F/C chassis integrity (2 Viewers)

[Keith Burgan]

I may be off base here, but wouldn't the heat treat process make the metal more brittle as well as stronger? Would a non heat treated tube have more of a tendancy to flex and bend instead of fail completely?

Brian,
the increase in tensile strength over the "regular" 4130 is minor. The main reason for the post manufacture heat treat is to make the numbers more consistent so that the chassis all react the same. If the tubing is on the low side of the spec the car works like a wet noodle. It is the amplitude and frequency of the vibrations that is causing the cars to break and for now there appears to be no simple solution.

Roo

 

[Smiley]

Brian,
the increase in tensile strength over the "regular" 4130 is minor. The main reason for the post manufacture heat treat is to make the numbers more consistent so that the chassis all react the same. If the tubing is on the low side of the spec the car works like a wet noodle. It is the amplitude and frequency of the vibrations that is causing the cars to break and for now there appears to be no simple solution.

Roo

Keith,
Thanks for the explanation.

 

[Jay]

I read where Bill Miller said that by NHRA heat treating the dragsters It was the dumbset thing they could have done, Due to making it brittle, Many have said Corys car would not have broke like it did if it had not been heat treated. I understand what some of you are saying about heating them just enough, I take it the longer the treat the more brittle it gets. I'm like Randy I think that car was in a cracking procces when they took it up there to run it. Harmonics I'm sure was hudge part of this as well has the chutes. I was in Joliet when Gary Selz. backhalf came off when the chutes hit.

 

[Keith Burgan]

I read where Bill Miller said that by NHRA heat treating the dragsters It was the dumbset thing they could have done, Due to making it brittle, Many have said Corys car would not have broke like it did if it had not been heat treated. I understand what some of you are saying about heating them just enough, I take it the longer the treat the more brittle it gets. I'm like Randy I think that car was in a cracking procces when they took it up there to run it. Harmonics I'm sure was hudge part of this as well has the chutes. I was in Joliet when Gary Selz. backhalf came off when the chutes hit.

Jason,
Cory's car suffered what was basically an elongation fracture which would not have happened if the tubing was too brittle.

Heat treating is not a time based process as such and the post manufacture heat treat is very tightly controlled. That is why they use the process--to get the tensile strength to a narrow window. This is not a wave a big rosebud tipped torch over the tubing deal. The tubing is placed in an oven and heated and cooled at specific rates to specific levels.
From my understanding (and I am talking to people a lot closer to this than you) the frame was broken before the chutes blossomed. I was told specifically that the tire was the first thing to fail and that it chunked initially to set up the harmonics that caused the rails to fracture.

Roo

 

[Silly Savage]

The "harmonics" is what caused all the issues with Eric's car also....you have to really understand how much rubber is swinging around and shaking when they fail or even during tire shake. John was very lucky that the chutes caught the wall at the end and kept the cage from bouncing and continuing to roll down track with his legs exposed...would have been MUCH worse. It shows that all the work they did on the cage area and the belts kept John from worse head and neck injuries. With all that was blowing up around him, he was well protected. With my new car that is just about done, I have used some of the ideas that they used for seat belt mounting...when I had my crash I would have loved to have the head protection they have now....the belt mounting is an idea that was way over due.

 

[TJ]

I am w/ Randy G on this one as nothing has changed but everyone is looking for a fix....
I was looking @ some old timeslips in 92 when low e.t. in Dallas was a 5.07 @ 292 mph by Force and he was using a Plueger chassis w/out roll cage padding and a simple 5 point harness...
Now the teams are pushing 3 tenths quicker then in 92 and everything has changed in regards to chassis mods?
Maybe it is time for the NHRA to have a new chassis guru for them to go to for advice aside from Murf's, and his cars which are basically a Plueger clone...And these clones are not welded-up one-by-one by Murf himself...Murf builds a nice car but cannot compare to Plueger's stuff...

 

[Old Sg]

For those of you who are interested here is the technical properties of chrom moly tube. I have also added the definitions of the terminolgy.

Aircraft Alloy Structural Tubing ie: 4130 , MIL-T-6736
Available in two specifications

4130N condition N (normalized)
Min Tensile Strength = psi 95,000
Min Yield Point = psi 75,000
Elongation in 2" = 12%


4130HT condition HT-125 (heat treated)
Min Tensile Strength = psi 125,000
Min Yield Point = psi 100,000
Elongation in 2" = 12%

Here is a brief explanation of terminology.

Tensile Strength - In tensile testing is the ratio of maximum load to original cross-sectional area.
The maximum conventional stress, tensile, compressive or shear, that a material can withstand.
Yield Strength - The stress at which a material exhibits a specified deviation from proportionality of stress and strain.
Elongation - In tensile testing, the increase in the gage length, measured after fracture of the specimen within the gage length, usually expressed as a percentage of the original gage length.


