Who is interested in roll cage and sub frame connectors twice as strong as 4140?

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I am a believer in building a car to what you intend to use it. 50% or deaths in crashes happen below 35 mph just saw that on the net today and the net does not lie, lol.
Not joking. I worked with Swedish Steel to use their materials in automotive and farm equipment designs to make stronger and lighter.
I am working with Swedish Steel to see if they are willing to make inch sizes in tubing or just metric. The current SCCA rules call for roll bars to be 1.5" .120" thickness tube for roll bars on cars over 1,500 lbs. or 1.75" .095" wall.
I am working with as mfg of tube benders and they currently do not support the millimeter sizes. The Domex material that Swedish Steel makes is twice the strength of 4140 and 4 times the strength of current sub frame connectors so a big gain is out there.
I am going to make the investment to build my cars using the new materials that are way better. There are no weld issues because the Swedish Steel Domex does not depend on high carbon to gain the strength. There are no weld issues like with 4140.
Give me your thoughts. Would anyone want to buy a cage or sub frame connector way ahead of any made today? I am going to do for my track days car and the Q code vert. Not going to have a car without bars with those capabilities. The track days car will be to the Kar Kraft specs plus some.

 

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I have a MS in engineering mechanics and worked as a structural engineer for many years. I have worked with some fairly exotic materials in the aerospace industry. 4140 is crap steel and I cannot think of a single area where it would be used except in tooling (great for that). MIL-HDBK-5 has been replaced with a SAE document that I can't recall. Problem is we don't do much welding on high strength steels. Fty of 4140 is around 60 ksi (yield strength above which the material yields but does not fail, i.e. it takes a permanent set where the material does not return to quite same shape). Many good aluminum alloys are 70-75 ksi however aluminum is about 1/3 the stiffness and weight of steel. If the material you are talking about can be hobbyist welded then it is a good choice. For a reference I used steel that was 220-280 ksi (PH13-8 up to AERMET 100). Any of these steels would likely require special inspection techniques after weldment. There are some very special techniques required for welding these types of steel.

 
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The welding of this material was never an issue and the program we use on was awarded the Swedish Steel best use for that year. It is way better than anything out there and way easier to weld. Why knock it?

 

cwalker509

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Not knocking the swede steel at all. If it is hobbyist weldable then it is an excellent choice. I can look into alternatives that are not proprietary that may be easier to source and less expensive. 4140 is great foe so many applications because it is cheap and easy to work with 

 
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The cost is not the issue. My customers always looked at cost. They would not have used it it was not cost effective. If you want the best cost has little influence. Ether best or junk.

 

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What is the reason no one makes a "bolt in" subframe connector? A pre-welded one piece X or Ladder style that snugs right up to the floor would be great. 

 

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What is the reason no one makes a "bolt in" subframe connector? A pre-welded one piece X or Ladder style that snugs right up to the floor would be great. 
It's hard to insert through the door or windshield, don't you think?

 

Horsin' Around

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No roll bar/cage,  just bolted to the bottom to stiffen up floor pan.

 
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I think someone did not read the information. The reason for the Swedish Steel being better is there are no weld issue. BTW has anything you worked on been given the most innovative use of there steel before, mine has. Their steel is way ahead of others. This is way ahead of anything being used in sub frame connectors or roll bars currently. If not so please publish the information.

 

cwalker509

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I pulled the brochure on domex. It comes in various grades from around 52 ksi to 100ksi. From what I remember it seems like where domex may shine is that it is easily cold formed. It also offers some improvement in weld strength characteristics particularly hydrogen embrottlement. It did mention that MAG (metal active gas) seems to be preferred. Anyone certified for wlding like this? I am not in any way shape or form. All this being said....what is the underlying rationale for doing this? Is it stiffening the structure? Does yield strength even play into it? I do not know. Many things are designed with deflections in mind as opposed to failure strength. I have designed for both. For instance residential floor joist spacing is designed by deflection and not failure strength. Someone would need to analyze the loads and stress in something like this. Just food for thought. Stronger is not necessarily better if you never approach the yield strength. I am just trying to give a perspective of how I would approach designing something like this. That is why 4140 is used in tooling. It is stiffness designed rather than strength designed so it is good enough.

 
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Well gents, I know squat about types of steels beyond the basics. My background includes machining and as such, have only used 4140 in tooling, it's also known as Pre-Treat. I recently found out that apparently some cheapo leaf spring manufacturers also use 4140 for springs. Really! Springs!

Why I chimed in here is simply this, what does NASCA or other racing organizations specify? If it's good enough for racing at 200mph and drivers survive horrible looking crashes, why the need for some other exotic steel? Just asking the question, not to start a war. 

 
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droptop73

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I believe the tubing used in racecars is 4130 or commonly called chromoly. 

4140 is oil hard tool steel. 

 
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Don C

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I like the idea of using steel that is both stronger and weld friendly. However, just because a steel is stronger (generally shown by tensile and yield strengths) a good steel also has to have toughness, ductility, and weldability. In other words reduced fatigue cracking and work hardening (embrittlement) and hardening from welding. Railroad rails are a good example of a steel that has both strength and ductility but welding requires a certain process to prevent brittleness.

So in other words I would need to see the specs on it and I definitely have an open mind for trying something rather than 4140. And one other thing, it needs to be compatible with welding to the subframes in our cars. To me a bolt-in subframe connector wouldn't be that effective.

 

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You'd have to buy a f-ton of tubing to get someone to make you a special size. 

I can't believe that tube bending equipment suppliers are not supporting metric sizes, it's not 1955 any more. You can order mandrels, dies and wipers in any size you need, as long as the equipment supports it and it'll form properly. If you're going to form these components, you're running the tubing through a mandrel bender, and there are far more tube forming equipment manufacturers in "metric" countries than there are in the US. 

The market will never support anything more costly than 4130 in any volume. We sell 100 mild steel cage kits and hoops to one 4130 kit sold. 

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Tnfastbk

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You'd have to buy a f-ton of tubing to get someone to make you a special size. 

I can't believe that tube bending equipment suppliers are not supporting metric sizes, it's not 1955 any more. You can order mandrels, dies and wipers in any size you need, as long as the equipment supports it and it'll form properly. If you're going to form these components, you're running the tubing through a mandrel bender, and there are far more tube forming equipment manufacturers in "metric" countries than there are in the US. 

The market will never support anything more costly than 4130 in any volume. We sell 100 mild steel cage kits and hoops to one 4130 kit sold. 

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Something like this for the metric bending is what we use

https://www.swagelok.com/downloads/webcatalogs/en/MS-01-179.pdf

 
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droptop73

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Strength is also as much about the design of the structure as the material. Most if not all racing sanctions will sonic check the tubing thickness based on the material used. To introduce a new material and get sanctioning bodies to accept it may be a challenge too. That said, I've seen some very scary stuff at the track. 

I may not be smart enough to be scared but I don't like the look of a roll bar in a convertible. Not in mine anyway. 

 

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From what I gathered from David's post, the strength trade off is lighter weight. If you can make your cage/subframe lighter, but just as strong, then you have a performance improvement. But how much lighter?

 

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By making it lighter you are also making it less stiff. I am uncertain if roll cages are primarily for safety (i.e. roll over) or for stiffness. I lean towards the former so make it out of the strongest material available. High quality 7000 series aluminum is stronger than most "basic steels". It is roughly 1/3 the density and stiffness of steel. Look at some of the alloys used in F1 and get out your checkbook. There are lots of options but "value" of going a specific way is subjective so long as it meets requirements 

 

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