What is the Science Behind the Samurai Sword?

[Evo]

A new NOVA on PBS tonight. I was going to place this in History, but since it's such short notice, thought I'd stick it here in case anyone wants to watch.

They're going to show the 6 month process of creating a samurai sword and the science behind them.

These swords are so cool.

 

[Astronuc]

Cool!

But I'll take a claidheamh mòr over a katana any day.

BTW - an interesting essay - The Weighty Issue of Two-Handed Greatswords

http://www.thearma.org/essays/2HGS.html

 

[Astronuc]

Cool program. Thanks for the heads up, Evo!

 

[Evo]

Yes, it was very good. I had seen a Samurai sword made before but this took it to a much more detailed level. Hmmm, a five body blade.

I couldn't believe the daughter firing an arrow at her father's heart and he cut it in half before it penetrated his body.

I also never knew about the clay before.

 

[zoobyshoe]

Yes, it was very good. I had seen a Samurai sword made before but this took it to a much more detailed level. Hmmm, a five body blade.

I couldn't believe the daughter firing an arrow at her father's heart and he cut it in half before it penetrated his body.

I also never knew about the clay before.

The cutting of the arrow was pretty remarkable. Not the sword, but the guy's reflexes: he could have knocked the arrow from it's path with a stick: amazing eyesight and speed.

I am pretty repelled by the testing methods for blade quality. You start out feeling the samurai are great, then you realize they were insane socipaths.

 

[Huckleberry]

Cool!

But I'll take a claidheamh mòr over a katana any day.

BTW - an interesting essay - The Weighty Issue of Two-Handed Greatswords

http://www.thearma.org/essays/2HGS.html

I remember many years ago when I was in Cologne, Germany. I saw a statue, marble perhaps, with it's head missing. I was told that the head was lopped off with a sword. The neck of the statue was at least 6 inches thick, with half of that distance sheared clean and the other half rough. It looked as if one mighty blow had penetrated about 3 inches through the stone before the head broke loose from the neck of the statue. Does that sound reasonable, or was I lied to?

 

[zoobyshoe]

I remember many years ago when I was in Cologne, Germany. I saw a statue, marble perhaps, with it's head missing. I was told that the head was lopped off with a sword. The neck of the statue was at least 6 inches thick, with half of that distance sheared clean and the other half rough. It looked as if one mighty blow had penetrated about 3 inches through the stone before the head broke loose from the neck of the statue. Does that sound reasonable, or was I lied to?

Marble is too brittle to be sliced by a blade in any manner except a sawing motion. A blow from a heavy sword could crack it all the way through, though. The swordsman may have sawn halfway through, then given the statue a sharp rap upside the head to finish the job. Alternately, the crack may have originally been irregular the whole way through and someone smoothed half the surface later in an abandoned attempt to make the statue look neater.

 

[PerennialII]

Marble probably exhibits cleavage like fracture? "Small" initial crack with a sword, accompanied by enough kinetic energy to open the crack and give it some "propulsion" and the rest of the fracture will take care of itself all by itself.

 

[turbo]

Here's a little tip that the antiques dealers don't want you to know. When Japanese men joined the military, they were sometimes given their family's ancestral swords to carry. The mounts, scabbard, etc were removed and stored and the blade was remounted in uniform fashion - plain leather-wrapped scabbards appropriate to their branch of the service, bronze guards with molded cherry-blossom motif, etc. If any of you have relatives that served in the Pacific theater during or after WWII, and they brought home a Japanese sword, you should arrange to have the sword inspected. Likely, it is a mass-produced blade, but you never know. One tip that it is likely mass-produced is if the edge of blade is dull or rounded where it enters the thin collar ahead of the guard. Some blades that are quite old can still be of modest value if the quality or condition are poor or if the maker is not held in high esteem, , but if the signature chiseled into the tang under the grip is that of a respected maker, the sword is worthy of further research, and perhaps restoration. Proper restoration takes a long time and is quite expensive, but the increase in the value of the sword may justify it, especially if you are thinking of selling the sword.

 

[rewebster]

yeah--I heard about a guy that found one, took it to Japan, and sold it for over 70K

 

[turbo]

yeah--I heard about a guy that found one, took it to Japan, and sold it for over 70K

This is a very common game of speculation among dealers of militaria. As long as they can get military-mounted Japanese swords for a few hundred bucks, they buy them, cull out the mass-produced stuff, and dump those back on the market in some anonymous little auction to start the cycle again. Once in a while, they hit paydirt. It can be tricky, because often the signatures are hard to decipher, and many makers emulated the styles of the masters they learned under and/or signed their swords with the names of much more skilled makers so that they could get more money for them. Once you get into the problem of attribution with a questionable signature, you need the services of an expert who can compare the construction techniques, blade profile, temper lines, etc with that of examples that are generally accepted to have been properly attributed.

 

[zoobyshoe]

Marble probably exhibits cleavage like fracture? "Small" initial crack with a sword, accompanied by enough kinetic energy to open the crack and give it some "propulsion" and the rest of the fracture will take care of itself all by itself.

