What's the strongest a fixed blade can be without weighing too much?

[RX-79G]

Knives usually break at the tip, then somewhere along the edge, then in the first inch of the handle. Usually the break goes along with a stress riser that is part of the design.

It isn't common, but why did this happen?

The knife was abused, as a survival or military knife might also be when the chips are down. This type of break, cracking at the first rivet hole, is not an uncommon type of break for a full width tang knife. The problem is that tang narrows for the index finger, has a hole in the same spot, and the scales (G10 in this case) aren't rigid enough to prevent the tang flexing where your hand ends (thumb and index finger) and finding that week spot.

Micarta might be more rigid. Epoxying the scales might also help. A smaller rivet hole might have helped. But a primary problem with any full width tang knife is that the support the scales can offer is always limited by the fact that the can't be bonded all that well to the handle, and don't touch each other. So when stresses mount, the tang and each scale can slide around relative to each other, like leaf springs over a bump. As soon as that happens the stress goes right to the first rivet.

 

[RX-79G]

Why did this one break?

It didn't break just because it is a stick tang. This one broke because the tang was supported by a stack of short pieces. When force was applied against the handle, the glue between the layers sheared and the tang could flex enough to crack. The basic concept isn't that weak, but the handle didn't support the tang enough to reinforce the weakest part of the tang.

This one didn't break because hollow handle knives are weak (they actually have a very low instance of failure. Check the hollow handle thread on the Ourdoor Gear subforum), but because there was or there developed play between the fairly thin aluminum ricasso cover and the blade. Eventually, it just wiggled enough space to not be supported and then the rivet was doing all the work.

This is actually very similar to what happens on tension assembled knives with wood handles as they age. The strength comes from the blade being pulled into the handle by the tang pommel nut or rivet. When the wood dries out, the tang loses tension and is floating in the handle. The first big stress breaks the tang because it is no longer part of the handle.

 

[RX-79G]

This Cold Steel knife broke where the tang dramatically stepped down from the ricasso. The plastic handles pretty much start where the tang starts, so they can't help anything. It wouldn't be much different than if you had cut two slots in the top and bottom of the ricasso - the dramatic change to where there is and isn't steel. Other "tough as nails" knives are also made like this, including Busses. Busse is a good example of how the design limitations can be overcome by brute strength - the steel in the tang is damn thick and metallurgically tough.

This knife broke, but the tang did not. Unlike the Helle stick tang above, this tang was relatively strong compared to the handle material. So instead of the majority of the handle remaining intact and providing the leverage to break the tang like on the Helle, the homogenous handle material fails above the full length of the tang before the tang itself could receive any force. This is something of a win, because the handleless blade has enough of a tang left for a crude field repair, or could be used without. Ultimately, the knife busted in a familiar manner, and while the right part broke, no breakage at all would have been better.

Another type of stress riser break at the point where there is the least amount of metal:

 

[stonproject]

So what's the question exactly? how heavy can a knife be...? In regards to your posts, and pics, it seems like thickness, not weight is the factor here

 

[TinyDog]

All examples show weakness in design, ultimately causing failure, not weight related....

 

[RX-79G]

I'm having trouble posting the whole thing.

 

[Armadew]

Are you on a quest to design an unbreakable knife? Not gonna happen, imo. There will always be a weakness. Knives usually wont break if you treat them like knives.

 

[trevitrace]

Knives usually break at the tip, then somewhere along the edge, then in the first inch of the handle. Usually the break goes along with a stress riser that is part of the design.

It isn't common, but why did this happen?

The knife was abused, as a survival or military knife might also be when the chips are down. This type of break, cracking at the first rivet hole, is not an uncommon type of break for a full width tang knife. The problem is that tang narrows for the index finger, has a hole in the same spot, and the scales (G10 in this case) aren't rigid enough to prevent the tang flexing where your hand ends (thumb and index finger) and finding that week spot.

Micarta might be more rigid. Epoxying the scales might also help. A smaller rivet hole might have helped. But a primary problem with any full width tang knife is that the support the scales can offer is always limited by the fact that the can't be bonded all that well to the handle, and don't touch each other. So when stresses mount, the tang and each scale can slide around relative to each other, like leaf springs over a bump. As soon as that happens the stress goes right to the first rivet.

I'll blame that failure on the knive company forgetting to stamp an "S" on that blade, making it nicer than any run-of-the-mill CPM...35VN.

Or its handle wasn't of cast aluminium.

 

[marcinek]

Steel is weakest where is cross sectional area is smallest. Bigger cross sectional area=stronger.

Not sure what your question means either.

 

[craytab]

Knives usually break at the tip, then somewhere along the edge, then in the first inch of the handle. Usually the break goes along with a stress riser that is part of the design.

It isn't common, but why did this happen?

The knife was abused, as a survival or military knife might also be when the chips are down. This type of break, cracking at the first rivet hole, is not an uncommon type of break for a full width tang knife. The problem is that tang narrows for the index finger, has a hole in the same spot, and the scales (G10 in this case) aren't rigid enough to prevent the tang flexing where your hand ends (thumb and index finger) and finding that week spot.

Micarta might be more rigid. Epoxying the scales might also help. A smaller rivet hole might have helped. But a primary problem with any full width tang knife is that the support the scales can offer is always limited by the fact that the can't be bonded all that well to the handle, and don't touch each other. So when stresses mount, the tang and each scale can slide around relative to each other, like leaf springs over a bump. As soon as that happens the stress goes right to the first rivet.

