[TheForge] work hardening question

Mon Jan 28 10:39:21 2002

To All,Work hardening is the storing of strain energy in the (micro)structure that is the result of plastic deformation.  The lamp post or antenna that is swaying in the wind is deforming elastically.  Plastic deformation results in a permanent changee in shape and elatic deformation is recoverable.  The classic work hardening experiment is to take a wire coat hanger and bend it back and forth making sure that you hve some permanent deformation, i.e., you exceed the yield strength.  You will notice that it will "spring" back a little after each bend.  That is the elastic component. If you bend it back and forth rapidly it will get hot at the bend. If you bend it slowly and leave time between bends it will appear not to get hot but the release of thermal energy is the same.  There is a little rate sensitivity but not much.  If you bent the coat hanger so that the stress in the wire is 80% of the yield strength (no permanent deformation) and you do it a million times or so it will break from fatigue.  That is a diffe
rent but related phenomena.

Hochewa

In a message dated Mon, 28 Jan 2002 10:07:16 AM Eastern Standard Time, [email protected] writes:

> hello;
> 
> this question occurred to me this past saturday and again yesterday
> while watching the antenna tower by the house sway back and forth in
> the wind.
> 
> i may be overlooking something rather simple but here is the question.
> 
> what keeps the metal in antenna towers, street light poles, even the
> sears building in chicago from work hardening after all the time of
> swaying from wind?
> 
> it would appear that after swaying back and forth over the years
> that the metal would be work hardened and become brittle.
> 
> -- 
> Terry L. Ridder
> Blue Danube Artistic Forge (Blaue Donau Kunstschmiede)
> "We do not bend metal, we sculpt it."
> 
> digging deep, i feel my conscience burn
> i need to know who and what i am
> this hunger jolts me from complacency
> rocks me, makes me meet myself
> ----kendall payne---closer to myself---
> 
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