Other factors which way in on metal fabrication of buildings, bridges, aircraft, race cars, etc.
Cyclical Loading - creating a fatigued structure
Heat affected Zone - The portion of the base metal which was not melted during welding, but whose microstructure and physical properties were altered by the heat.
Hydrogen Embrittlement - A condition of low ductility in metals resulting from the absorbtion of hydrogen.
Ductility - The ability of a material to deform plastically without fracturing, ie:elongation test.

SFI Foundation website SFI Web Site
What I am wondering is there any actual design load criteria set forth in the formulation of the requirements for chassis design?

I have a feeling it is just "seat of the pants" design.

In reviewing the SFI chassis design documents I have never seen any actual design loads given.

In other arenas such as buildings, bridges, aircraft there is always a registered professional engineer who takes responsibilty for the design. Commonly designated as the Engineer of Record.

Denny J.

 

[Silly Savage]

This is pure speculation, but something that I was thinking about....what if when the tire went and it wrapped up in the rear end and tore the body up, it locked up the rear end causing the torque to rip the chassis in half....??? Just a shear guess, but maybe a possiblilty??? Basically like locking up the axle rotation at 300+ miles an hour......I'd think that kind of force could bust that chassis in that area....

 

[.]

This is pure speculation, but something that I was thinking about....what if when the tire went and it wrapped up in the rear end and tore the body up, it locked up the rear end causing the torque to rip the chassis in half....??? Just a shear guess, but maybe a possiblilty??? Basically like locking up the axle rotation at 300+ miles an hour......I'd think that kind of force could bust that chassis in that area....

How could it wrap around the rear end when it's still mounted on the wheel?

 

[Smiley]

This is pure speculation, but something that I was thinking about....what if when the tire went and it wrapped up in the rear end and tore the body up, it locked up the rear end causing the torque to rip the chassis in half....??? Just a shear guess, but maybe a possiblilty??? Basically like locking up the axle rotation at 300+ miles an hour......I'd think that kind of force could bust that chassis in that area....

Funny you should say that - in one if the close up videos from the side.. As you see Kenny's car go by, it almost looks like the right rear on John's car is locked up for a split second, right before the smoke starts to billow off the tire.. If you watch the video, keep an eye on the white stripe, it seems to stop for just a moment, than you see the smoke.

You can also see a chunk of something flying off the car, probably a piece of tire.

 

[.]

Funny you should say that - in one if the close up videos from the side.. As you see Kenny's car go by, it almost looks like the right rear on John's car is locked up for a split second, right before the smoke starts to billow off the tire.. If you watch the video, keep an eye on the white stripe, it seems to stop for just a moment, than you see the smoke.

You can also see a chunk of something flying off the car, probably a piece of tire.

I think you're seeing the strobe effect of the camera, not the tire locking up. I just watched it again 5 times in slo-mo and don't see it locking up at all. Both tires would have to lock since it's a single solid axle. Also, the rubber you see flying off is from the left tire, not the right.

 

[Keith Burgan]

Now the teams are pushing 3 tenths quicker then in 92 and everything has changed in regards to chassis mods?
Maybe it is time for the NHRA to have a new chassis guru for them to go to for advice aside from Murf's, and his cars which are basically a Plueger clone...And these clones are not welded-up one-by-one by Murf himself...Murf builds a nice car but cannot compare to Plueger's stuff...

Terry,
things are waaaay different than they were in 92, or 88 when I was with Smith and Etchells, or 66 when I first started racing.
That 3 tenths (4 actually, and the 40 mph) improvement has a huge bearing on everything. In 1992 the cars did not have around 7000 pounds of downforce loading the tires, the motors were turning less rpms and so were the tires. Back then the cars were not running 265 mph at half track either.

A couple of weeks ago I had a Murf (Bernstein) and a Plueger (Densham) in my shop at the same time and although they have the same basic layout (engine in front etc) the McKinney car is definitely not a copy of the Steve car. The tubing layout is quite different between the two cars in several areas. The welds on Plueger's cars are awesome but the Murf cars are not failing in that area so that is a non factor in this discussion. The welds on Steve's chassis are the only place that I would class as superior as the detail bracketry and small component mounts on the Murf are a lot nicer. That said, the welds on a Hadman car are not as nice appearance wise as the Murf but they dont fail either.
One of the reasons that SFI listens to what McKinney has to say is that he has qualified engineers on staff and uses high end software to analyse his chassis designs. He has also instrumented cars with load cells to verify the computer generated load numbers.
I have known Steve personally since 1984 and first met Murf in 1998, I worked with Brad Hadman when we put Gary Scelzi's car back together at Frank Parks' shop after his 1999 Topeka crash and I also know Davey U, Don Long, Bob Meyer etc. All of them build race cars to the best of their ability which is considerable but right now we are starting to get into the twilight zone with these cars.

