Proposal of New Fatigue Evaluation Method in KD-3 of ASME Section VIII Division 3

Abstract ASME Section VIII, Division 3 is the most advanced pressure vessel standard, primarily using elastic-plastic analyses with a strain-hardening material model. The current fatigue evaluation in KD-310 through KD-330 of ASME Div.3 is based on elastic analysis and maximum shear stress (Tresca’s theory). The fatigue evaluation procedure using elastic-plastic analysis is not described in KD-3 of ASME Div.3 except for the fatigue penalty factor Ke in KD-323. The fatigue evaluation using an elastic-plastic analysis and equivalent strain range based on Mises’s theory are specified in 5.5.4 of ASME Section VIII, Division 2. The stress amplitude based on elastic analysis and Tresca’s theory of ASME Div.3 is greater than that based on elastic-plastic analysis and Mises’s theory of ASME Div.2. The current fatigue evaluation in KD-310 through KD-330 of ASME Div.3 is more conservative than that of ASME Div.2. The fatigue evaluation procedure using elastic-plastic analysis and equivalent strain range in 5.5.4 of ASME Div.2 is appropriate because it matches experimental results more closely and is also consistent with plasticity algorithms in numerical analysis software. Therefore, we propose using the Mises equivalent stress amplitude and equivalent mean stress. The example calculations for open-end cylinder with wall ratio Y = 2.5 made of SA-723M Gr.1 Cl.4 and SA-508M Gr.4N Cl.3 were performed in accordance with the proposed procedure. The thick-walled cylinder fatigue data due to cyclic internal pressure for open-end cylinders in the range of 103 to 105 cycles to failure by Davidson, et al. have been also used to show the validity of the proposed fatigue evaluation procedure.