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Why Midare Hamon?


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#1 Valric

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Posted 24 July 2017 - 12:23 AM

Something that has been nagging at my mind. Perhaps a naive question but I can't seem to come up with an answer. 

 

Why the wavy midare hamons? 

 

If you want to maximize structural strength you need to ensure stress is evenly distributed. From an engineering perspective this means suguha hamon does it best. Why the wavy stuff in the Koto period? (Shinto is a different story as aesthetics begin to trump functionality).

 

Straight and shallow suguha minimizes risk of catastrophic failure assuming the blade has no taper on either dimension. 

 

Now, I figured out smiths probably knew where impacts are the most likely to be had. Even if you derive some sort of probabilistic heat map of the odds of structurally threatening impacts, you would then again do a variant of suguha to ensure stress is minimized on this surface. 

 

Wavy midare adds spots of brittleness to the blade, where the hamon is deep. Why? 

 

Some elements I've been considering which may lead to unforeseen non-linearities in impact stress response. 

  • The hada gain orientation usually correlates with midare versus suguha, why?
  • Some smiths have produce differential thickness of martensitic crystals on the valleys compared to the apex of the waves.
  • The orientation of the martensitic crystal could change as a function their point along the curvature, which may change structural properties. 
  • We're assuming frontal impacts. How does force reverberate across lateral impacts?
  • More broadly, how does impact vibration contribute to stress? 

If someone has an engineering simulation that would be just wonderful. It's hard to imagine nobody tried to do it. Software to model stress on steel of differential hardness exist for sure... 

 

In fact is someone did come up with such a model it would be fantastic to see what the model predicts as optimal structural form against how famous schools designed their blades. 


Chris H. 


#2 Ken-Hawaii

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Posted 24 July 2017 - 12:47 AM

Chris, I wrote about this in a different thread. The big wars were over when Tokugawa Ieyasu unified the country, but tosho still had to make a living, & with no wars, their target market was now mostly Samurai. But Samurai no longer went to war, so they wanted "pretty" blades that they could show off, & we start to see Shinto blades with garish hamon...& little, if any, jihada.

 

But, as an engineer, I'm not sure that I agree with you that "wavy midare adds spots of brittleness to the blade, where the hamon was deep." On what are you basing that statement?

 

Ken

 



#3 Valric

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Posted 24 July 2017 - 01:48 AM

Hi Ken, thanks for your input. 

 

I'm not referring to post-unification blades - but old swords. 

 

Steel in the hamon is harder than steel outside of the hamon. The harder the steel, the higher the likelihood the blade will break and not bend. If hard steel is not equally distributed, so is brittleness. Hence, where the hamon is deep, the blade is more brittle. Masahide observes and records that large hamon make for brittle blades - but my inquiry is not about these exagerated shinto hamon, it's about the koto blades with undulating or uneven hamons. 

 

From a purely engineering perspective, why would you favor an undulating or flamboyant hamon rather than a simple but sound thin suguha? I presume it's through trial-and-error, and that for these traditions it simply "worked" - but I don't understand the physics of this at all. One explanation is that it was already at the time, aesthetics that prevailed. But this goes against the common saying that swords were foremost designed around function at the time. 

 

I must be missing something and this is why I'm puzzled. 

 

Let's illustrate with some of Darcy's incredible pieces-

 

Take the Hasebe/Chogi. Hamon is thick in the first segment, shallow in the upper segment. This was a massive sword and durability was critical. There is no way this wasn't done for functional purpose by the smith. 

 

http://www.nihonto.c...be-3/index.html

 

Take another masterpiece, the Rai Kuniyuki. Again, you would assume that Kuniyuki designed the uneven geometry of the hamon for functional purposes. 

 

http://www.nihonto.c...ki-2/index.html

 

Here we have the exact opposite. Thick hamon in the upper segments, shallow in the lower ones. So we have two great smiths with a complete opposite take on hamon geometry. We can notice that the Hasede (on top of being massively thick) has no taper, while the Kuniyuki has a slight taper. But would such a difference in taper warrant the completely at odds hamon geometry? Why? Why not opt for a fine and even suguha, like so: 

 

http://www.nihonto.c...ijo-tadahiro-4/

 

I must be missing something. I doubt this is purely "artistic freedom" and has to be product of trial-and-error and data accumulated from customer feedback over generations.

