i have a swaybar made of 1.5/0.25" tubing. (even that size of tubing is hard to find.) does a size of "chromoly" tubing exist that would provide roughly 20% more stiffness? e.g. 1.5/0.375, 1.562/0.25, maybe 1.562/0.3125. it needs to be heat treated to at least 180 000 psi (1250mpa).
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4140 tubing
- Thread starter dian
- Start date
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Orange Vise
Titanium
- Joined
- Feb 10, 2012
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- California
At 1.5" OD / .375" wall thickness, you're looking at DOM tubing, which is low carbon steel, e.g. 1020, not thru-hardenable.
Are swaybars subject to stresses that high? Can high stress areas be reinforced with gussets? Elasticity is unaffected by strength/hardness.
Are swaybars subject to stresses that high? Can high stress areas be reinforced with gussets? Elasticity is unaffected by strength/hardness.
Swaybar acts like a torsion bar and low alloy steel makes bad springs.
And if you reinforce the weak areas its not springy anymore..
4130 and 4340 would be viable alternatives, or the european 42crmo6 or 34crnimo6.
4130 is even available online in various sizes from aircraft spruce:
4130 ALLOY STEEL ROUND SEAMLESS from Aircraft Spruce
4130 is even available online in various sizes from aircraft spruce:
4130 ALLOY STEEL ROUND SEAMLESS from Aircraft Spruce
WizardOfBoz
Diamond
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So the OP asked for a dimensional change that gives 20% more stiffness. The material will not make a difference in terms of stiffness. The strength required of the material is pretty high. And, has been pointed out, if the dimensions chosen end up being too thick, the spring becomes a ridgid design element.
IIRC, the torsional stiffness is proportional to the cross-sectional moment of inertia, I = PI x .25 x (R^4 - r^4). Using the initial 1.5" diameter and 0.25" thickness, I get a new thickness of 0.421" Obviously, that size tube doesn't exist in nature. If we look at 0.375" wall, the increase in stiffness should be about 16%. Would that be enough?
Check this work before proceeding. I would see if you can find 1.5" od by 3/8 wall. You can play with the formula to see if other ODs and thicknesses give you what you want. Alloy won't matter for stiffness. Obviously the spring has to be strong enough in UTS and yield strength, but it is a spring and you need to check fatigue point. 4140 has generally good fatigue properties.
But I marvel at your UTS spec. Most of the chrome-moly steels I see are in the 850-1230 range. 1250 MPa exceeds even the strongest 4140 steel's UTS.. You are heading into the range of 18Ni maraging steels with that spec!. Given that you have such a bar in service, unless it's currently 18Ni, I suspect you may be ok with a lower strength spec, especially since you are increasing cross-sectoinal area.
That is to say a part's strength depends upon material, material treatment (HT, stress risers from machining) and dimensions. Does your strength spec take into account the extra 35% of cross-sectional area that your thicker walls allow you?
If you really need 1250 MPa and have to go to 18Ni or other exotic allow, your point about tube of the required dimensions being rare becomes a problem to the 4th power. Good luck!
IIRC, the torsional stiffness is proportional to the cross-sectional moment of inertia, I = PI x .25 x (R^4 - r^4). Using the initial 1.5" diameter and 0.25" thickness, I get a new thickness of 0.421" Obviously, that size tube doesn't exist in nature. If we look at 0.375" wall, the increase in stiffness should be about 16%. Would that be enough?
Check this work before proceeding. I would see if you can find 1.5" od by 3/8 wall. You can play with the formula to see if other ODs and thicknesses give you what you want. Alloy won't matter for stiffness. Obviously the spring has to be strong enough in UTS and yield strength, but it is a spring and you need to check fatigue point. 4140 has generally good fatigue properties.
But I marvel at your UTS spec. Most of the chrome-moly steels I see are in the 850-1230 range. 1250 MPa exceeds even the strongest 4140 steel's UTS.. You are heading into the range of 18Ni maraging steels with that spec!. Given that you have such a bar in service, unless it's currently 18Ni, I suspect you may be ok with a lower strength spec, especially since you are increasing cross-sectoinal area.
That is to say a part's strength depends upon material, material treatment (HT, stress risers from machining) and dimensions. Does your strength spec take into account the extra 35% of cross-sectional area that your thicker walls allow you?
If you really need 1250 MPa and have to go to 18Ni or other exotic allow, your point about tube of the required dimensions being rare becomes a problem to the 4th power. Good luck!
Most spring steels are over 1250 MPa ultimate tensile strenght so there is no need to go to superalloys yet at this level.
1250 MPa design stress on the other hand would be crazy high and probably even beyond what the superalloys can handle.
WizardOfBoz
Diamond
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I must be using different units than you. A common spring steel, SAE 1070, has a hot rolled UTS of about 700 MPa (93,000 psi). The OP asked about 4130 and 4140. 4140 comes in different mechanical property grades, but the strongest maxes out at about 1230 MPa. More common specs run less than 1000 MPa. What am I missing here?
