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residual stress

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magicme

Mechanical
Sep 24, 2003
128
hi

i have results from an elastic analysis (using ANSYS)that indicates some regions of a structure go possibly 10ksi above the yield point under a certain load.

is there a sensible way to determine the residual stresses thoughout the structure after this load is removed (some material has yielded).

what i actually need to do is to determined the new unloaded distortion of the structure without doing a plastic analysis.

i am inclined to run the following elastic case..... apply a stress distribution to the structure (the original loads removed) that is shaped like the loaded stress distribution and that takes the yielded region to 10ksi. this inherently implies that the residual stress in the yielded region is 10 ksi and the surrounding stresses are proportional to the loaded case.

i believe this would be conservative, but would appreciate any comments.

plastic analysis is not an option.

thanks

daveleo



 
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daveleo,

One possible solution, and it would be very conservative at that, is to take the FEA strain value and plot this value on the material stress/strain curve. Then draw a line from this point at the same slope as the Elastic modulus back to the zero stress line. Read off the corresponding stress at this location. This is the residual stress in the part. If you can show this good, then you are laughing.

This tends to be very conservative for small areas of plastic strain surrounded by a large mass of elastic material. This is because the energy of the elastic material far exceeds that of the plastic zone and forces a return to a near zero displacement. For example, hole cold working or shotpeening. In these examples, the springback is large enough to induce compressive residual stresses in the plastically deformed region.

Also, the plastic strain reported by FEA is conservative as you would likely have load redistribution due to yielding.

Regards,

jetmaker
 
jetmaker..... we are thinking along similar lines on this. it's not a perfect academic method, but it should put me in the ballpark....if the resulting deflection has lots of safety margin, i can say we are okay.

thanks for the input.

daveleo

 
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