Tube Frame Safety / Design

[fabr]

Yep,a chain made of rubber willl be better than a chain of glass.

[JimmieD]

"What they need is the elongation that is absent with heat treated 4130 that allows the entire chassis to be the spring."

Yep! And ditto the chain made of rubber! What I see there is a compounding of potential failures in basic design structural intergrity, and materials and fabrication method. No other big league racing body would ever allow such a design/construction on the track.

I remember Colin Chapman and his quest for lighter & faster and I think it was somewhere around #19 - #22 disaster struck, but it's been so long ago. It cost a very precious life and Colin never fully recovered from the loss. Then later losing Clark [at Spa Francorchamps?] was over the top, too much. I never considered either crash to be Colin's fault or the fault of his excellent design, but it caused a fundamental change in design thinking and execution and soon monocoque designs appeared.

I remember one wreck of Jimmy's, I believe at Nurburgring in a #23 or 23B, and seeing him sitting in the tubular space frame Formula car afterwards grinning his funny little grin. The wheel, tires & stub axles were gone, along with all body panels, and most of the drivetrain and Jimmie was sitting there on the apron in the naked spaceframe, very alive, that time. Good design. Chapman, Costin & Phipps are good tutors even for today's space frame design.

Sorrry for rambling but it all brought back some old memories that still apply to today.

[fabr]

I KNOW what you mean about surviving with a shit eating grin. No better feeling than realizing you're still alive. The dragster in the last pic is the one I ran for many years made of ANNEALED 4130 mostly.059 wall. the sucker ran 7.0's 1/4 for over 8 years,hundreds of runs. Ran on one of the roughest tracks in the US. MOKAN near Joplin ,Mo. I literally would off the track a few inches up to about 18" in the shut down area 4-5 times every run. I have pics somewhere of it with all fours off the ground about 12". I'll try to find them. Very dangerous but WTF. It was lots of fun. The point is not that I'm comparing my 180 MPH dragster to a TF/FC but rather that 4130 can and DOES hold up well if properly built. Not bragging but ,yes,I did build it.

[fabr]

Oh,the doorslammer was all 4130 also and was resurrected to live again in less than 60 days. NOT A VERY GOOD PIC. I still finished 8th in points that year at Mid America dragstrip at Arkansas City,Ks. Another VERY rough track as engineer can testify to.I built it also----- TWICE!!!! 

[JimmieD]

Ouch, one of those 'done there, been that' things! Just could be that somebody up there likes you 

The difference can be real simple on survival & longevity: ENGINEERING more than materials. Some designs you look at, supposedly topnotch stuff and you just say, "Hey, wait a minute, why did they do THAT!??"

You most likely added simple logic in your designs based on experience as to what works, what don't work. Some of the pros need to do the same....

Overall it's a downright miracle some of us survived.

[fabr]

Ouch, one of those 'done there, been that' things! Just could be that somebody up there likes you 

The difference can be real simple on survival & longevity: ENGINEERING more than materials. Some designs you look at, supposedly topnotch stuff and you just say, "Hey, wait a minute, why did they do THAT!??"

You most likely added simple logic in your designs based on experience as to what works, what don't work. Some of the pros need to do the same....

Overall it's a downright miracle some of us survived.

Most likely. I cannot take credit for it.
For myself I'd say that good designs require first the choice of material and then proper engineering to make it work utilyzing the chosen material. In that order.

IMO,that is where all engineering came from originally. Math and stuff was added to the mix later in the evolution of designing and real engineering to prove out new designs.

[Yummi]

Long as this is a safety / design thread, I ran across this car and thought - hmm something does not look right.  I guess it is the bend at the upper bar that throws me.  Any input on this design? 



I have no doubt a properly designed arch would take the force of a roll, but for some reason, this orange car just looks wrong.

here is another radius roof car that would survive a roll better imo.

[fabr]

Personal opinion is that either one will function equally well. Aesthetically, I do not like the bottom one at all. Structurally though, I see little difference in the 2 cars in general.  Yes, there are a ton of differences in where they could fail but for sand cars they seem to me they are both safe.

[BDKW1]

The arch roof versus the bent with flat sections is about the same strength. The Kreger 10 cars have the round roofs on them and have been throughly roll tested with excellent results.

