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.

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right. Then,
I'll make up one with the correct rate in the correct material.

Thanks, Brian

Do some study on Young's Modulus (Modulus of Elasticity).

Bob Swinney
"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.

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right.
Then, I'll make up one with the correct rate in the correct material.

Thanks, Brian

Thanks for the non-help - since when does Young's Modulus address fatigue
factors in typical mild steel - which was my question? Not in my
experience.

Brian


"Robert Swinney" wrote in message
...
Do some study on Young's Modulus (Modulus of Elasticity).

Bob Swinney
"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.

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right.
Then, I'll make up one with the correct rate in the correct material.

Thanks, Brian

You gave no dimensions or otherwise allowing for any help. Your question
read as if you were ignorant of the basic physical facts re. your "problem".

Bob Swinney


"Brian" wrote in message
.ca...
Thanks for the non-help - since when does Young's Modulus address fatigue
factors in typical mild steel - which was my question? Not in my
experience.

Brian


"Robert Swinney" wrote in message
...
Do some study on Young's Modulus (Modulus of Elasticity).

Bob Swinney
"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.

My thought is to replace the ARB with a 4130 heat treated version , but
I want to drive the car first to see if the bar rate is close to right.
Then, I'll make up one with the correct rate in the correct material.

Thanks, Brian

Your question is incorrect: Since the bar took a tweak, it is NOT
elastic deformation. Look at a standard stress/strain curve to failure
for a mild steel: elastic region (straingt line upwards) on the left,
then inelastic wobbly line to failure on the right. You have used up
some of the available space between elastic and failure. How much is
hard to judge. If it took a substantial tweak, I don't want to drive it
at speed.




Brian wrote:
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.

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right. Then,
I'll make up one with the correct rate in the correct material.

Thanks, Brian

since when does Young's Modulus address fatigue
factors in typical mild steel - which was my question?

But you really asked two questions:

1. Is it strong enough? Which everyone here agrees is "no,"

and this one:

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right.

which the Young's Modulus answer DOES address. This is
because the YM of mild and 4130 is the same, they just
fail at different points (the 4130 can take more load
before failing but under the same load both respond the
same). This means the behavior and handling with the
existing bar will be the same as with a 4130 replacement
of the same design.

--Glenn Lyford

It is extremely unlikely that your suspension bar is mild steel. Most are
heat treated alloy. You have twisted it past the yield point of the
material. When you twist it back you will have to exceed the yield again
only the second yield likely will be a greater force. If you manage to get
it back to the original shape without fracturing it just might fracture when
you are putting it in service.
Imagine bending a paper clip back and forth only you are doing it with a
considerably less ductile steel.
Randy

"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.

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right. Then,
I'll make up one with the correct rate in the correct material.

Thanks, Brian

"Brian" wrote in message
.ca...

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right.
Then,
I'll make up one with the correct rate in the correct material.

I'm going to skip the lecture about how the bar has already exceeded its
yield strength and may fracture in use, as that has already been covered by
earlier posts. Therefore, I'm simply going to focus on the practical
applicability of your plan outlined in your last paragraph.

It will be impossible for you to gather any meaningful data based on the
drivability of your current (damaged) bar, because you will never know the
true spring rate of that bar. Since it will have been subject to plastic
deformation (twice: once when damaged, and once when "fixed") and possible
heat treatment/tempering in the course of your bending it back to shape,
you'll have no clue as to the properties of that (now non-linear) spring. It
certainly won't behave anything like an identical, undamaged bar.


"R. Zimmerman" wrote in message
news:EqX9f.378971$oW2.57594@pd7tw1no...
Imagine bending a paper clip back and forth only you are doing it with a
considerably less ductile steel.
Randy

And rarely ever does a fracturing paper clip put anyone's life or valuable
property at risk.

- Michael

Mild steel has very good, but not infinite fatigue resistance. Constant
repetitive bending, like bending baling wire in half will quickly lead
to failure. In your automotive application, probably not a problem.
Bugs

In article , DeepDiver says...

It will be impossible for you to gather any meaningful data based on the
drivability of your current (damaged) bar, because you will never know the
true spring rate of that bar. Since it will have been subject to plastic
deformation

Good post.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Step one Think of what might happen if the bar fails while you are
driving it to see if the bar is close to right.

Step two would be to twist it back into alignment cold. The bar is
almost sure to have been heat treated ( unless you know it was made of
mild steel )

Step three would be to twist it within the limits of what you expect it
to occur in use and verify it does not take a set
( or break ).

Step four would be to do your test drive if you feel like it is safe.

Step five would be to remove it and measure the spring rate. It may
not be the same as it was originally, but it can be measured.

Note Well, I am not advocating doing this. Just how I might approach
doing it. I certainly would not try it anywhere except some place like
an airport where there is no objects that can be hit.

Dan

Not true, the spring rate will be the same evne if it is dead soft. But
the maount of deflection before it takes a new set or breaks will be
unknown. Thus you can use it for setup but NOT for driving.

DeepDiver wrote:
"Brian" wrote in message
et.ca...

My thought is to replace the ARB with a 4130 heat treated version , but I
want to drive the car first to see if the bar rate is close to right.
Then,
I'll make up one with the correct rate in the correct material.


I'm going to skip the lecture about how the bar has already exceeded its
yield strength and may fracture in use, as that has already been covered by
earlier posts. Therefore, I'm simply going to focus on the practical
applicability of your plan outlined in your last paragraph.

It will be impossible for you to gather any meaningful data based on the
drivability of your current (damaged) bar, because you will never know the
true spring rate of that bar. Since it will have been subject to plastic
deformation (twice: once when damaged, and once when "fixed") and possible
heat treatment/tempering in the course of your bending it back to shape,
you'll have no clue as to the properties of that (now non-linear) spring. It
certainly won't behave anything like an identical, undamaged bar.


"R. Zimmerman" wrote in message
news:EqX9f.378971$oW2.57594@pd7tw1no...

Imagine bending a paper clip back and forth only you are doing it with a
considerably less ductile steel.
Randy


And rarely ever does a fracturing paper clip put anyone's life or valuable
property at risk.

- Michael

"DeepDiver" wrote in message
...

It will be impossible for you to gather any meaningful data based on the
drivability of your current (damaged) bar, because you will never know the
true spring rate of that bar. Since it will have been subject to plastic
deformation (twice: once when damaged, and once when "fixed") and possible
heat treatment/tempering in the course of your bending it back to shape,
you'll have no clue as to the properties of that (now non-linear) spring.
It
certainly won't behave anything like an identical, undamaged bar.

It's unlikely that it will show any difference in elastic twisting after
being bent back. Young's modulus is a property based on the inherent
material property and the geometry of the part, not on residual stresses or
temper condition, in steel and most other metals. It probably will be as
linear as it was before bending -- up to the point of plastic deformation.
If there's a kink in it now, though, it will depend on how the bar is
supported when it's loaded.

--
Ed Huntress

"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

...A rough measure can be had by having the bar Magnafluxed. If there is
any
intragranular tearing, it should show up as microcracks.

That should read "intergranular tearing." Fatigue is a phenomenon that
occurs BELOW the elastic limit, from repetitive cycling. The tearing I'm
talking about is a result of strain failure BEYOND the elastic limit, and
which could hasten actual fatigue failure.

It could take the form of cracks that start on the surface, and which will
show up clearly with Magnafluxing, but the insideous form is tearing that
occurs just below the surface. Again, it's unlikely that you have a problem
that won't show up with Magnafluxing.

--
Ed Huntress