SEDL / STP / STP1332-EB / STP14971S

Fatigue Durability Enhancement by Controlled Overloading

Tipton, SM
Professor and Associate Professor, The University of Tulsa, Tulsa, OK

Sorem, JR
Professor and Associate Professor, The University of Tulsa, Tulsa, OK

Pages: 15    Published: Jan 1999

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Abstract

Controlled overloading techniques, such as the proof loading of lifting components, the overspeed testing of turbomachinery, and the overpressurization of high-pressure components, are routinely employed to affirm the structural integrity of engineering components and systems. This usually occurs following the manufacturing process but prior to service, and typically without regard to its influence on fatigue behavior under service loading. Proof loading often induces localized yielding and subsequent residual compressive stress at regions of stress concentration, which can lead to an increase in fatigue durability for some types of service loading. The nature of residual stresses imposed by overloads is described and their interaction with fatigue mechanisms overviewed. A technique using notch strain analysis and the “reverse plasticity criterion” is described for predicting optimal proof load levels and its domain of applicability is discussed. Through example applications, it is demonstrated how the approach can enhance fatigue lives by orders of magnitude.