I was recently asked to evaluate the capacity of a 1/2 in.
dia. wire hook supporting 80 lbs. vertically. My results indicated
max VonMises of 27ksi. This number seemed arificially high most
likely driven by the tangential peak. When I modeled the same hook
using a square profile with the same area moment of inertia, I get
a result ~18% lower. Is it safe to assume that the round profile
results are more artificially conservative (local yielding at the
tangent) than an equivalent test on a square profile?

Regards,

Dave Trent

dave.trent@insightbb.com

Regards,

Dave Trent

dave.trent@insightbb.com

max bending stress = M*c/I

Because you made the square the same moment of inertia, I'd assume the c value (or furthest point from the neutral axis) is now shorter (I'm calculating something like 0.438" side to the square?). So your analysis will be a little bit lower because you are calculating closer to the neutral axis than with the circle. However, there will be in increase in the normal stress due to the decreased area of the square... so maybe that will compensate... I dunno...

Have you tried doing a hand calculation for that critical point to see if its reasonable? (I'd give it a try myself but dimensions are missing)

Of course it could just be that COSMOS is liking your square profile better when it meshes.

EDIT: Miscalculated equivalent square, changed number in text