How to analyze a bent beam: Stress concentration?

Question

I am analyzing a beam, that has a bend in it. Intuitively and inspecting FEA results using a linear solver, there is a stress concentration at the bend of this I-beam.

The part was not a straight I-beam that was later bent. Instead it was made with this bend by welding a curved web onto two flanges constructed of formed pieces of sheet metal. While there was some plastic deformation in the forming, the I-beam has mostly not gone through any yielding. My question is more related to, what stress concentrations arise from this modified geometry. Most analysis of beams pertains only to straight beams.
When I was learning about stress concentrations in Shigley's, they talked about notches and holes, but not bends. Is there a factor one should apply for an x degree bend?
Any thoughts?

kamran · Answer

If the bend has passed the elastic limit ( assuming material is steel) it have caused strain hardening in that spot.

Hardening or stiffness both attracts stress and keeps residual stress.

We take advantage of this hardening when we want to break metal wires by bending and unbending them repeatedly until stress concentrated at the bend will break it.

NMech · Answer

Given:

the size of the mesh
the difference of element sizes (large elements contacting small - apparently there is some contact definition between the two)
the perceived ratio of stresses (there is no actual legend for the scale)
no detailed of the analysis performed  (type, element formulation loading, etc)

I would say it would be very dubious any attempt at interpreting the data.
Given the above, my suggestion is that if the actual ratio of the orange areas compared to the green ones, is within 20% to 50% I would attribute the errors on simulation artifacts. The relative error will be artificially larger if there are loads, or constraints near the stress concentration areas.

How to analyze a bent beam: Stress concentration?

2 Answers

Add your own answers!

Ask a Question