 

How do swords even break? Do they break at the point of impact or point of maximum tension (lower close to the base)? I know very little about material stress, but I assume its the latter. The diminishing suguha towards the base would then make perfect functional sense, and we could surmise that the optimal hamon has this shape (I faintly recall reading somewhere that kotetsu tended towards diminishing hamons, and he was an empirically-minded smith). But then, the Hasede doesn't make sense... 


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#4 Vermithrax16

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Posted 24 July 2017 - 02:30 AM

Fascinating thread already!

 

Agree, I would figure a tight suguha hamon would be most resilient to damage, but I also know the smith's had great love for making works of art. Interesting.


Jeremiah L.

 

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#5 Valric

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Posted 24 July 2017 - 02:30 AM

I think I have a theory. 

 

Let's assume a sword is struck. If you have a even structural rigidity, the point of break (PoBR) is the same as the point of bend (PoBE). If you want to maximize the odds of bend at the expense of break, you should voluntarily introduce a PoBE that is different from the PoBR. If you have an undulating hamon, you're basically distancing PoBE from PoBR. This means the sword will take a bend rather than a break with a higher probability as the PoBE will absorb impact. Undulating hamons will create multiple dissociated PoBEs at each shallow valley. 

 

Furthermore, if you know don't know where the impact occurs and you're unsure about the area of likely maximum stress, you're better off creating multiple PoBE compared to just one. Moreover, a bend could be distributed over multiple PoBE rather than a single one, further reducing the odds of shattering the sword. 

 

If we take the Kuniyuki, The hamon geometry at the base of the sword is clearly designed as a PoBE. 

 

For the Hasebe, let us remember that the sword was massively cut down from its original size. There probably was an area of shallow hamon at the base designed as a PoBE. If we assume that indeed both swords have a PoBE at the base, we can further observe that the upper segment of the sword has a more shallow hamon as well, perhaps another PoBE designed to absorb kissaki strikes?


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#6 Vermithrax16

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Posted 24 July 2017 - 02:40 AM

Chris,

 

I don't know about all that, I am only a molecular biologist, not a physics/metallurgy guy!

 

I think about the ikubi kissaki; short, stubby, great stabbing end. But if anything happened to the end, it was a finished sword. So they moved to longer kissaki to enable repairs? Maybe the hamon size increase allows repairs after use? Just thinking out loud.


Jeremiah L.

 

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#7 hxv

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Posted 24 July 2017 - 03:09 AM

I don't think Japanese swords are made to either break or bend. They are made to absorb impacts with vibrations. Repeated folding of the metal, introducing ashi (so I have read), differential hardening, soft shingane+hard kawagane are all parts&parcel of the same effort. So I have read ...

 

Hoanh


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#8 PNSSHOGUN

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Posted 24 July 2017 - 01:57 PM

I have always wondered if anyone has made a list of O-Wazamono smiths/blades and looked at which type of hamon was most common among them.

 

 

Obversely the Mantetsu swords were made with suguha, and they were scientifically made to be the strongest and most durable swords for combat at the time.


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#9 Valric

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Posted 24 July 2017 - 02:44 PM

To go back to the Hasebe, the theory seems to hold. Almost UBU sword. 

 

http://www.sho-shin....e-kuninobu3.jpg

 

Area of shallow Hamon at the base designed as PoBE. 

 

Of course we'd need more data points from the top smiths with excellent repute for durable swords. I am not sure the "wazamono index" is fitted to this - as it was not created as a measure of durability but of cutting ability in soft medium. 

 

As to swords being designed to absorb impact through vibration, of course I agree - but there is a point of failure where the vibrations alone cannot absorb the stress and this leads to catastrophic failure (breaking) or, if well designed - a good bend. 


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#10 PNSSHOGUN

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Posted 24 July 2017 - 03:59 PM

I'm not sure I follow your logic there, Chris. Cutting capability is directly linked to blade durability and strength. I don't know about you but cutting through an entire human hip bone length ways is not a "soft medium"....


