Comp. Plus Chassis Article

http://competitionplus.com/index.php?option=com_content&task=view&id=4358&Itemid=24

 

I don't know about any one else, but i saw TWO blocks blowen in to the lane of Forces car, and the second one hit the body just in front of the back tire. the first one went by the back of the car and did not hit the car,

 

Gene; correct, there were two, but as has been stated hundreds of times........neither hit his car.

 

Cones?

Could it be possible that the debris from one or all of the four reflectors that are on the cones could have done some damange without being detected on film?? i would think at 300 plus some of that plastic or aluminum back plate could certainly take out a tire at that speed. i was just looking at the trophy cone i have and thats alot of material that could become little missles? And at that velocity might be hard to see with everything else that was happening.

 

My dad has run over many of those cones at 250 mph directly with the rear tires. Didn't leave a mark. Find another theory. The tire did go down, that isn't the major concern. The chassis failure is the concern.

That is the point of the entire article: Heat treated tubing is fragile. And I don't care which stress or strain data show that its "stronger" (IE deflects less under a given load) it is still the same material, it just behaves differently under load. The way most materials are categoized is by a .2% yield strength test. It is assumed that the material remains elastic within that region: meaning that it returns to its original shape when deflected (strained) to 1.002 * its original length or width. The force per unit area (F/A) required to attain that deflection is the stress. Now on a stress vs. strain plot that yield point defines the elastic region. Once past that point you enter the plastic region where additional stress deforms the material to where it doesn't return to that orginal shape.

(This file is a decent presentation of what I'm talking about.)
http://azkef.org/ChE231DR/Chapter_07A_outline.pdf

By heat treating a steel you create internal stress. (Heat treating is not normalizing, normalizing relieves the stresses in the crystal structure where as heat treating rapidly freezes the crystal structure in a semi disorganized orientation which counteracts deformation.) This pre-strains the material which gives it a higher yield and ultimate tensile stress value. If you find the plot on page 17 of the page above there is a plot of the stress vs. strain. Essentially what you are doing by heat treating is moving the elastic region to the right to achieve a higher yield stress value and creating the brittle material shown. This process cuts into the plastic region so that less deflection (strain) can be withstood before failure. Heat treating is best for parts like gears or shafts where wear and strength are major concerns. Tubing needs to flex. Remember even though you've heat treated it, its still the same material.

Here are 2 4130 materials, the first is a normalized sample.

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M4130R

The second is a heat treated sample.

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M4130T

Yes the heat treated sample has a higher yield and ultimate tensile strength, but the % elongation before failure for the heat treated sample is only 16.4% compared to the normalized tubing's 25.5%.

So when the chassis is twisted up, because one side is on the skids (or at least a deflated tire) and one is on a fully grown tire, the heat treated tubing won't flex far enough to allow the chassis to remain intact. If people believe the parachute pulled the car apart they are severely mistaken. Don't get me wrong, that additional force helped, but that is not the sole reason for the failure. In my opinion, the downforce of the body pushing on only one fully grown tire twisted the cage apart from the rest of the car becuase it would not twist far enough to have one side riding on the skids and one on the tire at its maximum growth.

The question you need to be asking is whether a normalized tube would have allowed the necessary deflection or if it would have still split the car in two? Are the skids on the cars close enough to the ground to prevent too much torsion on the chassis? If they strengthen the failed region and the same twisting occurs won't it just transfer that torsional stress to another region on the chassis resulting in another form of the same catestrophic failure?

So in conclusion (this is what we have to do when we write up lab reports) The best solution to this problem is to place skids directly below the rearend that would not contact the ground at launch when the tire is wadded up, but would provide a lesser amount of torsional travel when such a failure occurs.

Cody "The Flash" Perkins

 

OR how about going back to liners, or liners in the beadlocks?

 

Read this

Read this

http://www.nitromater.com/nhra/10854-prominant-fc-chassis-builder-speaks-his-mind.html

And this

http://www.nitromater.com/nhra/11036-compplus-story-fc-chassis-problems.html

The chassis Robert Hight is now running for the rest of the year was the former John Force Plueger car Todd Paton had for sale right here on Insidetopalcohol.

Here is an eyeopener if you care...

http://www.nitromater.com/nhra/10671-dragster-chassis-technology-ignored.html

 

This is interesting. My bolding
http://www.nhra.com/content/news/24477.htm

Bottom line. The world champ believes Steve Plueger's cars are safe. But at this point in time he will not allow any driver on his team to climb into a McKinney. I think that about says it all right there.

 

That response by JF was the politically correct version according to JF employees.

