Author Topic: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle  (Read 21181 times)

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Offline Kiwi Paul

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #45 on: November 19, 2011, 11:07:36 PM »
Larry, You make a really interesting point about secondary tubing. I am actually building this into my 26-7 T Coupe bodied Comp Coupe. With the roof being flat, I am building a complete steel framework for it out of 1'' square, .083 tubing. I am going to attach it to the cage with some short pieces, and make slip joints with Grade 5 bolts, so I can remove these bolts and then lift the body off the frame for major change/maintenance. What do you think?

Offline hotrod

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #46 on: November 20, 2011, 02:57:09 AM »
Sounds like the idea has possibilities. Basically you want an energy absorber to undergo as much destructive crushing as possible to use up energy.

In some racing classes they specify a block of high density foam in the drivers side door to help provide crush in case of a drivers side T-bone. There are several materials that can be used for crush elements. High density poly urethane type foams, and aluminum honey comb both use up a tremendous amount of energy as they are crushed.

When I was a teenager my Mom was trying to understand how the then "new fangled" padded dashes prevented injury because to normal finger pressure they felt pretty darn hard. I had a wild hair and ran into the bed room and grabbed a block of 1.5 inch thick styrofoam I had been using for model making and dashed back into the kitchen placed my hand on the floor and set the styrofoam on top and told my Dad to stomp on it. He immediately figured out what I was up to and promptly stomped on the block of foam as my Mom let out a yelp of protest. I showed her the block which had a clear imprint of the back of my hand on one side and the heel of my Dad's shoe on the other. Then the light dawned for her that under an accident the forces were so high that that "hard dash" was much softer than the typical pressed steel dash boards of the 1950's.

Same goes for a crush zone on a body or above a roll cage. You would want to create a crush element that used up the maximum amount of work possible as it was being crushed between the roof skin and the roll bar tubes.

It could be a thin wall square tube like you are talking about filled with high density foam, or a thin wall tube like a 1.5 inch exhaust tubing tacked on the top of the roll cage tube. The impact would have to crush that thin wall tube flat before the main roll cage tube really had to do any work. If you wanted more crush resistance you could nest several smaller tubes inside a large diameter tube.

For example a 2 inch exhaust pipe tube with several pieces of 1/2 inch electrical conduit inside, tacked together then filled with high density foam. You would want it attached strongly enough that it would not "squirt" out of the way on impact but stay in place to be crushed.

Square tubing filled with balsa wood or any other crush-able material could be devised depending on what you had on hand.

It might be interesting to have a local engineering school graduate student figure out how much energy it would take to crush flat several different simple designs.

As the saying goes, it is the sudden stop that hurts you. If you can just double the distance it takes to stop from 1-2 inches to 3-4 inches of crush, when the car impacts a very hard surface, you have made a huge reduction in peak G loads. That difference just might be the difference between breaking major structural welds and serious injury to the driver.

Larry
« Last Edit: November 20, 2011, 03:01:20 AM by hotrod »

Offline Koncretekid

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #47 on: November 20, 2011, 06:44:38 AM »
is using mild steel erw and 4130 moly on same chassis legal ?,(example would be mild steel frame rails and 4130 roll cage)
I would not think that it would be a good idea to mix the two types of steel in the same structure.  The mild steel will need to yield in a crash situation, i.e. bend, stretch, compress, or do whatever the situation requires.  The higher strength steel will not yield (bend, stretch, compress) as much before it reaches it's breaking strength.  I think the result will be that all the load will come onto the stronger members before the mild steel has had a chance to it's job, which is absorbing energy.  The welds would probably fail, and the entire structure would no longer act as a unit.

A similar example of this is the use of too much reinforcing steel in a concrete beam.  A beam with the proper amount of reinforcing steel, will actually bend, stretching the steel (which becomes stronger as it stretches), and hence the failure mode will be slower and noticeable.  A beam that has too much steel, will literally explode, as the concrete exceeds it's compressive strength, and fails catastrophically before the steel has reached it's yield strength.  Think about that when you're driving beneath all the overpasses on the way to the races!

Tom, B.S.M.E.
We get too soon oldt, and too late schmart!
Life's uncertain - eat dessert first!

Offline Kiwi Paul

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #48 on: November 26, 2011, 02:09:48 AM »
Hmmm......Looks like I need to find an Engineering Student capable of being `Salt Trained`...... :-P

Offline Peter Jack

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #49 on: November 26, 2011, 07:23:00 AM »
There should be no troubles beyond those already expressed for 4130 if it is welded to a mild steel main frame rail. As a matter of fact 4130 is generally welded with a mild steel rod, 70S2. This is a double deoxidized rod with no moly. The welding engineers I've talked to and the articles I've read all seem to feel that enough molybdenum is picked up from the base metal that the weld is more than satisfactory. A weld between 4130 and mild steel should gain the desired characteristics between the two alloys and would likely be a little more malleable than a weld between two pieces of 4130 and thus be a little more forgiving. Always remember that the most important parts are the design of the joint and the weld and the skill of the operator applying the weld.

Pete

Offline salt27

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Re: Roll Cage 4130 Chrome Moly is it legal for LSR vehicle
« Reply #50 on: November 26, 2011, 11:54:23 AM »
A friends single seat off road race buggy was built out of mild steel with chrome moly members welded on it to hang the front suspension from.
It took a lot of abuse and he broke a lot of parts but I don't remember the mild steel to chrome moly welds ever being an issue.
Other than that I know nothing. :-D

Don