How big should I make a corner bracket?

[JamesCH95]

Some time ago @jtrv asked me to model corner brackets for 1x1 tubes to see how big they should be to strike a reasonable balance between size and strength. Here are the results!

3in → 4in bracket is a 43% stress reduction
4in → 5in bracket is a 38% stress reduction
5in->6in bracket is a 6% stress reduction

I would seem that a 5in triangular bracket is the right size range for 1x1 tube brackets.

Each bracket was modeled with a 3/16 spot weld at 1in-spacing as is typical of many FRC tube ecosystems. The spot weld is of course a simplification for whatever fastener might be used. It was not reasonable to model rivets or bolts (which are quite complicated to accurately model) for a relative-results type of model like this.

One end of the joint was modeled as fixed and a unit load was applied to the other end to bend the whole joint. Plane half-symmetry was used, thus the split bodies. SolidWorks Sim was used for this analysis.

Happy to answer any detailed questions and discuss other questions that can be answered with modeling.

Album: https://imgur.com/a/X2PPzGJ

[Nate_Laverdure]

Which direction is the joint lapped in each model? Like this?

[john3928]

I’d be curious to see how much more effective this “triangle” shape is than an “L” shape.

[ASmith1675]

Or even a radius.

[lowtorola]

Would it be possible for you to compare the strengths/yield strength of L-gussets with no/different-sized radii in the “corner?” We just guessed on how big the radius on our gussets should be this year and it would be cool to see the real strength gain there.

[Nate_Laverdure]

Also is this result independent of the gusset thickness?

[JamesCH95]

@Nate_Laverdure

Which direction is the joint lapped in each model? Like this?

I think so, but I’ll check when I get back to the computer where this model is stored.

@john3928

I’d be curious to see how much more effective this “triangle” shape is than an “L” shape.

@ASmith1675

Or even a radius.

@lowtorola

Would it be possible for you to compare the strengths/yield strength of L-gussets with no/different-sized radii in the “corner?” We just guessed on how big the radius on our gussets should be this year and it would be cool to see the real strength gain there.

Can-do. A sweep of a bracket with a small to extremely large radius will demonstrate both pretty well.

@Nate_Laverdure

Also is this result independent of the gusset thickness?

I have not run a sweep on gusset thickness. This model was with ~0.1in thick gussets as is common from FRC vendors.

[JamesCH95]

Note the max stress callout location, your sketch is correct.

[JamesCH95]

@john3928 @lowtorola @ASmith1675

I suspect that the 3.5in radius bracket does a good job of spreading load between multiple fastener locations, but that the 5in ‘corner’ bracket (without any radius) will ultimately be stiffer.