How do blood grooves improve a sheath knife?

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R.c.s said:
Is this really a myth ? .slender blades and most Daggers don't have them . slashing blades sutch as the cavalry swords don't have the them . back in the day their were put on large thick stabing weapons . I don't think this was for looks or whight maybe this is one for the mythbusters :D
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Most cavalry swords that I have seen have fullers.

Regards

Robin
 
So I decided to draw up the “KaBar” FUK (Fighting Utility Knife) based on old Mil-Spec drawings. I had to assume the fuller was a full round profile because the drawings are quite degraded and I couldn’t get a great view of the profile. I think this will work though as it really accentuates what a fuller can do for us. I drew a section of the knife 2” forward of the guard, this section represents a slice through the middle of the fuller. I then modified the section twice to try to represent what has been said here:

Fuller%20MOI%20Examples_zpsgajnlyrf.png


The Ix and Iy values represent the sectional moment of inertia (MOI) measurement in 2 directions. The Ix values represent the MOI parallel to the direction of cut (direction when chopping with a blade's edge), the Iy values represent the MOI across what we call the thickness of the blade (direction when bending a blade during prying). A higher MOI will directly relate to a stronger and more rigid beam when force is applied in that direction.

3 Blade Profiles:
A: Standard “KaBar” profile, 9/64” thick.
B: “KaBar” profile but without the fullers, still 9/64” thick. Note: this section has greater area (the knife would weigh more) than “A”.
C: “KaBar profile but without the fullers, 0.1186” thick. Note: the thickness has been reduced to keep the blade weight the same.

Conclusions:
A: Standard KaBar profile, we will compare the other two profiles against these figures.
B: This profile has almost 18% more area than “A”. The MOI in the direction of cutting is 60% greater! The MOI in the direction of bending a blade is 5% greater.
C: This profile has the same area as “A”. The MOI in the direction of cutting is 3% less. The MOI in the direction of bending a blade is 9% less.

Conclusion: A fuller on the KaBar Fighting and Utility Knife slightly increases strength in both planes of loading (ONLY IN THE SECTION OF BLADE WITH A FULLER) over a thinner blade with the same cross-sectional area without fullers. You could argue that the strength increases are almost negligible and fullers do not significantly increase strength per weight of the blade. On the other hand, a KaBar blade made simply without fullers would be SIGNIFICANLY stronger in the cutting direction than a KaBar blade with Fullers.

Also: The original drawings for the KaBar knife call the fuller a “Blood Groove”…

 
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This is why I am partial to the KaBar USN Mark 1 Deck Knife design. With their Chromium-Vanadium Steel, it appears to be a better design for general utility purposes. No frills and great functional durability. :cool: :thumbup:

Hooray for the U.S. Navy spec Deck Knife design!

(It works for me!)
 
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I always thought mass production, they needed rigid blades that service men would not destroy, or it would be tough for them to destroy. Needed a way to shave some weight without putting too much time and effort?
 
I've always thought they were just an ornament on small sheath knives, can't see the purpose on them and can't say I like them much either. Suspect they may have been put there to give the blade a bit more of a sinister look....
 
The practical features of a "service knife" should be much as the "maximum minimalism" features of the civilian "peanut" knife. Maximum serviceability at minimal weight, accompanied by the highest level of efficiency and function either in the field, or the deck of the ship. :thumbup:

Captain O
 
Macchina said:
The Ix and Iy values represent the sectional moment of inertia (MOI) measurement in 2 directions. The Ix values represent the MOI parallel to the direction of cut (direction when chopping with a blade's edge), the Iy values represent the MOI across what we call the thickness of the blade (direction when bending a blade during prying). A higher MOI will directly relate to a stronger and more rigid beam when force is applied in that direction.

3 Blade Profiles:
A: Standard “KaBar” profile, 9/64” thick.
B: “KaBar” profile but without the fullers, still 9/64” thick. Note: this section has greater area (the knife would weigh more) than “A”.
C: “KaBar profile but without the fullers, 0.1186” thick. Note: the thickness has been reduced to keep the blade weight the same.

Conclusions:
A: Standard KaBar profile, we will compare the other two profiles against these figures.
B: This profile has almost 18% more area than “A”. The MOI in the direction of cutting is 60% greater! The MOI in the direction of bending a blade is 5% greater.
C: This profile has the same area as “A”. The MOI in the direction of cutting is 3% less. The MOI in the direction of bending a blade is 9% less.

Conclusion: A fuller on the KaBar Fighting and Utility Knife slightly increases strength in both planes of loading (ONLY IN THE SECTION OF BLADE WITH A FULLER) over a thinner blade with the same cross-sectional area without fullers.
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I've been a structural engineer for over 40 years so I'll address this-

Your description of moment of inertia Ix and Iy is correct, but the numbers in the images are reversed. It is common to refer to Ix as "strong axis" and Iy as "weak axis". When chopping with a knife you are bending it in strong axis. When prying with a knife you are bending it in weak axis. Also moment of inertia is a direct measure of the STIFFNESS of a section. It will hint at strength but is not a direct measure of its strength. (Strength is represented by section modulus of a section, usually referred to as S or Z, depending on the type of material and type of bending behavior being represented. It is easy enough to find a cross section with higher moment of inertia than another but that actually has less strength.)

