"Brian" wrote in message
.ca...
I have an anti-roll bar from a Formula Ford race car that has suffered a
bit, and has a twist. It's obviously not up to it's original use in a
mild
steel spec, but I modified the suspension design somewhat and it will not
see nearly as much potential twist in use. What I wonder is can I simply
twist it back into alignment, either hot or cold, and have it perform
pretty
much as it did before it got twisted and then untwisted? I can't see why
not, but I have cumulative fatigue factors in mind that I don't know
about.

Probably its torsional spring rate will be indistinguishable from the bar in
its original condition. As for its fatigue life, it will depend on whether
any damage was done when it took a set (when you bent it past its elastic
limit). With mild steel, probably not. But you couldn't tell without a
metalographic examination -- or by running it until it breaks. Keep an eye
on it. If you're going to replace it with 4130, do it as soon as you've
judged whether you have the right torsion rate.

A rough measure can be had by having the bar Magnafluxed. If there is any
intragranular tearing, it should show up as microcracks. There's an almost
equal chance, though, that any cracks that show up were there before the bar
got bent.

Fatigue usually gives plenty of warning in ductile materials like mild
steel. You may have to Magnaflux it again after running the car a few times,
if you keep it in the car that long.

--
Ed Huntress