Materials for a nanofabricated giant monster

Question

In How large a bioengineered mobile lifeform could exist on Earth?, I asked how big my nanoassembled war beasts could be, and it was suggested that I make my question more specific.

I am designing a large autonomous or semi-autonomous war beast that is intelligently designed (not evolved) and constructed by - and to a degree made from - self-replicating nano-assemblers. I want this critter to be as large as possible while still able to function in its role as a weapon of war. Its intended target is Earth or other earth-like worlds, so it should be able to support itself and function in any oxygen-bearing atmosphere at up to 1.3 standard gravities.

Based on this answer to my question, I have made the decision that the war beast will be a fairly short, thick serpentine being that can roll itself into a torus where the diameter of the central hole is approximately equal to that of the average diameter of the roughly circular cross-section of the body. In this configuration, it can move rapidly by rolling, providing impetus by distortions of its toroidal shape from a circle to an oval. When in its serpentine configuration, it would also be able to move by undulatory locomotion, sidewinding, concertina locomotion, Rectilinear locomotion and rolling on its side, forming a curve that it distorts circularly.

In order to make this critter as large as possible, I need to know what to make it from. The material needs to be very strong, in elastic compression, shear and tension. Since this is a war beast, whatever material it is made from also needs to be very tough, and not prone to fracturing at points of damage (as materials such as graphene are prone to doing).

Additionally, the beast must be armoured to withstand as much physical damage as possible, from modern conventional weapons including kinetic penetrators and high explosives, as well as atomics. The best armour materials are very tough, very dense and have a very high melting point to minimise thermal ablation from the high temperatures of atomic explosions. High strength is a bonus allowing greater size.

What materials would best be used for the internal, load-bearing structure of the beast, and what materials would best be used for the external armour plating, and how large a creature (in its toroidal configuration) would they support? Assume that the critter is effectively solid material, though in practise this would not be the case. If the materials are readily available in the earth's crust, that is a bonus, but not a necessity.

I'm looking for an answer backed up by numbers, but I'm also willing to entertain reasonable educated speculation regarding composites and compounds for which no hard figures can be found.

EDIT

The terms "war beast" and "battle robot" should be considered to be interchangeable. This is intended to be an artificially designed and constructed mechanism that is intended to function like an independent living organism, and it is not based on Earth's biological organisms. It need not be carbon-based at all, and given that it needs to be as big as possible, it is most likely that only metals will have the required strengths simultaneously in tension, compression, shear and torsion, as well as having high density (to resist kinetic penetrator damage) and a high melting point (to resist energy or atomic weapons).

Answer 1

Hm. This is an interesting one. Well, in terms of internal structure, I’d suggest making it have a triangular lattice, arranged in hexagonal shapes stacked down the length of the beast, with some extra padding around the edges to make it circular, and some space in-between the stacks to allow it to bend around. This would also give it roughly equal strength all around the circumference of its body, which is useful given that it sounds like it’s going to be rolling around a lot.

I’d also say maybe have lots of little muscles, all working in unison, instead of it being one big one. It’s easier to expend a lot of little bits of energy healing lots of little things than it is spending a lot of energy healing one huge one. This also has the benefit of having lots of backups if your beast pulls something while rampaging through downtown Tokyo, and being able to make very precise movements, even on a very large beast.

On the subject of musculature, I’m assuming you want this thing to be a strong as possible, for general war beast-ing purposes. So how would you get this thing as strong as you can? Well, normally the way that any muscle gets stronger and more durable is through use, so when you do something that damages the muscle cell fibers, then the body fuses the fibers back together into bigger ones, or myofibrils. However, this only happens when the rate of protein synthesis is greater than the rate of muscle protein breakdown, so usually when you’re resting. So what if, whenever this creature isn’t currently out and about, and is just sitting in its hangar somewhere, it’s continuously breaking down and rebuilding its muscle fibers, continuously getting stronger as it rests. Then when it’s called into action, it can switch this biological process off, and charge into battle better than it was before.

The last thing I have to contribute is for the armor, or outer covering. Now this would be in two layers, a harder armor plating, and a inner shock absorber, so I’m going to take them one at a time.

The outer covering would be made of lots and lots and lots of little scales, made out of the same stuff as limpet teeth. Little structures generally are harder to break than bigger ones because they have less room for flaws and are usually very compact, like how you can’t crush a thimble as easily as you could an aluminum can. The scales would be made out of tightly packed fibers of goethite, wrapped in protein. This is the same stuff that limpet teeth are made of, the strongest known biological substance, so it should stand up pretty well to whatever you throw at it.

The inner substance would be some sort of natural-made non-newtonian fluid. You know oobleck, right? Well this is like that, but scaled way up. It acts as a liquid when there isn’t any pressure acting on it, but when a sudden pressure it applied, it suddenly hardens. Non-newtonian fluids have already been used to deflect bullets and make liquid armor. The first line of defense is good against general wear and tear from rubble, and kinetic weapons, while the second line should deflect explosives and high-velocity projectiles. I’m not too sure how you could emulate non-newtonian fluids biologically, but oobleck is just plant starches and water, so I’m sure there’s a way to do it.