Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
Frank :
The crack will start at the edge simply because the steel is thinner there and that is usually the focus point of the impacts. You can start a crack above the edge by beating on the flats, but the cracks don't run along the steel they turn very quickly and the blade breaks in half or loses large pieces, it doesn't split lengthwise. Aside from the theory, I have seen many crack start at the edge and run up breaking the blade, I have never seen any run lengthways and split it. They will run at an angle minimizing the energy required by taking a path which gives the lowest resistance which is a combination of lower stock thickness and impact toughness. So transverse impact toughness is important, but I don't think it is critical. It would be interesting to test a few blades varying these properties. I would suspect that increasing the transverse toughness would minimze the size of the chips formed while increasing the perpendicular toughness would minimze their formation in the first place.
That was the point, I wanted the blade not to be able to cut into the impact material as otherwise the impacts it sees are much reduced as the energy is dissipated during the cutting. The blowouts I saw were worse than any I had seen before and I have subjected a lot of steels to such impacts, so it appeared to me that the high toughness of 3V was not showing itself. However on reflection I don't thick the chips were caused by direct impact fracture. I took an A2 MPK from Mission and did the same thing, and it chipped out, and then a crack ran from the apex of the chip right up the blade and cracked it in half. I was using maybe 1/4 of the force of the 3V impacts. I have a few shots of the blades I'll link to shortly.
I think the breakouts in the 3V blade were due to a ductility issue. I took the blade again and gave it another dozen hits far harder than I hit the A2 blade and I could not break it in half. Considering the impact toughness numbers are for notch testing and this is basically unnotched, it doesn't surprise me then that I could not induce a gross fracture as you are looking a a many to one increase in toughness going from notched to unnotched. To confirm that it was a ductility issue you would want to look a the impact under high speed photography. I expect the edge is bending out and then breaking, not simply fracturing under the impact. This may be why I was seeing much better edge durability on other steels as since they were softer .
You could also of course look at the steel with a lower RC, try 56 and 58. The impaction resitance and strength will be lower here, but the ductility gains should be significant and it might be a lot better at preventing blowouts in such extreme contacts. It might also minimize micro-chipping for much smaller inclusions of a similar nature.
I assume you mean 3V here.
Back to Luke's blade, here is the new edge profile :
0.010 x 0.016"
0.016 x 0.020
0.037 x 0.071
0.053 x 0.107
0.066 x 0.148
0.080 x 0.182
The blade showed a large increase in wood cutting ability with the new thinner profile. Just a few quite slices showed that the blade had jumped up another level. Repeating the dowel cutting the performance was now 11.2 +/- 1.4, a major improvement from 16.3 +/- 0.7 slices. Checking the blade in the kitchen it was now able to slice vegetables much easier, though it would still break the larger carrots at the top when they were one inch or more thick. Just doing a quick visual check against Luke's BA3, I was surprised that they performed so differently as the bevels look by eye to be identical, yet the BA3 is massively different taking only 2.5 +/- 0.2 slices on the hardwood for example. Comparing the bevels in detail :
BA3 :
0.005" x 0.015"
0.010" x 0.035"
0.037" x 0.089"
0.059" x 0.160"
0.078" x 0.230"
The difference in in the last bit of the edge. This shows just how much of the force that materials exert is concentrated at the edge for harder materials like wood, and also how this varies for different materials as the rope cutting performance is much clower between the two which you would expect, though still heavily in favor of the BA3. Of course this is just a geometry issue, Luke could easily take his knife down to the same level, though it would not be able to do chopping and such then, let alone harder work like splitting.
As to that, the blade was also used for lots of chopping to verify that the new profile was not too thin, and no problems developed. The knife was a little smoother in the wood, but you would have to be counting hits to notice the difference, or be cutting up a lot of wood. The knife was then used to split several pieces of seasoned spruce (six months) which had many small knots plus at least one large cluster. It took about two dozen heavy hits to split the rounds which were small, three to four inches thick. The edge bevel showed no major damage, but it did gather small chips during the splitting. These were not visible by eye, but could be felt by thumbnail. A quick check under magnification showed them to be 1x1-2 mm in size [x20 mag]. Note Missions A2 MPK which is softer, did not chip out in the way, I think this is more of a ductility issue than toughness.
To clarify, this isn't the optimal way to profile an edge on such a knife. It is far better to take the primary profile down and leave a thinner edge. Having a bevel that is about a quarter of an inch wide really slows down sharpening as you have to remove metal from a lot of edge. The knife will also be more prone to shallow edge damage .
In regards to really hard edge impacts, the blade was used to hack into some concrete before I did the above thinning. The blade fractured about the same level that the Camillus CU/7 did. It chipped out readily up to a depth of about 0.030".
