The paper investigates the current rules for fatigue analysis on plastic basis of the ASME Boiler and Pressure Vessel Code. It addresses the question: When these rules are used for a vessel or component, is it designed with respect to crack initiation or failure? Using available fatigue test data, the question is answered for blunt double-notch plate specimens made of AISI 4340 steel. When the rules are applied to these specimens, it is found that they are designed with respect to the initiation of a crack of a certain length that decreases as the strain range increases. The plate specimens are not designed with respect to failure. It is concluded that for geometries that exhibit a strain range gradient away from the surface, the number of cycles allowed by the current rules includes the initiation phase but not the propagation phase of a fatigue crack. If this result is unsatisfactory, new rules have to be written.

Issue Section:
Research Paper
Keywords:
nuclear engineering computing, pressure vessels, fatigue cracks, plasticity, steel, geometry, boilers, fission reactor design
Topics:
Cycles, Design, Failure, Fatigue analysis, Fracture (Materials), Steel, ASME Boiler and Pressure Vessel Code, Stress, Finite element analysis
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 by ASME
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