A rough Finite Element model shows that the Cho can reduce stress in a blade

Justin,

That is just what I was going to say!

 

Interesting. It would be good if you could share your results.

Have you tried varying the depth of the cho (perhaps as a function of thickness and height of the spine)? That should make a big difference in stress relief. And, of course, one wonders if your mesh is appropriate for the analysis ... but that's a standard worry for mechanical or electromagnetic models of this sort.

We old lab physicists often stop cracks (in metals and some ceramics) in their tracks by making a small bore hole (drilled -- mechanically or optically) just at the apex of a crack. We've always believed this relieved the local stress.

 

I believe what Justin is trying to say is - Cho is Good! Thanks for the very interesting post. I've never run across a story about a khuk breaking at the cho, which would seem a logical weak point. Very cool info. Thanks again Justin.

 

That is an extremely interesting observation. What about that hollow characteristic reduces stresses within the blade?

 

I felt the air off of that as it flew right over my head. Fast too!

 

Hepkat I've never thought about the Cho possibly having that kind of effect, and even if it turned out not to be the case that is still sharp thinking and for that I tip hat my hat sir.

 

Fascinating insight. I'd love to get a copy of that pdf.

 

Well do I remember my doctoral work. That, of course, comes first.

Still, it will be interesting to see the stress concentrations.

You probably need an adaptive mesh, one that has a higher concentration of properly formed shapes near the highest gradients and a lower concentration where conditions are more stable.

If you e-mail those pictures, I'll see if they will post up. I can be reached through the e-mail function on this forum.

 

Justin, thanks for the explaination. It actually makes sense, even though it seems to oppose common logic. I have heard of khuks breaking at the tang juncture, which seems to be a proven weak point in any knife as you say. I should add that, to my knowledge, any catastrophic blade failure with HI seems extremely rare. I don't want anyone to get the wrong idea. The stress relieving cho idea is pretty darn cool and does make sense, in a way. But, knowing the tangs are also thick, I wonder if this would just make the cho a tang juncture of sorts. But, then again, I've never heard of a blade failure at the cho. It could be that moving that point out further away from the handle alleviates/mitigates some of the forces created during a chop. I also figure cut angles at the tang or cho play a part. I've already confused myself and probably anyone else trying to make sense of my post Anyway, thanks again to you and OldPhysics for some interesting insight. I am no engineer. In fact, numbers are part of my axis of evil, so I'll let y'all do the heavy lifting on this one. Take care.

 

Interesting concept. I wonder if there was any need for that type of stress relief in modern or historical khurkis or if they are more prone to isolated chipping/breaking at the point of impact or due to general hardening errors.

Here's the button to add an attachment when making a post.


Take a look at this thread where the cho didn't help when using an irregular batoning technique - it also has an example of attachments on a thread (although you may need a paid membership to attach files)
http://www.bladeforums.com/forums/showthread.php/609283-Broken-Khukri

At the end of the thread you can see some serious stress relief by Auntie's customer service

 

Looking forward to the pictures. I often put mine in facebook with the privacy setting set to "everyone" and then link to it.

 

I do. Hepkat you might just solved a multi-million dollar riddle!

 

Bric, you just had to make me a fibber! Just kidding I never saw that thread, even though I've spent a fair amount of time in the archives. Broken CAK is something for sure! This whole thread just gets more interesting. I'd love to get a run down on every khuk failure to look for a pattern and see if you and OldPhysics could come up with a theory. Though as has been stated many times, over hardening seems the likely culprit. But it would still be interesting to see what info could be gleaned. Luckily, these sorts of failures seem so rare as to be a real oddity. IIRC Ferguson also had one, but I recall it being from the no longer made, aluminum handled museum model. I'll be checking in on this thread. Take care everyone.

 

jdk - that was not meant as a rebuff to you. If I read your posts correctly, I am inclined to agree with you. "Even if" the cho provides stress relief under certain circumstances, there is still the question as to whether that is the "purpose" of the cho. To propose this theory I think would be suggesting that historically cho-less blades were more prone to failure and someone discovered that blades with cho were less subject to these failures. In modern-day HI Khukris I do not expect that this phenonemon (cho-less blade failure) is the case, take the Tarwar or Mongolian short sword for example. Also the blades stand up to batoning (hitting back of blade with heavy piece of wood) and in this use I would think that very little of the force gets distributed to the cho area.

As to whether historical cho-less Khurki were prone to failure...I would have no way to know. It does seem that chopping wood has it's own stress relief built in to some degree with the blade undergoing a less rapid decellaration than hitting a rock.

It seems like some of the greatest arguments come out of "purpose" discussions, which is also not my intent. Cheers Hepcat for a new application of Khukri fascination and curiosity!

 

No problem Bric. I was just giving you a hard time. I promise. I'm glad you posted it since I'd never seen it before. The whole idea here is pretty neat. Whether it relieves stress by design or is incidental, it's a good thing and a very interesting topic. Like someone said on another subforum, it's more interesting than another "what knife are you EDC'ing this week" thread. Take care.

 

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I'm sure he'll send them to me soon ... I provided him with my direct e-mail yesterday. Remember, he's a young fellow in grad school and has classes and his dissertation to worry about.

It will come soon!