Local Buckling of Tube

[rjoto]

Hi all

I've browsed this forum for a while, have found it very helpful, and recently decided that I'd like to get more involved.

I have a conveyor that I'm rolling things across. Recently some excessive forces were applied to the top of one of the rollers by another tube on top of it and I ended up with a large dimple in the top of one of rollers. It's an end supported galvanized steel tube (1.9" OD, 12 ga/.1084" thickness) that I have subjected to bending in the middle (by having another much larger tube on top of it). I'm familiar with bending and general column buckling but this seems to be some sort of local buckling and I've never come across that before. Can someone help me identify this failure mode and help me figure out how to calculate the strength of the tube?

I'm trying to figure out how much more strength I would get by going to solid rollers. A simple MOI analysis says that the solid roller should be about 2.6X stronger in bending.
pi*(1.9^4-1.683^4)/64=.246 for hollow
pi*(1.9^4)/64=.640 for solid

But I have a feeling that it should be higher than this because a solid roller shouldn't have any local buckling issues.

 

[Tmoose]

My first cut, Double the wall thickness, make it 8X more difficult to bend the wall locally ??

If all the action is in the vicinity of the lone dent, maybe slip a solid slug into the roll that is 2 or 3 times longer than the dent zone?

Does the dented roll spin while being loaded heavily?