Local Yielding
Local Yielding
(OP)
This is a general question about stress analysis. Let's say you're reviewing stress results and there is very nearly some yielding in a local area. The area is not one that looks too concerning to you, e.g. not on a weld, not near a sharp corner, etc., the stress magnitude is not close to the material's ultimate strength, the part is not in a fatigue situation and no one will die from part failure.
I know that everything always depends on the situation, material, function and many other factors, but I just wan't to get some input from others. Again, sorry if it is too general.
What concepts, like creep, would you consider for situations like this? Could it be just a little strain hardening and nothing to worry about, or would you be concerned that over time it would lead to failure?
Thanks!
I know that everything always depends on the situation, material, function and many other factors, but I just wan't to get some input from others. Again, sorry if it is too general.
What concepts, like creep, would you consider for situations like this? Could it be just a little strain hardening and nothing to worry about, or would you be concerned that over time it would lead to failure?
Thanks!





RE: Local Yielding
Tata
RE: Local Yielding
RE: Local Yielding
The question isn't from from any particular situation, it just popped into my head and I was wondering what I would do if that came up. At first I thought that it would always be unacceptable to have stresses near/at yield, if your using a factor of safety greater than one, but then I reconsidered that there may be situations where the area you're concerned about is fine even though some other area looks high.
Here's a hypothetical. A thin plate supported at both ends, with some type of mass in the middle of the plate. The assembly is dropped landing on the wall supports. The middle of the plate experiences high stress but the plate to wall connection is very well designed and suffers acceptably low stress. Now, I know an analysis of this would be wrought with many assumptions and after all is just a simulation so you're stresses could be much different in actuality, but it's just the best I could come up with right now, so just take that as the general idea: a situation where high stress is happening in an area that does not look like it will lead to failure.
Thanks to anyone who replies despite it being conceptual and not specific.
RE: Local Yielding
by you can accept high stresses if you understand them and can rationalise them away. i'll accept high compression stresses (> ftu) on a solid (= thick) flange in bending where they are limited to a small depth of the flange, arguing that localised load redistribution (= plastic bending) will keep things together.
RE: Local Yielding
Can anyone else think of a situation where you've made an educated judgment to deem a high stress area acceptable? Thanks.
RE: Local Yielding
Dynamic Case (Velocity Shock): Some yielding is good because this will create some damping saving the mass, but the plate will have to be replaced.
Dynamic Case (Vibration): Yielding is not good and will cycle to failure.
Static Case: If you're going to sell this at Walmart, yielding does not matter. Plan to use this on the NASA shuttle, yielding is not good. Since us engineers want to design and build quality products, we should keep stress under the Sy point.
If the material has reached its Sy point, it is just a hop, skip, and a jump away from Su, so why risk it? When we do analysis, we do it in an ideal world where we assume simple case of static load or dynamic load where in reality other degrees of freedom will occur making it a worse case then we thought. When the product fails, try explaining it to your boss/customer that you knew it yielded but decided to continue with the design anyway.
Tobalcane
"If you avoid failure, you also avoid success."
RE: Local Yielding
Chris
www.value-design-consulting.co.uk