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another thing, hypothetically, if the square got hit from the corner, wouldnt the steel theroretically collapse? or am i reading too deep?
and also what would be better, hot or cold rolled? i really dont know the diffrence in speaking with metal terms. yeah i know 4340 chromo is the blingy of steel, and 7075-t6 being aluminum, but what would be the better type in DOM?
Speaking strictly from a materials standpoint, I would go with cold rolled. Cold rolled has a higher hardness, slightly higher modulus of elasticity, as well as higher tensile and yield strengths. The downside is that it has less ductility (formability), because the cold-rolling process increases the amount of martensite in the material. This makes it slightly more brittle, in turn meaning that it has lower impact strength.
Hot rolled has a much higher ductility, but lower tensile and yield strengths, and is nowhere near as hard. Because of this, I would go with the cold rolled. Cold rolled is usually beneficial in structural applications, like cages, links, and non-wheeling related structural parts (I-beams). Hot rolled is usually reserved for when ductility and formability are needed. Hot rolled is also slightly easier to weld, but that can be corrected with proper pre- and post heating.
Normalized 4340 chromoly will have a much higher stiffness, tensile strength (more than 2x higher than 7075), yield strength (almost 2x higher), and hardness (HRB-100 compared to HRB-87 for the 7075). Aluminum does serve its purpose for links though, since it is roughly 1/3 the weight of steel, making it a smart choice for people who are serious about shedding weight on the vehicle.
In your case, I don't see a reason to waste money on chromo's or aluminum. Go with a plain carbon steel like most of the home-made or manufactured long-arms use and you'll be fine.
Last edited by dp96zj; 12-01-2011 at 08:38 PM.
Not unless you hit the entire length of that corner. I have bashed a couple of mine right on the corner and it scratches and dents ever so slightly but it definitely does not fold. Smaller diameter might be a different story.
DOM is the process not the material.
2x2x1/4 is about 5.41lb/fit.
2.5x2.5x1/4 is about 7.11 lb/ft
2" 0.375 DOM is about 6.51/ft.
So assuming we are talking about 6 feet of tubing for the control arms, you are only talking 3.6lbs or 10lbs difference depending which size/shape we are comparing it to. Not a huge deal unless you want to design it such that every pound counts, but seems like it would be well worth the tradeoff in weight for a trail rig built to be bombproof. I think most people wouldn't care about the "looks" of their control arms.
Running all of the calculations with the square tubing rotated at 45 degrees (which would simulate the type of hit you are describing) yields the same numbers as if it was oriented "flat". Although IIRC, square tubing loses some strength if it's rotated somewhere between 0 and 45 degrees. I don't remember the calculations off hand to give you an idea of how much. Although from what I've seen, the "flat" orientation is a good estimate of their overall strength in a control arm application since most of the hits they see are primarily going to be oriented up/down instead of at an angle.
One other thing to consider is that if you need to bend your control arms for some reason, working with round tube will be easier, but you may need to sacrifice wall thickness depending on how thick of tubing your bender can use.
OK my last post for now. Can't you see I'm just padding my post count? These are key points that might give clarity to all the nitty gritty overtechnical shit posted above.
This applies to DOM/steel links of comparable material:
Round is stronger by weight
Square is stronger by diameter (uneven loading/corner impact excluded)
Increases in diameter increase MOI/strength much more significantly than increases in wall thickness
i just prefer the look of 2" square. over 2.5" due to size.
and as far as performance.....round trumps square in my books. Keep in mind that it has been a long time but i did run several square links and i bent every single one of them. seriouse abuse but they bent.
i have yet to bend a round link more then a few degree's.
i know that the aluminum ones are getting bent all the time. but you never really hear about that on the forums since aluminum is the new bling.
Also the weight is less for same material for square or rectanguler tube vs round tube of somewhat larger size but less capability. So round is used for cost of manufacturing not strength. Uppers can be round and smaller since they do not take a hit. But lowers should be square or rectangular (tall side vertical) if you are planning on hitting them.
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