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Flexability and stiffness


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Hey, I got thinking, could there be some other factor at play here also?

 

I certainly can't just brush off Patrick's expieriment, nor what is established as mettalurgical fact, with regards to Modulus...

... but still, what I see in sword blades, over and over again, is something that superficially at least made me think that hardeness had a definate correlation to stiffness.

ONe of the things I've always done is hold blades around the area where the handle would be, and give the tang a bump sideways, it helps find the vibrational centers and helps with figuring out how it's all going to be balanced and adjusted, etc. I do it alot, usually before and after hardening, between tempering cycles, while it's getting mounted, after it's finished, etc. Especially on longer blades, the vibration is very noticeable.

What I've noticed, during all of this, is that the frequency, and the "amplitude?", or the amount of travel in the vibration, *seems* to change quite significantly from full soft to full hard, and from the various temps used in the tempering cycles, all with the same sword blade without any changes other than condition of hardness. It *seems* that the harder condition vibrates at a higher frequency and smaller amplitude that the softer conditions.

Now, it may still be in my head and if it is I'll just have to deal with it. :0)

But over quite a few years of doing this, I'm pretty sure I'm not THAT nuts, it really appears to make a difference.

I always made the connection to "harder=stiffer", simply because that was the simplest connection to what I am expieriencing. But if the "modulus of elasticity" rule is correct, and there isn't nessecarily any reason to assume that it isn't, then is there some other factor involved here that would cause this difference I'm seeing?

Randal

www.rhgraham.simpl.com

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I think you might be on to something Randal.

 

Might sound kooky and it could very well be psychological, but I'm gonna go out on a limb here and say (without any sort of scientific/metalurgical proof or data) that a blade feels pretty darn different in hand to me before and after its been hardened... :blink:

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I think you might be on to something Randal.

 

Might sound kooky and it could very well be psychological, but I'm gonna go out on a limb here and say (without any sort of scientific/metalurgical proof or data) that a blade feels pretty darn different in hand to me before and after its been hardened... :blink:

 

Well hey, I'm totally down with the idea I may be just simply wrong about it and there may be all kinds of reasons that I've maybe "convinced" myself that hardness/flexibility has some relation, or maybe I'm expieriencing something entirely different that would make me feel that way about it. I'm hoping I ain't such an old dog yet that I can't learn more about it anyway.

:D

It "seems" harder blades are "stiffer" to me, but just because that's how it seems, doesn't mean that's the way it is. And awfull lot of this gig is feel sometimes, and that can certainly be flawed.

Randal

www.rhgraham.simpl.com

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I'll only add at this point that this "modulus of elasticity" rule (while counter intuitive and disruptive to what I have been doing in my mounting of katana....) really explains the particular plateau and sticking point in my theories and studies geared towards getting the kind of handling characteristics and cutting prformance I have been after. According to this theory an unhardened mock up blade of A36 has the same relative flex characteristics as a fully hardened and tempered blade of 5160 so long as the "set point" is not breached and neither blade becomes permanently deformed.

 

This disturbes me but really explains *many* balancing and flexation under cutting load problems I have been encountering in tuning my blades and mounts and actually removes a variable from the equation that I thought was inescapable. It introduces a whole new concept and I feel now that the resolution and adaptation of these issues and the incorporation of this concept will ultimately help me to understand and refine what it is that I have been doing to a very high degree.

 

Understanding the actual, physical limits and rules (terms of engagement) in terms of flexability and the factors at work here is gonna make me a better sword maker once I get it all roped and in place. You can bet on it. ;)

 

My theory on why a hardened blade "feels" different than an unhardened blade? It transfers shock/vibration waves in varying levels of difference...The actual crystaline stucture of the blade is different. Like the transference of shock/sound waves thru water happens differently than it does thru air.

 

A hardened and tempered blade blade can sustain a different amount of deflection and still return straight...it can store more energy in the form of a spring than an unhardened blade. While it's defelection under an equal load might be identical it's ability to return energy or sustain vibration from shock is different.

 

This can be felt. IMO. It's a theory.... :rolleyes:

 

Brian

Edited by Brian Vanspeybroeck

"Imagination is more important than knowledge" - Albert Einstein

 

"The innovator is not an opponent of the old. He is a proponent of the new."

- Lyle E. Schaller

 

http://home.mchsi.com/~hermits/BrianRVanSp..._Edged_Art.html

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Vibration ? You introduce a different subject and I don't know if there is any relationship to MofE. I recently watched an entire bridge truss reach resonant frequency !! Awesome ! Of course that's structural steel not hardened....Balls for ball bearings are checked for hardness by bouncing them from a hard steel plate .Those not properly hardened don't bounce the same . ...My experiences are that hardened steel attenuates vibration less than soft steel and the hardened steel may have a higher resonant frequency. I don't know the science behind it.

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Yeah, there was some amount of "bell ringing" in my ears on the subject of flexation....it's a hard thing to rationalize without the experiments Patrick was describing but I have no doubt at this point that this is indeed a hard and fast rule. I have reviewed my notes and been rethinking a number of destruction tests of various blades and in *every* case the anomoly I discovered points to the subject at hand.

