Isogrids

[Ciro Pabón]

Can isogrids be used in F1? Should they be used? They are not new (1997 or so), so I guess I'm missing something.

Flat panel isogrid


Conical isogrid section


The concept is simple: stiffen the structure with equilateral triangles. There are some magnificent examples.

3.2 Kg structure, designed to take a 17500 kg load


Now, isogrids are for uniform loads. When you have directional loads, you can change the shape of isogrids to advanced grid structures (AGS).

Payload shroud cone for rocket


So, simple: could an isogrid or an AGS used "on top" of a "regular" carbon fiber chassis? Would it help to diminish weight? Is it already being used but I am not aware of it?

The layout of isogrids on top of composite structures is automated.

Isogrid machine
[youtube]http://www.youtube.com/watch?v=Rp9oCZnuziY[/youtube]

So...

[RacingManiac]

would you use that in the sandwiching of the panel?

The layup of the composite in F1 is already a pretty developed science in that they can be pretty much tailored for different purpose....not sure what this can add to it?

[DaveW]

Reminded me of the Vickers Wellington, a 1930's design inspired by Barnes Wallis, I believe. Not much new in the world...

[Jersey Tom]

Most billet parts are already designed with weight relief pockets like this. Not so much triangles necessarily, but stiffening webs in the directions needed.

[DaveW]

Most billet parts are already designed with weight relief pockets like this. Not so much triangles necessarily, but stiffening webs in the directions needed.

You're right, of course, JT, but I expected you to cite biased ply tire constructions...

[Carlos]

Autogyro mentioned the unique geodetic construction designed by Barnes Wallis for airships, the Vickers Wellington and was also used to build a single-engined fighter, isogrids look like a direct descendant of the geodetic fusealage mentioned and was an alternate method, lighter than the new aluminum monocoque, the aluminum cast and riveted grid pattern also distributed shell damage loads more efficently, a Wellington could fly practically with all the fabric blown off of it, also allowing heavier bomb loads. Although more efficent than a monocoque, it was not a construction technique that could quickly be adopted to a wide variety of airplanes, without a complete rescale; very costly and slow. At the time I gave it a great deal of thought, IMO it could be adapted to F1 as a composite diamond grid chassis. I think it might have been Jersey Tom who mentioned a composite spaceframe FSAE car, which echos this idea and also reminds me of the Birdcage Maserati chassis.There's a Canadian sports plane that uses this technique today and boats also adopted geodetic design for the same reason as airplanes.

Although geodetic construction was said to be time consuming to modify and build, the Wellington went though many variations.

[Jersey Tom]

With regard to Ciro's earlier question about using them on top of a composite structure... really no need to.

In a homogeneous material like a block of aluminum, you can cut out an 'isogrid' so you have relatively high area moments of inertia in multiple directions with a pretty significant reduction in weight. The strongest, most rigid structure in the same bounding box volume would still be a monolithic block (albeit much heavier!)

In a composite 'sandwich panel' laminate you're gaining all your stiffness by putting distance between the load-bearing face sheets to increase the MOI that way. The idea is to have the core material to just be enough to space the stuff out and to not bear any load itself... which is why super flimsy Nomex and aluminum honeycomb work well. Layup orientation of the face sheets then determines the directionality of the thing.

Adding this sort of structure to a composite (like a carbon tub) would defeat the purpose, IMO.

[Ciro Pabón]

Well, I think there is more to it than weight relief pockets, or triangled structures like the Wellington.

I believe the idea behind isogrids is to "replicate" the lines of force on a stiffened flat sheet. You orient the fibers along the grid to resist tension. So, being carbon fiber so good in tension, if you align them, the plate only fails by compression, with little bending.

You can "earn" an order of magnitude in strength with this kind of alignement, at least in civil engineering structures (which, I concede, are more or less static).

Ideally, you would identify the main lines of force and reinforce the material just there.

You can use flat shells in compression and fibers laid by a robot to adsorb tension.

The shell is kept rigid by this tension fibers, because their tensile strength is very high (carbon) so it doesn't buckles easily. This lack of buckling gives you a very efficient shell in compression, like so many building designs made possible by this kind of construction since the 30's. As in all reinforced concrete structures, the reinforcing "fibers" are invisible, they are the steel bars that are embedded in the beams.

Pier Luigi Nervi, Hangar, Orvieto, 15 cm width beams using flat shell "theory", cover made of prefabricated blocks in pure compression.


