How much does it take to break a blade?

C

culter

Joined
Apr 22, 2001
Messages
121
Has anybody ever done a comparison of how much force you need to break blades made of different steels?
I doubt I will ever use a knife as a crowbar so I'm just asking out of academic interest. What if I have to use my knife as a crowbar? How much can an ATS 34 blade take. Will it bend first or just snap? Would I have some warning (like the blade bending) or is it impossible to tell beforehand? (Of course I'm aware that blade shape and thickness matter as well)

I've seen the test on INFI steel, which can be bend out of shape quite a bit and just springs back. How about more common materials like ATS 34, CPM 440 V etc?

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Seek simplicity, and distrust it.
Whitehead, Alfred North (1861 - 1947)
 
Hello Culter

I know Fallkniven has done some testing on their knives. The test were performed by a independent University.
You can find the results on their homepage:
www.fallkniven.com

 
Ask Cliff Stamp
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Medusa,when I saw the title of this thread, those were the exact words that popped into my mind.
smile.gif


[This message has been edited by Coonskinner (edited 06-01-2001).]
 
Thanks for your answers guys!

The answer seems to be: it takes a Cliff Stamp
smile.gif


I've just been on his homepage. I've read several tests. They answer some of my questions but I'm still interested in seeing a comparison like the one made by Fallkniven and Busse only extended to different blade materials preferrably for the same blade(style). Although Cliffs tests are impressive and I am astonished how much punishment some knives can take, the knives are too different to make any comparison of the materials.
Also I couldn't find an extensive test on a CPM 440V blade since he only tested the lock of the military and not the blade.

(edited typos)

------------------
Seek simplicity, and distrust it.
Whitehead, Alfred North (1861 - 1947)

[This message has been edited by culter (edited 06-01-2001).]
 
The thicker, the less it'll bend and the more strength it'll take to break it. The thinner, the better it'll flex.

I doubt anything you can do to a knife can break a John Greco A-2 5 inch fighter. And i do mean crowbar-type work.

the kind of steel matter a little, but the thickness makes a big deal too. Like 5160 doesn't need to be thick, because if stressed, it'll rather bend then break, especially if done differentially. They make awsome slicer for that reason too. the more brittle the steel, the thicker the blade needs to be to stay strong.

Just my toughts. If you want more info, mail cliff Stamp.. he's the expert on this matter.

greetz, bart.


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"If the world wouldn't SUCK, we'd all fall off !
You can E-mail me at bart.weijs@student.kuleuven.ac.be any
time....guaranteed reply !


Member of the BKS

<A HREF="http://www.student.kuleuven.ac.be/~m9710483/index.html" TARGET=_blank>My
knife-page</A>
 
culter:

[ATS-34]

<font face="Verdana, Arial" size="2"> Will it bend first or just snap?</font>
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Assuming it is tempered to the common ~60 RC it will snap violently. How much it will flex to will depend on the geometry, thinner blades will be able to take much more flexing, as well as any sharp changes in the geometry such as abrupt angles will readily cause fracture to happen at a much lower angle, smooth convex grinds for example are *very* strong and not just simply because of the cross sectional area.

There are a couple of reports from makers in the archives, Drew Wilson broke two of his ATS-34 blades and Lynn Griffith broke one of his Bowies.

-Cliff
 
Thanks Cliff! Great homepage by the way.

------------------
Seek simplicity, and distrust it.
Whitehead, Alfred North (1861 - 1947)
 
How much does it take? Loan it to a fireman.
wink.gif
Theres a saying you learn in the acadamy,"fireman proof".So far nothing has been built "fireman proof" although an anvil comes close.If you want something broke its hard to beat our combination of strengh and stupidity.
smile.gif
 
<font face="Verdana, Arial" size="2">
So far nothing has been built "fireman proof" although an anvil comes close.If you want something broke its hard to beat our combination of strengh and stupidity.
</font>
Click to expand...

Well, you guys have the ultimate excuse after all, so go for it! My blessings and admiration go with you as well!

On the testing issue though, I don't think you can get really meaningful results unless you compare not just similar, but virtually identical geometries at the same hardness. The blade geometry first, and then the heat treat, have much more to do with this than the steel I believe.
 
<font face="Verdana, Arial" size="2">How much does it take to break a blade?</font>
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The bottom line is we don't know. Most consumer products aren't tested like this and, even if we wanted to make an educated guess, it would be virtually impossible to find a meaningful way to communicate a number.

It would depend on where the force was applied, how fast the metal was stressed, how often the metal has been stressed previously, the geometry, composition, and temper of steel, the environmental conditions, and a number of other issues. Even, if we had such a number, or series of numbers, it would be far more exact then anything you can gage in use.

The more practical way to go is to understand that any blade can be easily broken. The very properties that allow you to concetrate force on a small area to effect a cut will create an area that can easily be damaged if improperly stressed.
 
Hey Culter -- it is my guess that most of the stainless steels are going to be relatively brittle in comparison with carbon steels.

I can say more strongly, that if you want a blade that will bend and not break, then you should be looking at the knives of the Master Smiths. They have to make at least one knife for their Masters test that will bend 90 degrees without breaking. Few, if any, will spring back to true, but most go back a ways.

Ed Fowler, for instance, tests one knife in 30 to destruction. This ensures that the other 29 are just as capable. I just watched Ed's video of him making a knife. One of the most remarkable parts is where he proves a blade is sharp, then purposely dulls it to the point it will barely cut, but grinding the edge at 90 degrees on his oilstone, then hits it a couple licks on the stone, and the sharpness is back.

A forged knife of 5160, I believe made by Rick Dunkerly, was tested against a CPM440V knife at Wayne Goddards a few years back. The forged knife cut within 10% of the 440V, then was proven it could bend 90 degrees multiple times without breaking.

If you're looking for "high performance" knives, I think you'd do better to look at forged steel by certified bladesmiths, than to stick with the common folder steels.

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Asi es la vida

Bugs
 
Thanks for your answers.

Bugs, I'm not really looking for an especially tough blade. I use my knives for cutting and am only asking out of academic interest. I just came across tests like the Busse one and was impressed by the INFI steel. But then I wondered if that steel is really that outstanding since I lack data on the more common steels.
I'm aware that steels like D2, M2 etc are tougher than ATS 34 or CPM 440V if the other parameters remain fixed. I was just wondering if somebody ever bothered to make the same blade in different steels and compare resistance to lateral forces.

------------------
Seek simplicity, and distrust it.
Whitehead, Alfred North (1861 - 1947)
 
Its more than the type of steel and geometry. You also have the heat treatment to consider.

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Roger Blake
 
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