This is the reply I posted on the site showing the (new) NASCAR cage design.
NASCAR cages are almost completely dependent on the bending strength of each tube as they bend and collapse in a crash. The design has very few diagonals that can distribute crash loads through out the chassis efficiently. The NASCAR approach, as shown by the addition of the new “brow bar” in front of the top halo’s front bar, is to add additional tubes that provide additional bending strength rather that attempt to transfer the crash loads to the rest of the chassis. It works for them and they know the car weights, and speeds and just add tubing until the cage can carry the crash loads. An FEA analysis of this chassis would be interesting. Lots of highly loaded weld joints and tubes in bending.
They are not structurally efficient but they do a fair job for the cars that NASCAR runs, and as I said if they need to be stronger just add more tubing. I also happen not be a supporter of the SCTA flat gusset rule as it is presently written and think that I may take DW up on his suggestion.
Rex
Guys,
The priority of the "roll cage" (actually "roll-over structure"),
SHOULD be to provide a "survival capsule" for its' occupant in the event of a loss of vehicle control at speeds which present a danger to the survival of the "occupant". Let's not forget this part of the equation.
IF, by clever design, chassis rigidity can be enhanced, at
NO compromise to the "survival capsule", then that would be a bonus.
There are, of course, some other considerations:
1/ How the energy of a crash will be dissapated. . . .
A/ Will components be in tension/compression/shear? Materials have different properties in differing situations.
B/ Is it acceptable to dissapate energy by shedding/shearing high mass componentry from the vehicle? Can the "survival capsule" remain intact during this process?
2/ Strength of the materials used, and the strength of the methods of joining those materials,
A/ Conventional butt welding, even at 100% pentration, is a poor choice for joints subjected to tensile loads. The mandatory gussets added to these types of joints add
some shear strength to these joints.
B/ "Bent" tubes, are most appropriate for structures subjected to compression loads, such as "door bars" or "roof bars". Gussets may be necessary to help dissapate the
loads into surrounding structure. Non-gusseted "bent tubes" are going to flex in tension, as an FEA analysis will reveal.
3/ Etc, etc, ad nauseum. . . . . . . .
4/ Any thought that a vehicle and its' structure could be made "strong enough" to reuse after any high speed, energy dissapating event, is probably unrealistic. . . . . . . . . .
AND, anybody with a lick of "common sense" certainly would not be piloting it. . . . . . .
I definitely agree with Rex. This is a very complex subject worthy of detailed discussion and analysis.
I'm getting thirsty already.
Fordboy
