----------------------------------------------|
| TABLE II |
|--------------------------------------------------------------|
| RATIO OF STRENGTH OF WOOD IN TENSION AND IN COMPRESSION |
| (Bul. 10, U. S. Div. of Forestry, p. 44) |
|--------------------------------------------------------------|
| | Ratio: | A stick 1 square inch in |
| | | cross section. |
| | Tensile | |
| KIND OF WOOD | strength | Weight required to-- |
| | R = ----------- +----------------------------|
| | compressive | Pull apart | Crush endwise |
| | strength | | |
|---------------+-----------------+------------+---------------|
| Hickory | 3.7 | 32,000 | 8,500 |
| Elm | 3.8 | 29,000 | 7,500 |
| Larch | 2.3 | 19,400 | 8,600 |
| Longleaf Pine | 2.2 | 17,300 | 7,400 |
|--------------------------------------------------------------|
| NOTE.--Moisture condition not given. |
|--------------------------------------------------------------|

Failure of wood in tension parallel to the grain occurs
sometimes in flexure, especially with dry material. The tension
portion of the fracture is nearly the same as though the piece
were pulled in two lengthwise. The fibre walls are torn across
obliquely and usually in a spiral direction. There is
practically no pulling apart of the fibres, that is, no
separation of the fibres along their walls, regardless of their
thickness. The nature of tension failure is apparently not
affected by the moisture condition of the specimen, at least not
so much so as the other strength values.[3]

[Footnote 3: See Brush, Warren D.: A microscopic study of the
mechanical failure of wood. Vol. II, Rev. F.S. Investigations,
Washington, D.C., 1912, p. 35.]

Tension at right angles to the grain is closely related to
cleavability. When wood fails in this manner the thin fibre
walls are torn in two lengthwise while the thick-walled fibres
are usually pulled apart along the primary wall.

|--------------------------------------------|
| TABLE III |
|---------------------------------