LocostUSA.com

So a long term lurker, but I would like to get some opinions on this before I begin purchasing metal.
I have been looking at aluminum extrusions like these for quite a while and wondering if a decent monocoque chassis could be constructed from them.
Using Silkaflex and bolts to create an aluminum tub. With steel front and rear subframes bolted onto it.

The floor would be 16 guage steel, with rubber washers to isolate the aluminum extrusion from the floor panel and provide a decent clearance for the bonding glue to adhere to both metals without being all squeezed out during the compression process.

It could be. As for me, I don't like the idea of trusting my life against fatigue failure of an industrial 8120 rail.

You know nothing about the material specs on the extrusions. Steel on the other hand is cheap and forgiving.

My 2 cents, your mileage may vary, yada yada yada

_________________
Too much week, not enough weekend.

OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216

We have a bit of confusion here Monocoque construction relies on the skin for strength. You talking about using Aluminium extrusions for strength so that is not monocoque construction. But hang in there I think you idea might have merit, just a little more detail, maybe you thought process.

Graham

That extrusion was an example, I have found some in 6061 T6, which I believe may be more up to the task of a lightweight chassis frame.
Btw your two cents is very very valid.

So basically I have always thought of a monocoque as a frame in which the entire system is stressed, skin, tubes, and all take the loads in compared to a space frame in which the strength is in the triangulation of the tubes to negate or direct suspension, etc loads to the desired areas.
Sorry for the confusion.

To explain, my idea is to use two thick ones, boned together to create the side sills, 16 guage steel floor since weight savings there does not mean much compared to Intrusion safety, three beams would then go across one in front to attached the door hinge ala Lotus Elise, one across the floor where the knees bend for structural safety in a side impact, and the back.

In monocoque structures, as with exoskeletal insects, the skin is structural, bearing tension and compression loads.

Checkout https://www.motortrend.com/features/bod ... ifference/

Graham

Check out Ashland Chemical. They have a 2 part adhesive, with micro balls, designed for automotive chassis and body contruction.

a la modern Lotus construction.

Remember AL has fatigue limitations, meaning you have to properly over-design those components to "stay below the knee" and keep the advantages (lightweight) of using AL in the first place.

The 8020 rail is extruded from 6105-T5, which may or may not be weldable. Though welding 6061 is not necessarily a slam dunk like welding low carbon steel typically is.

The basic chassis, sides and floor, consisting of these aluminum extrusions and steel floor are really the easy part. If you are serious persuing this path I'd start seeking solutions to some of the more fundimental problems that chassis needs to overcome. How are you going to hang the suspension off of the chassis in a way that it will survive the point loads. How are you going to mount 300lbs of engine, and how you are going to hang a differential and keep it from twisting out of the rear end.

A crude drawing would help give us a visual idea of where your heads at. We all enjoy offering advice and will try not to totally discourage anyone from persuing a non-traditional chassis building approach.

_________________
My build http://www.locostusa.com/forums/viewtopic.php?f=35&t=7370

I wish I could find the video, a guy in Australia made a chassis tub out of Aluminum skinned Structural Insulated Panels (SPI). He routed angled groves and folded it up like origami and bonded it together. Amazingly strong yet simple. Then used bolt on from and rear subframes. I will keep looking.

Graham

The book "How to Build Motorcycle-engined Racing Cars" has a few chapters on honeycomb panel chassis construction.

https://www.youtube.com/watch?v=42RuCSZUy-Y
nichols n1a are made by extrusion Aluminum

Those extrusions are not optimised for strength or stiffness, the shape is created to maximise the ease of attachments using bolted connections. I.e each side works with T-slot fasteners, the hole in the end is generally a tap drill size for a common thread.

Generally the t-slot is much, much heavier than using an equivalent strength/stiffness square or rectangular section.

Your idea for a chassis using 2 main rails and then a stressed skin (sort of a semi-monocoque) can work but I don't believe these type of extrusions will be suitable.

_________________
Scratch built turbo V8 hot-rod in progress
http://locostusa.com/forums/viewtopic.php?f=18&t=19549

Can it work, yes. Will it last, that depends entirely upon the design. Will it be efficient, weight-wise? Absolutely not. If you insist on using aluminum for anything other than non-structural skin, I highly recommend buying Carroll Smith's books on race car construction methods - and then take a Materials class to learn about how aluminum work-hardens when it's flexed any amount, and will always eventually fail, even if exposed only to vibration.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/