estimating residual stress due to cold bending

[Qluq]

Hi everyone,

would someone be willing to point me in the right direction for estimating residual stresses in sheetmetal plates due to cold bending? the only case i need to learn about is when a 90 degrees flange is set. relevant articles or forum threads? is this usually done using some set of rules or maybe FEA?

any help is very welcome.

Thanks,
Mark

 

[Qluq]

Okay, i realize the opening post was probably a bit too concise. So some elaboration is in place:

I am in the process of designing a sheetmetal structure assembled of plates that are attached to each other by cold bent flanges, all 90 degrees. The flanges of adjacent plates are bolted together.
The structure will be loaded quite heavily by transient events, which are however not cyclic. It is easily verified that the plate webs are strong enough, but near the cold bent areas bend stresses become important. Residual stresses due to the cold bending process are added to these bend stresses. They become the center of attention when fatigue is taken into consideration.

So that is why I am interested in estimating the residual stresses due to the cold bending process. I am aware of the qualitative theoretical model which helps to form an image of the way these stresses arise but is not very helpfull in determining actual residual stress levels. I do not know how these stresses are estimated in real life situations. We do not have the means to perform experiments on already formed plates.

Thanks! Mark

 

[wadavis]

Residual stresses in a fully deformed rectangular cross section approach yield along the center line and 50% of yield at the outer extents. But you're aware of the theoretical model, so more on target:

Many design codes for applications with high fatigue, or other causes of fracture typically require heat treatment or notch toughness testing of the plate material. Other design codes where stability or plastic failure modes govern have conservative methods to discount and ignore these residual stresses. Which group does your project fit in?

Wadavis
E.I.T.

 

[Gumpmaster]

I would recommend that you design per the AISI cold formed steel code which takes into account the residual stresses as well as the effective flange width of the cold formed sections. I don't know if it's as simple as running an FEA model, unless you're doing elastic design, because material non-linearities come into play with plastic design and effective flange widths. You can get quite in-depth in the design of cold formed steel, I recommend that you read the AISI code before you get too deep in the wrong direction.