RRO INSANE A-ARMS: Updated w/ pics

KJ 119 · **Posted:** Sat Jul 18, 2009 11:03 am

Question about the RRO's-are they made with tube or round stock?
When I swapped to the JBA's ,I wondered why he uses tube instead of stock.
If for cost reasons,I would've paid more.

*This is not a bash on JBA,I love my Al's arms,just thought they should be solid.*

JeepinJarhead03 · **Posted:** Sat Jul 18, 2009 1:19 pm

I'm going to let boiler field the tube vs solid thing

but I used to have some big misconceptions about solid vs tube stuff too

ramlebliberty · **Posted:** Sat Jul 18, 2009 6:39 pm

Tube is stronger, solid stock while still pretty strong will be more likely to bend. Think of it this way, you have an empty and full beer bottle, if you were to hit yourself in the head with the full one it would bust rather easily, maybe it would leave a lump. However a empty beer bottle is more rigid and could possibly kill you if you hit yourself with it. Take it from experience

Neal · **Posted:** Sat Jul 18, 2009 6:57 pm

I can't believe that for the same kind of material tubing is stronger that solid-----

JeepinJarhead03 · **Posted:** Sat Jul 18, 2009 8:53 pm

think of it as having 2 walls inside and outside surfaces that have to give in order for it to change shape, the forces enacted on it have 4 (in very very simple terms) surfaces to distribute against instead of two

ATXKJ · **Posted:** Sat Jul 18, 2009 9:17 pm

Not exactly - if the material is identical the solid is stronger - but it's trivial compared to the weight gain.
the calculation is the Diameter to the 4th power and if it's hollow you subtract the inner diameter to the 4th power.

the outer wall is doing all of the work

(probably more of an issue to weld solid also)

JeepinJarhead03 · **Posted:** Sat Jul 18, 2009 9:23 pm

well you can take two 10 foot lengths of the same steel, one hollow one solid and the solid will bend

I leave the why's to the physics

stumpjumper_09 · **Posted:** Sat Jul 18, 2009 10:06 pm

where the he@# is boiler when ya need him.

JeepinJarhead03 · **Posted:** Sat Jul 18, 2009 10:16 pm

haha

I'll be honest, the only parts that I comprehend when Boiler or anyone else explains why -such and such- when it comes to metal and metalurgy and what not, is the part where they say something like "So.. therefore wa wah"

:lol:

stumpjumper_09 · **Posted:** Sat Jul 18, 2009 10:37 pm

I have known for a while that tube is stronger than solid but I want to know the reason.

tjkj2002 · **Posted:** Sat Jul 18, 2009 11:33 pm

stumpjumper_09 wrote:

I have known for a while that tube is stronger than solid but I want to know the reason.

Tube is stronger from the fact it has 4 surfaces to resist bending forces and solid only has 2.Now it also depends on how thick the wall thickness is compared to the diameter of the solid stock.

A 1.5",0.5" walled tube is stronger then a 1.5" solid stock but a 1.5" solid is slightly stronger then a 1.5",0.120" walled tube.

KJ 119 · **Posted:** Sat Jul 18, 2009 11:37 pm

JeepinJarhead03 wrote:

well you can take two 10 foot lengths of the same steel, one hollow one solid and the solid will bend

I leave the why's to the physics

Now THIS makes the most sense to me.
Thanks Jarhead,the science is well is over my head.

JeepinJarhead03 · **Posted:** Sun Jul 19, 2009 12:04 am

just keep in mind

PART of the reason why the solid bends in comparison is because it weighs more

but you can take sections that don't bend under their own weight and tie dumbbells to them and the solid will droop

regardless..

from what I've understood the problem with some of the jba A arms was the weld not the material

Green Renegade · **Posted:** Sun Jul 19, 2009 12:43 am

A solid bar is always stronger (in bending which is how 99% of structures fail) than a tube of the same diameter. Bending stress is (M*y)/(I) where M is the bending moment (torque) y is the position on the cross section where we want to know the stress, and I is the second area moment. I is the only term that changes between the two cross sections.

for a solid bar Is = (pi/4)*r^4 where r is the radius of the bar.

for a tube, It = (pi/4)*(ro^4-ri^4) where ro is the outer radius and ri is the inner radius.

from the equations you can see that if ri is greater than zero (making the cross section a tube, and not a solid bar) It will be less than Is.

Since I is on the bottom of the stress equation, as it gets smaller the stress gets larger. therefore a tube will reach the yield stress of the material before a solid bar will.

Now, depending on the density of the material, I suppose it is possible that the added weight of the bar may contribute enough stress to make it weaker than a tube, but I doubt it. The main advantage of a tube is the reduced weight.

