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Author Topic: Tube Frame Safety / Design  (Read 8881 times)

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nvheattreating

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Tube Frame Safety / Design
« on: December 30, 2009, 02:42:19 PM »
Gents,
I thought you might find this article interesting.  Bill Miller is a customer of mine and has some definite opinions on frame design and fabrication.  Especially when people he knows have been killed because of improper design and fabrication.

http://www.bmeltd.com/Dragster/tubulartales.htm

patm@nevadaheattreating.com
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Offline fabr

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Re: Tube Frame Safety / Design
« Reply #1 on: December 30, 2009, 02:44:55 PM »
COOL,we'll /I'll read it now. Gotta get to the shop now to do some VOODOO HT experimenting. rofl rofl
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"There can be no divided allegiance here.  Any man who says he is an American,
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loyalty to the American people."
Theodore Roosevelt 1907

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nvheattreating

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Re: Tube Frame Safety / Design
« Reply #2 on: December 30, 2009, 03:01:51 PM »
VooDoo Heat Treating is my life.  ;D

I wish my employees were as interested in heat treating as you are.

Pat
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Offline fabr

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Re: Tube Frame Safety / Design
« Reply #3 on: December 30, 2009, 03:06:33 PM »
Yeah but YOURS is MODERN VDHT! LOL!!!!
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

Offline fabr

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Re: Tube Frame Safety / Design
« Reply #4 on: December 30, 2009, 03:07:11 PM »
Over and out for now .The shop is seriously calling. Got some powder coating to do in the other oven. Oops,I need a new topic.  ;D ;D
« Last Edit: December 30, 2009, 03:10:07 PM by masterfabr »
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

JimmieD

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Re: Tube Frame Safety / Design
« Reply #5 on: January 25, 2010, 09:22:08 AM »
Very interesting, thanks! Looking at the chassis pictures there, typical of Funny Cars, I'm impressed with how bad the overall chassis design is. Heat treating or not is one issue, but all the heat treat in the world can't help a basically bad design. Looking at the bending moments in the pictured chassis, either before or after extra bracing, it's a recipe for disaster and an accident waiting to happen!

I wrote up a critique but it takes many words to describe and I don't want to blow bandwidth here. The forces fed into that chassis are all focused on 2 unsupported frame members so even after one run, assuming the driver lives through that, the chassis is rendered junk from then on! Scary, man, scary!
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SPEC

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Re: Tube Frame Safety / Design
« Reply #6 on: January 25, 2010, 09:37:59 AM »
Lets hear it J...
We have all the room you need ;D
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Offline fabr

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Re: Tube Frame Safety / Design
« Reply #7 on: January 25, 2010, 09:44:54 AM »
Please post up your opinions. We have all the room needed. As for the funny cars ,they are speciality vehicles that have proven time and time again how safe they are in an accident. We may be comparing apples to oranges . Let's talk!
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

Offline BDKW1

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Re: Tube Frame Safety / Design
« Reply #8 on: January 25, 2010, 10:39:13 AM »
Quote from: JimmieD on January 25, 2010, 09:22:08 AM
Looking at the bending moments in the pictured chassis, either before or after extra bracing, it's a recipe for disaster and an accident waiting to happen!

Dragsters are an animal unto themselves. They need to flex and bend. A really rigid chassis would do nothing but smoke the tires.
 
That being said, only a fool would weld heat treated tube without any post process heat treat of the entire chassis.
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Offline fabr

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Re: Tube Frame Safety / Design
« Reply #9 on: January 25, 2010, 11:26:20 AM »
Apparently that is what is done in TF and FC. I've been away from the sport for about 5 years now. I also paid little attention to TF/FC materials specs. I am just amazed at the stupidity of using WELDED JOINTS on HARDENED TUBE.  That brings up the point od our ongoing arguments of 4139 vs Mild. I am a proponent of 4130 but NEVER in a million years would I use hardened OR CONDITION N. Neither have the ductility needed when welded IMO. I only use ANNEALLED 4130. I once bought some 1 5/8" .095 4130N and when bending it broke. In my pea brain I thought -none of that crap for me! Always made sure then that all I bought was annealed. I guess my blind luck pointed me in the better direction.   
  THat was a very informative article and much appreciated IMO. Great food for thought.
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

JimmieD

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Re: Tube Frame Safety / Design
« Reply #10 on: January 25, 2010, 11:47:02 AM »
Okay, here goes. Hard to explain without posting drawings, and I'm no doctorate in frameology, but...

