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Sam, I somewhat agree with you. The part that I don't agree with is the ability of a foam core to do just what you are asking it to do. With two thin skins made of whatever with essentially a marshmellow in between has no rigidity in torsion. In such a case, the structure relies mostly on the structural performance of the two single sheets alone. Probably less structural performance of a single panel made the thickness of the 2 thinner sheets of the sandwich without the weak "stabilizing" layer.

Now if the core had some features different then marshmellow (a.k.a.foam) which is the OP's question, then it depends on the performance of that layer and the ability of it to stay bonded to the outer skins.

Of course I am not structural engineering expert. It just seems to be a consideration based on my semi educated guess.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

That would be the case if there was no connectivity whatsoever between the two skins: for example if you had one perfect cylinder within another, and nothing but core material connecting the two.

In practice, that never happens: you're using 'panels' of sandwich material, with corners and bulkheads that limit the relative movement of the skins.

Chuck, you need to remember that panels tend to distribute loads across the 'membrane', and the same thing goes for the core. If the shear strength of the adhesive is adequate then cores with much lower compressive and shear strength than the surface skins will carry considerable load. On another forum I follow (i550class.org) a builder wanted to substitute a foam-cored glass for a 6mm BS1088 plywood deck panel. He made up samples of 12mm Divinycel or Corecel foam with 8 and 10 oz single skins of glass each side. The panels were stiffer and more puncture-resistant than the ply, and lighter too. But they were more expensive. He did have to plan for where his fittings were going though, because those spots got a plywood core for local compressive strength. As Sam 68 pointed out, his deck panels had edge constraint too, but that tends to be the norm for load-carrying structure. I don't know that I could pull it off: I change my mind about where stuff will go much too often,

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Warren
Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601

The kinda solution for that is to use bobbins instead of moulded-in hard points. These can be bonded in place afterwards, and use the flange of the bobbins (usually multiple, for any significant point load) to feed the forces into a sufficient area of the skins. Refer to the pics of my Westfield FW400 on the 'carbon fibre' topic linked above, or to the 'Motorcycle-Engined Racing Cars' book to see how this works.

You do still need to think about how to feed in the really big loads (drivetrain; suspension) right from the drawing-board stage, though, because these usually need to be contrived to be fed into the structure in two planes so that they can be resolved into 'horizontal' and 'vertical' components on panels each side of a corner, in order that each component load is fed into the skins in pure shear.

if I use vacuum bag?

hot to remove the core like this?

did 1001 core panel have enough strength?

A vaccuum bag would be an excellent way of squeezing the excess resin into the core material, where it will permanently add weight.

Commercially manufactured sandwich panels are made by laminating and at least partially curing the skins first, then bonding them to the core material using film adhesive in a heated press.


I'm pretty sure that if I could read Chinese (I'm guessing that with your user name you can?), the text to that diagram would tell me that it was a repair patch.
Yes, you can potentially add hardpoints like that, but in practice it's easier to do it with bobbins.



Too dense; too heavy.

FYI, For translation, if you have an android try "Translate" in the Google Play store. Point the camera and read. It really is is that simple. Technology is amazing. It still comes thru as a straight translation and you must interpret what the English really means. Just trying to help a little.

_________________
Chuck.

“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE

And don't forget my Cushman Truckster resto Locostusa.com/forums/viewtopic.php?f=36&t=17766

it is just Chinese version of "How to Build Motorcycle-engined Racing Cars"

it talk about how to bounded core panel, but the book didn't said how to cut the panel joint

Ah, in that case, IIRC, it's showing how to 'butt joint' two panels together (but the principle is the same as letting in a repair patch).
You rout away one skin and almost all of the honeycomb core material at the edge of each panel, then bond them together with adhesive.

Easy to do with a flat panel on a workbench. Sometimes less easy to do with a panel in-situ on a finished monocoque (whereas to bond in a bobbin with external flanges, you simply need to drill a hole).

I have only posted a couple of times on the forum because I have realized that the chances of me ever building a locost 7 are less than slim to none. I do enjoy reading about your locost 7 projects. I am still plugging away at the engine swap into my 1966 MG Midget. Be that as it may my hobby through most of my life was ocean racing sailboats up and down the coast of California and down to Mexico. This included a life long self study of naval architecture. In the strength to weight ratio nothing beats carbon fiber foam sandwich held together with epoxy cured in an oven. In boat construction next inline is stitch and glue epoxy plywood followed by typical fiberglass, aluminum and finally steel.

A locost 7 is a bunch of flat panels. No compound curves to speak of. Stitch and glue plywood works really well with flat panels. And it is a relatively easy construction method. The joints don't have to be very precise because the joints get filled with thickened epoxy covered by strips of fiberglass cloth. You could build the tub in two weekends. Build the jig to hold the panels in place the first weekend and build the tub the following weekend. I'll do a sketch in Google Sketchup over the next couple of days and post it when I get it done. 1/4 plywood would probably be sufficient for most of the panels with 1/2 for the bulkheads. Somebody who know the forces involved would have to figure that out.

In the long run building the tub out stitch and glue really won't save you much time because the time consuming part of any project is all the little things.

This thread had quite a bit of discussion about monocoque chassis for a 7:
viewtopic.php?f=39&t=18798

One of the Robin Hood 7s was a monocoque:
https://en.wikipedia.org/wiki/Robin_Hood_Engineering

I remember a kit called a "Pirate 7" that was a monocoque, but I'm not getting any hits from the search engines this evening.

We've also had a quite substantial thread dedicated to wooden cars:

https://www.locostusa.com/forums/viewtopic.php?f=39&t=17162

Can you stitch and glue carbon fiber sheets?