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#11 seattle1

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Posted 24 July 2017 - 05:01 PM

Hello:

 Chris H. raises a very interesting issue, one that has not gone entirely unexplored, and for which the answer lies partially in the records of tested swords, and partially in the history of changing yakiba and jihada relationships.

 An extremely interesting article which assembles longitudinal data showing the staggered departure and arrival of new sword groups after the Mongol invasions of 1274 and 1281 is "The Ichimonji Swordsmiths" by Saulius V. Ploplys, Newsletter, JSS/US, Vol. 49, No.2 (May - April, 2017), pp.6-22. It is a real eye-opener and in my opinion illustrative of the provocative issue raised by Chris which suggests the vulnerability of midare hamon. It shows the rapid decline in Ichimonji sword production after those events and the hypothesis put forward is that the beautiful, flamboyant, wide temperlines of the Ichimonji types failed in battle against the Mongols. Saul's data as presented shows the Ichimonji decline and the increase in output of groups known for narrower and less irregularly varied hamon, such as the Kosori, the early Osafune, etc. Those changes were not aesthetic variations; they were imbedded in the results of practical use.Saul's background is in physics and the objective data-laden article is outstanding in my opinion.

 Arnold F.


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#12 Gakusee

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Posted 24 July 2017 - 05:11 PM

Some of this is covered in the key literature (not sure which publication but could be Connoisseur's and others). The wavy and Bizen hamon in particular with its choji with ashi indeed minimised the risk of breakage along the hanand contained the potential damage. You also have the combination of alternation of soft (pearlite) vs hard (martensite) which also relieves tensile pressure better apparently. Quoting out of memory here and I am sure someone else will elucidate better
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#13 Valric

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Posted 24 July 2017 - 06:57 PM

Thank you Arnold, this corroborates my intuition. Studying hamon geometry lately moved my inquiry away from simple midare versus suguha, towards structural soft areas of steel incorporated into the design as PoBE. The Hasebe sword and the Kuniyuki illustrate this. How do I even find your reference... I wish such things were indexed by google scholar. 

 

John, soft medium was the wrong word. But body and bone do not pose a large risk of break if the strike is well executed, and it was given that it was performed by professionals. A Kabuto, plate amor, or mongol reinforced leather, or another sword, are a different matter in terms of stress and risk of catastrophic failure. This is why I don't think the wazamono index is appropriate to measure durability. It's a different thing. 

 

Michael, I haven't found any particular in depth discussions about the physics of stress applied to sword manufacture besides the oft repeated observations of Masahide. Large Shinto hamon make brittle swords. There has to be more than that to it. I'm starting to think that the midare geometry as designed by some master smiths of the koto period were specifically made to increase durability as per the argument laid above. 

 

As a side argument, if the theory that the base of koto swords were (in some cases) designed as PoBE, this would be another argument devaluating Suriage swords. We keep hearing about "true shape" being altered, and in some minor accounts balance. But in fact, we may be facing swords that are largely inferior to their ubu counterparts due to the added brittleness. 


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#14 Okiiimo

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Posted 24 July 2017 - 07:37 PM

Chris,

 

Respectfully, I feel that the point of bending/breaking theory in hamon design might be a bit narrow in scope for explaining hamon selection/evolution. I believe that minimizing bending/breaking is one of many design considerations but the bend/break approach is only looking at the sword design from a singular quality of blade deformation/failure from impact. How does point of bend/break theories address considerations of edge chipping mitigation and repair, cold weather performance, cross sectional profile (e.g. hira zukure vs shinogi zukure), variations in blade length and sugata, variability in raw material and etcetera. I feel when we look at the massive record of Japanese sword development, we witness the trial and error experimentation that is a balance of tradition and teachings, availability of materials and market demand. In the end, I believe that market demand is the ultimate driver of what is produced by the smith.


