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Here's a snippet of the question that was asked a couple of years ago in university exam: A cantilever beam made of cold rolled steel for which ultimate tensile strength =540 MPa and Yield tensile strength = 360 Mpa. the expected reliability is 90% and Fos =1.8. Find diameter d for a> infinite life for load of +- 125N and b> use static approach where P varies from -125N to 125N. In both cases I am getting the same answer ie:11.49 ~ 12mm.

My approach for the first question was: find the bending moment at the fillet= 12500Nmm and then use the factors to find out corrected endurance limit which came to be = 150.79 Mpa. and from there I used sigma endurance / fos = 32xMb/(pi x d^3) PLease help

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    $\begingroup$ Isn't the static approach just about simple strength without considering fatigue? $\endgroup$
    – Tomáš Létal
    Commented May 18 at 7:09
  • $\begingroup$ i thought so too, just consider the least csa and design but when I told my prof, he denied saying it's about finite life and it makes no sense $\endgroup$
    – user47882
    Commented May 18 at 9:08

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