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# Stress Concentration on Bolts

## Stress Concentration on Bolts

(OP)
Hi All,

I have a small plate that is going to be in bending. It is being held by two bolts on one side. I want to see if the bolts can hold this by adding a stress concentration to the stress in these holes to see the stress on the threads. Do any of you by chance know the Kt formula to take into account the stress in the threads using the material grade of the bolts, course or fine bolt and bolt diameter?

Thanks,

### RE: Stress Concentration on Bolts

is this for work ?

bolts come with allowable loads, why calculate one based on the Kt ?

there are so many reasons why professionals don't do this calc.

### RE: Stress Concentration on Bolts

(OP)
Essentially, I can't run FEA with bolt connections as the fixed geometry I'm threading into is really complicated. I'm pretty new at this so unsure how to move forward. The force is applied on end of plate so it will create moment, I'm not sure if I can simply take a bolt spec for load and say it can resist tensile load using area of bolt and number of bolts? Wouldn't it be a stress due to moment. I wanna make sure I pick the right grade bolts. So I decided to fix the inner portion of these holes and still run FEA just on this plate, but I want to see how much stress the bolt has, so I wanted the stress concentrator to magnify the stress I get just running stress on this plate. Is there something I'm doing wrong, have I understood something wrong, is there a better way of doing this? Add info: The plate is made of 6160 Aluminum, 5/16 bolt sizes and 500 N of force.

### RE: Stress Concentration on Bolts

you're showing an out of plane load on a plate with 6 fasteners ?

a reasonable assumption would be the bolts react out of plane (tension) load (with minimal bending from clamping under the head).

bolts have allowables, no need to worry about the Kt of the thread; the plate can be solved with hand calc or FEA.

if the load is in-plane, then same ... fasteners have shear allowables.

### RE: Stress Concentration on Bolts

You need to get a decent mechanical engineering design handbook, and read the section on bolted joint design. Shigley wrote one such. Use the hand calcs to inform your decisions on modelling the plate (i.e. what does the bolted joint actually do vs. the idealized fixed/free FEA boundary conditions). But you shouldn't feel any need to model a bolt in detail, that's been done and very good hand calc. methods exist, which account for Kt and fatigue and a lot of other stuff as well. The hand calcs can also inform what torque specs you might impose to the assemblers.

https://www.amazon.com/s?k=shigley+s+mechanical+en...

### RE: Stress Concentration on Bolts

"It is being held by two bolts on one side."

1 - It would "help" to make it clear in which of the six holes the bolts reside.
2 - If those two bolts provide the only restraint as you seem to imply, it is of the utmost importance to be accurate about the goings-on at the bolted faying surface.
This - https://www.alamy.com/claw-hammer-pulling-nail-ima...

Versus this - https://encrypted-tbn0.gstatic.com/images?q=tbn:AN...

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