But we can make comparisons based on stiffness- here are the numbers from the images, switched to the correct labels:
A
Ix .01122
Iy .0001105
B
Ix .01181
Iy .0001773
C
Ix .01024
Iy .0001071

Compare the Ix values. They don't vary much from one profile to the next, meaning the material removed to make the fuller has little affect on the strong axis bending stiffness of the section. This is because the material is close to the bending neutral axis. The numbers look a little suspicious though, I would expect the Ix value for profile C to be lower than it appears. The theory is that a blade with a fuller is stiffer in strong axis bending than a blade of the same weight that does not have a fuller.

Now compare the Iy values- they do vary quite a bit because the material being added or removed is farthest from the bending neutral axis. So playing with thickness and profiles makes a big difference in sideways bending stiffness. This would change the dynamics of a sword-length blade but probably doesn't make much difference to a shorter blade.


The information posted in quote #13 discusses historical background behind fullers and makes the issue more complicated. Apparently the comparison should not be between a flat blade with a groove and a flat blade without a groove, but between more complex cross sections. Of course having a computer program that calculates properties for various cross sections would allow for easier comparison, all you need to do is define the dimensions.

"You stiffen the blade. In an unfullered blade, you only have a "single" center spine. This is especially true in terms of the flattened diamond cross section common to most unfullered double- edged blades. This cross section would be rather "whippy" on a blade that is close to three feet long. Fullering produces two "spines" on the blade, one on each side of the fuller where the edge bevels come in contact with the fuller. This stiffens the blade, and the difference between a non-fullered blade and a fullered one is quite remarkable."
 
Some scholarly posts here :thumbup:

silenthunterstudios said:
I always thought mass production, they needed rigid blades that service men would not destroy, or it would be tough for them to destroy. Needed a way to shave some weight without putting too much time and effort?
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Maybe they thought the 'cool factor' of a 'blood groove' would ensure more guys actually carried the knives, rather than leaving them in their packs, or worse! ;) :D

I remember reading an article many years ago, where the author argued that the real genius of the AK-47 bayonet was that the Russian military had found a way of getting troops to carry wire-cutters, which if they hadn't been integral to a knife/bayonet would have otherwise been dumped at the first opportunity! ;)
 
Pipeman said:
Most cavalry swords that I have seen have fullers.

Regards

Robin
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Likevise with a lot of medieval swords. In early medieval time, when swords were designed more to cut than stab, fullers were common. Later, when thrusting as a technique started to be more appreciated the diamond cross section became more common. Fullers did not disappear from the swords even then. http://www.myarmoury.com/feature_oakeshott.html
 
. . . .
These are cavalry sword's from around the 16 hundred's . my be I should of said most . the point I was making is that sometimes their is a little bit of truth to a myth . this is one that I would like to see put to the test . out of pure curiosity ;)
 
R.c.s said:
These are cavalry sword's from around the 16 hundred's . my be I should of said most . the point I was making is sometimes the is a little bit of truth in a myth . this is one that I would like to see put to the test . out of pure curiosity ;)
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I would say some of those could be from the 19th century Napoleonic wars. My impression is that in a sword the fuller helps in having torsional rigidity in a cutting blade, but at the same time the blade can bend sideways in a cut. This helps in keeping the blade in on piece during cutting and parrying.
Watch this. See how the blade bends in the cut. https://www.youtube.com/watch?v=IDFPiF3xXCQ
 
HFinn said:
I would say some of those could be from the 19th century Napoleonic wars. My impression is that in a sword the fuller helps in having torsional rigidity in a cutting blade, but at the same time the blade can bend sideways in a cut. This helps in keeping the blade in on piece during cutting and parrying.
Watch this. See how the blade bends in the cut. https://www.youtube.com/watch?v=IDFPiF3xXCQ[/QUOTE..

You my be right I am no sword expert . you couldn't really tell whether or not the full cerved blade had a fuller . though it was evident in later cut and thrust sword .. But that's not the point the point is I would like I see it put to the test with a plan blade a one with a blood groove . I don't know what would happen . it would be something very interesting to find out :)
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Captain O said:
If acts as does an I-beam it would be requred on both sides of the blade to increase structural rigidity. What other advantages are gained from the blood groove?

Captain O
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What everyone seems to be missing is that when a blade is stuck in flesh. A seal forms around the blade creating a strong suction making it very hard to pull back out. The grooves in the blade keeps this seal from forming so there is no suction and the blade will slide out easily.
 
arod8 said:
What everyone seems to be missing is that when a blade is stuck in flesh. A seal forms around the blade creating a strong suction making it very hard to pull back out. The grooves in the blade keeps this seal from forming so there is no suction and the blade will slide out easily.
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Is this true? I don’t think so. First post. I call troll post.
 
Henry Beige said:
Is this true? I don’t think so. First post. I call troll post.
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I don’t know if it’s true or not because I’ve never stabbed anyone nor do I hope to start. (It is a thread necro but why assume it’s a troll?)

That being said we’re all very squeamish about the idea around here. Example: original Ka-bar drawings call it a blood groove. Yet, most of us would say “blood groove is a pop culture thing beloved of 12 year old boys, as responsible adults we know this feature is called a fuller and is solely for achieving a lighter blade without much reduction in strength.”

Yet it’s been called a blood groove by actual knife designers and military men for a long time, (witness the ka bar document posted above in this thread) so the whole concept is clearly not made up entirely. It is distinctly possible. Really no way to know probably. Most of us won’t have the misfortune to stab someone with a flat ground blade and then stab someone else with a fullered blade and compare performance. Maybe an EMT who has dealt with knife trauma in a hospital could say. The blades in question are generally designed for combat/stabbing however. A ka-bar isn’t a very good hunting knife, carving knife, kitchen knife, or letter opener.
 
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