non-homogenous mat'l properties due to metal forming

[EngForm78]

How does everyone analyze a problem where cold forming has changed the material properties in certain areas.

Example:
Geometry: A simple "L" bracket cold bent from flat steel.

Loads: Turn 45 lke a "V" and pull apart like <- V ->

Properties: ???, The material propties will be different where the forming has taken place, in the notch of the "L"

Results: If I use uniform material property of the material before forming it will effect the deformation. Also if the yield strength is increased it will effect the yield criteria.

Thanks
EngForm78

 

[NickE]

Firstly the modulus of the material is raely if ever affected by the forming operation.. For steel its still ~30,000ksi.

the yield strength will go up in relation to the amount of cold work, that is just the way materials behave. To analyze the post yield behavior you will need non-linear material capability. Then you use teh actual stress-strain curve from material that is cold worked to the same extent. That way the software can determine stiffness (modulus) at varying amounts of strain that are in excess of the yield strain.

 

[harry123456]

Or you could do a combined analysis. Input the non-linear material stress strain curve for the material. First step cold form it and second step apply additional loads.
harry

 

[EngForm78]

Is there a way to predict the material properties after cold working or is it all experimental?

 

[NickE]

Thare is information on properties vs amount of cold work. Since sold work is equivalent to the amount of strain induced by the forming operation you could use your Forming Limit Diagram to get a location vs strain map. Then it should be possible to get a strength map.


Although hardness traverses across the formed area might be easier. (Esp if you have no forming limit diagram.)

 

[broene]

Although material thinning and stretching is not considered, this paper describes the method we use to quantify cold working in our fe analysis.

http://www.dynalook.com/documents/7th_International_ls-dyna/Session_3-6.pdf

 

[MMATguy]

Actually cold work can affect the elastic properties of a material. This effect is called texturing because the grains after cold work are aligned (not perfectly aligned) along the direction of material flow. This tends to give some anisotropy in material properties.

Regards

MMATguy