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Primary Membrane Stress Range for Thermal Stress Ratchet

LS_SMS

Mechanical
Sep 18, 2020
118
Folks, I am looking at 2023 ASME Sec. VIII, Div. 2, Part 5.5.6.3 for the Thermal Stress Ratchet check. This equation is provided...

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Pm is referred to as "primary membrane stress." Is it supposed to be a primary membrane stress range? Everything in the fatigue and ratchet assessment up to this point uses stress ranges from the two peaks that form the stress pair. If I'm dealing with two peaks for this calculation of X, it is unclear which primary membrane stress should be used? My intuition tells me it should be the range for the two peaks in the pair. Can anyone share some feedback?
 

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