Go Bars...(Material)

[Farrell]

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