Why did this one break?

It didn't break just because it is a stick tang. This one broke because the tang was supported by a stack of short pieces. When force was applied against the handle, the glue between the layers sheared and the tang could flex enough to crack. The basic concept isn't that weak, but the handle didn't support the tang enough to reinforce the weakest part of the tang.

This one didn't break because hollow handle knives are weak (they actually have a very low instance of failure. Check the hollow handle thread on the Ourdoor Gear subforum), but because there was or there developed play between the fairly thin aluminum ricasso cover and the blade. Eventually, it just wiggled enough space to not be supported and then the rivet was doing all the work.

This is actually very similar to what happens on tension assembled knives with wood handles as they age. The strength comes from the blade being pulled into the handle by the tang pommel nut or rivet. When the wood dries out, the tang loses tension and is floating in the handle. The first big stress breaks the tang because it is no longer part of the handle.

This Cold Steel knife broke where the tang dramatically stepped down from the ricasso. The plastic handles pretty much start where the tang starts, so they can't help anything. It wouldn't be much different than if you had cut two slots in the top and bottom of the ricasso - the dramatic change to where there is and isn't steel. Other "tough as nails" knives are also made like this, including Busses. Busse is a good example of how the design limitations can be overcome by brute strength - the steel in the tang is damn thick and metallurgically tough.

This knife broke, but the tang did not. Unlike the Helle stick tang above, this tang was relatively strong compared to the handle material. So instead of the majority of the handle remaining intact and providing the leverage to break the tang like on the Helle, the homogenous handle material fails above the full length of the tang before the tang itself could receive any force. This is something of a win, because the handleless blade has enough of a tang left for a crude field repair, or could be used without. Ultimately, the knife busted in a familiar manner, and while the right part broke, no breakage at all would have been better.

Another type of stress riser break at the point where there is the least amount of metal:

Not sure why you are looking for our input. Seems like the only questions being asked you are answering yourself just fine.

 

[d762nato]

Maybe differential hardening/forging to be softer in certain high stress areas of the blade would make it stronger. I think I'd ask this question to some of the knife makers we have here on the forum as well.

 

[unimogbert]

I enjoy looking at pics of failures.

But anything can be broken - even smooth round stones.

How much weight is "too much?"

 

[shqxk]

Strongest fixed blade with out being so bulky? Sound like Busse or SwampRat

 

[Lycosa]

Yes to, Mission Ti knives or Busse.

 

[Insipid Moniker]

Ummm, knives break at the fulcrum because that's how physics works. Tip broke? Probably because it was used to pry, placed the fulcrum at the tip. Knife broke around the ricasso? Probably got batoned with a caveman club, placing the fulcrum at the ricasso.

Material weakness obviously adds to this, but usage and physics are as, if not more, important in determining where a knife will break.

 

[Rhinoknives1]

Question? Didi you actually break any of these knives?

 

[marcinek]

Strongest fixed blade with out being so bulky? Sound like Busse or SwampRat

Again..what is "so bulky" or "too heavy"? One could put an edge on an Ibeam and it will not break!

Or just take a piece of rebar wrap some paracord around it and call it a knife...no stress risers! Cross sectional are the same across its length!

Or how about a 1/2 inch thick knife with a 2 inch blade....that wont break!

I'm just not follwing the premise. Maybe the OP could clarify.

 

[craytab]

Again..what is "so bulky" or "too heavy"? One could put an edge on an Ibeam and it will not break!

Or just take a piece of rebar wrap some paracord around it and call it a knife...no stress risers! Cross sectional are the same across its length!

Or how about a 1/2 inch thick knife with a 2 inch blade....that wont break!

I'm just not follwing the premise. Maybe the OP could clarify.

I could very easily break all of those.

 

[marcinek]

I could very easily break all of those.

Well...we are all not from planet Craypton like you, are we?

But, you take a thick, strong/tough steel, eliminate stress risers, dont put holes in it...and it becomes less likely to break.

Take the same design, give it a greater cross sectional area (for example, by making it thicker), and it becomes even less likely to break.

Of course that increase in cross sectional area means more metal, and more weight. You could go on without upper limits.

Now where this "weighing too much" limit that the OP proposes is...who knows? (He may have the strength of 10 Crayptonians!) So the question becomes meaningless.

Unless the OP clarifies. Which everyone has been asking for since the thread started.

 

[tiguy7]

This Cold Steel knife broke where the tang dramatically stepped down from the ricasso. The plastic handles pretty much start where the tang starts, so they can't help anything. It wouldn't be much different than if you had cut two slots in the top and bottom of the ricasso - the dramatic change to where there is and isn't steel. Other "tough as nails" knives are also made like this, including Busses. Busse is a good example of how the design limitations can be overcome by brute strength - the steel in the tang is damn thick and metallurgically tough.

This knife broke, but the tang did not. Unlike the Helle stick tang above, this tang was relatively strong compared to the handle material. So instead of the majority of the handle remaining intact and providing the leverage to break the tang like on the Helle, the homogenous handle material fails above the full length of the tang before the tang itself could receive any force. This is something of a win, because the handleless blade has enough of a tang left for a crude field repair, or could be used without. Ultimately, the knife busted in a familiar manner, and while the right part broke, no breakage at all would have been better.

Another type of stress riser break at the point where there is the least amount of metal:

The bottom knife looks like it broke in two stages. The bottom of the tang is rusty indicating a crack. So the tang was already weakened when it finally let go.