Marble, formed from limestone with heat and pressure over years in the Earth's crust. These pressure or forces cause the limestone to change in texture and makeup. The process is called recrystallization. Fossilized materials in the limestone, along with its original carbonate minerals, recrystallize and form large, coarse grains of calcite.

Impurities present in the limestone during the recrystallization period affect the mineral composition of the marble which is formed. At relatively low temperatures, silica impurities in the carbonate minerals form masses of chert or crystals of quartz. At higher temperatures, the silica reacts with the carbonates to produce diopside and forsterite. At a very high temperatures, rarer calcium minerals, such as larnite, monticellite, and rankinite, forms in the marble. If water is present, serpentine, talc, and certain other hydrous minerals may be produced. The presence of iron, alumina, and silica may result in the formation of hematite and magnetite.

The minerals that result from impurities give marble a wide variety of colors. The purest calcite marble is white in colour. Marble containing hematite are reddish in color. Marble that has limonite is yellow, and marble with serpentine is green in colour.

Marble does not split easily into sheets of equal size and must be mined with care. The rock may shatter if explosives are used. Blocks of marble are mined with channeling machines, which cut grooves and holes in the rock. Miners outline a block of marble with rows of grooves and holes. They then drive wedges into the openings and separate the block from the surrounding rock. The blocks are cut with saws to the desired shape and size.

http://www.mineralszone.com/stones/marble.html

 

[Astronuc]

I think PerennialII's assessment is correct. Six inches of marble is not much. A heavy sword could penetrate few inches, shearing the fracture surfaces before acting like a wedge, the effect of which would pry apart the remainder of fracture.

The question would be - when was the statue damaged?

Certainly if one wants to cut marble in a control fashion, one must 'saw' the marble.

 

[~christina~]

I just saw this yesterday! It was a cool shot especially when they went and explained how they used 2 different strength iron's with different ammounts of carbon together to create both flexibility (in the core) while sharpness on the outside (more carbon).

I didn't get to finish the show though..I was doing physics =(

 

[zoobyshoe]

I think PerennialII's assessment is correct. Six inches of marble is not much. A heavy sword could penetrate few inches, shearing the fracture surfaces before acting like a wedge, the effect of which would pry apart the remainder of fracture.

What do you mean "shearing the fracture surfaces"?

 

[Astronuc]

What do you mean "shearing the fracture surfaces"?

Shearing force is parallel to the surface, rather than the case of tensile or compressive force which is normal to the surface. A shearing force would leave a smoother surface, as opposed to a normal force which would leave a rough (faceted) surface, particularly if the material is brittle.

 

[Astronuc]

I just saw this yesterday! It was a cool shot especially when they went and explained how they used 2 different strength iron's with different ammounts of carbon together to create both flexibility (in the core) while sharpness on the outside (more carbon).

I didn't get to finish the show though..I was doing physics =(

The core of the sword is ductile and tough. There is not so much deformation, so flexibility is not a requirement. Greater hardness and strength often come at the expensive of toughness, the ability to resist fracture in the presence of a flaw. Carbides are strong, but prone to brittle fracture. By supporting the harder outer surface, the more ductile core prevents fracture of the sword under high impact loads. That's not to say fracture will not occur, it's just less likely.

The other factor is the direction of applied force. In practice the force is applied parallel with the plane of the sword. If force was applied across the plane of the blade, then it would likely fracture, especially if struck by a heavier and stronger sword.

 

[radou]

I heard there was a special move with the samurai sword to shake the blood off the blade (it has a specific name, but I didn't remember it) in order to prevent rusting. Namely, only a few minutes are enough for the process of rusting to start eating away the surface of the blade.

 

[zoobyshoe]

Shearing force is parallel to the surface, rather than the case of tensile or compressive force which is normal to the surface. A shearing force would leave a smoother surface, as opposed to a normal force which would leave a rough (faceted) surface, particularly if the material is brittle.

OK, I understand that the sword would be applying a shearing force by definition based on its orientation to the marble, but I don't believe you could get any blade three inches into a piece of marble and have a smooth surface. Having gone at a piece of marble with hammer and chisel myself, I am pretty sure the blade would create a roughly V shaped trench. The displaced marble shatters and crushes and flies back at the sculptor. Safety goggles reccomended, type situation. The hole made is much larger than the chisel.

Instead, the smooth surface might represent the latter part of the blow: once the head had been cracked away from the neck, the blade was then free to act as a scraper and clean up the irregular surface.

 

[PerennialII]

Yeah, would think that the typical situation of hitting a rock/ceramic etc. similar material with a sword would result in a flying debris and the crack the sword would initiate would be blunted fairly quickly (rather a small notch than a crack really), and the crack(s) arrest without any remarkable propagation. What I was assuming up there was that if the marble could in this case be oriented in such a way that one wouldn't hit it with a sword in such a "crack arrester" angle, but rather in a favorable orientation with respect to crack propagation (if thinking about fracture toughness anisotropy, the orientation of "least resistance" to crack growth ... if can think of marble in some terms as a "layered material", hitting it in a "crack propagator" angle [if borrow some composite terms]) , and this favorable orientation was continuous through the neck, the brittle crack could feed on the energy of the collision and propagate within this band of low toughness. Such brittle cracks typically result in a very smooth fracture surface, which in some cases are of mirror quality. Whether such is possible in marble ... don't really know, but if it were the "one hit and decapitate" - theory might have something to it. Perhaps it's easier to sculpt it to the direction of greatest resistance (smaller pieces fall off and can get better surface quality), in which case the decap - direction being an easy fracture path makes sense marble being orthogonal property wise? .

