Is it true that if the structure damaged or corroded, the stress will be lower?

Question

I am comparing the stress results between original or non-corroded model to corroded model. I found that the stress value in non corroded model is lot more bigger than the corroded model, is it correct?

Answer 1

Maybe it is correct, maybe it isn't.

Suppose you "corrode away" a small radius that was causing a stress concentration, and it becomes a bigger radius. Quite likely the maximum stress in the structure (at that concentration) will decrease because of the corrosion. For example an "average" stress of 1.0 and a stress concentration of 10.0 might become an "average" stress of 1.1 and a stress concentration of 9.0. Whether you count that as a "decrease from 10 to 9" or an "increase from 1.0 to 1.1" is your choice.

On the other hand if you reduce the cross section of a structural member like a beam, or the thickness of a plate, the stress will probably increase - i.e. stress = load/area, and you decreased the area.