After reading a couple web sites about bow building and optimal wood cuts, and then reading William's comments below, I think I'll have to do a complete 180 on my comment about shear not being a factor in the broken go-bar launched as a spear. No doubt the go-bar was cut slightly off from parallel to the grain - that would induce the weakness needed to fail due to shear stress - and the fact that it broke in the shape of a nasty sharp elongated spear would support that the break was to some degree a shear failure - and certainly, as William points out, stress is applied to the go-bar at both ends - essentially the definition of shear stress. So, Joe Garrett, I eat my words. I suspect it is a combination of shear stress and bending stress that go-bars experience. Terry Farrell ----- Original Message ----- SNIP > When go bars are installed, they are subjected to some amount > of "Compression Stress" parallel to the grain - force pressing into the > bar > from top and bottom, and some amount of "Bending Stress" perpendicular to > the grain. This is usually measured by applying a force to the middle of > a > piece of wood which is supported on its two ends. SNIP > BTW, shear strength is a "breaking strength" and is most often measured > parallel to the grain. Picture holding a square block of wood, and trying > to slide one half past the other. That is (roughly) shearing. > > Regards, > William R. Monroe
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