Delbert,
Depending upon how the knife was loaded, the handle material and how it is attached could certainly be a factor. It the case brought up above, the point of the knife would be imbedded in something and then loaded with someone standing on it. In that case, as I indicated above, the highest stress would be right at the point where the blade entered whatever it was stuck into so the handle should not be a factor. That said, areas of high stress concentration could indeed cause failure someplace else with the plunge being a good example. Stress does concentrate when there are rapid changes in cross section or at sharp edges and the increase can be significant. The smoother the transition from one thickness to another, the lower the concentration, so a large plunge radius is better than a small one as related to local stress. Holes can also be sources of stress concentration. Frankly, determining the stress of a knife in bending is not a simple task due to the many factors of blade shape, load application, surface finish, finishing method, bevel shape, plunge, holes, etc. A good analyst with a finite element program could certainly do it but it is far from trivial. In machine design, there are a lot of rules of thumb we apply when starting a design but, in the end, things always get changed based upon results of analysis and test. A knife is a relatively complex structure with multiple material types and lots of geometry, finish and strength variables. Doing real world tests as many makers do is probably the best way to ensure a design will work and last as intended. The test results, even failures, help provide the knowledge needed to know what is really needed for a given application.
Randy
