Nascar Chassis's

[Billet Benny]

From what I remember, chrom-moly chassis will fracture and create a "spear" effect. Where MS chassis will not do this. Any body hear this?
Thanks, BH

Oh, yea. We've all *heard* it. Doesn't mean it's accurate!

[jweller]

From what I remember, chrom-moly chassis will fracture and create a "spear" effect. Where MS chassis will not do this. Any body hear this?
Thanks, BH

Yeah I read a bunch about that back around the time Eric Medlen died. there was a lot of poop going around about the different types of materials used in funny car chassis and what was wrong with them. I'm just a race fan, not an engineer, so I really couldn't offer an opinion worth more than the air I'm breathing, but I have heard reputatble people blame cromoly. I know John Force changed his chassis after his accident.

[Billet Benny]

Yeah I read a bunch about that back around the time Eric Medlen died. there was a lot of poop going around about the different types of materials used in funny car chassis and what was wrong with them. I'm just a race fan, not an engineer, so I really couldn't offer an opinion worth more than the air I'm breathing, but I have heard reputatble people blame cromoly. I know John Force changed his chassis after his accident.

Chromoly is not to blame. The poor engineering decisions, bad manufacturing methods, and improper use of a material are not faults of the material itself. No need to get into the details of the information I've gathered and the conclusions I've drawn, but it's just not right to jump to such a conclusion considering just the material. The material is just one variable in an equation of hundreds of variables and unfortunately it's the variable easiest to see and first to get questioned. Oh well. I guess if some shops stop using it then that just makes demand go down and it'll get cheaper for me!!!

[Laiky]

Chromoly is not to blame. The poor engineering decisions, bad manufacturing methods, and improper use of a material are not faults of the material itself. No need to get into the details of the information I've gathered and the conclusions I've drawn, but it's just not right to jump to such a conclusion considering just the material. The material is just one variable in an equation of hundreds of variables and unfortunately it's the variable easiest to see and first to get questioned. Oh well. I guess if some shops stop using it then that just makes demand go down and it'll get cheaper for me!!!

If you would be willing to get into the details you know, i would love to hear them. I understand if not though.

[mustange70]

Also, if 4130 was subbed for mild steel and wall thicknesses lessened to maintain the same amount of yield strength the 4130 chassis would be LESS stiff than the mild steel chassis which would have more material and thus be the reason the mild steel chassis is stiffer. This is all covered heavily in old threads.

Mild steel is used because of how it behaves in crashes, as it will deform more before failure, whereas 4130 will have less deformation before failure, and will do so at a much higher force, thus transfering more energy to the driver raising the risk for injury, and it also makes it harder to be really sure when a piece of tubing has been damaged to the point of needed replaced, in this instance chassis stiffness has not a lot to with it, because good design will overcome that.


Also the more material for the same strength but a stiffer pipe, i dunno i find that hard to take, as correct me if i'm wrong but stiffness is calculated with using the size as well as the properities of the material, and with 4130 being both a stronger and stiffer material to begin with, i would think the stiffness would be the same, but i don't have that information on hand so i'm not completely sure.

[Billet Benny]

Mild steel is used because of how it behaves in crashes, as it will deform more before failure, whereas 4130 will have less deformation before failure, and will do so at a much higher force, thus transfering more energy to the driver raising the risk for injury, and it also makes it harder to be really sure when a piece of tubing has been damaged to the point of needed replaced, in this instance chassis stiffness has not a lot to with it, because good design will overcome that.

Hey now, we've been through this. Some of the archived threads have miles of my text in them..

The problem arises here when you compare materials and not the condition they're in. Citing normalized 4130 and normal 1018 mild steel you will find the elongation for both at break are not much different. This means both will plastically deform a large amount before fracture/failure. What is different is the 4130 will hang on longer and rupture at a much higher load. 4130 will also elastically deform more than mild steel and thus begin plastic deformation later. All in all, if you look at the area under this stress-strain curve (toughness) you will find 4130 normalized will plastically deform a fair amount before failure (just like mild steel) but will do so under a greater load so the area will be larger. This measure of toughness is another way of stating a material's ability to absorb energy. 4130 is technically a better energy absorber.

This sounds all well and good, the problem comes in manufacturing and design. 4130 has some pitfalls due to its hardenability. These come to light and produce more of the failure I think you imagine when improperly welded and/or improperly designed. The zones where the hardening may occur needs to be reinforced, welded correctly, and designed right so they don't see the greatest stresses and failure occurs somewhere in the rest of the parent material which is the normalized 4130 which is the great improvement over mild steel. Again I repeat myself, 4130 is an experienced builder's tool and leaves much less margin for error in design and construction methods than mild steel. A well done mild steel structure will still beat a poorly done 4130 structure everyday of the week. Compare two properly built structures and the 4130 comes out way ahead.

Mild steel is used in Nascar because it's tradition, it works, and with the way the rules are written 4130's advantages are negated and it would only increase the costs of the chassis. The cost increase would come from the material itself and the extra care and time needed to manufacture the chassis properly.

Also the more material for the same strength but a stiffer pipe, i dunno i find that hard to take, as correct me if i'm wrong but stiffness is calculated with using the size as well as the properities of the material,

Correct. The considerations are shape (od, id, square, round, etc.), length, material. Small changes in shape can actually have the largest effect.

and with 4130 being both a stronger and stiffer material to begin with, i would think the stiffness would be the same, but i don't have that information on hand so i'm not completely sure.

This is where you're off. 4130 is stronger yes, stiffer no. You'll see differences in numbers for the modulus of elasticity for 4130 and mild steel, but remember they're small changes when you consider the magnitude of the modulus of elasticity for 1018 which is around 29,000,000 psi and you can find mild steel numbers from 27,500,000 to 30,000,000 psi. That's the range of published numbers for 4130 too. In the real world it is practically zero difference and even the most delicate machines can't consistently measure a difference. Shape becomes a much more influential factor.

[Conrad_Turbo]

Mild steel is used because of how it behaves in crashes, as it will deform more before failure, whereas 4130 will have less deformation before failure, and will do so at a much higher force, thus transfering more energy to the driver raising the risk for injury

I certainly wouldn't want a 4130 1.5" tubing failing and "hitting" a driver...but I'm sure it'll be just as leathal if it was a mild steel 1.5" tubing as well. If 4130 is improperly welded it will break sooner than a mild steel connection that is properly welded, which has the same mentality of less deformation (since the 4130 broke much sooner) than a mild steel connection, so in this case the mild steel would transfer more energy.

[ASKANDY]

The welding is where we see the most problems with 4130 and the people that dabble in it. You tend to find some people trying to mig this stuff, which it will but because the arc transfer is more "harsh" with mig than TIG, the toes of the weld are not infused or dilluted properly with the base metal which can also cause cracking in that brittle area.
There is nothing wrong with 4130 chassis when done right. This is why the NHRA and IHRA demand that chassis of 4130 in the faster classes have to be tig welded.
The main reason I see people getting hurt is that they "Think" they can use lighter, thinner tubes because they believe it is a stronger material. Then they go and weld it with mig and wonder why they don't get the elongation at the joint when it takes a severe hit.
We saw quite a bit of 4130 being used in some parts of the NASCAR chassis and suspension systems where they wanted to save weight. NASCAR put an end to this by changing the rules on material thickness by giving each part a min material thickness thereby eliminating the advantage of the 4130 since at any given thickness, the difference between 4130 and mild steel is negligable.

Have fun!
Andy