On Sun, 24 Oct 2004 03:15:45 -0500, Archimedes Plutonium
wrote:

Fri, 15 Oct 2004 03:53:30 GMT Charles wrote:



Different kinds of strength are shown here.

http://www-materials.eng.cam.ac.uk/m...c/IEChart.html
--

I was unable to get that site.

This one may be more easily accessible:

http://www.fpl.fs.fed.us/documnts/pdf2001/green01d.pdf

But I wonder if anyone has offered a math equation for stiffness of wood in relation
to strength of wood.

The PDF cited above includes an adequate review of the mathematics of
the many stiffness and strength properties that are used to describe
wood.

Some important points to get from reading that document:

Wood is orthotropic: its properties are unique and independent in each
of the Cartesian axes and in each shear plane. These properties are
very different from species to species, and not all properties vary in
the same direction.

There are standard measures of these properties, and there are
standard methods of measure. In the U.S., the procedures are given in
ASTM D143, which any library at an institution with a materials
science program should have.

Stiffness, or rigidity, denotes elastic resistance to deformation: it
applies at loads insufficient to cause permanent deformation or
fracture. Strength denotes resistance to loads that cause permanent
(plastic) deformation or failure.

The two are correlated, but the correlation is only moderate; there is
nothing like an equation relating stiffness and strength, nor could
there possibly be: the physical mechanisms at work in elastic
deformation and plastic deformation of wood are quite different.

For example, two important structural woods, Loblolly Pine and Red
Oak, differ to quite different degrees in stiffness and strength. They
are practically equal in stiffness: modulus of elasticity in bending
for Red Oak is 12.5 GPa; for Loblolly Pine, it is 12.3 GPa. But Red
Oak is noticeably stronger than Loblolly Pine: modulus of rupture in
bending is 99 MPa for Red Oak, but 88 MPa for Loblolly Pine. However,
Loblolly Pine is stronger in another important measu modulus of
rupture in compression: 49.2 MPa vs. 46.6 MPa. And if you are not yet
adequately convinced that there is no exact relation, note that Yellow
Poplar, a relatively weak wood in most other properties, is far
stronger than either in tension parallel to grain: 154.4 MPa vs. 101.4
MPa for Red Oak.

If not, then this science area has been neglected and very shabby.

No, it has been well understood for hundreds or thousands of years.
Mathematical development, of course, was possible only in the last few
centuries. But wood is such an important structural material that it
is not at all neglected. Any handbook of building materials and any
building code will have extensive data on the strength and permissible
loading of various types of wood.

If someone has attempted to relate stiffness to strength of wood then this area of
science has received due diligence.

As indeed it has, and has been for many years.

--
Chris Green