Carbon Fiber Floor Mount Adaptors

[bigjae46]

I made them!




I think the commercially available aluminum floor mounts are garbage (like VAC, MS). The problem is the aluminum around the bolt holes will gall if you apply the correct torque to the fastener. The holes are also oval which allows fore and aft movement.

I made my own aluminum floor mounts from 3/4 thick 6120. They did fine...never really tested them thank god. The bolt holes were drilled to 1/2" which is slightly larger than the M10 OE fasteners



I researched S glass fiberglass, kevlar and carbon. Settled on carbon fiber. Carbon has a tensile strength 3.8 times aluminum where as carbon has poor elongation and any strength and stiffness in carbon steeply falls off once the material fails. Most performance data on carbon fiber is for plain and 2x2 twill weaves which provide strength in 2 directions. I'm using unidirectional carbon which provides all of its strength in one direction. A twill divides the strength in half vs a unidrectional AND a twill adds weight since you get epoxy build up anytime the threads cross.

My carbon floor mounts are 3/8" thick - 24 layers of unidirectional 400gsm carbon and I added a pretty 2x2 twill layer on top. The CF floor mounts are 1/2 the thickness of my aluminum mounts. I calculate them to be 4x stronger than the aluminum mounts. I hand laminated two halves and vacuum bagged them. Later, bonded the halves together. Everything went pretty smooth until I had to trim the inner mount. Its 2" wide and really had no good way to hold it in a position where I could hold the shop vac and dremel at the same time. So yeah...it looks like a kindergartner cut my inner floor mount...lol. Other things, I had to cut a slot into the side adaptor so it would clear the rear bolt head.

The final weight is 2 lbs vs 6 lbs. My final weight calculation should be 1.9 lbs. Ten extra .1 is probably the pretty twill layer.

Also moved the seat back 3" (was sitting a little too close) and lowered the seat so my helmet no longer makes contact with the forward hoop on the roll cage.

I would do some things different and make some improvements for next time.

1. Do a resin infusion on one 8" wide sheet and then make 3 cuts to produce the left and right mounts. Ideally a table saw with a fine tooth blade should work.
2. The unidirectional CF comes with a binder thread which runs across the CF tows. I'd remove about 1/2 of them or maybe more. Should reduce the epoxy content and make the part lighter and stronger.
3. Insert a couple layers of twill weave to add some strength left of right on the mount. Can do this with a minimal weight and thickness penalty.

Sitting in it...feels the same.

Here is a coupon I cut off the end



The final result





Any BTW...my idea of using studs on the inboard side of the seat to make installing much easier...works!

[heinzboehmer]

Very cool! Never seen CF floor mounts before.

I do have one question though. I've always though that CF is very strong along the same axis as the fibers, but relatively weak along an orthogonal axis. So, why aren't these mounts snapping when you sit in the car (and bounce around while driving)? Is it just because you made them thick enough to support all the forces they'll see in that direction?

[bigjae46]

Very cool! Never seen CF floor mounts before.

I do have one question though. I've always though that CF is very strong along the same axis as the fibers, but relatively weak along an orthogonal axis. So, why aren't these mounts snapping when you sit in the car (and bounce around while driving)? Is it just because you made them thick enough to support all the forces they'll see in that direction?

They are just a hair under 3/8” thick. When I trimmed the ends, the carbon is solid and there is stiffness and strength side to side.

What I’m a little worried about is once you exceed the tensile strength of CF, it fails and comes apart. Whereas Kevlar, aluminum and steel will fall off in strength before it fails.

Needs some on track testing first. I am already planning the V2 adding some layers of 2x2 twill and +/- 45 degree biax to improve side to side strength. I also want to add some mounting points to the floor to better support the outboard mount.

Once I perfect the floor mounts, I’m thinking about trying composite side mounts. I’m leaning towards using carbon fiber with some layers of Kevlar to add toughness.


Sent from my iPhone using Tapatalk

[mrgizmo04]

https://youtu.be/QYqOMjoz_i8

Sent from my SM-G950U using Tapatalk

[bigjae46]

Couple of events on the CF mounts. They are holding up, no issues.

I get better feel in the seat with these mounts. I like them better than the aluminum mounts.

I did have to adjust sitting lower but the extra headroom has been great.


Sent from my iPhone using Tapatalk

[Slonik]

hmm, you are brave enough. i'd prefer not to use them on the floor mounts, really (even with the fact, that i'm maniac with carbon stuff). it works in the different direction - on the flatness.

about weight savings. a LOT easier, to use way with CNC machining of aluminum and cut some unnecessary areas. typical aluminum adapters weight (pair for 1 seat) i get - about 2lbs.

[bigjae46]

hmm, you are brave enough. i'd prefer not to use them on the floor mounts, really (even with the fact, that i'm maniac with carbon stuff). it works in the different direction - on the flatness.

about weight savings. a LOT easier, to use way with CNC machining of aluminum and cut some unnecessary areas. typical aluminum adapters weight (pair for 1 seat) i get - about 2lbs.

