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I want to create a sword that when sheathed remains limp/flexible or soft but upon being unsheathed it become hard like common steel.

So, something like the sword going soft when not exposed to oxygen or something from outside but will harden when exposed to that chemical from the outside.

So, something like oxygen or some other chemical from the outside hardening the sword but cutting the access to said element results in the sword going soft.

The flexibility would be similar to those in the old Chinese movies where limp or flexible swords (not historically accurate) are used, or Indian whip sword (real historical/traditional sword), but is only in that state when it is sheathed or not exposed to outside elements.

Undesirable methods of achieving this:

  • Something that basically involves using heat or the lack of it is out of the question.
  • Something that when pumped from inside makes the sword hard is out of the question too, because I already have that type of weapon.

Is there method or chemical that can achieve what I describe?

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    $\begingroup$ Do you want this to be done multiple times, or is just once okay? The latter is possible, the former pretty much isn't. $\endgroup$ – Halfthawed Nov 22 '19 at 2:42
  • $\begingroup$ @Halfthawed i actually want it to be multiple times, but if its imposible, then i want to see the just once method that you know. $\endgroup$ – Li Jun Nov 22 '19 at 4:08
  • $\begingroup$ Unfortunately, I can't think of one. Air isn't very reactive, and you've banned heat. I mean, you'd have better luck if you cheated by using specific gas clouds to draw the sword into, but even still, this is a pretty touch challenge. $\endgroup$ – Halfthawed Nov 22 '19 at 4:21
  • $\begingroup$ @Halfthawed well it just an example, not necessary need to be or because of oxygen, so other gas/chemical is acceptable, but it must be naturaly around in the surface/outside area just like oxygen (its still in earth though not other planet) $\endgroup$ – Li Jun Nov 22 '19 at 4:45
  • $\begingroup$ btw i was reffering india there not native american one, so iam not sure indian is a good wording for it. $\endgroup$ – Li Jun Nov 22 '19 at 8:22
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Zippered Sword

This will not be an easy feat in smithing, but: The sword consists of two chain-link sides that are flexible when apart, but zipper together to become inflexible. The scabbard top would function as the 'runner' of the zipper, zipping the sword togetherwhen drawn and unzipping it when it is sheathed (maybe part of the top comes off with the sword to cap it).

It could feasibly be done by having long links overlap, so that the connections on one side lie along the middle of a link on the other side, preventing it from bending. I don't know enough about zipper technology to say exactly how this is done, but I believe it would be possible.

A consequence will be that the sword edges are serrated, with each link having a half-moon edge. It is probably not possible to make a clean point, so it will be a slashing sword rather than a stabbing sword.

It may be easier to make a version where the two halves roll up in a short, wide scabbard rather than being truly flexible, but if the point is to make it easier to carry, this would work as well as a flexible sword; maybe even better. Imagine a large belt pouch from which a long sword is drawn.

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    $\begingroup$ The memory metal in slap bracelets might work also. $\endgroup$ – arp Dec 12 '19 at 21:41
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Origami rapier and ballon shield.

The simplest way would be a flat, thin piece of triangular metal or plastic that folds several times along its length (along pre-machined lines), to form a somewhat stiff skewer. It will be more of a thrust than a cut-and thrust sword, think small sword or even rapier. The actual tip is manufactured from a hardened steel. The hilt provides a small mechanism that does the folding when drawn.

Such a weapon will be significantly weaker, structurally, than a solid sword, especially against blows against one of the flat sides of the material. It's conceivable that such a sword could be drawn and resheathed many times before material fatigue sets in, but it won't survive hard blade to blade contact.

It will be challengin to find a suitable fencing style: AFAIK many styles avoid blade-blade contact, but to my totally lay opinion especially fencing styled for thrusting sword like rapiers and smallswords do parry with the blade. For a fold up rapier, the wielder needs an additional defensive weapon:

The airbag shield:A Balloon of very tough material that is integrated in a solid glove. Upon command, a small explosive charge blows up the ballon (that stays, in away that is still to be properly desinged and engineered attached to the glove) which gives the wielder something to put between themself and incoming blows. The shield will be very unwieldy and won't have the mass to really block blows, but can cushion them and adsorb energy.

Stabs pose a real danger of puncturing the shield. The inside is engineered to stick to intruding objects, the ballon readily crumples once deflated, all in hope to trape the weapon - there's a chance that a solid stab with a spear or rapier goes right throu shield and wielder, but if the stab misses the shield-wielder or the weapon is simply too short, the attacker cannot quickly escape.

