Plastic Deformation and Material Properties of Aluminum

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Monty

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Does anybody know of a good source of information on the effect of plastic deformation on material properties for aluminum?

For instance, when one forms a wing rib from 6061 T6 sheet what does the process do to the properties of the aluminum?

Likewise, If you were to introduce a 10 degree bend in the form of a gradual curve over a span of say 2 feet in aluminum angle how would that effect material properties?

There are a lot of instances where a bend in a stringer would be much lighter than a break with a doubler.
 

orion

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When aluminum yields the hysteresis curve just shifts to one side however, to the best of my knowledge, the yield and strength values remain nearly identical. The only difference is when this is done several times and you get strain hardening of the material. But I have never seen the actual properties of that level of working.

The reason there isn't too much data regarding this subject is simply that for most structures, any form of permanent set (yielding) is considered failure so therefore it would need to be replaced. But of course hydro-forming of aluminum is done regularly in aerospace and no ill effects remain as long as the stretching is done within particular limits, which are governed by the alloy and temper. I used to have a table of those limits however I lent them to someone and have not gottent them back.
 

Monty

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I can understand why a complete structure is considered failed after yield, but why a formed part that is then incorporated into a structure? Does deformation through yield do anything to the fatigue properties?
 

WonderousMountain

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When we were cold bending pipes small angles could be made without measurable disturbances in deflection, although the application was such that maximum strength wasn't required, so stiffness, or rather controlled chassis suspension was encouraged. Cold bending aluminum might raise cracking concerns.

All that said, I would do it, but wouldn't count the 2 ft bent section towards the strength in that vicinity. The key is having a large radius, small diameter, and thick wall. The more of these factors you have the better your chance to retain strength.
Try it on a piece, if you see signs of deformation, it's useless.

I love destructive tests, Wonderous Mountain
 

Monty

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Try it on a piece
Yes, time for an experiment.

I think that I may be able to accomplish this without going past yield, and the induced stress actually works in my favor. Guess I'll have to re-acquaint myself with strain gauges.

If it works......I'll reduce my center section weight by a significant %. :)
 

wsimpso1

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On most of the stronger alloys/tempers, it won't make a huge difference. The absolute max difference it can make is to take the yield strength up near the ultimate strength (maybe 30% higher) , and you do not want to take even half of that strain. As far as a piece of aluminum angle bent in a gentle curve goes, you will hardly be able to tell there was a difference in yield strength.

As a practical matter, 6 mm LSLA steel drawn into a cup with a 6mm radius bend at the corner adds about 10-20% to the yield strength, and that is a lot more strain than you will get in most airplane part forming operations.

The other side of the coin is copper based alloys. Cartridge brass can be annealled dead soft (like in the neck of a rifle case) and yet be strongly cold worked at the head (back at the bolt) and have three times the yield strength of the material at the neck. Which is why cartridge brass is used to make cartridge cases.

Billski
 

Marc Bourget

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I think you'll find a good technical discussion on this topic in the ASM Vol. 4.

Problem is the book retails for something like $295.00

Mine's being shipped on Monday!

Marc Bourget
 
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