Roo

 

[TJ]

Roo,
Yes evrryone building cars today is doing a fine job, including yourself....Tony P was very complimentry of your work when talking to him @ the airport..
But in terms of choice the majority of fuel funny car owners would take a Plueger chassis over anyone else but there is a catch...Steve will not turn a funny car chassis over in a couple of weeks and leave welding up to paid employees...Murf did alot of lobbying to have NHRA connected to him..And that is great for his business and his cars look great..
Plueger is the only f/c chassis builder that Force gave his championship trophy too when Steve did not win the Car Craft builder award...
JFR wanted to hire Plueger just to build cars for his team a few years ago but Steve builds em one @ a time for anyone w/ the $$$$ and patience..
Whenever I stop by Steve' place in Whittier it is always an open shop w/ the best stories and the best place for 'whats going on in fuel racing' w/out being politically correct...

 

[Speedy_Sticks]

I know I am contriversial when it comes to these accidents.

But the driving job that John did before his chassis split was amazing! It was only after the split did John's car vier into Kenny's car.

But I really think NHRA need to look at F1 and have the F1 Safety tubs the F1 guys sit in.

In TF it would be easier to impliment, but harder in FC.

IF they had a tub like that, at least their body parts should be aok?

Even that nasty F1 crash this year when the BMW driver I think got a broken leg, could/should the NHRA be implimenting it?

As for the crash it's self, it was a FREAK accident.

Cheers

James

 

[timmydcarguy]

RG for president!!!!

 

[Gregg Pickens]

Why isn't anyone talking about just slowing the cars down? Maybe we have reached a point where the speed and load that is being placed on these cars has exceeded the capacity of the chassis, tires and just about everything else including the drivers. I love to watch a 330 mph run just as much as anyone else but I don't want to see it at the risk of killing or severly injuring more people. I don't recall the number of chassis/tire issues being as high when they where running "just" 300 mph.

 

[Nick Name]

I am not for slowing anybody down....But......Maybe now is the time to take a hard look at making these cars look like cars again. Get rid of the big dump truck air dam and spoilers on the trunk, etc. Slowing down will be part of the package as the crewchiefs will have to tune them way different to get them down the track.

Jay

 

[farmje]

I am not for slowing anybody down....But......Maybe now is the time to take a hard look at making these cars look like cars again. Get rid of the big dump truck air dam and spoilers on the trunk, etc. Slowing down will be part of the package as the crewchiefs will have to tune them way different to get them down the track.

Jay

Jay, in my opinion that would be a very bad move. These accidents happen how often? Not very. We just need to focus on making the cars safer. They will always find a way to go faster.

 

[Randy]

I said I was done...almost.

The year is 1906. There are two piles of "I" beams (steel) next to a river and the task is to build two bridges. Have engineer "A" build the first bridge and engineer "B" build the second.

After 5 years engineer "A's" bridge falls in the river along with with a couple cars and trucks that were going over it. Disasterous.

After 100 years engineer "B"'s bridge looks none the worse for wear even though millions of cars and trucks have been pounding it the whole time, plus dozens of earthquakes, strong winds and high water have been beating on it.

Same amount of steel, same location, different results.

After 101 years it has been determined that a critical beam on engineer "B's" bridge needs to be replaced because of rust and corrosion. Some bright engineer looks over the situation and decides he's smarter than engineer "B" and relocates the original rusted beam just slightly during the single beam replacement project. Within 6 months the bridge drops in a pile to the bottom of the river. Why did it happened? The engineer just scratches his head.

A flat tire on a funny car destroys the drivers compartment in less than one second. NHRA better park the entire field for the rest of the year before someone else gets killed. Or, NHRA needs to mandate engineer "P's" design and bring back the sanity. It starts with the top of the cage...before one of those comes off, too. And that's not a joke.

There are tube fitters and then there are structural engineers.

The story above tells the story.

RG

 

[Randy]

To Keith Burgan:

The following article gives insight to the properties of mild steel 4130, 4130N and the effect heat treating has with regards to the material and it's ability to withstand various stresses. It also discusses material failure points during stress and has an informative graph which clearly shows how dangerous heat treaded mild steel is when used in a stress related application. It even suggests that mild steel is so durable with regards to stress that a poor design won't result in a failure of the material. But if the design is poor and the material is heat treated the material will likely fail.

Poor design...Heat treated. Key words.

Let me know your thoughts. Be sure to click on all the links and read up on it. It's a long read but well worth it.

I would encourage all of you who have been following this thread to sit down and take the time to read this web site so you can learn and understand chassis material and what this discussion is all about.

KineOptics ... Mechanical, Optical, & Scientific Instruments

RG