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    $\begingroup$ Any blade with folds will be very weak compared to a normal weapon of a similar size. This is unlikely to survive the first heavy parry, and possibly risks crumpling against even leather armour. $\endgroup$ – Dan W Nov 22 '19 at 12:39
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    $\begingroup$ Sorry to Necro this – yes, some styles avoid blade-blade contact in rapier (e.g. many Italian styles), whereas some strongly favour it (Spanish styles). However, some styles include cuts with the rapier, which you'll need to completely avoid. You'll need to use a style which avoids contact as much as possible, however, this may not be possible depending on your opponent. You should probably look at late rapier styles and smallsword styles, perhaps even sport fencing which uses a floppy blade. $\endgroup$ – Dan W Feb 13 at 9:40
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    $\begingroup$ It's important to distinguish parrying (misdirecting their blade) and blocking (stopping their blade). Blocking isn't good in rapier at all, but particularly with a weak blade, blocking will be fatal. Parrying can be done without blade contact. You can also keep yourself safe by voiding (dodging) their thrusts. $\endgroup$ – Dan W Feb 13 at 9:42
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    $\begingroup$ The airbag shield is an interesting idea, but you're probably better off with a leather glove on your off-hand. We use a gloved hand to parry incoming thrusts – you hit the side of the incoming blade, misdirecting it, not trying to stop the thrust. $\endgroup$ – Dan W Feb 13 at 9:44
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    $\begingroup$ So I think you've two alternatives – use a gloved hand and fight in a single-rapier style, or try the balloon shield and fight it as rapier and buckler (can't find any treatises on this to hand, but it was done). $\endgroup$ – Dan W Feb 13 at 11:01
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There is a bit of research on this in regards to robotics

Here is an article on materials research into structural rigidity, deformation and flexibility in materials that can be controlled using various methods to allow on-demand or controlled use.

The typical application in a modern context is in actuators, devices that allow controllable movement, in particular tendons, artificial muscles and so on, for use in robotic arms, mechanical devices which require on-demand flexibility and strength.

The candidates you could consider include:

  • Thermal induced material control: You've ruled out heat however some chemicals respond to minor changes in temperature such as Thermoplastics which are crystalline at room temperature but at slightly elevated temperatures can become liquid. Another option is a ring of nichrome wires surrounding a expanding thermoplastic core at room temperature, stiffening into a hard rod when the wires become tensioned.

  • Pressure induced material control: Some materials also change state when their container is altered in terms of pressure. Granular materials and fluid polymer materials are examples - if given the opportunity they arrange themselves into matrices or stiff objects depending on pressure. Your 'sheath' could essentially alter pressure to allow control.

  • Magnetic field induced material control: Magnetic fields have the advantage that they can have instant results - if your sheath has a property where MR Elastomers can be affected by fields, you could soften or harden a material in such a way to create the effect you want

  • Electrically induced material control: Electroactive gel can be used that stiffens when a current is passed through it - your sword hilt could be a 'battery' with conductors that pass current through such material to create rigidity.

  • Other alloys: There is research into Shape Memory Alloys, ie, metal that is a rigid shape, but undergoes variable rigidity when exposed to either currents or heat as above. This is ongoing research.

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Tape Measure sword

A tape-measure uses a curve in the thin metal strip to impart strength. Unfortunately, the strength only runs one way. This can be countered by using two opposing spools of 'tape-measure' (or three to form a triangular blade). The tips would be joined with a hardened sharp tip. Some mechanism with interlocking teeth or magnets could help to further stabilise the blade.

This will create a weapon which packs down compactly into 2-3 spools, but should be stiff enough to allow a smallsword sized weapon to thrust. This should be sufficient to inflict a fatal wound against an unarmored target.

Floppy toy

If you've got kids, you're probably familiar with the 'floppy animal' toy: An animal made of separate pieces; a string inside pulls it taut, and when the string is allowed to go slack, the animal flops.

Provided you have sufficient materials science in your world, you could create a sword from this principle.

Blade pieces would be maybe 5-10cm long, with a thin hollow inside for a cable. They'd have an interlocking end to aid in keeping them stable when 'drawn'. The issue is finding a strong enough cable – it'd probably have to be something like kevlar for the tensile strength – and a mechanism which can apply sufficient force – this might need to be a miniature electric winch, or a pulley/lever system to gain sufficient mechanical advantage.

This would again allow thrusts, and would probably be a bit stronger against hits to the side, with the added benefit that if it does take a bad hit, as soon as the cable is re-tightened, it'll snap back to it's shape.

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  • $\begingroup$ is this the toy ? sorry since i dont know what floppy toy look like, but it an interesting concept. $\endgroup$ – Li Jun Feb 13 at 10:22
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    $\begingroup$ @LiJun – sorry, no – this is the kind of thing: images-na.ssl-images-amazon.com/images/I/31Ru3EuHHIL.jpg – they use a spring to keep tension, with a button on the bottom to release tension. $\endgroup$ – Dan W Feb 13 at 10:32
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    $\begingroup$ On the floppy toy idea, you don't actually need that much tension on the cable if you have two independent nested sets of pieces. To relax the sword, you would relax the cable and do something that shifts the inner set to line up with the outer set. $\endgroup$ – David G. Feb 13 at 12:12
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    $\begingroup$ @DavidG. Interesting idea, that would certainly reduce the tension needed. But nested pieces would necessarily be thinner, so I'd be more worried about them bending, preventing them from sliding? Maybe something more like a tongue and groove would get the benefits without making them too thin? If I had a lathe I'd be tempted to try this out! $\endgroup$ – Dan W Feb 14 at 10:24

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