JeepinJarhead03 · **Posted:** Sun Jul 19, 2009 12:57 am

ok well in terms of jba a-arms has anyone known one to break at other than the weld, if not it's moot for the most part

now, in terms of solid and tube strength, if i do recall, stress above yield strength produces a permanent distortion right?

out of curiosity isn't there a secondary equation that is actually along the lines of the rigidity or flexibility of the material in given lengths that does not produce a permanent distortion in the material

in that case doesn't the solid flex (but rebound) when the tube does not flex

giving the tube higher rigidity (less rebounding flex) but a lower max yield before permanent distortion?

Metalurgy obviously aint my thing

Boiler · **Posted:** Sun Jul 19, 2009 1:26 am

Green Renegade wrote:

A solid bar is always stronger than a tube of the same diameter.

<GOLF CLAP>

His thread looks correct. His equation gives stress at a given distance from the bending axis, which is the center of a symmetrical part. Typically when sizing a beam I use section modulus, which is a derivation of that equation.

Bending moment / section modulus = bending stress.

Consider:

Round tube 1.25" OD with 1/8" wall vs. 1.25" D round stock, materials being equal:

Section modulus for the tube is appx. 0.113 in^3
Section modulus for the round is appx. 0.192 in^3

If you devide a torque by that, the larger section modulus object will have a lower outcome stress.

Tube is great, don't get me wrong. Per pound it beats the pants off of round in bending. If you're designing a part with limited size constraints and minimal weight issues though, round bar would probably be better. In bending, material the farthest from the centroid of a member carries the most load. That's why the tube is more than half as strong while only being a small fraction of the weight.

Also for shear or tensile pull applications, tube has no weight advantage over round, in fact, I'd say its slightly worse since there is more surface area for defects, plus it is typically welded and has a seam.

All that said, those arms could have a safety factor of 20:1 for all I know. I don't know how big they are, how they are loaded...etc. If they have adequate safety factor, I'd make them tube too.

Diggerfreek · **Posted:** Sun Jul 19, 2009 1:32 am

I should have never opened this thread at this time of night.... the math is making my head spin :shock:

Boiler · **Posted:** Sun Jul 19, 2009 1:47 am

JeepinJarhead03 wrote:

ok well in terms of jba a-arms has anyone known one to break at other than the weld, if not it's moot for the most part

Pretty much :lol:

JeepinJarhead03 wrote:

now, in terms of solid and tube strength, if i do recall, stress above yield strength produces a permanent distortion right?

Yes. If you you pull a piece of material in tension (or bending, whatever) it will stretch a certain amount and spring back to original. If you pull it twice as hard, it will stretch twice as much and spring back to original. If you pull it until the stresses are above the yeild stress, it will stay stretched permanently (it will spring back some, not completely though).

JeepinJarhead03 wrote:

out of curiosity isn't there a secondary equation that is actually along the lines of the rigidity or flexibility of the material in given lengths that does not produce a permanent distortion in the material

You just blew my mind. :lol:

You can determine the maximum bending stress using the above equations and then compare the results to yeild stress. You can also determine axial stress (stretching a specimen along its axis) and compare to yeild stress. As long as you don't stress it beyond the yeild stress, it won't permanently deform.

JeepinJarhead03 wrote:

in that case doesn't the solid flex (but rebound) when the tube does not flex

No. If a tube has equal outside dimensions and material as a solid, it will flex more easily than that solid. Tube resists flexing better per weight though. "Flex" (deflection) is different than permanent deformation. The equation for deflection in bending is divided by the moment of inertia, (I) so if a member has a higher moment of inertia, it will deflect less under the same load. NOTE: deflection also figured by dividing by Modulus of Elasticity, which is based on the material. That's why an aluminum tube that is the same shape as a steel tube deflects 3x as much. It doesn't mean it will break any faster, it just bends farther when loaded in the elastic range. It is also why many aluminum structures are designed with larger members. Larger members have higher Inertia (and section modulus, for that matter) to smaller members of equivalent weight.

JeepinJarhead03 wrote:

giving the tube higher rigidity (less rebounding flex) but a lower max yield before permanent distortion?

As stated, the tube is more rigid than the solid pound for pound, but the solid is still more rigid.

JeepinJarhead03 wrote:

Metalurgy obviously aint my thing

Boiler · **Posted:** Sun Jul 19, 2009 1:54 am

Jeez...I can barely read my own threads, and I know what I'm saying. From now on I'll answer like this, but if anyone disagrees I'll be forced to numb you all with math and science and kill the thread.

A 1" square tube is not as strong, in any way, as a 1" square solid bar made out of the same material. Just assume I'm right and lets all go to bed...

JeepinJarhead03 · **Posted:** Sun Jul 19, 2009 2:33 am

what i do know

is I like grape jelly

RRO INSANE A-ARMS: Updated w/ pics

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