Spaceframe Ultima steel ?
Discussion
02PRUV said:
If they did a cromolly option I would be all over it like a fat kid to a cupcake.
But then, wouldn't that be counter productive? 
Wouldn't you have to go thinner walled to get weight benefits for the same stiffness? Or maybe stiffer for the same weight?
Other than the raw material cost (which could easily be an 'option'), what is really problematic about using chromoly steel? It welds the same doesn't it?
I wonder what could be cooking behind this thread 
I've been looking into Moly tubing here, and it's about 4X the price of the normal ERW stuff and 2X the price of the CDS. I also have a guy local to me that's a Tutor at a our local Engineering College, and he knows all the in's and out's of Moly, Inconel and Titanium.
He asked me if i was using moly, and proceeded to explain the issues with having to heat treat moly after welding was only on realy heavy wall stuff. The 3mm and below wall thickness does not need to be heat treated, and he has the fracture and stress tests to prove it. So realy moly is an option, just an expensive one as he also explained you need a Pro to weld it to get it right....
But also of note I was told by him there are alot of race series in North America now that don't allow ERW in a tube frame chassis, they want CDS as a minimum. It's something to do with welded seem down the pipe fracturing and being a danger to the driver / passenger. But suspect that would have to be a pretty bad accident to get that far on a road car. FYI
He asked me if i was using moly, and proceeded to explain the issues with having to heat treat moly after welding was only on realy heavy wall stuff. The 3mm and below wall thickness does not need to be heat treated, and he has the fracture and stress tests to prove it. So realy moly is an option, just an expensive one as he also explained you need a Pro to weld it to get it right....
But also of note I was told by him there are alot of race series in North America now that don't allow ERW in a tube frame chassis, they want CDS as a minimum. It's something to do with welded seem down the pipe fracturing and being a danger to the driver / passenger. But suspect that would have to be a pretty bad accident to get that far on a road car. FYI
http://www.scribd.com/doc/63386005/22/COMPUTER-AID...
verry interesting, to read,
and there are a lot ways to better things up to the purpose,
wilfried.
verry interesting, to read,
and there are a lot ways to better things up to the purpose,
wilfried.
Interesting but was it me or did they miss-out the fact that the cage is made from 3mm CDS as should be the small sections of the cage extending to the floor between the frame rails, and also it should be 3mm cds on the 38mm tube extending of the front bulk head that takes the bending/ twisting load of the Suspension Shock mount. Also the engine and gearbox when bolted in do have an effect to the stiffness, yes there rubber mounted but they still effect the rigidity, maybe not by much but still...
Not that I'm picking holes but the X brace on the rear Diagonals would hit the engine on any LS7 Ultima chassis I know off. I put in that X brace but my bars go to the rear of the chassis, and the engine is lower.
Not that I'm picking holes but the X brace on the rear Diagonals would hit the engine on any LS7 Ultima chassis I know off. I put in that X brace but my bars go to the rear of the chassis, and the engine is lower.
The difference by input of 1.5 or 3mm is possible
the explanation why there cad diagnostics had a lower
Nm/deg output than the physical test, there input in the cad diagnostics
for the steel was A36 steel type, what i think is not correct and must
have been 1041 steel and would give the same result as the physical test.
now we can do a simulation with 4130-4140 alloy with an estimated
outcome of >7800 Nm/deg for an unmodified chassis.
We need to know facts, before planning mods or building our own chassis/frame.
wilfried.
the explanation why there cad diagnostics had a lower
Nm/deg output than the physical test, there input in the cad diagnostics
for the steel was A36 steel type, what i think is not correct and must
have been 1041 steel and would give the same result as the physical test.
now we can do a simulation with 4130-4140 alloy with an estimated
outcome of >7800 Nm/deg for an unmodified chassis.
We need to know facts, before planning mods or building our own chassis/frame.
wilfried.
GTRCLIVE said:
Interesting but was it me or did they miss-out the fact that the cage is made from 3mm CDS as should be the small sections of the cage extending to the floor between the frame rails, and also it should be 3mm cds on the 38mm tube extending of the front bulk head that takes the bending/ twisting load of the Suspension Shock mount. Also the engine and gearbox when bolted in do have an effect to the stiffness, yes there rubber mounted but they still effect the rigidity, maybe not by much but still...
Not that I'm picking holes but the X brace on the rear Diagonals would hit the engine on any LS7 Ultima chassis I know off. I put in that X brace but my bars go to the rear of the chassis, and the engine is lower.
I am surprised that there was no bracing suggested (in an x formation) between the rear suspension mounts - if this was made removable so it was practical, it would be highly advantageous (though clearly not as effective as being welded in). This is something we are looking at.Not that I'm picking holes but the X brace on the rear Diagonals would hit the engine on any LS7 Ultima chassis I know off. I put in that X brace but my bars go to the rear of the chassis, and the engine is lower.
I also never gave any thought to the front roll cage mounting - this is an area where some serious triangulation would be beneficial.
bauermann said:
... but much stronger,stiffer.
It won't be any stiffer. Stiffness in a space frame is related to the Young's Modulus and the tube cross section. Young's Modulus is pretty much the same for all steels so unless you change the tube sizes stiffness won't change much.GTRCLIVE said:
So realy moly is an option, just an expensive one as he also explained you need a Pro to weld it to get it right....
Good point. The best material in the world won't make your design any better at all if you lack the means to use it properly.There are two issues. Which is more important depends on the design of the chassis.
If the chassis is close to a properly triangulated structure then the chassis stiffness will depend on the Young's modulus and cross sectional area of the tubes. The only "but" in this is if the tube cross sections are so small that buckling becomes an issue.
If the chassis is not properly triangulated then the size, as opposed to just the area of metal, in the tubes becomes more important. With little triangulation the chassis will depend entirely on the shape and wall thickness (second moment of area in engineering talk) and the Young's modulus (again) of the tubes. The cross sectional area will be far less important.
If the chassis is close to a properly triangulated structure then the chassis stiffness will depend on the Young's modulus and cross sectional area of the tubes. The only "but" in this is if the tube cross sections are so small that buckling becomes an issue.
If the chassis is not properly triangulated then the size, as opposed to just the area of metal, in the tubes becomes more important. With little triangulation the chassis will depend entirely on the shape and wall thickness (second moment of area in engineering talk) and the Young's modulus (again) of the tubes. The cross sectional area will be far less important.
i would think it would be unwise to locally stiffen just one area of a chassis as this would result in extra load being applied to the next joint or section of the chassis, if this is to week then it will flex more than it would previously, this would quicken the fatigue rate in that section and posibly result in an early failure compared to if it had not been modified.
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