First time monocoque team SEF help

[Shane_V]

We are a first year monocoque team, and we have been going back and forth with SAE in attempts to satisfy our SEF for a couple of months now. We are at the point where we almost don't know what they are asking. We have two outstanding issues:

1. Roll hoop mounting - we ran a destructive test showing that the hoop will withstand 30kN, as stated in the rules, but they still want comparisons to the steel frame chassis. The only thing that we can think of to do is to mimic the exact mounting setup for the monocoque, and one for the tube frame, then do destructive testing on the both and compare results. Also, they are concerned about the mounting locations. Should there simply be 2 bolts at every location where a tube would be welded to the frame??

2. Seat belt mounting - with the nature of our monocoque, we are mounting our belts to aluminum. is there a source where I would be able to find the "as welded" strengths? The books that are sourced in the rules are proving to be very hard to find.

Any help from past experience would be greatly appreciated. We are starting to run quite late in our build process because of these issues, any help would be wonderful.

[Shane_V]

We are a first year monocoque team, and we have been going back and forth with SAE in attempts to satisfy our SEF for a couple of months now. We are at the point where we almost don't know what they are asking. We have two outstanding issues:

1. Roll hoop mounting - we ran a destructive test showing that the hoop will withstand 30kN, as stated in the rules, but they still want comparisons to the steel frame chassis. The only thing that we can think of to do is to mimic the exact mounting setup for the monocoque, and one for the tube frame, then do destructive testing on the both and compare results. Also, they are concerned about the mounting locations. Should there simply be 2 bolts at every location where a tube would be welded to the frame??

2. Seat belt mounting - with the nature of our monocoque, we are mounting our belts to aluminum. is there a source where I would be able to find the "as welded" strengths? The books that are sourced in the rules are proving to be very hard to find.

Any help from past experience would be greatly appreciated. We are starting to run quite late in our build process because of these issues, any help would be wonderful.

[The AFX Master]

Shane

Regarding (1), i think they want you to demonstrate that the roll hoop pick up points are enough, and in a logical array to mimic a tube frame chassis. Also to fully restrain hoop movement in a fail safe fashion (if something breaks, the hoop can still receive the 30kN).
Seems to be that you´ll need at least 3 brackets each side of the chassis. A lower point (like a lower side impact node at main hoop). A mid bracket (like upper side impact), and one or two upper brackets located near the harness mount tube.

Try to make those brackets with small triangulation ribs (to avoid excessive bending stresses)

Regarding 2: Are you crushing the core?, Or, Are you mounting the aluminum plate between the carbon skins, and not the other way?.

Give a little explanation of both setups too

Regards

[Shane_V]

Our front monocoque is going to be composed of carbon panels (aluminum honeycomb core), and joined together with aluminum extrusions. The chassis will bond to the roll hoop along the entire perimeter of the hoop, and bolted in required sections. I think what we are going to do is do two comparison tests (tension and compression) of the exact mounting setup to the roll hoop, and compare that to a welded tube. We will also specify the exact locations of the bolts.

For the second part, we will be welding the aluminum belt attachment plate to the extrusions, which will be exposed on the inside of the car. This is why we need to know "as welded" strengths of steel compared to aluminum, and what is required

[Essayee]

I hear the welded strength of Al without returning to a heat treated stage is junk. But hey, that might just be hearsay, who knows.

Why don't you look into alternate methods of attaching the plates to the extrusions? I doubt you would weld your suspension points onto their respective hardpoints if you don't know how that process would degrade the suspension tabs' material properties. How did you mount those? Did you bolt into the hardpoints? Did you use adhesive? We're not running a monocoque so I haven't really paid attention to how the rules limit the ways in which you can attach the harness mounting points, but if you can do either method, you might be better off.

Plus, we've done some welding near our weaksauce non-structural composites before, and the two don't get along. We have literally had parts ignite, and then reignite multiple times when we put out the fire until we realize it's igniting because it's in such close proximity to the hot steel. I would hate to know what would happen if you weld directly into a monocoque.