Very nicely stated.
it might not be meaningless, if I understand the OP correctly and having seen quite a few sports cars, and either designed, modified or made replacement/new parts for them, the bar in this case doesn't act as a spring, because there are links at the ends that act as a spring, and it is by design, one of those links is "fixed" to the bar, the other one can be rotated, think of the "fixed" ones cross section being "I" shaped to resist bending and stay light, and the other link is adjustable, from completely "vertical" I to 45 degrees / to "horizontal" -, making the sway bar assembly act rigid or soft depending on the needs of the driver
so I suspect that the OP thinks the bar does act as a spring and wants to prevent it, to give greater control over the stiffness of the assembly by adjusting one of the links
regarding the question, we have a local distributor that carries some sizes, designations are exUSSR terminology, st45=1045, st20=1020, st30HGSA in usage is similar to 4140, you can check the sizes here - Rimans - Steel (Tube) | Catalog of industrial, constructional and tool steels , small quantities can be ordered, but they won't handle shipping, I can help out with that is you find something that you can use, would be easier if the destination was in EU though, seeing that the OP is from Switzerland
Can you post a pic of such setup or do you know what car models would use it?
Curious as I have never seen such a setup.
Winterfalke
Stainless
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I don't know if it's different outside of the few cars I'm used to playing with, but the BMWs and Audis I have driven absolutely do act as a spring. Same with my friends Mustang; to reduce body roll you install a thicker swaybar. The thicker swaybars have a higher torsional strength, and transmit more of the suspension compression forces to the other side. It's been that way as long as I can remember. Although I must admit I've never seen a tubular sway bar, even up to 30-35mm they've all been solid. I can't imagine any sized bar would be effective at transmitting suspension level of forces across a car without twisting, but I'm not really familiar with modern suspension geometry, so maybe? What cars use that type of setup?
I haven't seen a 35mm solid sway bar on a road car... that sounds like one hell of band aid to fix poor/cheap design by slapping what essentially is a weight anchor to the poor thing...
road car sway bars gi from one swing arm to the next basically, with a vertical connecting rod, sports cars (when regs allow) use a totally different concept, I'll post pics when I'll get back to my home pc, I'm sure I have some examples
road car sway bars gi from one swing arm to the next basically, with a vertical connecting rod, sports cars (when regs allow) use a totally different concept, I'll post pics when I'll get back to my home pc, I'm sure I have some examples
You wouldn't use hot rolled steel for (high performance) springs without further hardening and tempering. (or cold drawing)
ultimate tensile strength or yield strength correlates with hardness and to make good springs you need suitable hardness.
ie fiqure 5. https://www.asminternational.org/documents/10192/1849770/06181G_Sample.pdf
4340M or 300M would get you close to 2000MPa UTS and around 800-900MPa fatique limit IIRC from ASTM books.
https://www.cartech.com/globalassets/datasheet-pdfs/300m.pdf
https://www.ovako.com/PageFiles/5856/Performance in all directions.pdf
I think I found one example
Elephant Racing • QuickChange™ Blade Style Swaybars For Porsche 911/912/930
Never seen before and I have to say that I'm not 100% sold for the claimed benefits
yes, that is exactly what I tried to explain, and the benefit is that you can adjust it while you're driving sideways on a 35km special stage with slow and fast sections and to compensate for tire wear (because tires may last just 50-100 SS kilometers btw, or even less, and the grip changes affecting handling) etc to change the balance of the car to make it easier (thus faster) to drive, and I also see absolutely no benefit for one of these on road cars though 
unfortunately I can't find pictures of the cable-adjustable one, but the idea is that you are able to rotate the blade via a steel cable with a lever while sitting behind the wheel and driving
unfortunately I can't find pictures of the cable-adjustable one, but the idea is that you are able to rotate the blade via a steel cable with a lever while sitting behind the wheel and driving
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WizardOfBoz
Diamond
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- Sep 30, 2006
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I know. I was just going by what the people selling the chrome-moly specify as their top strength. For example, Timken sells a 4140HW (supposedly better than 4130). It maxes out at about 170ksi, less than specified, if you use a quench in the range that they recommend. But it looks like you could get more UTS and yield strength (with less ductility) if you used a lower or now quench. See their brochure here:
I will say this: material specification information on the web absolutely sucks when you compare it to things like the old "Carpenter Matched Tool and Die Steel" book. In that book, they they gave properties as annealed, as heat-treated, and then separately as tempered.
So you use a chrome-moly, and heat-treat it to a very hard condition, and then use minimal tempering. Got it.
Thanks for posting that article. But it appears to show that 4340 only achieves that UTS at the very low end of its tempering range - it is almost untemperered, correct?.
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Milland
Diamond
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I'm curious how the analysis was done that showed such a massive bar was going to be under such high strain that it needed that UTS. What is the vehicle, a tank?
One has to remember that the loads are acting through the frame, suspension, and anchoring to car, at some point you can rip your anchor points off or twist the frame more than the bar...
One has to remember that the loads are acting through the frame, suspension, and anchoring to car, at some point you can rip your anchor points off or twist the frame more than the bar...
moonlight machine
Diamond
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Been in use in Indy and top level sports cars for about 40 years, back to 935,962 Porsches, March and Lola GTP cars on up to every IMSA GTLM and prototype car. Old news, Very old.
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