Tubular Tales for EveryRacer.

[Mopar 151w2]

Jon Asher, the ‘Conclusion” of Tubular Tales, From the BME website:

Elongation is of critical importance, because race cars are constantly flexing, twisting and bending in ways that we can only imagine – or try to replicate on a computer. “Seeing” those twists is impossible without serious instrumentation, but one thing does appear to be certain: Minimum elongation properties for chrome moly tubing should be a minimum of 10 percent of the length of the tube in question. Simplistically, a piece of tubing 10-inches in length should be flexible enough to stretch an additional inch without breaking.

Correctly heat treated tubes can produce somewhat greater tensile strength, but that additional strength comes with a commensurate amount of lesser elongation. In testing, a heat treated tube may exhibit greater tensile strength, but when it reaches the failure point it does so rather abruptly. A similar Condition N tube will flex and bend and also ultimately fail, but when it does so it will, in the vast majority of instances, remain in one piece. A bent and misshapen race car frame is certainly safer than one broken into numerous pieces.

Some points well taken:
Sherm cautions against Bill Miller’s ego, and a trip around the BME website confirms – as big a self promoting, gaping (be nice…), as Ky Michaelson (Rocket Man)., and ready to raise a stink in a second! But he put a ton of work and money into this deal, and really did the sport a service. I go on a good bit about qualifying sources of information, I trust Tubular Tales because of Jon Asher – one of the few ink-slingers who have paid the bills, and the dues, of a top-running dragster, the “Jade Grenade”, and is well respected throughout the sport.
Research into this sort of thing is kind of like strip mining – you have to dig a LOT, and move plenty of overburden, before you get to the good stuff.

Ask Don Taylor – Joe’s Racer Discount Steal! Is not where you buy rollcage tubing!! As things turn out, it’s quite possible to have steel DOM tubing that is soggy soft, or, more concerning, “cold worked” until it is too stiff. ASTM spec min. is 5% elongation on some grades, and it’s not enough to avoid some ugly failure modes. “Bent is better than Broke!”is no joke. And neither is Don’s observation that we don’t want the car to “spring back”! Smooshy is good, it’s where you use ERW and/or body panels to absorb energy!
All of the favored cage tubing – “good” DOM, 1018 CDS, 4130 (n), and Rocol R-8, as supplied by Stock Car Steel in Charlotte or AED in Indianapolis, has elongation in the 12% to 15% range. CDS and Rocol R-8 have been carefully engineered so that the failure modes are “soft” and welds are homogenous with both the specified material, and most mild steels.
Spell out the % of elongation, or, at least, the 10% minimum, when you purchase cage tubing. If your supplier has a consistent spec from the mill, that meets your needs, write your Purchase Order up that way. (Avoids Goodenuff, May B, ‘last 1 in the rack”)
If they don’t want to hear no fairy specs, too bad, welcome to the big leagues!
Their industrial customers demand it as part of quality control, (metal spec has to match part print, especially under the ISO 9000 initatives), and it’s the backup for a fabricator’s choice of materials.
I can make no better argument for this than this cross-reference I’ve been pecking at for months:
Physical properties of steel in common tubing

Type of tubing source of spec. sae alloy # Yield Strength,kpsi Ultimate Tensile, kpsi % of Elongation Rockwell B (brinell) hardness
ERW ASTM a513 1015 35 49 15
ERW Rectangular ASTM a500 1018 46 58 23
ERW ASTM a513 MIN 1020 39 52 12
DOM ASTM a513 MIN 1015 55 65 5
DOM ASTM a513 MIN 4130 85 95 5
DOM ASTM a513 MIN 1026 55 70 5
DOM stress relieved ASTM a513 MIN 1015 50 60 12
DOM stress relieved ASTM a513 MIN 1026 65 75 10
DOM (n) ASTM a513 MIN 4130 80 90 10
Seamless ASTM a519 min 4130 60 90 20
Seamless ASTM a519 min 1025 36 55 22
CDS AED 1018 53.7 63.8 15 Rb 71
CDS Stock Car Steel Republic steel 53.7 63.8 15
DOM AED 1018 72 87 15 Rb 80
DOM AED 1026 72 87 10 Rb 89
Rocol R-8 GTAW AED dual phase 100 116 13
CDS per FIA Reynolds 531 4T45 89.9 101 ?

This is a first cut, and I’ll try and keep it up, on the Kitchen Sink Engineering Facebook page. Steel is really cool stuff!