Scelzi was a little more to the point when he said this:

http://www.competitionplus.com/index.php?option=com_content&task=view&id=4415&Itemid=1

 

I've seen many statements that the tubing has been heat-treated above the N-Condition requirements, but, how do they know that? Maybe I missed it, but, where have the actual results of the McKinney "heat-treated" testing been posted?

From what I have read, McKinney was reprocessing (reheat-treating) the tubing to N-Condition, which is not uncommon.

Don't get me wrong, I don't think raised hardness on 4130 tubing is good, for the many reasons posted on the web, but, I think alot of people have jumped to conclusions without having any facts such as the test results.

The phrase "heat-treated" has been bandied about alot on the web without a clear definition. Heat-treat can be from anneal to normalization (N-Condition) to elevated hardness levels above 50C Rockwell.

In other words, you can heat-treat to N-Condition.

 

Paul; call it what it is "AB" Normalized tubing. I'm desperately trying to get my x-wife a ride, so I hope they don't ban them for that reason alone.

 

Hey Bob, I have an old broom you can have cheap if your x needs a new ride.

 

chassis

Cody What you are telling is true what they shoulld have looked for was signs that the chassis had rubbed the track before it came apart.

 

Paul,
Go here http://rgl.faa.gov/Regulatory_and_G...99C827DB9BAAC81B86256B4500596C4E?OpenDocument download chapter 4 and read 4-1 b

 

Bob, understand that, but look at 4-1.C, normalizing.

When I was in the aerospace industry as a design and manufacturing engineer, I had the chance to work with chrome-moly every so often, and, it was often sent it out for normalizing during the manufacturing process.

All I'm saying that a lot of people have speculated as to the "heat-treatment" without knowing what was done. If the tubing was hardened above N-Condition then that was wrong. If they were trying to redo the tubing to N-Condition for better control, that shouldn't be a problem.

 

I agree, but 4-1.C deals with the entire structure after it has been built and annealed/normalized in a highly controlled environment. Not using heat treated tubing before bending, welding.

 

Uncle Bob ! ! ! ! !

Ain't you glad you build Alcohol Floppers ! Those genius's that are building the S__T boxes with the Nitro Motors in them are not listening, at least one of them is not, and absolutely , without a Doubt , another driver is sure to die before someone wakes up................Sorry the truth hurts ! By the way, when will David S s car be running ? Happy Trails, Larry..........

 

Mike,

That is a good point. I'm not sure if there is a camera angle that would capture that but thats probably the only way to tell since after it broke apart the cage portion of the frame did a good bit of pounding around probably marking up the areas that would need to be inspected.

Gene,

Liners in the beadlocks would probably be a good place to start.

Paul,

What I was saying before is that the tubing is sold based on values such as yield tensile strength, such as the .2% offset. You seem to know that. It is possible to take a poor material and heat treat it so that it meets the yield strength of normalized 4130. It passes the standard tests of hardness, yield strength etc. but if you then normalize it, it returns to a poor material for all the necessary properties. I highly doubt this is the case.

I'll say it again, heat treating involves quenching and therefore is not the same as normalizing which is a slow air cooled process. I could heat treat mild steel to the point that it has the same characteristics (hardness and yield strength) as N condition tube but it would be an inferior material (and brittle as hell) because it lacks the necessary carbon, chromium, manganese, and molybdenum which are what make chromoly tubing so desireable. I don't know what better definition for heat treating I could provide.

Flash

 

When I was in the aerospace industry, the term "heat-treat" was used to signify whenever the material was subjected to elevated temperatures to control and/or change the metallurgical properties, such as anneal, normalize, precipation harden, temper, artificial age, etc. This process may or may not include an accelerated cooling like quenching. Here is a LINK to a definition of "heat-treat" as was used in the industry.

An example would be during the hydroform process, due to work hardening from each draw, the material may go thru many anneals, which does not have a quench, until the final form is achieved. This process was referred to as "heat-treat to full anneal condition".

Like I stated before, I don't know what the properties of McKinney tubing was after processing, and, I'm pretty sure most on the web don't either.

I'm not trying to start an arguement, just trying to quell harmful conjecture.

As an added note, I am more concerned with the welding than the heat-treating. It was reported that Wilkerson's chassis cracked in a weld. A cracked weld is from a bad weld that finally grew to be visible. From what I saw, Forces car had failures at or near the weld joints and that is very troubling.

I don't care about the heat-treated tubing, the weld joint should have been in an annealed condition and be as pliable as normalized.

There are many more variables in a weld that can cause problems like wrong filler rod used, contaminated weld, incorrect heat affected zone and insufficient penetration to name a few.

 

No arguement. I understand how your refering to the heat treatment process. In my experiences (Not many at only 21) heat treating is different than annealing or normalizing. I think we all seem to agree that we as alcohol racers are lucky that we didn't have to back half our cars to replace good materials with fragile dangerous materials.
Flash