Material smarts (1 Viewer)

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scottryana

scottryana

Joined
Feb 2, 2004
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This is a pretty smart group so I am kind of calling on Mud to help me think through something and see if I am even close.

With all of the 3/4link threads going on and since my builds are kind of on hold because I am broke I thought maybe I would do some miniature scale testing on links and materials. But here is where the hold up comes. Is it possible to just downscale everything by the same amount?

Say you wanted to compare 48" lowers in:

2.25" x 0.375" DOM
1.75" x 0.188 4130
2.25" solid 7075

Everything is divisible by 6.

2.25" x 0.375" would become 0.375" x 0.065"
1.75" x 0.188 would become 0.313" x 0.035"
2.25" solid rod would become 0.375"

Would it be worth while to get an 8" piece of each and then hang some weight off of them, etc?

The reason I ask if you could just divide each measurement by 6 and get an accurate representation is if you do it by weight. 2.25"x0.375" is 12.5lbs/foot. The 0.375"x0.065" is only 0.19lbs/foot

Similarly the 2.25" solid aluminum rod is 4.817lbs/foot and 0.375" solid rod is 0.14lbs/foot

So they do not scale with regard to weight. So how could/would you scale them to accurately test them?

Just curious and a little bored. Ha
 
I have zero clue, but like where your head is at. :cheers: and onward!
 
Simple answer is no. The bending calcs use the area moment of inertia, which for a circular section has the 4th power of the diameter as a term. And for simple bending, the length factor is the 2nd power. Simple linear extrapolation isn't going to get you there in this case.
 
Wouldn't it be easier (and cheaper) just to run the math on each material? Assuming you're talking about bending strength...
 
It would be easier to use the math if they were all circular. I used those 3 options because they are the easiest to explain with, but I actually wanted to compare an I-beam shaped aluminum truss as one of the options.

Bending strength was the first idea simply because the coilovers/bypasses would be mounted on the links like a trailing arm, so the link would have to support the weight of the vehicle as well. I was looking at the TIG welded trailing arms used on desert trucks and some of them are close to $4,000, and I was curious if something similar could be done with say a 3"x6"x48" piece of 7075 in like a said a modified trussed I-beam.
 
While that test wont give you precise scaled values for deflection it will give you relative strength of one shape vs another. Sorta. You must be bored.
 
If you know someone with SolidWorks or ProE with the materials displacement package then you can determine anything you want with whatever material you want, with any force you want, at any shape you want. Here is what I had done for my Rear Air Tank Shelf last year. And before you ask...I had to pay someone to have this done. I needed the piece of mind. :p

Screen Shot 2017-02-06 at 9.45.15 AM.png
Screen Shot 2017-02-06 at 9.45.29 AM.png
Screen Shot 2017-02-06 at 9.45.39 AM.png
 
Yeah I constantly have to be thinking about something or I find myself pretty bored.

But if the scaled down versions won't work I am not really sure how to get an accurate idea of how they would react. For instance if the 2.25"x0.375" DOM that weighs 12.5lbs/ft is scaled down linearly and only weighs 0.19lbs/ft, 65x less than it's full-size counterpart . Yet a solid 3"x6" aluminum bar weighs 22.03lbs/ft and linearly scaled to 0.5"x1" weighs 0.62lbs/ft which is 35x less than the original how could you compare the scaled down versions. I would think maybe you would have to do it based on weight.

Anyways it sounds like this little experiment is a bust. Kind of a bummer since I was hoping it would be a little easier, since the scaled down materials in 10-12" lengths are only $6-14ea. lol.



nukegoat said:
While that test wont give you precise scaled values for deflection it will give you relative strength of one shape vs another. Sorta. You must be bored.
Click to expand...
 
Sounds like you already know the answer. You have to do the calculations for each shape, taking into account the Young's modulus and moment of inertia for the load cases. This is all the software does.

PM me if you don't have the resources.
 
It's too early for this, but here you go:

I just ran through these numbers and the the stiffest (least deflection) option is going to be the DOM in the dimensions you mentioned.

