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High stresses around bolt holes

Question asked by Ansel Misfeldt on Aug 9, 2019
Latest reply on Aug 12, 2019 by Ansel Misfeldt

Hi!

 

I'm having trouble with high stresses around bolt holes on my simulated bolt connections.  I've been reading up on simulating bolts in Simulation and I'm aware of the warning that 'reported stresses will usually be higher than reality', but I'm wary of simply ignoring stress concentration around bolt locations.

Stress concentrations around bolts

I'm designing a part that has to bolt to a long beam with a load at the end to another piece (part of a larger assembly) and the weak point is always right around the bolt hole (see picture below).  I've tried many, many things to fix the problem ranging from using larger bolts, changing the number of bolts, changing bolt pattern, bolt face, bolt type, thickness of the materials, bolt torque values, etc. and can't quite get it to the goal of 1.5 FOS.

 

As mentioned, I'm wary of simply waving my hand and saying it's OK because I know the stresses around bolt holes aren't great in Simulation, but I'd appreciate any guidance or suggestions around how much this might be over-reporting the stresses (I don't know if it's showing 5% higher or 50% higher).

 

Alternately if someone has an idea on a better setup to connect the two I'm open to suggestions

Three quarter view of assembly

Face view of assembly

Some more details of the simulation setup

- 6061 material (2024 is much better but still doesn't quite get it there)

- ~200lb load on the end of each 30" beam (identical beam part, load is 'up' in the screenshots)

- Currently using x6 3/8" bolts in a circular pattern

- Surfaces being bolted are 0.5" and 0.75" thick so I'm surprised by the reported stresses

- Tested bolt torque range of 50in-lb through 150in-lbs (at the proper 23ft-lbs of torque the simulation won't run)

- No penetration contact with 0.2 friction coefficient

- I've tried about 60 simulations so far on this and am quite stuck...

 

I've included the models and a screenshot of the stress pattern for reference, any suggestions or advice would be appreciated!

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