[nvheattreating]

I haven't read the frame article in a while, but I think part of the the message was that new rules forced the teams to use frames/materials in that condition. 

[fabr]

I believe you are correct. What really amazes me is that a long time,well respected ,chassis builder would even consider using hardened 4130 in a welded structure in the first place. I underatand why the condition N is spec'd for it's increased tensile but even it is much more susceptible to HAZ issues than annealed 4130.  This opinion makes me question the failures shown of 4130 cages. Are the failures due to the 4130 or the HT condition before welding.

[fabr]

One question for the pro. What really defines "heat treat"? To me it seems that most people assume HT means improved or altered in some way as to make the part harder or tougher than as manufactured to enable part to handle stresses or wear better. But what does that mean? Harder is more brittle. Tempering toughens it. Annealing softens it.  But that's still not an explanation of the term heat treating that a person can use to designate anything. . IMO,NHRA failed in it's obligation to specify the exact terms of heat treat in its' standards.Yes they said conditionN -OR  EQUIVALENT. They left a big door wide open on that.    Hell,IMO, annealed condition is heat treated. It took treating it with heat to accomplish. Same goes for hardened-takes heat to do it. Well ,so is normalized.  Soooo, WTH did NHRA mean by stating "or equivalent". McKinney took  it to mean whatever he wanted it to mean,and I would have also in his shoes but I would not have used "hardened". Why do I quote "hardened"? To me condition N is heat treated or hardened also.

[BDKW1]

Of the 2 chassis that I know of that were actually stuck in an oven, they were both normalized and stress relieved.
 
Heat treating without tempering would be a bad idea in My book. The whole process could turn into a large can of worms on a weldment that large...........

[fabr]

I cannot speak from any point of fact but It appears in the article that McKinney was using hardened in the lower frame rails only and normalized in the rest so no post heat treating could have been done while keeping part of the chassis normalized and other areas hardened. Am I wrong? Another question is how in the world could you keep a chassis straight in an oven for anything other than tempering where the heat is much lower? There's no way you're going to keep it straight at the higher temps of normalizing the thing overall.

[JimmieD]

As to the post on NHRA & heat treat, the answer starts with a P, ends with an S and rhymes with POS: POLITICS! The standard good old boy system run right into the ground. If you look at the politics in the original linked article the buy-offs glare out at you from the page. Big name, one of the boys, 'in' the 'In Crowd', must be allright was how the sanctioning bodies ruled the roost. Their clever exclusions of guys that knew what the hell they were doing, and inclusion of guys that simply happened to be currently building, as the only qualification for membership on the review panel, says it all.

I'd call that first car Orange Crush but I'd add 'and stab'. Both cars lack critical support members, whether they can manage to survive a rollover or not, but the second car is better thought out.

What an indescribable horror if the first car hits REALLY HARD the wrong way. Instant apendectomy & colostomy as those control arms come ramming into your guts? One should never design such that a component can ever reach the driver in a crash. Scary with that ultra-long shock on the rear too, in that respect. Could end up with your head resembling a shish-kabob? Should have a loop of tube around them as a guide for where they'd go if top shock mount broke loose at impact or a hard landing, also to prevent pole vaulting.

Also needs diagonal supports at lower points of roll cage, from about steering wheel height down to top rail at a minimum in front, slightly higher and connecting farther forward on top side rail at rear hoop. Without those a weird end-o could collapse the cage at a top-rear impact.

The sides appear to be ladder frame sections by the screws in the side panels? I'd say triangulation is much preferred, using diagonals? Would also be nice to have a horizontal tube about shoulder height behind driver/passenger for some 5-point belts and to help prevent seat fold-over? I would have also run a horizontal bar across the forward shock support hoops to stabilize. All that would only add what, maybe 10 pounds?

Second car could use the front & rear diagonals too, and both cars need a u-joint in the stab-me-hurt-me steering shafts. Second car gets huge extra points because no frame or chassis member could intrude into driver seating area to impale or injure driver. It could use a horizontal cross-chassis tube right about at rear mounting of front diagonal roll cage support tube, where verticals tie in, to cut down on frame flex.

I've been designing a chassis for about 18 months and always try to envision it as built from 2" cedar, so that support is given where needed. Then when it's built from 1.25" & 1.50" thinwall steel I KNOW it will take serious abuse. The trick is to keep it light at the same time....