I don't have any tests of that type of study. The OP asked for someone to provide an example of a knife that failed expressly by throwing, which is what I provided.
:thumbup:
Also, I've never batoned a knife without holding the handle (seems really dangerous, it could fly out). And even if you didn't hold the handle, the most of the force of the blow from the baton is transferred through the blade to the material being split. Same concept applies when you hit a croquet ball that is touching another croquet ball to send one of them flying.
It is my understanding that when throwing the energy doesn't transfer as cleanly, and more is left "in the blade" to dissipate by resonating...
When splitting logs with a wedge, you hammer the wedge into the wood until it is held in place by the compressive force of the material, then you step back with the sledge hammer and give it a good solid blow, inducing a split down the grain of the wood. If you wedge is sufficiently deep to be held securely by the wood, there is little chance of it flying loose when struck properly, and even so the energy should have dissipated into splitting the wood such that very little is left to send the wedge "flying". The same principles apply when batonning wood or, as you mentioned, playing croquet - put a wall on the other side of the ball you're going to "send" and see how far it goes
. When throwing (well), the kinetic energy of the projectile is dissipated on impact just like when batonning, however the force vectors present on impact may not all be directed into the material being stuck (unlike proper batonning), so the energy may return up the projectile which, if it withstands this return, then dissipates it into surrounding material as able (depending on properties of the projectile and the material struck). The "resonance" being discussed is vibration, rapid alternating bends along the free length of the projectile. If the projectile is very stiff, these bends may be very minute but also very rapid vs. longer & slower. In theory, a longer & slower bends dissipates energy over a greater amount of material & time and so reduce stress on any one section. However, the stiffer projectile which does not experience these long/slow vibrations has the opportunity to transfer more of the energy into the object struck. This explanation is all very rough, "lay man's terms" if you will. It sounds like
robertl could confirm, better explain, or walk all over this, so I'll leave it to the engineer. My summation, the forces involved in throwing a knife are less controlled than those involved in batonning, and that is all. A knife not designed for these less-controlled forces may not be able to withstand them. However, which aspects of the knife determine how well it can withstand such forces goes beyond mere hardness-level.
So wait, what you just said was what I said... Basically a small flaw became a larger flaw through repeated stresses. ... Under the assumption that no single piece of steel is completely flawless you could have just described why it is that hardened blades have broken while throwing...
...not subject to much "hard use", and we want the edge holding and super acute angle...
Yes, the BK2 broke because it was flawed to begin with, unable to withstand "hard use" i.e. repeated stresses involving a large amount of man-induced force. :thumbup: It's a good thing those knives come with a lifetime guarantee. And putting that guarantee on an implement implies that the maker is sufficiently confident in the quality of their work in
reducing the incidence of such flaws. Read up on Bussekin QC measures in doing just that. A manufacturer can engineer their product to withstand man-induced stresses (i.e. throwing, bending, torquing, pounding, etc. without aid of machinery/levers, you get the idea?), and hardness is only one way of accomplishing that. While no tool is "flawless", it may be manufactured such that the "flaws" are never uncovered by these stresses because they are able to withstand them. Would a properly HT'd 5160 or S7 or 52100 or INFI tool of the same dimensions
and hardness not have been able to withstand the stresses? How many cycles? Would the 1095 BK2 at 50 Rc faired better? And finally, if it is common for 1095 knives at ~60 Rc to fail from man-induced stresses, at what point do you sacrifice one desired property (e.g. a hard edge) for another (a strong spine)? Note, not all throwing knives need be so soft...
A Myth is something that doesn't have any truth, but a theory is something that could be true, but is as of yet untested/unproven.
Semantics, but I think a "myth" is a theory or story or explanation propagated AS truth despite a lack of evidence fully supporting it.
Every good myth has an element of truth.
I learned how to throw knives by using a 4ft tall Pillsbury doughboy that was made out of Styrofoam (buddy worked at a grocery store and got the old floor ad) as a target. Turns out... Styrofoam doesn't care what angle your blade hits it... it just always goes in
. It was great fun though.