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#15 Carlo Giuseppe Tacchini

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Posted 24 July 2017 - 08:06 PM

A sword is like a chain. Is as strong as her weakest point. Not so sure the type of ha ever overwelmed  the class of the Smith in therm of reliability . IMHO a chu saku sword with whatever type of ha hardly beats a JoJosaku sword with the same ha type in therms of reliability. Guess THIS was the criteria with which the pre-Edo Samurai choose their blades. After 1600 is another story...

I'd bet than a lot of the swords broken against the mongols where of lesser smiths, with some notable exception that, for its very nature, is recorded and remembered much more and better than the rest. The kissaki matter is out of this topic.


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#16 Valric

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Posted 24 July 2017 - 08:12 PM

Hi Allan, 

 

Thank you for your input. 

 

It's because breaking is such a disaster compared to the other outcome you describe that surely that was the number one priority to be optimised. Edge chipping is no big deal in battle. A broken blade tends to cause death. And we know just how shameful it was for a smith to have his blade break in usage, the ultimate dishonour and for good reason. 

 

What you mention (Cold weather performance, cross-sectional profile, material availability, blade length and shape) all of these are parameters which are featured into the odds of breaking/bending calculus. The singular goal was to create a blade that cuts (hence, hard) which at the same time does not break (hence, bends).

 

Hello Carlo, 

 

The amount of broken blades against reinforced boiled amor was such that is spanned a mini revolution in sword geometry. I agree that sword smith classification in the koto era correlates with durability - and presently I'm focusing on the top smith to see if I can find patterns in hamon formation made specifically to mitigate break in favour of bend. As Arnold pointed out, the wild ichimonji hamon failed w.r.t to durability. This corroborates the notion that unstructured midare is poor design. 

 

The key to a successful midare was perhaps the structured midare (shallow towards the area of high stress) - maybe even superior to the descending suguha (suguha that tapers off towards the habaki). Because otherwise I just don't see why midare even came about during the Koto period, during which battle functionality was the prime and only criteria. 

 

As for the Ichimonji, I have a theory. Because of the unique arrangement with the exiled emperor, the smiths therein were engaged in something closer to a beauty contest compared to a functionality context against hard targets that would damage the sword regardless. But I digress. 


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#17 Mark S.

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Posted 25 July 2017 - 03:20 AM

Not sure if this adds anything to the discussion, but the article does address hamon and blade strength...

http://www.nihontocr...i_Masahide.html

#18 Darcy

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Posted 25 July 2017 - 05:16 AM

I am not an engineer of course so engineering is going to be over my punching weight.

 

Throwing this out there first, Kenji Mishina and I were looking at newly made Juyo some years ago at the Museum and I asked him what swords he preferred and who his favorite smith was and what he thought of Shinto blades. He pointed at a Shintogo and I said "I like this." About the Shinto blades he said that under his stone he could tell that they were different from the koto blades. They were less pliable and he felt harder, with the exception of Sukehiro. He said Sukehiro's blades felt more resilient to him. 

 

About the hamon then, a few things... you need to first think of the sword in terms of a massive investment in resources if you are going to get a master smith make it for you. Same as today. 

 

Now you are going to be handling that thing with a cloth and gloves and you will freak out if someone spits a little drip of spit on it.

 

Back then you would cut someone in half with it. Through bone and blood and then you'd maybe be looking for someone else to cut in half. 

 

It was a tool.

 

This is brutal use and they would be damaged. 

 

You need a few things then in the hamon. You need to provide enough hardened steel so that the blade can be polished. Sometimes when Japanese dealers write emails and they are not so good in english they will say even now, the blade is "being sharpened." But that anyway is good to think about because I don't think back then people would be thinking, "Oh, my blade needs a polish" after cutting a couple people in half. They would be thinking, "Oh, my blade is screwed up from smashing and killing people, it needs sharpening."

 

They were made with a use projection that included being damaged, being repaired, and being damaged again. You cannot do that with a smallish hamon. So in this you end up with, by necessity, a wide hamon. Too wide and you break.

 

Being able to make the widest hamon then without breaking is going to be a stunt pulled off by the most talented guy. Also it will be the most valuable sword. Not because it's flashy because you can tell your customer, you can get the most sharpenings out of this thing before replacing it.