On that chassis with before & after pics, looking at the sides as one big panel made up of three slant parallelograms plus a forward girder, there is first a rear triangulated wheelie bar attached at bottom to the most rearward vertical tube [v1], at a point a few inches above chassis bottom-most point, and again by a short strut brace a few inches above that connection welded to v1. It is then attached at top to the uppermost frame side rail.
 
From wheelie support there are 3 slant parallelograms forming driver seating area, followed by front chassis section as a girder. Next forward from wheelie support is the first tube side panel with X bracing from v1 to v2 inside a slant parallelogram, which v2 is also attached to the same upper frame tube that wheelie bar attaches to. Next forward second side panel is another slant parallelogram, but with a single bracing strut from bottom of v2 on to the top of v3, no X bracing. Next side panel again has single bracing strut from bottom of v3 to top of v4.

Directly above at v3 is the new lateral bracing hoop, with a horizontal tube as triangulation from top of new hoop to upper frame tube, connecting in front of upper roll cage forward hoop mounting point, and braced from top of v3 to top of v4. Next forward the whole front of chassis is a single cross braced girder section attached to the forward most v4 of last side panel. The entire roll cage upper is attached to the upper frame tube and nothing else, no cross bracing or gussets at attachments.

During wheelie the wheels are lifting entire chassis, pivoting on rear wheels, and wheelie support causes a downward force to be transmitted into upper frame tube, at a bending point directly in front of forward roll cage hoop. All the wheelie force will cause a pull on bottom of v1 vertical tube and further transmit a downward push into upper frame tube and stress lower tube.
 
As car slams down from wheelie event another force on girder front section when front wheels hit pavement is transmitted back into exactly the same hinge point in upper frame tube, just in front of forward roll cage hoop, and into the unsupported v4 connection. There's no triangulation from v4 to front girder section, so a bending hinge force impacts all girder connections at v4.

Upper frame tube is flexed downward by wheelie, plus rear wheels are leveraging frame lower tube and first parallelogram side panel upward, until wheelie is completed and then harmonics continue in upper tube, as the bouncing front end then transmits upward/downward bouncing forces trying to tear front girder off. At the same time all the force of rear wheels fighting for traction causes harmonics to set up along side panels and further impacts upper frame tube at forward roll cage hoop.

Along with thse forces there's frame twist and continuous vibration throughout structure. Added up the frame might want to fold at top tube just in front of rollbar front hoop, and girder that forms front end past driver's feet has forces on it to shear it off. Just like bending a piece of wire back & forth until it breaks the same forces are present in that chassis design, bending up & down plus lateral forces.

Hope all that came out right to explain....?

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JimmieD

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Re: Tube Frame Safety / Design
« Reply #11 on: January 25, 2010, 11:55:14 AM »
Don't know if image attachment worked but crude added lines & arrows may help explain. Hope it posts.
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Offline BDKW1

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Re: Tube Frame Safety / Design
« Reply #12 on: January 25, 2010, 12:40:15 PM »
One thing that I am noticing that is lacking on the simulations is the motor. The blocks on those are solid mounted to the frame in the high stress zone and will actually contribute the the strength of the chassis. On the other hand the additional load placed fore and aft of the motor due to it's reduced flex may pose additional problems.........
 
Unless you have all the components on the frame in the simulation, it's nothing more than a pretty picture.......
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Offline fabr

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Re: Tube Frame Safety / Design
« Reply #13 on: January 25, 2010, 01:53:39 PM »
From what I read the issue is not construction. They want those "weak spots" in there on purpose in the event of a crash so the drivers pod will come free of the engine and fuel and hopefully slide safely to a stop .. What they need is the elongation that is absent with heat treated 4130 that allows the entire chassis to be the spring. Yes a chassis design is a POS for us but in the interest of safety they do not want the car to stay intact in the event of a crash.
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"There can be no divided allegiance here.  Any man who says he is an American,
but something else also, isn't an American at all.  We have room for but one
flag, the American flag... We have room for but one language here, and that is
the English language... and we have room for but one sole loyalty and that is a
loyalty to the American people."
Theodore Roosevelt 1907

-----------------------------------------------------------
 " You have all the right in the world to believe any damn thing you'd like, but you don't have the right to demand that I agree with your fantasy"

Offline Engineer

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Re: Tube Frame Safety / Design
« Reply #14 on: January 25, 2010, 02:20:40 PM »
I couldn't get through the whole wall of text, but it seems he was hinting that in the Medlen crash the chassis may have failed taking out the tire.

With the amount of stress that tire shake puts into the chassis, I would be concerned about using steel that snaps instead of bending. 

Overall there are far to many variables for a "beef it up" solution to work IMO.  At the speeds these guys are going no chassis engineering will save them from all possible senarios. 
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