Relative deflection:
DOM: 1
4130: 3.7
7075: 3.19

You should read this as the 4130 will deflect 3.7X as much as the DOM (in the listed dimensions at any load), and the 7075 will deflection 3.19X as much.

Depending on the heat treat of the 7075, I might not recommend it. It generally has an elongation of 7-9% which makes it fairly brittle. It won't bend too much before it breaks.
 
Hmmm interesting, 7075 links were all the rage on Pirate for a while.

The calculator posted below does it a little differently and says 1 is bending to deformation and the further from 1 the less likely the load is to bend the material permanently.

It shows
The closest to bend permanently is the
4130 - 2.48
then the DOM - 5.72
and finally the 7075 - 6.76

Haha it is kind of why I would love to have had it be linear so I could just make up some mini links and actually test it myself.


RogueEngineer said:
It's too early for this, but here you go:

I just ran through these numbers and the the stiffest (least deflection) option is going to be the DOM in the dimensions you mentioned.

Relative deflection:
DOM: 1
4130: 3.7
7075: 3.19

You should read this as the 4130 will deflect 3.7X as much as the DOM (in the listed dimensions at any load), and the 7075 will deflection 3.19X as much.

Depending on the heat treat of the 7075, I might not recommend it. It generally has an elongation of 7-9% which makes it fairly brittle. It won't bend too much before it breaks.
Click to expand...
 
I appreciate the offer, it isn't a huge deal, and the shape I would want to make would be rather complex so it isn't really something I could calculate easily. But I could make it fairly easily that is why I was hoping it would work to make up some mini versions and test them, but it makes sense that there is more to it.

Malleus said:
Sounds like you already know the answer. You have to do the calculations for each shape, taking into account the Young's modulus and moment of inertia for the load cases. This is all the software does.

PM me if you don't have the resources.
Click to expand...
 
This is my day job, so it's not much effort. Let me know if you change your mind. I don't really need a drawing, just the basic primitive shapes and their orientation and relationship to each other. And the material and dimensions of course, assuming the OP wasn't exact.

Once the calculation is set up, doing basic parameter changes is pretty easy, and you could do that yourself.
 
If you are looking at the material strength that might be correct, but he did not provide any material properties for these parts. 7075 is a high strength aluminum alloy we use on some aircraft component design. Depending on it's condition (T6, T651, etc) it can have a yield strength higher than your average normalized steel alloy. For instance, the yield of 7075-T6 is in the 70-75 KSI range where as a normalized 4130 2" tube is going to be in the 60-67 KSI range. In this scenario the 7075 has more strength - however the 7075 is going to deflection 3X as much as the steel under the same load because aluminum has 1/3rd the elastic modulus of steel (assuming they have similar cross sections.)

As soon as you start heat treating steels, however, they blow 7075 out of the water. A quenched and tempered 4130 2" bar will have a yield of ~140 ksi. I suspect that the steel he's looking at is not heat treated though.

"DOM" just refers to the tube production process "Drawn Over Mandrel" - but it is most likely 1010 or 1020 steel. Its difficult to say what the exact material properties of a cold worked tube are, but I suspect the DOM to be in the 30-50 KSI range for yield base on the numbers I have in front of me for hot rolled and cold rolled 1020.

The numbers I produced were from hand calcs, and not from the online calculator.


scottryana said:
Hmmm interesting, 7075 links were all the rage on Pirate for a while.

The calculator posted below does it a little differently and says 1 is bending to deformation and the further from 1 the less likely the load is to bend the material permanently.

It shows
The closest to bend permanently is the
4130 - 2.48
then the DOM - 5.72
and finally the 7075 - 6.76

Haha it is kind of why I would love to have had it be linear so I could just make up some mini links and actually test it myself.
Click to expand...
 
Made me dig out an engineering book so I could see the equations. I got the degree and then went off in the thermo/chemical realm and never really came back to this side. This is fun. Oh wait, I have a day job...
 
I didn't need the material specs. I have them...
 
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