Plastic overload and instability

[miketingscott]

Could someone please explain the main differences associated with plastic collapse and instability, in the context of bending failures of structures.

Thanks in advance,

Mike

 

[GregLocock]

What length essay would you like?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[miketingscott]

Sorry, that was a bit lazy. So far I have come to the conclusion that plastic overload is concerned with permanent deformation ie. no longer the same shape and that instability is not a permanent deformation but the ability for a structure to change shape from the desired one.

Would you agree on this statement. Obviously it needs tidying up and a bit more technical language in it, but I'm so far struggling to find it.

Thanks,

Mike

 

[GregLocock]

In the lab lateral elastic instability, and elastic buckling in general, can be demonstrated. In the real world the large resulting deflections usually result in something going horribly wrong and localised yield or failure occurs soon after.

Yes your statement seems OK, but bear in mind you can have plastic stability issues as well.





Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[SWComposites]

plastic collapse - material yielding to the extent that the structure can no longer carry load

instability - "buckling" type deformation; can be elastic or plastic; with elastic buckling the structure returns to the original shape when the load is removed

though there are many, many nuances to both cases, depending on the particular situation

 

[miketingscott]

Thanks for your answers. I have just realised that I mistyped the question slightly and that it should be the difference between plastic overload and instability. Unless I am right in think that an overload would mean the same thing as a collapse?

So instability refers to a particular action that can happen to a beam, which is 'buckling'. However, plastic overload is a more generic effect on a structure?

Thanks,

Mike

 

[SWComposites]

No, buckling/instability is a general term for an action that can happen to most any type of structure loaded in compression.

Do you have a specific application/situation where you need to understand failure modes?

 

[rb1957]

and isn't "overload" a general term for loading something over it's design load ?

and like SW above, instability relates to a structural failure mode (compression or shear, permanent or elastic) ...

i don't see how the two terms could relate to one another ...