bruinbro

This was the flat X design with a single plate reinforcement.

Bro

Cory M

I think the majority of the cages used in club racing, TT, and DE are not tied into the suspension pickup points. They are simple 6 or 8 point cages, so I wouldn't assume that the loads will be absorbed at the nodes. I think the distributed load does a better job of showing what would happen if the A pillar was contacted by a car and crushed into the cage, so I don't think it's a waste of time but the broadside and angled scenarios are probably easier to draw conclusions from.

The bottom tube in the model is the bottom box beam. It doesn't have the same properties as the actual doorsill but as long as all of the models have the same sized bottom tube we can compare them directly.

It is interesting that the gussets didn't change the deflection at all but I would think their main purpose is to strengthen the welded tube junction, not stiffen it in a the broadside direction. They probably help stiffen the structure torsionally too.

Should be intesresting to see how the Nascar bars fare, I'm guessing they will deflect more than either of the X designs since they are bent at the ends and the load won't have a direct path to the other bars.

bruinbro

I could post the stress results, but I'm not sure they would mean anything comparison-wise.

Bro

Geo

Cool. I'd be really interested in seeing the pyramind X results from the same impact. That will be an interesting comparison.

It's also rather interesting that even with the offset impact, the greatest deflection is still the center of the X.

bruinbro

Done.

bruinbro

Ask and ye shall receive.

Pyramid with central angled impact



Pyramid with offset angled impact

Mike S.

Bro...kudos to you for all the runs. You're doing great stuff here.

All...gussets are primarily used to distrubute loads over a greater area to delay (or prevent) the onset of a failure which would generally be a cracked of severed tube for this application. Most often you'll find the maximum stress(es) to occur at the intersection of tubes...enter Mr. Gusset. As Bro mentioned, the stresses in some areas are way way past the point of yielding. This stucture will now have a permanent set once the load is removed.

Notice the double ended arrows at the ends of the vertical tubes in the side impact cases? These locations are not allowed to move. Do you believe this is so? Pretty decent choice at the bottom (sill). But how about at the top? Pretty good, but only if the front and back tubes are tied into the car...which most often they are not. Once Geo or somebody gets Bro some full cage geometry, Bro be turning this excellent simplified design study into some extraordinary.

Ok, how about this situation. ..non-tied in cage...side impact. How do flat vs. pryamidal or bowed out X compare?

Flat X...side impact...verticals at the top get drawn toward each other...severe tensile loads/stresses in the X at top tie in points...X has the ability to head further toward the driver. Thus, an "impoded" look per John H. If the deflection is sufficiently large, this is not desired. Improvement opportunity...add horizontal bar to top of the X...hope the collision fundementally remains below this...plus live with aggravated normal entry/egress.

Pyramidal or bowed out X....verticals at or get pushed away from each other...severe compressive loads/stresses in the X at top tie in points...X has the ability to head further toward the driver. If sufficiently large delection, this isn't desired. But, this deflection has to be much greater with the space created with bowed out door bars. Improvement opportunity...add a bar stop tightly fit to the front and rear verticals so the load goes immediately into the chassis...bar stops only are practical if you have a real tight fitting custom cage...kind of fussy and hello more $$$.

I'm coming to the general (partial) conclusion that for sufficiently severe applications, tight fitted to body cages judiciously tied into a car having a fundmentally stiff body/chassis can provide some meaningful advantages.

Foofd for thought and comment....you really want to create sufficiently low G-loads on the driver or occupant. Brick S*%$ House designs that don't mitigate the impact G-loads are not the answer. And obviously highly deformable designs where tubes enter the driver or occupant space are no good either. We all strive to dance somewhere in the middle...but where??? I say welcome to experience (John H., Tinman, Joe, Geo et als) and engineering (Bro, Sunday Driver, et als) as this is an unbeatable combo.

On a related note. My gut tells me a tremendous opportunity exists (to lower the driver experienced G-loads) between the cage and the H&N system....the seat! Whether that be the method of suspension and/or mini torso and head air bags. Get to it you entrepreneurs and engineers!


Mike

Geo

Bro, this is some awesome stuff. Your data clearly shows my assumptions were not correct. Good to know, although with the main hoop set back from the door opening in my car, there was no way for me to do a pyramid anyway. But this is great. The NASCAR bars should be interesting as well.

If I can get over to the shop tomorrow, I'll get you all the dimensions to use to construct a cage.

bruinbro

You guys are easily amused.

Thanks for the praise, it really isn't that difficult, just time consuming. And time is a commodity that most of you don't have ( and I wish I didn't).

Gonna give some cerebral CPU time to energy absorbtion.

Bro

bruinbro

Here is the NASCAR geometry I'll be using:



It is somewhat modeled after this:



Is this OK?

Bro

Bill935K3

Cory: I agree definitely more than half do not tie in. Only GT can legally. Rollover and side impact crush is the biggest threat and what you guys are modeling side impact on a concentrated point (6-12”) at different angles is definitely the biggest threat to the driver.

I see what you mean RE the bottom bar under the X replaces the sill for modeling.

I think for NASCAR model you should have 3 bars (arched) and 1 sill (strait) I believe this is the “true” NASCAR setup (see photo). The big advantage to NASCAR in my mind is surface area of protection. The both arched X and NASCAR give great crush protection. But the open area over the X makes me nervous. The reason I like NASCAR is it helps keep Sh….. out of the car. The local circle track guys even tack squares of sheet metal over the square openings in their NASCAR setups. The run very thin plastic body work.


HI Bro:
RE being easily amused. (don’t take this the wrong way your postings are great stuff!!)
If you really looking of a challenge: I’ll get you the dimensions and tube info on the nose of my car. A frontal impact simulation on that would be a pretty far out project and keep your electrons humming for a while!

M758

Interesting. Seems to be showing a bent "offset" X is the better than a simple flat in plane X.

I too am waitng to see the NASCAR bar's.

bruinbro

Not really looking for a challenge, but I'll model your front nose tubing. What you must remember that I'll be running a very simplistic analysis that doesn't really take into account the energy absorbtion and permanent deformation that will occur. As mentioned previously, the absolute deflection and stress numbers are only good for comparison to other designs, not for detailed hardware design. In other words I can tell you if design A would be better than design B for given performance criteria (deflection, deflection/weight, stress, stress/weight, etc.), but not the specifics on how design A should be built (specific attachment points, joint design, geometry with relation to the car, tube sizing, etc,). So, send me the info and we'll see if we can play some "what if" games.

Bro

bruinbro

Are you ready to rumble?!!!

Here's the NASCAR bar analysis:

Wide loading



Narrow loading



I'm now taking requests for additional loading/design modifications.

Bro

M758

Bro,
Can you summarize a bit.

For example a chart with following

...................Flat X..........Pyramid X........NASCAR
Pure Side....
Angle Side...



Thanks