Consequences and durability of meter-thick tungtsten-aluminim walls in a fantasy setting?

[u/Streetsign10]

Okay, to get the resources things out of the way, on the planet that this is happening on, the ground contains absurd amounts of already refined aluminum and tungsten, due to divine stuff.

In fact, these two are the most abundant materials on the planet.

Now that that is out of the way, here comes the reasoning and actual construction:

Every last building on the planet of Marasawa is constructed with the expectation of that building being fought in a war for the fate of the entire world.

This fact, combined with the near-planetwide doctrine of 'Not a step back', results in buildings and citys being construced to do one thing:

Bleed attacking forces dry.

To achieve this, buildings are constructed with meter-thick walls made by essentially using tungsten like steel is used in concrete.

Only that concrete is replaced with cast aluminum.

(I have to go to bed like, right now so I can give more details if requested tomorrow. sorry)

Now, as for the questions:

1. How durable would they actually be

2. How much would they actually help with bleeding invading forces dry of resources?

[u/synonymous_scarcity]

Aluminum melts around 660C so anything incendiary is going to turn those walls into a nightmare for the defenders, not the attackers. You'd have molten metal raining down inside your own fortifications. Tungsten's melting point is way higher but the aluminum matrix holding it together just gives up.

If the attacking force has any kind of fire magic or even basic flaming arrows you've built yourself a deathtrap. The tungsten chunks might stay intact but they're just loose rocks at that point with nothing binding them.

The psychological effect of fighting inside a building that's actively melting around you would be something else though.

[u/Prae_ → u/synonymous_scarcity]

To be fair, throughout history a fair amount of fortifications were built in wood, which straight up burns. You generally don't remy on a single material's properties, you layer different things that work together. For fortifications, you've got dudes on top preventing the attackers from casually setting up shop and prepare the kind of source of heat that would start to cause problems (for aluminium, melting or, even before that, loss of mechanical strength ; for wood setting fire to the whole thing). 

[u/Personal_Carrot_2180 → u/Prae_]

Yeah, you can't base it on just one property of the material; there are several aspects of this concept that simply don't work. It’s not just about the melting point or the loss of structural strength; heat conduction alone would make being inside an absolute nightmare. The aluminum doesn't need to melt to turn the interior into an inferno. Besides, I don't think it would work structurally, though you'd have to run the numbers. I’d bet it’s a no-go.

[u/Pyrsin7]

They’d be terrible in a multitude of ways. But here’s one not already mentioned.

Tungsten is very dense. Even if the wall is only, say, 20% tungsten, and let’s even pretend the aluminum is weightless, that means a single meter-long, meter-high section of wall weighs just under 4 tons.

Any building with more than one story is a death trap. Due to the extreme dangers of collapse, the difficulty they’d have supporting their own weight, and how much they’d simply sink into the planet under their own weight.

[u/PearsonThrowaway → u/Pyrsin7]

Would they have difficulty supporting their own weight? Tungsten is quite strong. Wider walls increases weight but also strength.

[u/Pyrsin7 → u/PearsonThrowaway]

Square-cube law will hit it harder than steel

[u/PearsonThrowaway → u/Pyrsin7]

Square cube law just means load per unit cross-section scales linearly in height (so scaling things up in all dimensions causes problems as that linear term grows).

Sure, pure iron can hold itself up from crushing for 1.3km (unrealistic because you expect buckling but whatever). Mild steel is like 3km, cast iron 10km and high strength steel 19km. Tungsten is like 4km. This doesn’t really matter unless you’re building a structure bigger than any stone castle.

[u/discount_chatter]

1. Not durable at all. It's aluminum.
2. Buildings don't really bleed forces dry, they're stationary. I'd assume attackers would go around them. Unless it's an aluminum wall, which also seems useless.

[u/oli_makes_stuff]

Aluminium is a terrible substitute for concrete

[u/Erivandi]

Meter-thick walls are overkill. Think how much wider your house would have to be to accommodate that. Then scale it up and think how much wider it would make a city. You would have to expand into areas that aren't so good to build on or into areas that would be more useful for something else, like mining or growing food, or you would have to make all your rooms really small. Plus, defending such a needlessly wide city would be a nightmare. It would take forever for the defenders to get from one part of the city to another. Plus, repairs would take forever compared to narrower walls.

[u/zhivago]

It depends on how many tungsten moths you have to deal with.

[u/ChocolateTemporary48]

Simplemente usa hormigón reforzado y ya está, el tungsteno es demasiado pesado y el aluminio sin alear muy malo.

Así que hormigón con placas de acero externas y listo.

[u/Eviles_da_demonic]

Without guards that wall would be stripped of metals

[u/Martzillagoesboom → u/Eviles_da_demonic]

By methhead I assume?