material tubing thickness

[Rex Schimmer]

Saltfever,
I agree that a piece of material that has been strained past its yeild strength is typically weaker but that is mostly do to the reduced material cross section and not the actual strength of the material itself. Most materials that we work with, steel, aluminum etc actually exibit improved physical properties once they have been stretched. This is a type of cold working that refines the metal grain sizes and increases strenght, but what happens, as Willie's test have shown, the material thins and the percent of thinning vs the percent of increase in material properities can make the part weaker.

Strain hardening is an important component of most of the "heat treatable" aluminums. To get 6061 to the T651 the material has to be stretched a certain percentage to get the desired properties.

I do agree that once you have a structure that has failed in "plastic deformation" it is junk and not repairable.

Rex

[manta22]

Willie;

Sorry, you won't get me on a motorcycle. There seems to be something inherently wrong about draping yourself over the outside of a vehicle. You are then protecting the vehicle in a crash; I'd rather have the vehicle surrounding me. 

Yes, a long unsupported straight tube is not a good idea-- but that is solved by triangulation with intermediate bracing. If a tube is bent into a hoop, it is already partially collapsed-- that bend is where it will buckle in compression.

Regards, Neil  Tucson, AZ

[willieworld]

this thread is 7 pages --read 3577 times--lots of time spent testing -lots of time spent posting---if we all rode motorcycles it would be irrelevent---the bike thing- some people get it some dont -to bad     willie buchta

[saltfever]

Rex:
I was referring to the typical stress/strain curve (below) for structural steels that shows loss of strength after the "ultimate" is reached. However, as you correctly indicated, this loss of strength is due to the typical "necking" that occurs. Since "necking" in beams and coupons, or wall thickness changes (in tubing) always occurs in structural steel, my point was it is best if design loads are within region 4 (below) rather than at ultimate.

“Roger that” for the aluminum T651 condition. Good information.