 

Like if you buy a new set of tires and they last one week, they are not as valuable to you as tires that last four years. You would pay more for the four year tires unless the one week tires were special race tires or something. Anyway you get the point.

 

If you could make a wide hamon then and an unbreakable sword it would also behoove you to advertise that and a little bit of flamboyancy never hurt. The thought that the Ichimonji mei meant "Muteki" in that there was no enemy who could stand against it is also in agreement with this thought. 

 

Why make a midare hamon on a sword?

 

Because you could. Because the other guy can't. His will break. Yours, you can do this and it won't. Because Muteki. 

 

Because you're just better and this is how you show it.

 

Now suguba was there always and will be there always and there are maybe indeed some functional differences in that it is ideal in some ways. But if you are good enough and your testing shows that you're getting 98% performance with 500% sex appeal, what do you think your marketing department is going to report to the CEO in terms of next year's product design?

 

It all hinges in your ability to pull off the stunt.

 

Clearly the Ichimonji blades did this because they were around a long time.

 

With all due respect to the various theories about the mongols, we keep hearing this from time to time but it is relatively anecdotal.

 

The Mongol invasions in Japan were 1274 and 1281. 

 

Ko-Ichimonji is a label placed on certain stylistic developments happening in Bizen around 1200 that are taking place in Fukuoka. There is an overlap with the groups that we go on to call the Fukuoka Ichimonji school. Fukuoka Ichimonji goes on from the early 1200s and there are smiths still working in Fukuoka around 1300. Yoshioka Ichimonji branches from Fukuoka and starts around late middle Kamakura. There are often blades attributed to this time period with remarks that the workmanship looks like Yoshioka or Fukuoka work. The Noami Bon says that Yoshioka work peters out at the end of the Nanbokucho so lasts roughly a century, winding up around 1360. Iwato Ichimonji is a thing of the very end of Kamakura and so goes into Nanbokucho as well. Katayama Ichimonji is from around the time of Fukuoka and goes into the Nanbokucho period as well. Katayama work is as flashy as Fukuoka work. Katayama Ichimonji Ietsugu, Fujishiro has him at 1368.

 

Note in the late Kamakura into the Nanbokucho as well that Aoe made flashy hamon. At the middle and end of the Nanbokucho of course Hiromitsu and Akihiro maxed out the concept of "how far can we go" in terms of hardening the surface of a blade. Chogi and Kencho as well made super flashy flamboyant pieces. 

 

Winding back to the late Kamakura, though Rai Kunitoshi started making calm pieces his very last dated work is 1321 and is done in his Niji Kunitoshi style with a wide hamon and very similar to the Kuniyuki on my site. Rai Kunimitsu made this style from time to time and so did Rai Kunitsugu into the mid Nanbokucho. 

 

There is unbroken evidence of flamboyant midare hamon being in use from the middle Heian all the way through to now. 

 

There is no full stop experience anywhere that made midare hamon no longer be used.

 

The Ichimonji smiths did not fall because of the Mongol invasions. Yoshioka kept on for almost a century after. 

 

My own personal theory on Ichimonji is that the school spread both because of demand for the product and because of exhausting local resources. If you go to the river for iron sand consistently every day of the work for 40 years you may indeed run out of the best quality of ore you're looking for. If you are already pressed for resources and your school is growing and you have more customers, well you might send the sons out to establish their forge somewhere in the region but not in your back yard. Somewhere they could find again good local resources, and not compete with you for your dwindling supplies. Eventually everyone extinguishes as the best resources are used up and then product quality starts to fail. Sooner or later (this has happened time and again through history, some of us exist here because grandpa and grandma back in the old country bailed the hell out for brighter horizons) you might pack up and move too. 

 

Either to where the better, untapped resources are, or to where the action is for selling your product.

 

So: honestly, I think this mongol-invasions-killed-midareba holds no water because midareba was not killed, Ichimonji was not killed, and there is no direct evidence for any of that and all the direct evidence is that Ichimonji kept on keeping on. If there is any document from the Kamakura period that says Ichimonji swords are bad because we can't kill mongols with them I would like to see it.