Can you expand on this?

I know that carbon lacks some toughness so once carbon fractures that it loses all of its strength unlike aluminum, kevlar or fiberglass which is a disadvantage. But wouldn’t the weak point still be bolt that connects the side mounts to the seat?

I’ve used the commercially available floor mounts like VAC - I don’t think there is much margin for error. Relatively thin cast aluminum underneath the floor bolts that galls when torqued.


Sent from my iPhone using Tapatalk

[Slonik]

Can you expand on this?

I know that carbon lacks some toughness so once carbon fractures that it loses all of its strength unlike aluminum, kevlar or fiberglass which is a disadvantage. But wouldn’t the weak point still be bolt that connects the side mounts to the seat?

I’ve used the commercially available floor mounts like VAC - I don’t think there is much margin for error. Relatively thin cast aluminum underneath the floor bolts that galls when torqued.


Sent from my iPhone using Tapatalk

Side mounts connects to the carbon fiber/fiberglass on the !sides! of the seats and load direction in that case along on the plane, and that's the main advantage of the carbon fiber (check fiber directions). check some interesting fact, that some time ago motorsport also had bottom mounted seats, but then they have banned them.

[bigjae46]

Side mounts connects to the carbon fiber/fiberglass on the !sides! of the seats and load direction in that case along on the plane, and that's the main advantage of the carbon fiber (check fiber directions). check some interesting fact, that some time ago motorsport also had bottom mounted seats, but then they have banned them.

The floor mounts are unidirectional CF. All of the strength goes front to rear. Only the top layer is 2x2.

Wouldn’t that be the direction you’d want if most of the force is in the direction?


Sent from my iPhone using Tapatalk

[Slonik]

hello paint ahahahah
possible applying load during crash on the seat could be like this. and driver weight will make force much higher, that your floor mounts level. so, to the floor mounts, load would come with different direction.
i will not draw side impact load, cause it will looks similar to the back impact, with changed direction only.

[bigjae46]

hello paint ahahahah
possible applying load during crash on the seat could be like this. and driver weight will make force much higher, that your floor mounts level. so, to the floor mounts, load would come with different direction.
i will not draw side impact load, cause it will looks similar to the back impact, with changed direction only.

Lol…thanks for the info.


Sent from my iPhone using Tapatalk

[Casa de Mesa]

I'm not an engineer. Stating that up front.

However, I have been through ringer with respect to safety gear and have had the unfortunate experience of having to use/test that safety gear on occasion.

I used to think that seat mounts in a lateral impact weren't that important. "It is the harnesses that contain you" was my thought. Fast forward to a practice session on a NASA race weekend, I lost my brakes (complete and sudden hydraulic failure - truly lost them as in no brakes whatsoever) at the end of the straightaway clipping along at 135mph or so.

Skipping ahead to my point, I managed to get the car slowed down to somewhere around 60 to 80 mph I figure. In an effort to further reduce speed with a treeline approaching, I tossed the car sideways and landed in the trees laterally on the passenger side of the car. Most of my weight went towards the center of the car and slightly forward - maybe 10 degrees off the perpendicular axis.

Because of how I hit the trees, it literally bent the steel seat mounts and elongated two of the holes on the left side of the seat mount. Much of the force went into the side of the OMP seat in my right shoulder (which was bruised pretty good). While the 6 point harness certainly did its job, both the lap and shoulder belts stretched on impact and much of the force was transferred into the seat itself.

All of this to say, I truly admire your creativity, but that seat mount scares me a bit. It certainly feels like the carbon fiber sheet/mount could pull through those bolts in an accident similar to what I described. Once that fails, your a lot closer to rollcage tubing than you were moment before.

Please don't take this as me trying to rain on a parade. If you are an engineer and have calculated the loads and understand the material strengths that you're using more than this guy (me) does, I will go back into my corner quietly. Hell I'll do it anyways! I clearly have already made my point.

I apologize in advance if I have offended you. "Safety above all" when it comes to motorsports, so I had to say something.

Bryan

[bigjae46]

Seats are made of fiberglass and carbon fiber and can withstand crashes - are FIA certified and meet other requirements.

I have done a lot of research. The issue you run into with carbon is material toughness and elongation. Once a carbon structure is compromised the strength falls off, pretty much zero strength. Kevlar and steel have a higher elongation.

Carbon weave should be oriented in the direction where the strength is needed. A twill 2x2 weave has strength in two directions. Most carbon parts will have a biaxial layer that’s +/- 45 degrees from the twill layer(s).

I used unidirectional carbon fiber tape which has all of its strength in one direction. At 3/8”, that is 2x stronger than aluminum that is 2x thicker.

I could do some things to add more stiffness and strength - post cure heat & use a soric or nonexistent honeycomb core. Also considered laying up the part 50/50 unidirectional and biax layers.

I’ve jumped up and down on the mounts - they don’t move. Not really concerned about the bolts pulling through. If you look at the coupon I cut off the end, it’s a solid chunk of carbon that as hard as steel.


Sent from my iPhone using Tapatalk