-Cliff
The crack will start at the edge simply because the steel is thinner there and that is usually the focus point of the impacts. You can start a crack above the edge by beating on the flats, but the cracks don't run along the steel they turn very quickly and the blade breaks in half or loses large pieces, it doesn't split lengthwise. Aside from the theory, I have seen many crack start at the edge and run up breaking the blade, I have never seen any run lengthways and split it. They will run at an angle minimizing the energy required by taking a path which gives the lowest resistance which is a combination of lower stock thickness and impact toughness. So transverse impact toughness is important, but I don't think it is critical. It would be interesting to test a few blades varying these properties. I would suspect that increasing the transverse toughness would minimze the size of the chips formed while increasing the perpendicular toughness would minimze their formation in the first place.
That was the point, I wanted the blade not to be able to cut into the impact material as otherwise the impacts it sees are much reduced as the energy is dissipated during the cutting. The blowouts I saw were worse than any I had seen before and I have subjected a lot of steels to such impacts, so it appeared to me that the high toughness of 3V was not showing itself. However on reflection I don't thick the chips were caused by direct impact fracture. I took an A2 MPK from Mission and did the same thing, and it chipped out, and then a crack ran from the apex of the chip right up the blade and cracked it in half. I was using maybe 1/4 of the force of the 3V impacts. I have a few shots of the blades I'll link to shortly.
I think the breakouts in the 3V blade were due to a ductility issue. I took the blade again and gave it another dozen hits far harder than I hit the A2 blade and I could not break it in half. Considering the impact toughness numbers are for notch testing and this is basically unnotched, it doesn't surprise me then that I could not induce a gross fracture as you are looking a a many to one increase in toughness going from notched to unnotched. To confirm that it was a ductility issue you would want to look a the impact under high speed photography. I expect the edge is bending out and then breaking, not simply fracturing under the impact. This may be why I was seeing much better edge durability on other steels as since they were softer .
You could also of course look at the steel with a lower RC, try 56 and 58. The impaction resitance and strength will be lower here, but the ductility gains should be significant and it might be a lot better at preventing blowouts in such extreme contacts. It might also minimize micro-chipping for much smaller inclusions of a similar nature.
I assume you mean 3V here.
Back to Luke's blade, here is the new edge profile :
0.010 x 0.016"
0.016 x 0.020
0.037 x 0.071
0.053 x 0.107
0.066 x 0.148
0.080 x 0.182
The blade showed a large increase in wood cutting ability with the new thinner profile. Just a few quite slices showed that the blade had jumped up another level. Repeating the dowel cutting the performance was now 11.2 +/- 1.4, a major improvement from 16.3 +/- 0.7 slices. Checking the blade in the kitchen it was now able to slice vegetables much easier, though it would still break the larger carrots at the top when they were one inch or more thick. Just doing a quick visual check against Luke's BA3, I was surprised that they performed so differently as the bevels look by eye to be identical, yet the BA3 is massively different taking only 2.5 +/- 0.2 slices on the hardwood for example. Comparing the bevels in detail :
BA3 :
0.005" x 0.015"
0.010" x 0.035"
0.037" x 0.089"
0.059" x 0.160"
0.078" x 0.230"
The difference in in the last bit of the edge. This shows just how much of the force that materials exert is concentrated at the edge for harder materials like wood, and also how this varies for different materials as the rope cutting performance is much clower between the two which you would expect, though still heavily in favor of the BA3. Of course this is just a geometry issue, Luke could easily take his knife down to the same level, though it would not be able to do chopping and such then, let alone harder work like splitting.
As to that, the blade was also used for lots of chopping to verify that the new profile was not too thin, and no problems developed. The knife was a little smoother in the wood, but you would have to be counting hits to notice the difference, or be cutting up a lot of wood. The knife was then used to split several pieces of seasoned spruce (six months) which had many small knots plus at least one large cluster. It took about two dozen heavy hits to split the rounds which were small, three to four inches thick. The edge bevel showed no major damage, but it did gather small chips during the splitting. These were not visible by eye, but could be felt by thumbnail. A quick check under magnification showed them to be 1x1-2 mm in size [x20 mag]. Note Missions A2 MPK which is softer, did not chip out in the way, I think this is more of a ductility issue than toughness.
To clarify, this isn't the optimal way to profile an edge on such a knife. It is far better to take the primary profile down and leave a thinner edge. Having a bevel that is about a quarter of an inch wide really slows down sharpening as you have to remove metal from a lot of edge. The knife will also be more prone to shallow edge damage .
In regards to really hard edge impacts, the blade was used to hack into some concrete before I did the above thinning. The blade fractured about the same level that the Camillus CU/7 did. It chipped out readily up to a depth of about 0.030".
-Cliff