internal/female thread fatigue and remaining wall thickness

[1980c3]

Hello all,

I have a scenario in which I am tapping m10x1.5 threads into cast iron close to an edge - ~0.120". (imagine a 2x2 that is 6 inches long, with a hole drilled in the end faces off-centered such that the edge of the hole is .120" from the sides).

This distance should not move - it's pretty darn controlled dimensionally.

I am a touch worried about the small remaining wall thickness... I know that there are a few "rules-of-thumb" out there with respect to minimum distance to edge, but they are not always practical and arguably excessive. However, how would I quantify the local peak stresses I would see in the internal threads with a engaged thread length of about 20 mm? these are metric threads so there is no radius callout at the root of the thread, so I'd have to assume something geometrically...

I have tried using FEA, but it's not very clean at all, as you can imagine (levels around 400 ksi σ1 but I am fairly convinced these are just singularities)....

Anyways, any suggestions to what ails me above?

TIA!

 

[Tmoose]

Loading from tightening, side loading the bolts into the thin edge, ??

 

[1980c3]

Hi Tmoose,
I suppose I should have specified. There’s really no way for side loading to occur in this joint - the clamp load should provide plenty of resistance to slipping/subsequent bolt/thread moments occurring . It would be nice to be able to quantify somehow, but not the priority. So I would mainly say the loading from torque, and that loading from torque is also what I “attempted” to simulate. Thanks!