Sam...

"What I wish to get some corrected correlation for thin (D/T >> 100) 4/5-cut miter flexibility instead of 1.52/(h^5/6) as available in B 31.3 App-D. Welding elbow correlation in B 31.3 is 1.65/h.

4/5-cut miter is a close approximation of welding elbow and Fig-7 (c) & (d) & table-2 of Fujimoto & Soh's paper shows the same for flexibility in 0.01 to 0.2 range of h."


Your Statement "4/5-cut miter is a close approximation..." well yes and know the difference between the miter and a wrough elbow are substantial BUT maybe their peak stresses (at different locales mind you) and hence their fatigue strength may be similiar if so then as i correlates to h their flexibilties would also be linked. Unfortuanately you have only two sure ways to be 100% confident testing or FEA.

Lets look at the problem from another view point.... can you design the system with the SIF and h being off by 150-200% and still get things to work out? If so your margin of unknown things amy still be tolerable.