 

But what does happen is that Bizen remains dominant for 500 years of master smith after master smith after master smith and their reputation is untarnished until today. Midareba is an essential part of what Bizen is. 40% of all Juyo Token are koto Bizen swords. Half of all Tokubetsu Juyo are Koto Bizen Swords! Half of all Jubun and Kokuho are Koto Bizen Swords! This is not a sign of failure, this is a sign of mind blowing success. Midareba was there for all 500 years in Bizen without pause. 

 

This goes for the ikubi kissaki theory that is thrown around a lot as well. No direct evidence and as well, ikubi kissaki as iconic as it is, is not on every blade and chu-kissaki is quite common through all the ages. Chu-kissaki is the suguba of kissaki and people continued to depart from that design only to return to it. I think that is the beginning and end of the story on ikubi-kissaki.

 

Anyway back to the midareba, I'll just repeat again that basically the fact that your swords could look like that and not shatter is why you would do it.

 

Anyone here know what a tourbillon is?

 

https://en.wikipedia...wiki/Tourbillon

 

In summary it is a super technically difficult thing to make which helps a watch keep better time, and it is also completely unnecessary as well as being completely and incredibly overcomplicated and has extremely low benefit compared to the work and sophistication required to achieve it. Especially with pre-modern era tech. Is is internal guts of the watch.

 

The tourbillon is considered to be one of the most challenging of watch mechanisms to make (although technically not a complication itself) and is valued for its engineering and design principles.

 

Think about why you would want to put a tourbillion into a watch. This over engineered, difficult to make thing that may probably not even show noticeable benefit?

 

Why do any of these things?

 

Why go to the moon?

 

Why choose this as our goal? And they may well ask, why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas?

 

We choose to go to the Moon! ... We choose to go to the Moon in this decade and do the other things, not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win.

 

If you can make a functional tourbillion, if you can send a man to the moon and bring him home again safe, if you can make a sword that won't bend or break and send the hamon to the shinogi like fire, you are the best. You do it by choice, not because it's easy, but because it's hard. And if you succeed in making something functional, not just a fancy toy, everyone who is anyone will know you are the best at what you do. 

 

When you throw that gauntlet down, you can stand and look around, and very few will pick it up.

 

That's why midareba hamon.


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#19 Valric

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Posted 26 July 2017 - 12:32 AM

Hello Darcy, 

 

This goes against the general saying of "form follows function" - which I've often read, if we compare koto swords to watchmaking complications

 

The notion  that customers were after swords that will afford them many re-sharpening opportunity is something I didn't give much weight to. It's interesting because then you'd expect the Hamon thickness to coincide with strike areas, and this is often what you see. Shallow Hamon at the base, wide hamon in the middle/upper segment. Both the re-sharpening factor and the creation of a geometry that would be bend at the base then coincide. 

 

I agree that the mongol stuff is mostly overhyped in terms of actual battles. However, the psychological factor I believe at the time was monumental, and spawned levels of anxiety with regards to military preparedness (and hence, quality of arms) that was unheard of. The fear of another invasion attempt was very real. This is an existential threat and you need to do the rational thing. Study the tactics, arms, and armours of your foe. Reproduce them if you can and train against them. While this may be unrelated to the fall of the ichimonji it is highly likely that it is related to the trend towards more robust and designs. 

 

The more I think about it and the more I think the best way to think of a Hamon is in terms of wave frequencies. If you do a Fourrier analysis on a Hamon you can decompose it into different frequency variations. The repeating high and low undulations are in the high frequencies, while the asymmetry from the upper, middle, and bottom segment are low frequency variations. What sort of insights can be derived from this formulation I am still uncertain, however this can be very for the purpose of creating a stress simulation. Unfortunately I'm not a stress engineer and getting all the parameters right is probably far above my punching weight. 


Chris H. 


#20 Ken-Hawaii

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Posted 26 July 2017 - 01:06 AM

Chris, there was an interesting study done on the impact analysis of medieval weaponry by a mechanical engineering class. It doesn't address the hamon question, but does show the "sweet spot" of the katana. I've Attached it for your info.

