[TheForge] work hardening question

[Michael Boettcher]

At 09:06 AM 1/28/2002 -0600, you wrote:
>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

Steel and ferrous metals have a fatigue limit.  Non ferrous metals tend to 
not have one.  The fatigue limit is the stress to stay under if you don't 
want the part to break due to repeated cycling (fatigue).  The value for 
ferrous metals tends to be about 40-60% of its tensile strength.

Aluminum, on the other hand, will break with even very small stresses 
applied to it.  It'll take millions/billions of cycles, but it WILL 
break.  Its one of the main reasons that aluminum isn't used on production 
cars (or so I've been told).

Michael
madison,wi