I know the human bones grow along lines of force, as another example (Wolff's law).

Arrgh, I cannot find the picture I would like to show: it depicts femur head "lines" (small ridges you can see on the surface of bones) and the same image with the calculated stress lines. Both coincide. Here you have a video of fringe pattern analysis of lines of force in an isogrid, boring as hell, but this is the idea behind flat shells structures as opposed to skyscrapers (that work on the principle of separated parallel planes, as JTom describes).

[youtube]http://www.youtube.com/watch?v=PUqUzj1wz10[/youtube]

I just wondered if F1 designers use this as an alternative.

It's not opposite to sandwiched design, but a complement or better yet, an alternative.

In my opinion, watching nature, a possibly superior one, as the bones of mammals (strong fiber directionality) seem superior to oyster shells (sandwiched with alignement in the general direction of stresses) in weight/resistance. Frankly, every time you really want to carry the load to the limit, you start to reinforce locally, along lines of force.



A question: I think that in sandwiched structures, the core is not there to space tha "load plates": it also carries shear forces, it's not simply for spacing. The core shear is maximum at the "edges" or support points. Am I wrong?

[WhiteBlue]

All the Iso Grids shown in those pictures are open to one side whereas the structural parts like tubs use a sandwich structure which is closed from both sides. If there were an economical way of manufacturing "rib" structures for the sandwich core in the way the three dimensional structure of bones are made I could imagine that a part with IsoGrid core instead of a sandwich core would be advantageous.


We typically can learn something from a bionic engineering approach. I could think of transferring the way a bone is designed to the main truck of a big aircraft. Those are huge structures of complicated shape made from titanium and steel forgings or castings. With 3D totally encased IsoGrids I imagine you can save a ton of material. The question is how to manufacture those structures.

In F1 perhaps a wheel could be a good application although I believe that composite design is not allowed at present.

[Jersey Tom]

Well, I think there is more to it than weight relief pockets, or triangled structures like the Wellington.

I believe the idea behind isogrids is to "replicate" the lines of force on a stiffened flat sheet.

Weight relief pockets and slots on big billet parts are set up just this way though. You mill it all the way down as thin as possible (or all the way through) until you're left with support webs in the direction you need.

Likewise, with composite ply layups.. as the fibers are oriented in such a way to load things axially.

[timbo]

Won't such design only have superior strength in one dimension? E.g. good compression but poor shear properties?

[RacingManiac]

Yes, but you are designing with the understanding of what the load requirement is. Thats how you pare down weight....

With composite too you also alternate the layer of the layup to suit the need....

[The FOZ]

Very cool info, Ciro.

It appears that the isogrids perform a similar function to a honeycomb core - just, rather than being fully sandwiched, it's an open-faced sandwich.

The carbon tow laminating machine shown above is very cool - using isogrids, I wonder if it would be possible to lay up a full, 3-d component, like a tub, in one piece, with isogrids as a core, rather than using honeycomb? It would drastically cut down on hand layup time and the variances inherent to the process.

[Carlos]

This might shed some light (if anyone reads it-sigh ) A NASA paper ( just 4 pages and photos take up a lot of space) notes similarities between geodetic grids and isogrid panels.
Introduction:( trying to lure you in to actually read it - sigh )
"Geodesic grid structures have a long and
illustrious history, including the famous geodesic
domes of Buckminster Fuller and the damage tolerant
Wellington bombers of World War II (1). These early
grid structures typically consisted of wood or metal
grid frames and fabric skins, but in recent years it has
been found that grids consisting of unidirectional
composite ribs can be used to great advantage (2-4).
So far, the use of grid-stiffened composite structures
has been mainly restricted to relatively high cost, low
volume aerospace applications such as launch vehicles."

Yes, just 4 pages. I can't help but think if you read it, many may offer informed opinions ... rather than....opinions
http://www.speautomotive.com/SPEA_CD/SP ... df/i08.pdf

And the 'NASA Isogrid Design Handbook' for those that really have an indepth interest
http://femci.gsfc.nasa.gov/Isogrid/NASA ... Design.pdf

[Jersey Tom]

It appears that the isogrids perform a similar function to a honeycomb core - just, rather than being fully sandwiched, it's an open-faced sandwich.

Similar in look only, with fundamentally different functions.

A honeycomb core between two sets of face sheets in a composite panel is there to serve as filler space. It's not designed to take any significant amount of load.

An 'isogrid' structure is designed to be entirely load-bearing.