with respect to potential for fatigue and yielding failure.

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This lecture was presented on February 7, 2018. All retainable rights are claimed by Michael Swanbom.

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