Okay, I'm kind of misleading the discussion, so let's here's an idea: I'm going to list scenarios and see whether people have any ideas or comments to it. These two have absolutely nothing to do with any story I'm currently writing. I'm just making them for the sake of discussion.
Steampunk fairy-elves: for circumstances both comical and convoluted, the whole of human-fairy kingdom has found themselves away from homeworld, stripped of their magical homeland they could control, stripped of their magic in general and in need of industrialization for survival in a new world. They come to a new world with mostly medieval-ish tech. They have a few humans and others with whole libraries of science books (modern and better) to give them ideas and a strange but resourceful world around them that has everything they need. And they need to industrialize for long-term survival and because magic has left them.
Only problem: they have a ridiculous aversion and allergy to iron. Doesn't matter what form, what alloy, skin contact causes deadly rashes, inhalation of dust causes potentially fatal breathing problems, you don't even want to know what the mess is when ingested, they can't even be near the stuff and even having it is a mayor cultural taboo in their whole society. Microscopic amounts their bodies can deal with but not highly elevated amounts. Even daredevils will sooner play around with balloons of nitroglycerin and mercury than carry a bag of the stuff. Otherwise they are mostly human. The only people that even remotely would touch it are scientists and possibly miners who would have to deal with iron ore.
How would their technology adopt? How crippling is the lack of iron?
Sword of Ages: before they left their home for the newcoming humans, the Ancients gifted an unique sword to the founder of a human kingdom as a symbol of their approval of the founder's ideals. The sword was given so they would fight the leftover monsters the Ancients made and not-quite-intentionally released into the wild. There were other gifts, but let's stick with the sword: it's a Oakeshott Type 19 (or XIX for those that insist on still using a clumsier and outdated form of numbering)
blade, with an unusually-elaborate ringed crossguard and holes in the material for hilt (the Ancients supplied their own, luxurious version but allowed space for replacement) plus a wedged section for its pommel. It is not meant to do anything but be a good sword that is very, very, very durable, meant to serve all of the kings of the kingdom while it lasts. And that's it.
It doesn't need to do anything but last mostly-functionally for a very long time. The Ancients did other stuff and gave other stuff, but with the sword they figured the kingdom will last a few centuries or get lost. Their secret intention is that this grand gesture will impress the humans and the sword will gather enough of a history so the humans would remember the Ancients for a long time, which appeals to the Ancients' ego.
How would you build it?
I think fixating on the gigajoules and terrawatts of your armor assuming it is a spherical mass of iron QED neutrino heatsink radiators is a shit way to make some fantasy story, if one IS making a fantasy story.
For the story I've writing, I already made all the decisions I wanted about armor (and really, they were minor decisions*) before making the thread. In a way, the thread is sharing what I found and asking for comment. A lot of the responses are well-meaning repetition of what I've already read on other forums while looking into this question and what has been told to me.
*For context: there is a character that needs armor and other equipment. I've gone with spider silk (suggested to me by someone else than Sea Skimmer but yeah, as always, he's a man that knows what he's talking about) with protective gel (scavanged from dead but advanced civilization) woven in. The metal armor on top for not just more protection but additional aggressive use (imagine kneeing or elbowing someone with soft versus hard stuff). And this is made by a character that not only has all the resources he needs, with machines and metal literaly lying around but is intimately familiar with super-strong non-steel alternatives because he builds submarine vehicles.
Properly fitted armor really doesn't slow a person down or restrict their movement. Even a set of full harness (full-plate) doesn't really limit mobility, speed, or range of motion.
I actually know all this and didn't give clear enough context:
Don't think "has to get on a horse and maybe a few vaults" kinda of acrobatics. Think "if Prince of Persia character had a athletic lovechild with Mirror's Edge Faith" kind of acrobatics that does regular Assassin's Creed stlye parkour to boot.
Full plate is a marvelous technology that allows full range of motion for battle. But not for what I had in mind, so I shouldn't have brought it up.
Just no. This is all entirely wrong.
By your way of thinking it should be impossible to block or parry a steel sword with something like a polearm or staff. The difference between wood and steel is going to be far greater than any difference between something like tungsten and steel. So if wood wasn't facing these issues, what makes you think that they're likely to come up in metal on metal combat?
Yeah, reading back it does read stupid (I actually feel rather stupid right now and I feel I look stupid in this whole thread).
What I should have asked: say you make a sword out of tungsten blade held by an aluminum core as Sea Skimmer mentions. Would the difference between be as great or similar to the difference between an iron sword and a (good) steel sword?
By the way: I kind of realize that regardless of material, there can be no "uber sword". In the end, even if the sword was made out of indestructible diamond-sharp Unobtanium, you will only get marginal improvements due to the limitations of human strength. Maybe enough to give minor advantage over enemies wielding more regular weapons, but not one that really decides a fight. Even if the sword was diamond-sharp, human strength can't cut trough metal bars in one swing or even decent wooden ones.
For an uber-sword, it needs to DO something mostly on its own, its blade-analog to actively cut and destroy somehow like a lightsabre or even a chainsaw-sword. That is the kind of advantage where there is a point of having it. That's what a magic sword does: it does something that an ordinary sword doesn't. Cut when other swords don't cut, tell you the truth, guide you or just give you a heads-up if there are orcs around.
Why does she need extra-strong armor covering her knees and elbows but not, for example, her back?
Read my response to Shroomy. She already has light protection there too. Elbows and knees are especially vulnerable while moving around.
It depends on the amount of force being used. I mean, you can bang an aluminum bar against a steel bar without banging the aluminum, unless you're banging it really hard, at which point sooner or later you have to accept that with modern technology weapons are replaceable.
All weapons are replaceable and in the end, but there is the question whether a good whack on the flat will destroy it. But I guess you could somehow have the aluminum core a reinforced framework (maybe have a solid core?) so it would fail partially.
Your typical fantasy Valyrian steel sword or whatever is irreplaceable and it's unacceptable for it to be designed in a way that lets it become damaged in a fight.
I think that if you have magic that you imbue a sword with for a grand purpouse (say, have something that easily kills those damn undead things that crop up now and then), you will use some of to give it supernatural durability. Your "The departing gods made it so mortals can fight evil" Holy Weapon has to last trough the ages. And make sure you don't have it used for anything else.
Otherwise, all weapons will brake during use and you end up your special-purpose holy weapon to be worn away. Weapon on weapon contact, even if you try to mitigate damage, will add up.
I think you really do need to slow down and specify what this is for. <snip>
State the mission, and then we can talk about the tools intended to accomplish it.
This thread isn't for anything I need. I'm just badly asking questions trying to give the topic some discussion, sharing some of my ideas that spark off from responses (the DU dragon-killer thing popped into my head while reading SKimmer's post) and making myself look stupid.