Composite blade question

R

RAGS

Joined
Jul 11, 2000
Messages
538
First off, I would like to wish everyone here on the forums a happy Thanksgiving. Now to my question. Is it possible for these composite type blades to come apart during hard or extreme use? I've never really considered one before, but some of the new Kershaw designs are really catching my eye.But I'm not really sold on the whole composite blade thing. Will they stand up to hard use?
 
They are extremely tough, I wouldn't worry about the weld at all. I've tried, unsuccessfully, to kill my JYD II CPM-D2...it's tough as nails.
 
RAGS said:
First off, I would like to wish everyone here on the forums a happy Thanksgiving. Now to my question. Is it possible for these composite type blades to come apart during hard or extreme use? I've never really considered one before, but some of the new Kershaw designs are really catching my eye.But I'm not really sold on the whole composite blade thing. Will they stand up to hard use?
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I doubt you could ever get it to separate, and in the event that it did, you have the best customer service and warranty backing you. No worries , get one and enjoy it !!

D
 
generally speaking the bonded/weld area is actually stronger than either of the bases. In hence the blade edge will fail or the spine will break before the weld/bond will seperate.
 
spidyman said:
generally speaking the bonded/weld area is actually stronger than either of the bases. In hence the blade edge will fail or the spine will break before the weld/bond will seperate.
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Says who? I can't imagine what is esentially brazing with a piece of copper(?) based alloy is stronger than a solid piece of steel.
 
RAGS said:
First off, I would like to wish everyone here on the forums a happy Thanksgiving. Now to my question. Is it possible for these composite type blades to come apart during hard or extreme use? I've never really considered one before, but some of the new Kershaw designs are really catching my eye.But I'm not really sold on the whole composite blade thing. Will they stand up to hard use?
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Hi RAGS, Happy Thanksgiving to you as well. :)

In testing our CB blades, we have not found the weld area to be susceptible to separation. We have broken many CB blades (through abuse testing), but they showed to be as tough/strong and its standard blade equivalent. We don't feel it's a concern in the least.

Hope that helps.
 
FlaMtnBkr said:
Says who? I can't imagine what is esentially brazing with a piece of copper(?) based alloy is stronger than a solid piece of steel.
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Actually, the braze joint IS stronger than solid steel. IF you do a tensile test on a brazed piece, the failure will be in the parent metal, rather than the braze joint itself. Weird I know, but that's how it works out.
 
J_Curd said:
They are extremely tough, I wouldn't worry about the weld at all. I've tried, unsuccessfully, to kill my JYD II CPM-D2...it's tough as nails.
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Obviously you haven't tried hard enough :p!

If you want to induce a failure, add some heat to the festivities and torque the blade - I bet that'll help. And if the bond is faulty - have yet to hear of such - a high frequency load with a bit of torque added might do.

As to the original poster's question, I doubt you'll experience a failure in most reasonable uses one would expect a folding knife to survive through. Then, too, as previously mentioned, Kershaw does have a good customer service.

I wonder about long term use, but remember many bicycles and motorcycles have used brazed tube construction for years (not to mention turbine blades, etc.). This is relatively "old tech" applied in a new area - that is how I look at it, anyway.
 
The braze is a lot softer than either steel. So the steels will crack but the braze will hold everything together because it's far more ductile.
 
knarfeng said:
Actually, the braze joint IS stronger than solid steel. IF you do a tensile test on a brazed piece, the failure will be in the parent metal, rather than the braze joint itself. Weird I know, but that's how it works out.
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I've had problems with that.

The joint itself is "stronger", but separation has a tendency to occur in the material adjoining the joint. As such, the joint area still is a weak area, just not the actual joint itself.

Our professor made statements akin to yours, yet based on lab results I didn't see what the difference was - the area of concern as regards failure was still around the joint.
 
I'll have to check when I get back to work. AFAIK just from memory, when we design a brazed joint, we don't assign a strength knockdown because of the joint. I can remember the theory just off hand, but not the actual data from doing them. We don't design many brazed joints anymore because it's an expensive process to perform and quality check afterward. So I may have to do some digging. I'll have to get back to you.
 
I'd like to know if you did put in a strength factor for brazed joints. I never could find such in newer books on the topic, though; but these types of things usually are "trade secrets" in designing things and not written down "facts" unfortunately.

Its akin to designing a properly functioning ventalation system (a recent topic of import for me).
 
I work with Brazing Procedure Qualifications per ASME IX and i just ran one with a fairly high silver content brazing filler metal and my failure load was ~ 30,000 lbs. Of course when you look at the various cross sectional areas of my project, then the KSI can get bigger (or smaller). I had the 304L stainless go to ~90 KSI before this braze failed due to the small area (~.380 in^2)
 
Folks have been silversoldering gun parts together for decades. If it's strong enough for a rifle, I reckon it's strong enough for a knife.
 
Thanks to everyone for the replies. I guess my fears were unfounded.Hey Thomas W., any ETA on the Volt? Thats the one that has my eye:D
 
knarfeng said:
I'll have to check when I get back to work. AFAIK just from memory, when we design a brazed joint, we don't assign a strength knockdown because of the joint. I can remember the theory just off hand, but not the actual data from doing them. We don't design many brazed joints anymore because it's an expensive process to perform and quality check afterward. So I may have to do some digging. I'll have to get back to you.
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orthogonal1 said:
I'd like to know if you did put in a strength factor for brazed joints. I never could find such in newer books on the topic, though; but these types of things usually are "trade secrets" in designing things and not written down "facts" unfortunately.

Its akin to designing a properly functioning ventalation system (a recent topic of import for me).
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So talked to a couple of guys at work today. They told me we don't do a knockdown for a brazed joint. However, as is usual in design engineering, there is a bit more to it than that.

They also pointed out that our parts that contain a brazed joint are configured to have a brazed joint. That means they are not just a straight piece, like you see in these knife blades, but have bends and curves to maximize the surface area being joined. Now granted these blades do as well, but not as much as our joints do. So it is a combination of the material strengths and the shape that gives the part its strength. Probably not what you were looking for, but the best I can do for you.

Never the less, I don't think the brazed joint is going to make the blade unduly weak.

Frank
 
One major consideration with brazed joints is the gap dimension !! Maximum strength is with a .003" gap .Strength falls of quickly as you go less or more ! In addition capillary action to fill the joint with the brazing alloy is also maximum at .003" !
 
I'm sure their not going to say exactly how its done but I would say its a bit different from brazing. A bonded joint if done proper and with the correct bonding agent will be stronger than the material itself. I know it sounds strange but it is fact.
 
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