What causes different feedback when chopping?

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JaVa said:
...I'd say it doesn't really matter if it has a handle or not...

...I have yet to flick a forged gyuto with any handle on them that would not "ring". at least some what. but I have flicked several non forged knives and again regardless of handle the sound has always been more muted.
Click to expand...

I have to disagree. I think the handle has a huge effect.
I recorded this as a video response. This knife was forged and heat treated by me, 1084 monosteel.

[video=youtube;8CcQLDNh7bQ]https://www.youtube.com/watch?v=8CcQLDNh7bQ[/video]

I'm working on my other 'Kippington experiment' now. Gonna use W2 and mild for this one, hopefully I get the quench done before it gets too dark out.
 
Wow, that's super cool! Never thought the handle would have such a dramatic effect.

I have tested over 10 forged mono-steel knives and even several more of non forged mono-steel knives, all with different kind of handless and all the forged ones have had a much clearer sound.

Although just to be clear, I never meant that the handle would have no effect on "ringing" properties of a knife, because of course it would have. What I meant was that If a knife would have a tendency to vibrate and ring, then regardless of the handle that it still would at least to some extent. Even if the handle would mute the effect I never thought that a handle could kill the vibrations completely. Now I know better. :doublethumbsup:
I'm actually very excited. Cool stuff!

Love to be proven wrong and learn from that. Even more so, alway absolutely loving it to see something proven in practice. We can talk about stuff until we're blue in the face, but until it's shown in practice, its just theories and talk.

Can't wait for the "Kippington experiment"! :cool2:

Still, if that's the handle used on that knife, when in use, it will have very limited to non existing feedback due to the the dampening factor created by the handle. And still... Vibration is information, that is the only way information can travel from the cutting board to your hand. So regardless of what causes the blade to be able to vibrate or what kills those vibrations. Vibrations is the only thing that can enable feedback.

BTW Any chance you could add one more billet that could be non heat treated to see if there is any difference?
 
JaVa said:
Although just to be clear, I never meant that the handle would have no effect on "ringing" properties of a knife...
Click to expand...

Yea apologies for that, I did quote you a bit out of context to get a point across. :O

This experiment is proving to be more difficult then I had imagined. This is where I'm up to.
I took my W2 and structural mild steel bars (both annealed from the mill):
kI9qngF.jpg


They have different dimensions so I marked them and cut them like so:
m8tseax.jpg


Then clamped them together and went to grinding:
sIZPQrv.jpg


The mild steel was thicker then the W2 so I ground the surface to get them to a similar thickness. And this is what they look like now, no heat-treatment having been done:

ocTS85U.jpg


Close enough, right?

The problem is... they already sound different! When struck, they share the same pitch but the mild steel continues ringing for something like 2 seconds while the W2 dies off almost immediately! I'm at a loss to explain why this is...
There is mill scale on the surface of the mild steel that might be affecting the vibrations. It's too late for me to do any more grinding so I will have to wait until tomorrow!
 
Looking good! :)

Do those two steels share the same structural properties or Is there a difference in hardness, weight, density etc. That could affect that. Look, to me it's a no brainer that two different steels cut to a same size and shape would sound different of the bat. Even if their properties would be very close, that's not the same as identical. Not saying that's the reason here since it's been so strongly suggested otherwise. Just throwing it out there.

Even if the note is the same or close, the other steel might have a much higher dampening factor and it absorbs the vibrations quicker hence rings a shorter amount of time.

I'm very interested if someone would now their hardness? Which is harder and does the harder or softer steel ring longer?

There is also another possibility I'm considering, but I would love to hear first the answers to these questions before going there.
 
So I am a little late here to the game here but a very interesting discussion. I wonder if, in addition to the internal properties of the steel, the cross-sectional geometry and distal taper have much more to do with how a knife vibrates. The edge would vibrate like the string on a violin much as the geometry allows. Also the spine would vibrate at a different frequency than the edge probably due to their relative thicknesses.That said, I also recognize that tone woods (Rosewood, etc) operate differently that woods of similar hardness that are not in that group (Oak, Hickory).

I look forward to hearing more about what you all find out.
 
This is where having one of the material science experts weigh in would be great.

Also cross sectional geometry really is important and it is not just a linear proportion but something like a x^4. So minor variation could have reasonable effect.
 
