Knife design theory (Stress risers)

[8thsinner]

I have been thinking recently again about doing my knife, It seems I do every time i see the work coming out of the makers used by those from this forum.

I have thought about stress risers in relation to handle and spine design.
I have been trying to work out a decent handle and I have decided to go with a full exposure tapering handle to get as much chopping power in it as I can whilst retaining the ability to attach field made handles if needs me, given that I am trying to design a small but powerful chopper, in theory it will replace my penknife khukri.

I was thinking for the spine of maybe the first inch above the ricasso to be filed for grip much like the BRKT blades, the following inch or possibly two inches sharp square edges for fire steel use and the rest some sort of smoother finish.

The smoother finish to be either pointed and gently curved like my existing khukri, full semi circle, or gently curved flat after a small relief grind of 2mm or so at 40 odd degrees.

It will be used for batoninng, but the khuk, with it's gently pointed spine edge still works for batonning, so avoid the issue of which is better for batonning

Still, three questions arose.
1) Which spine pattern would be best suited to reducing stress and shock energies?
2) Would differing spine edges effect the overall strength of the knife by throwing energy in random directions? Should these changes be introduced slowly over the length of the spine?
3) How do expansions of the pommel base effect stress risers?

Are there any other considerations I should be aware off when designing the blade?

 

[Aussiepom]

My thoughts on your queries, in order:

1. Leave off the filing above the ricasso. It will greatly increase the risk of introducing microscopic cracks at exactly the place you would least want them. As an aside, leave the rest of the spine square; there are times when you may need to use the thumb of your left hand, whilst holding the knife in your right hand, to apply pressure near the tip of the blade to create sparks off a ferro rod.

2. I would suggest a radius would be optimum in terms of your query. However, the small percentage of difference in performance between the different spine geometries would be miniscule in comparison to other factors such as: a. The utility of the knife, (keep a square spine as per answer 1 above.) b. Heat treatment. c. Overall method of construction, (will the blank be forged - this will greatly affect grain structure and reduce stresses.) d. Geometry of the overall blade, not just the spine. e. Finishing of the blade, (make sure any finishing/polishing, where possible, is carried out along the blade, not across it. There will be others, but these ones spring to mind immediately.

3. I don't actually understand what you mean. Do you mean in terms of when the pommel is struck with a baton?

Any other considerations: I think I've touched on a few of these in my answer to query No. 2.

Hope some of this helps.