 

[zoobyshoe]

Yeah, would think that the typical situation of hitting a rock/ceramic etc. similar material with a sword would result in a flying debris and the crack the sword would initiate would be blunted fairly quickly (rather a small notch than a crack really), and the crack(s) arrest without any remarkable propagation. What I was assuming up there was that if the marble could in this case be oriented in such a way that one wouldn't hit it with a sword in such a "crack arrester" angle, but rather in a favorable orientation with respect to crack propagation (if thinking about fracture toughness anisotropy, the orientation of "least resistance" to crack growth ... if can think of marble in some terms as a "layered material", hitting it in a "crack propagator" angle [if borrow some composite terms]) , and this favorable orientation was continuous through the neck, the brittle crack could feed on the energy of the collision and propagate within this band of low toughness. Such brittle cracks typically result in a very smooth fracture surface, which in some cases are of mirror quality. Whether such is possible in marble ... don't really know, but if it were the "one hit and decapitate" - theory might have something to it. Perhaps it's easier to sculpt it to the direction of greatest resistance (smaller pieces fall off and can get better surface quality), in which case the decap - direction being an easy fracture path makes sense marble being orthogonal property wise? .

Odd Job could do it, but no one else.

 

[Evo]

Odd Job could do it, but no one else.

Oh definitely. I seem to recall him having decapitated at least one statue.

 

[turbo]

Shear typically occurs in well-organized (crystalline) materials. Topaz has perfect cleavage in preferential planes that makes it tough to facet (VOE, here), and even diamonds can cleave very easily if they are cut without regard to their cleavage planes and the stones are mounted in such a way that a corner of the stone could be subjected to a sharp knock.

Marble is not organized in this way. If you break a piece of marble, it breaks with a texture not dissimilar to that of a broken brick. If you try to shape marble, you'll see why sculptors love it. It is relatively easy to work, and you can use your tools with varying amounts of force AND with little regard for orientation, so you don't get "oops" moments in which big pieces go flying off with relatively small blows. It also takes a pretty good polish when you get to the finishing stages.

If I were to speculate about a decapitated statue, I'd say that the honoree had fallen out of favor and that the damage was a statement. The real guy might have lost his head to a sword, but it's tough to imagine a sword slicing through any thickness of marble. More likely, the neck was sawed part-way through, then the head was given a good whack with a heavy tool.

 

[zoobyshoe]

Shear typically occurs in well-organized (crystalline) materials. Topaz has perfect cleavage in preferential planes that makes it tough to facet (VOE, here), and even diamonds can cleave very easily if they are cut without regard to their cleavage planes and the stones are mounted in such a way that a corner of the stone could be subjected to a sharp knock.

Marble is not organized in this way. If you break a piece of marble, it breaks with a texture not dissimilar to that of a broken brick. If you try to shape marble, you'll see why sculptors love it. It is relatively easy to work, and you can use your tools with varying amounts of force AND with little regard for orientation, so you don't get "oops" moments in which big pieces go flying off with relatively small blows. It also takes a pretty good polish when you get to the finishing stages.

If I were to speculate about a decapitated statue, I'd say that the honoree had fallen out of favor and that the damage was a statement. The real guy might have lost his head to a sword, but it's tough to imagine a sword slicing through any thickness of marble. More likely, the neck was sawed part-way through, then the head was given a good whack with a heavy tool.

Well put, Turbo. It's a mass of very small crystals, not a monocoque crystal, and has no inclination to split straight or smoothly on any orientation, any more than a brick does.

 

[~christina~]

The core of the sword is ductile and tough. There is not so much deformation, so flexibility is not a requirement. Greater hardness and strength often come at the expensive of toughness, the ability to resist fracture in the presence of a flaw. Carbides are strong, but prone to brittle fracture. By supporting the harder outer surface, the more ductile core prevents fracture of the sword under high impact loads. That's not to say fracture will not occur, it's just less likely.

The other factor is the direction of applied force. In practice the force is applied parallel with the plane of the sword. If force was applied across the plane of the blade, then it would likely fracture, especially if struck by a heavier and stronger sword.

Oh...yep I did see the part where they explained that they had this pendulum which swung and cut the metal to determine the hardness. The ones that bended had less carbon but could withstand more force being applied before breaking while the ones with more carbon broke very easily b/c they couldn't absorb the impact well.

I didn't know that it would fracture if it was impacted with another blade parallel to the plane of the sword...that in practice wouldn't likely happen b/c usually the blade is impacted horizontally by another sword..even in close combat the sword would be at a slight angle to the other and thus wouldn't be parallel.