BloodrootVW said:
So I am a little late here to the game here but a very interesting discussion. I wonder if, in addition to the internal properties of the steel, the cross-sectional geometry and distal taper have much more to do with how a knife vibrates. The edge would vibrate like the string on a violin much as the geometry allows. Also the spine would vibrate at a different frequency than the edge probably due to their relative thicknesses.That said, I also recognize that tone woods (Rosewood, etc) operate differently that woods of similar hardness that are not in that group (Oak, Hickory).

I look forward to hearing more about what you all find out.
Click to expand...

To my knowledge the cross sectional geometry and distal taper of the blade has a lot to do with the resonance frequency and yes, the edge and spine would vibrate at different frequencies with each other. But that opens a new can of worms. As a general rule the thinner the blade is the less there's difference in the frequencies between different parts of the blade and the blade should ring better.

But there are other principals in play. Unfortunately I gotta run. I'll get back on this when I have a chance.
 
So we need to reel back a bit. Like somewhere earlier I mentioned that all things have a natural resonance frequency and that it's affected by certain properties like weight, shape size, density, material etc etc. and that usually things have several resonance frequency points, but only one is the natural point (where the object will vibrate the most). All those frequency points have a certain wave length which can vary anything from narrow to wide.

As the edge and spine are vibrating at their natural resonance frequency which is going to be different from eac other, if some of those resonance frequencies peak at the same places it enables the object to hold those vibrations better. That can be further assisted by if the wave length is wide as that helps the frequencies to be at the same spots for longer.

you can have a heavy workhorse knife that when tested will clearly vibrate, but might feel lifeless compared to a thinner blade that vibrates a little less. This is caused by the fact that the heavier that the heavier knife needs more force to cause those vibrations. A thinner knife will vibrate with less force and on the cutting board whan used right there isn't that much force directed to the edge anyway.

As the edge is the thinnest part of the blade there's also the matter, that some of the power of the vibrations is not only lost due to the dampening factor, but because the thinnest part of the equation receives the initial hit and transfers those vibrations thru to the increasing mass and tries to make the heavier part to vibrate.

So the more of the cross geometry, shape, distal taper and other properties are in tune with those resonance peaks as possible, (and the wider those peaks are the better) that would make it a lot easier for those vibrations to carry through.
 
You could study a bit into this through modal frequency analysis, at least for simplified models (monosteel).

Every knife is going to have different frequency characteristics if their geometry is even a little bit different. To do a consistent test you could have the same exact profile and same exact grind - not that difficult if you know what you're doing. Easier still would be to make little tiles of steel, like the keys on a xylophone. Use the same core steel, have some monosteel, some cladded, unhardened, hardened, tempered, untempered, forged, cold forged, etc.

Handles will certainly alter the characteristics. If you study into classical sword designs, practically everything is tied into vibration. The ratios can be derived to be quite similar to musical instruments. Dimensional ratios were scarily similar to fret patterns on a guitar. What happens if you mute certain parts of a guitar string? You could dampen the sound, or you may hit a harmonic node. Same thing with steel - it's all about vibration nodes throughout the shapes.
 
Don Nguyen said:
Easier still would be to make little tiles of steel, like the keys on a xylophone. Use the same core steel, have some monosteel, some cladded, unhardened, hardened, tempered, untempered, forged, cold forged, etc.
Click to expand...

Yes this is similar to what I'm trying to do. These results are not what I expected so I might have to retract some of my earlier statements. :(
I double checked the tile dimensions by holding them side by side (you can't see the gap between them):

elBrFJn.jpg


And checked the thickness with a back-light and a straight edge. Not perfect but close enough:

2Lhkx6F.jpg


Unfortunately I can't weigh them, don't own a set of scales.
So here I recorded the audio. Each piece was thrown up in the air and struck. I can hear a distinct difference between them... they share the same pitch but the W2 refuses to carry the vibrations for as long as the mild steel.

[video=youtube;W_XaaP3rT9c]https://www.youtube.com/watch?v=W_XaaP3rT9c[/video]

Blegh, I need to re-think what I said earlier.
I'll go and quench the W2 in water now. I'm guessing it'll grow slightly larger then its brother as this is what martensite is supposed to do over pearlite. But heck, I'm not so sure of myself anymore.
 