That sounds AWEsome
Fatigue. 80-90% off all metal failure is caused by fatigue. In this case, throwing the knife is probably exceeding the maximum stress for infinite life (surviving forever even though there is repeated stress) and it WILL eventually break, even though it looks fine. This maximum fatigue stress is related to the hardness, a softer knife will live longer at higher stresses than a hard knife. This is caused by the propagation of cracks and defects inside the material. I can point you to a study of this, but you won't recognize the guy's name and it wouldn't mean much to you. I can point you here
http://en.wikipedia.org/wiki/Fatigue_(material), which has a pretty decent article on it or to Chapter six of any of the norton machine design books.
Thank you,
robertl, good luck with finals.
"Fatigue" as described by "exceeding the maximum stress for infinite life" is very general, you might also call in "weakness". You might also postulate that throwing a knife accelerates rate of fatigue (moreso than, say, batonning) based on the stresses involved, but that would be true of ALL materials, including knives specifically designed for throwing, or you could transfer it to something like reusable projectiles, e.g baseballs or arrows - each has a theoretical fatigue limit for specific kinds and levels of stress. Heck, stairs have fatigue limits of how much impact and steady force they can bear before failure. This is structural engineering, one can go on and on....
But the point I see is that fatigue limits can be tested and the compensated for. Beams and joists can be made thicker or of different materials of varying hardness, and the same is true of knives - different steels at the same hardness behave differently depending on base chemical composition and heat-treatment. 1095 at 60 Rc may behave very differently than CPM-3V when subjected to the same stresses. And knife designers/manufacturers should know this. Softer materials may be more malleable than the same material at higher hardness, which means it is more likely to bend than fracture under certain stress conditions, but another material may still fracture at the hardness and a third may still bend at even higher hardness. And while all materials will break under the correct conditions, those conditions, the fatigue-life of the material, may be much greater than man can induce without aid of machines.
What i agree with is that, when a fissure is
already present, stress causes that fissure to propagate until failure (like a cracked windshield). What i disagree with is that ALL knives at hardness as high as 60 Rc are too brittle to throw without exceeding fatigue-life of the material, that throwing any knife at that hardness will destroy it within the lifetime of the thrower.
1. There isn't any torque on a knife when being thrown. In fact, you only get torque if you use your knife as a screw driver, otherwise its all bending stress. (this is just a general correction as mislabeling stresses is a pet peeve of mine)
2. ALL materials are flawed. This is a proven fact and has to be taken into account when designing something. This leads to stress concentration and fatigue failure. So every knife will have "Fissures" in it.
3. ''flex'' has nothing to do with ductility, and all to do with young's modulus, which is the same for all steels at any hardness rating. Ductility effects how much energy something can take before failure after it has yielded.
1) Does not the knife torque end-over-end when thrown, followed by vibration along the axis after impact? If my terminology is incorrect, my apologies. I have
no problem with being specific and thank you for the correction.
2) Yes, taken into account at the level of design to minimize flaws that can lead to failure at "normal" stress levels.
3) (From
wikipedia)
"...ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched..." - Bending stresses cause stretching of the material on the outside of the bend... or is it only "ductility" if the stretch does not return to true? i don't know and would appreciate education on the matter.
"The ductility of steel varies depending on the alloying constituents" - not all steels present the same level of ductility, let alone at the same hardness. This is why I look for a metallurgist to tell us about the properties of various steels at various hardness levels and via different HT protocols which can drastically effect carbide distribution...
...At the hardness rating that ESEE does their knives, throwing them will eventually cause failure (caused by fatigue) if you exceed a certain stress. This applies to most of the knives at the same hardness level as well. Which is why most throwing knives are at a much lower hardness level, so they can handle the stresses.
The "IF" and "eventually" are essential, especially since the amount of stress a man can impress upon it depends not only on the hardness level as the overall design of the knife - how thick, how long, how wide, where weight is distributed, etc. - and "eventually" could well exceed the life of multiple users. I do agree with the design of most throwing knives being at lower hardness to reduce brittleness since that is the primary stress they will be subjected to, but I do not see an inability to make a compromise that favors both higher hardness and higher toughness/ductility. But I also do not have the math in front of me.
Again, thank you for your contributions
robertl, and good luck on finals!
I'll shoot em a message as I'd love to hear their response...
Gotta love their reply :thumbdn:
Yup, definitely sticking with Bussekin.
, but he hasn't shown dishonesty yet.