 

One does not argue with physics and it's laws. I can't believe it took me 15 years to discover this. Hopefully it won't take me another 15 to incorporate this into what I do. Otherwise I might just quit it and take up fishing and start buying cutlery instead of making it.

 

But there is equally no doubt that a hardened steel blade "feels" differently and performs quite a bit differently in terms of how it handles shock and dissipates vibration than an unhardened blade does. I think a blade is pretty complex in how it reacts and responds to various stresses, shock, and vibration especially at lengths beyond about 15" or so. I don't know why.

 

I do sincerely appreciate everyones input on this. B)

 

Brian

"Imagination is more important than knowledge" - Albert Einstein

 

"The innovator is not an opponent of the old. He is a proponent of the new."

- Lyle E. Schaller

 

http://home.mchsi.com/~hermits/BrianRVanSp..._Edged_Art.html

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Well hey, I'm totally down with the idea I may be just simply wrong about it and there may be all kinds of reasons that I've maybe "convinced" myself that hardness/flexibility has some relation, or maybe I'm expieriencing something entirely different that would make me feel that way about it. I'm hoping I ain't such an old dog yet that I can't learn more about it anyway.

:D

It "seems" harder blades are "stiffer" to me, but just because that's how it seems, doesn't mean that's the way it is. And awfull lot of this gig is feel sometimes, and that can certainly be flawed.

 

 

I cant really verbalize what the difference I feel is (or imagine I feel) but its not just the hardness/flexibilty relation and I agree with Patrick and Brian, one cant argue with physics. So I dont wanna sound too "out there" but a hardened and tempered blade feels well...for lack of a better word, uhm, "heavier" and also somewhat "purposeful" to me. :unsure: Not very scientific terms I know, But the vibrating-on-a-different-frequency deal sounds better than "its-all-in-your-head". :)

 

...Am I alone on this one? :wacko:

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as far as vibrations (soundwaves) traveling through differant mediums the navy submarine sonar can read differant layers of water according to temperature and can use them to hide in.......

the differant crystalin structures of steel that you talk of Bryan may be the source of the differant "feel" as far as vibrating before and after heat treatment

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I cant really verbalize what the difference I feel is (or imagine I feel) but its not just the hardness/flexibilty relation and I agree with Patrick and Brian, one cant argue with physics. So I dont wanna sound too "out there" but a hardened and tempered blade feels well...for lack of a better word, uhm, "heavier" and also somewhat "purposeful" to me. :unsure: Not very scientific terms I know, But the vibrating-on-a-different-frequency deal sounds better than "its-all-in-your-head". :)

 

...Am I alone on this one? :wacko:

 

Well, the relative handling characteristics of a sword blade (I'll use that as a basis for comparison as I have some experience with this...) are dependant upon a number of different factors and how it flexes (and how much/how fast) is only the tip of the iceberg. Point of balance and weight distribution (on all the axis) as well as handle material/lack of it are really critical. But the actual construction of the blade has a pronounced effect on vibration transferrence, dampening, wave propogation and all of that stuff...you *can* feel it and I believe (if one was of a mind to...) you could measure this as well if we were trying to "engineer" a blade and mount. I think there is a science behind all this but developing it in the 21st century is probably a huge waste of time and resources. <_<

 

FWIW, I can tell the difference when cutting various targets depending on if the blade is differentially hardened, fully hardened and tempered, or is some percentage of Bainite. Old, antique Japanese blades with a soft core and chippy hard edges have a very different feel (during cutting/under load and even being swung or handled) than a blade of Bainite or hardened and tempered Martensite. Differentially hardened/soft cored blade have a feel when passing thru a target that is significantly different than a thru hardened blade. I used to believe (looking at the cut pieces and watching video of the cut) that this was in part due to the amount of flexion the blade was enduring based upon relative hardness. I now think that the amount of flexion is so similar as to be negligible. I think the differences are more due to wave dampening/transference and to the tendency of thru hardened blades to reinforce vibrations more than dissipate them.

 

I don't know why but hardened and unhardened/ differentially hardened blades *do* definately perform differently. But I'm convinced now that the difference is not due to flexation variances in identical blades due to the relative hardness of the steel. I used to feel that blades with Bainitic structures were more "boingy/springy" caused by (as I was convinced that thru hardened/springy blades were as well) their propensity to flex to a greater degree ( I felt they were less rigid...) under the same load stresses but this is not the case. They feel more alive and springy in the hand and under load because of some amount of as yet undiscovered or uncatagorized characteristic. They process and reinforce/dissipate energy imparted to them during movement that is subtle but a bit different depending on if they are soft cored/differentially hardened, fully hardened and tempered, or some percentage of Bainite and the relative hardness of *any* of the structures plays a role as well.

 

It's just not in the form of variances in lateral deflection under similar loads, IMO.

 

It's all rather fascinating...one of the things that keeps one humble and on the road to understanding/learning. But I'm with you, ....yer not alone in this observation. B)

 

Brian

Edited by Brian Vanspeybroeck

"Imagination is more important than knowledge" - Albert Einstein

 

"The innovator is not an opponent of the old. He is a proponent of the new."

