"blueman" wrote in message
...
Ray Mandeville writes:

For a comprehensive understanding of plywood modulus determination,
and plywood stiffness determinations this is a very good resource:


Interesting article.
From a quick scan of the math, it seems like to first approximation in
a multiply laminate (e.g., plywood) that the MOE (modulus of
elasticity) is only about 50% of the modulus for a similar thickness
of pure hardwood of the same species oriented longitudinally. The
logic being that the transverse-oriented plys contribute only
minimally to stiffness.
Your understanding is faulty. The modulus of elascticity is gives the
relationship between stress and strain.

What the article should have said is that the calculations apply to
computing the moment of inertia. As the article indicated, cross plies
don't contribute to the moment of intertia hence the stresses are higher
with plywood that with wood of the same thickness.
Jim

While somewhat intuitive, I would have thought with all the glues and
resins that you would get some benefit that would make the stiffness
more than just 50% of the equivalent pure hardwood.

Interestingly, one of the web deflection calculators gives fir plywood
about 2/3 the MOE of equivalent thickness douglas fir. So maybe there
is some benefit to the other laminations and resins...

In any case, it still would be good to get some general specs on the
typical MOE for Birch plywood.

Thanks