Ok, I've quenched it in water:

[video=youtube;XScJEd88-wU]https://www.youtube.com/watch?v=XScJEd88-wU[/video]

After the quench, the W2 has grown slightly larger in all directions as it should have - thank goodness! :lol2:

2RKmvjU.jpg


Here's what it sounds like after the quench - the same as before if you ask me.

[video=youtube;lGg5_56R2SM]https://www.youtube.com/watch?v=lGg5_56R2SM[/video]

I think if I was to differentially harden it there would be no significant change to the resonance in the steel.

I'm not sure what else to pull from this...
Should I differentially harden the W2 or break it instead while its still hard? Or maybe I could hit both the tiles with the same force to break one and bend the other if that helps prove anything, kinda like a home-made Charpy impact test. I haven't tempered the W2 so it should be right up there in hardness with very poor toughness.

Can anyone explain to me why the mild steel reverberates for so much longer then the W2?
 
I can just contribute my "feeling" on this subject... But I'm fairly sure I feel a considerable difference on blades with same (my own) grind. I've tried this with many knives, differentialy hardened, soft clad san mai and full hardened mono.

A full hardened feels more "direct" and shorter resonance on board, like it doesn't want to play music... While knives with soft steel will have a little bit more vibrations to them. I mainly use face grain wood boards also may be worth noting.
 
What I meant with "lossy" is friction inside the material when it is subjected to vibration, which will obviously take energy away and reduce "sustain"...
 
Reading this discussion I started out being pretty sure the hardness didn't matter much given Young's modulus stays constant and so on but it seems I was wrong.
 
One suggestion: for the sake of getting the best possible experiment it seems better to do the hitting with a piece of soft material rather than another piece of steel to rule out local plastic deformation.
 
The dissipation of vibrational energy to heat is typically called hysteresis and come to think of it it is not too far fetched that a different crystal structure has different hysteresis value.
 
I always thought hysteresis was what kept thermostats from becoming buzzers :) Or what was up with the melting point of Agar... So are we talking a fully reversible effect, or energy going into fatigueing the material by slowly knocking atoms out of whack?
 
Interesting stuff merlijn, thanks for the link.

I'm thinking the grains might play a larger factor in my test than the hardness. It definitely shows up in that hysteresis paper (check out Fig 11. the difference in error between coarse martensite vs martensite, both @ 45 HRC).

It also just occurred to me that when I cut the bar stock, I cut the W2 against the grain while cutting the mild steel along it (if they were cold rolled).

m8tseax.jpg


I will modify the grain in the mild steel and see if that changes anything.

merlijny2k said:
...do the hitting with a piece of soft material...
Click to expand...
Yes I made sure to do this. I used one of those soft bamboo chopsticks so there was no chance of denting the steel.
 
Bleh, normalizing and grain refinement had no effect on the mild steel acoustics.
Heat treating does not seem to have a large effect on vibrations in steel, which makes sense in terms of elasticity... but I'm still at a loss to explain why the two steels sound so different. It really seems to back up what some people are saying about the feel between clad vs mono-steel, much to my surprise.
 
Kippington said:
Bleh, normalizing and grain refinement had no effect on the mild steel acoustics.
Heat treating does not seem to have a large effect on vibrations in steel, which makes sense in terms of elasticity... but I'm still at a loss to explain why the two steels sound so different. It really seems to back up what some people are saying about the feel between clad vs mono-steel, much to my surprise.
Click to expand...

What is the chemical composition of W2?

Still doesn't explain the perceived difference for Honyaki
 
This specific W2:
Certification: C- .916 Si- .296 Mn- .215 P- .0050 S- .0020 Cr- .069 Ni- .042 Mo- .008 V- .165 W- .005 Cu- .047 Sn- .0060 Al- .006
Annealed Structure: 98% spherodized carbides

malexthekid said:
Still doesn't explain the perceived difference for Honyaki
Click to expand...
Agreed!
 
Cast Iron is way off in terms of shear wave velocity, bet that gives a very different sound. Also, differences in shear wave velocity affect the harmonic itself while difference in hysteresis only duration (damping).
 
Looking at it from this angle, there should be a far larger tone difference between brass and steel than between steels. Happen to have any leftover brass?
 
Also have you tried Soundbeam or another oscilloscope app? I'm curious to see the actual waves. Seeing where they differ might give us some usefull info like is it mostly the frequency or damping behaviour etc.
 
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