 

Attached File  Impact_Analysis_of_Medieval_Weaponry.pdf   2.22MB   22 downloads

 

Ken

 


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#21 Okiiimo

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Posted 26 July 2017 - 01:26 AM

I wonder what a Japanese sword would look like if it were optimized for a very specific performance standard, such as impact stress survival. I suspect that the comparison of an optimized sword to a "normal" one would be similar to a hypothetical human optimized to survive car crashes in comparison to a normal human (example photo attached). 

 

 

 

 

 

 

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#22 Vermithrax16

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Posted 26 July 2017 - 01:28 AM

This is becoming the best thread of all time! Great information and thoughts all!


Jeremiah L.

 

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#23 ROKUJURO

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Posted 26 July 2017 - 02:37 AM

I think the key to all this breaking risk discussion is impact stress distribution. A sword blade looks to be a mechnical unit, but its composite construction does not allow to predict the performance as if it was just one piece of hardened tool steel. Looking only at the HAMON is way too selective for statements of resilience, rigidity, or durability. 

HOSO SUGUHA is not necessarily the "best" HAMON for all purposes. If we remember that martensite (which forms the YAKIBA) has a bigger volume (= lower density)  than the ferrite/pearlite steel (corrected after a remark from Ken) of the blade's body, we understand that the cutting edge gets under pressure in the YAKIIRE process which to a great extent causes the SORI of a blade. ASHI are said to act as 'shock absorbers' in this risky stress zone, so there is no clear technical preference given for SUGUHA in my view. 

The same should apply to HITATSURA then.

A while ago we had a similar discussion about statistics of broken blades. If i am not mistaken, it was based on research made by SUISHINSHI MASAHIDE. If memory still serves, very wide 'fancy' HAMON of SHINTO blades had indeed a higher risk of breaking, but as there were no longer occasions to use blades in military actions, weaknesses showed up mainly in TAMESHIGIRI. The problem is that we do not know much about the 'inner' construction of these blades, so that we cannot compare the testing results scientifically with, say, KOTO blades.   


Regards,

Jean C.

#24 Randy McCall

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Posted 26 July 2017 - 02:41 AM

Supplimenting Ken's link above to the paper: Impact Analysis of Medieval Weapons, I'd like to supply the following link to an extensive (150+ page) paper on the physics of dynamically wielded weapons, before and during impact, which in part looks at percussion points and vibration nodes in a blade.

Dynamics of Hand-held Impact Weapons: http://armor.typepad...rd_dynamics.pdf
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#25 Greg F

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Posted 26 July 2017 - 05:14 AM

Darcy once again thank you for such an informative post. A very enjoyable thread indeed.

Greg

#26 Ken-Hawaii

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Posted 26 July 2017 - 05:53 AM

Jean, as I understand the metallurgy, the body of the blade is pearlite & ferrite that form below 1340F, not cementite, with the martensitic steel cutting edge. Where did you get your info on cementite?

 

Ken

 



#27 ROKUJURO

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Posted 26 July 2017 - 11:12 AM

Ken,

you are right. I should stay away from the computer when it's too late....(Corrected)


Regards,

Jean C.

#28 John A Stuart

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Posted 26 July 2017 - 04:18 PM

I think blade shape would be more determinate of a swords being more or less prone to breaking or bending. Hirazukuri v shinogizukuri for example. Boshi shape for type of strike, like tsuki preferences v kiri. If we compare owazamono lists with hamon type what correlation? Or lists of failures in kabuto tests? There should be a common baseline over and above the skill in making steel of an higher quality, being the predominate factor. John



#29 Andi B.

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Posted 26 July 2017 - 04:47 PM

Interesting discussion!
But having natural selection in mind and considering the varieties of existing hamon styles, I came to the conclusion that it obviously makes no big difference which hamon a blade should have to kill people...
Maybe I'm a yellow-belly but I would be even afraid if my opponents blade would have lots of hagire...
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Greetings
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#30 Valric

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Posted 26 July 2017 - 06:23 PM

Thank you for your inputs, I now have a lot to read in order to wrap my mind around this question! 


Chris H. 





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