Speedway Parts
- Thread starter herman
- Start date
one finger john
Active Member
So let me get this straght. If you take a Speedway chassis, that's made in China, and it's made out of 2in. bar stock (aluminum), and you put it between two cinder blocks (cement), and Ted stands in the middle of it, it's gonna FLEX ????
This surely is a wandering thread. I think we need George Barnes to chime in.
John
This surely is a wandering thread. I think we need George Barnes to chime in.
John
The key to all this was (pound for pound). Just like comparing aluminum to steel.
We have two benders in our shop. Years ago when we did dragster chassis we used a lot of 1" .058" moly tubing. You could bend it by hand with just a long handle. Now we do these radius rods 1" .219 wall and you have to use the hyd ram to bend it. We have not had any reason to try and bend 1" solid.
We have two benders in our shop. Years ago when we did dragster chassis we used a lot of 1" .058" moly tubing. You could bend it by hand with just a long handle. Now we do these radius rods 1" .219 wall and you have to use the hyd ram to bend it. We have not had any reason to try and bend 1" solid.
Noob said:I'm sure there is some math out there for this calculation. Not that I know what it is, but I'm sure there is some.
I posted a link to a thread on The H.A.M.B. giving the calculations, but I guess no one looked at it. A poster asserted that tubing was stronger than solid and another member posted this explanation. Here it is:
"This is not correct.
Tubing is stiffer for a given mass (or rather cross sectional area, but if you're dealing with the same material for both parts, the greater CS area yields the greater mass). A solid bar of equal diameter to the tube in question is obviously of greater mass, so it is also as stiff or stiffer.
It's all about moment of inertia. Think of the moment of inertia as the measure of the geometric stiffness of a given cross section.
For that 7/8" dia x 0.140" wall tube, the moment of inertia is equal to:
[Pi(D^4-d^4)]/64 = 0.049(D^4-d^4) = 0.049*(0.875^4-0.595^4) = 0.023
Where:
D = Outside Diameter of Tube in Inches
d = Inside Diameter of Tube in Inches
Pi = 3.15159
For the 7/8" dia round solid, the moment of inertia is equal to:
(Pi*d^4)/64 = 0.049*d^4 = 0.049*0.875^4 = 0.029
See that? Not a huge amount, but the solid is stiffer than the tube for the given 7/8" outside diameter. The closer that the tube gets to becoming a solid (IE the thicker the wall becomes), the closer those two numbers will get to being equal, but the tube will never overtake the solid. To do that, you need to increase the outside diameter of the tube.
What makes tubing great is that for a given weight, you get more stiffness (or, for a given stiffness, you get less weight). You can take that same mass of steel making up that 7/8" solid rod, and instead turn it into a 1 1/2" OD x 0.140" wall tube (very nearly identical cross sectional areas).
That 1.5" tube will be just a fuzz lighter than the 7/8" solid but nearly five (5) times stiffer. THAT is where tubing really shines."
If anyone chooses to disagree with the science behind this discussion, there's nothing else I can say to convince the non-believers.
Bob
fluidfloyd
Active Member
bobscogin: I posted a link to a thread on The H.A.M.B. giving the calculations, but I guess no one looked at it. A poster asserted that tubing was stronger than solid and another member posted this explanation.
If anyone chooses to disagree with the science behind this discussion, there's nothing else I can say to convince the non-believers.
Bob
Bob,
I did read your post over on the H.A.M.B. and you are on the money. The basic laws of physics haven't changed in my lifetime and I doubt they will in the future. The math just doesn't lie. Thanks for your effort in this on going discussion. The one thing some people forget to factor in is "application." Just because they know the strength of a material they forget that loading it into compression, tension, torisonal or shearing loads all make up for diferent results. I have no doubt that you know how to apply the correct size and material to the design to get the desired results. Only brute or mass material strength can sometimes over come bad design. In the old days there was a lot of that going on mainly due to a lack of training or understanding. So here's hoping to better designs through better engineering because of better education. Ride Fast, Ride Safe!
George
If anyone chooses to disagree with the science behind this discussion, there's nothing else I can say to convince the non-believers.
Bob
Bob,
I did read your post over on the H.A.M.B. and you are on the money. The basic laws of physics haven't changed in my lifetime and I doubt they will in the future. The math just doesn't lie. Thanks for your effort in this on going discussion. The one thing some people forget to factor in is "application." Just because they know the strength of a material they forget that loading it into compression, tension, torisonal or shearing loads all make up for diferent results. I have no doubt that you know how to apply the correct size and material to the design to get the desired results. Only brute or mass material strength can sometimes over come bad design. In the old days there was a lot of that going on mainly due to a lack of training or understanding. So here's hoping to better designs through better engineering because of better education. Ride Fast, Ride Safe!
George
fluidfloyd
Active Member
Ted Brown; Will you agree with this?? you have a 2" solid axle, can you tell me it will be less strong with a 22 cal. hole down the center?? or stronger?? You know it will be stronger, (in all directions) no matter what the math says... :lol:
Ted,
There will be amost zero difference in a bending load on the two axle sizes you have ask about.
2.0" solid bar that is 36" long and fixed at one end. Apply 200lbs of force and it will deflect 0.132"
with a bending stress of 9167 psi.
2.0" x .22" ID tube that is 36" long and fixed at one end. Apply
200lbs of force and it will deflect 0.132" with the same bending stress of 9167 psi.
If the bending stress exceeds the material yeild strength then the part will take a permanent deformation and will be considered failed.
That small cross section of only .22 diameter is the nuteral axis and really contributes minimum strength in bending or torsion. If you want the torsional comparisons just let me know.
George
Ted,
There will be amost zero difference in a bending load on the two axle sizes you have ask about.
2.0" solid bar that is 36" long and fixed at one end. Apply 200lbs of force and it will deflect 0.132"
with a bending stress of 9167 psi.
2.0" x .22" ID tube that is 36" long and fixed at one end. Apply
200lbs of force and it will deflect 0.132" with the same bending stress of 9167 psi.
If the bending stress exceeds the material yeild strength then the part will take a permanent deformation and will be considered failed.
That small cross section of only .22 diameter is the nuteral axis and really contributes minimum strength in bending or torsion. If you want the torsional comparisons just let me know.
George
Ted Brown
Member
Thanks George, that was very interesting, still funny that the stock axles drilled last soo much longer than in the stock solid form.. but who Iam I to say different... well I now am not worried how much differeance it really makes, as I do not drag race anymore, just slow crusin for Me. Thanks Ride safe
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