- Lyle E. Schaller

 

http://home.mchsi.com/~hermits/BrianRVanSp..._Edged_Art.html

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Ok, did some quick tests over the weekend, Mete, I'm totally with ya on Modulus of Elasticity now I understand that, and saw it... all is well

:D

 

I have a swordblade in the works also, and I was lucky to be going through the initiall normallizing and stuff on it, and now, it aint very scientific, but after normallizing it, i hung weight on it between saw horses and measured, and gave it that "bounce" test I mentioned earlier.... Then I hardened it and left it full hard, hung the weight and measured, and it bowed pretty much the same, which I was not "expecting" because of what I had assumed over the years, but totally shows me the Modulus of elasticity deal is spot on. Of Course.

BUT, the "bounce test" was WAY different, it felt "tighter", it seemed to me to vibrate at a higher frequency with much smaller amplitude than it did when it was in annealed condition. Which has always made me think that hardness had a relationship to "stiffness". BUt the test with the weight obviously shows this isn't the case and thier is something else involved. Which is kinda cool actually...

Very unscientific mind you, but at least makes me thing I need to study the subject a whole lot more

 

Pretty cool stuff, even if it is turning my brain into a noodle, thanks for the input everybody.

Randal

www.rhgraham.simpl.com

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Cool, Randal. These are the kinds of things that makes this stuff interesting.

"I find that the harder I work, the more luck I seem to have."

- Thomas Jefferson

 

"The difference between fiction and reality? Fiction has to make sense."

- Tom Clancy

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Mete:

Did you see that bridge truss vibration on 'Mythbusters' Can't remember the russian scientist, maybe Tesla that said something about matching the resonate frequency would cause steel material failure. Wicked cool that they shook the whole bridge from a 5lb device.

Could make a sword fail in theory. Excuse the spelling please, I am challanged.

Thanks,

Chuck

Edited by Chuck Bussey

"I find that the harder I work, the more luck I seem to have."

- Thomas Jefferson

 

"The difference between fiction and reality? Fiction has to make sense."

- Tom Clancy

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Guys, I happened to see this thread and it hits square on the head of one of my questions. I have been wodering what specifically makes a filet knife have its flexible qualities and still spring back and not break. I can make a filet knife, but its good to know the "whys". I was starting to "get it" too and Mete's graph with accompanying explanation clinched it and clarified the whole thing. Great discussion.

I also feel that a blade that is heat treated one way will give a different feel as compared to one with another level or method of treatment. From the experiments, I would also say it has to do with vibration/amplitude. I'm not a metalurgist, so I can compete on a technical level, but Its starting to be more clear and I thank you guys for the thread. Lin

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It's funny how this all ties in, if I had payed a lot more attention to the "failure mode" discussions in class some of this might not have been such a suprise and a brain-fry I bet.

Rashness of youth and all that.

:)

Randal

www.rhgraham.simpl.com

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It wasn't that kind of truss I was talking about.....:)

 

Regarding the Convention Center, there are so many things that could be wrong - deigned properly installed wrong - aka Hyatt Regency; Designed improperly, and installed per drawing; Properly designed, and pressure put on to change the drawings (The Big Dig) to save money....Improper design assumptions, procurement people changed the specifications because the engineer called for something more expensive (happens more times than you think)...Or properly designed, properly installed, but user abuse - that happens a lot!

 

But back to the discussion, the section modulus (only material property is E - the elastic modulus) governs stiffness. Microstructure only changes the modulus a couple of decimal points - probably not significant to measure with common shop tools....even a micrometer....

D. Scott MacKenzie, PhD

Heat Treating (Aluminum and Steel)

Quenching (Water, Polymer, Oil, Salt and Mar-Tempering)

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So, & please shoot me if I'm way off.

 

bars 1 & 2 are, of course identical in every way except tempering

 

& weight x is right on the point of bar 2's permanent deformation thingy but well within bar 1's

 

weight y is right on the point of bar 1's, but waaaay over that of bar 2's

 

would the amount of flex of bar 2 with weight y on more than that of bar 1 equate exactly to the amount of set after removal, or is there some weird metallurgical scale involving sins & cosins & weird stuff like that?

 

...or is there some weird metallurgical scale involving sins & cosins & weird stuff like that?

 

 

I bet there is :rolleyes:

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Wow, I haven't had such a revolutionary mental shock like this about something to do with knifemaking since grain refinement through simple thermal cycling was demonstrated to me years ago. It seems so simple yet counter intuitive, that stiffness is dependent only on thickness and geometry and not on the heat treatment. This explains all those old blades with the t-shaped spines as well as well as the move to blades with thicker diamond shaped cross sections in the later Middle Ages as well. I can't believe I've always known those shapes were adopted for thrusting purposes, i.e. more stiffness, but I've never once questioned why. It seems so obvious now but it's like stubbing your toe on a brick sitting in the path for years and then wondering what you stubbed your toe on while staring right at the brick. I'm still wrapping my brain around it.

Guy Thomas

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