Print
Word
PDFA large modulus indicates a stiff material. Thus in green wood tested in static bending it varies from 643,000 pounds per square inch for arborvitae to 1,662,000 pounds for longleaf pine, and 1,769,000 pounds for pignut hickory. (See Table IX.) The values derived from tests of small beams of dry material are much greater, approaching 3,000,000 for some of our woods. These values are small when compared with steel which has a modulus of elasticity of about 30,000,000 pounds per square inch. (See Table I.)
|------------------------------------------------------
------------------------| | TABLE I | |-----------------------------------------------------------
-------------------| | COMPARATIVE STRENGTH OF IRON, STEEL, AND WOOD | |-----------------------------------------------------------
-------------------| | | Sp. | Modulus of | Tensile | Crushing | Modulus | | MATERIAL | gr., | elasticity | strength | strength | of | | | dry | in bending | | | rupture | |-------------------------+----- +------------+----------+----------+----------| | | | Lbs. per | Lbs. per | Lbs. per | Lbs. per | | | | sq. in. | sq. in. | sq. in. | sq. in. | | | | | | | | | Cast iron, cold blast | | | | | | | (Hodgkinson) | 7.1 | 17,270,000 | 16,700 | 106,000 | 38,500 | | Bessenger steel, | | | | | | | high grade (Fairbain) | 7.8 | 29,215,000 | 88,400 | 225,600 | | | Longleaf pine, | | | | | | | 3.5% moisture (U.S.) | .63 | 2,800,000 | | 13,000 | 21,000 | | Redspruce, | | | | | | | 3.5% moisture (U.S.) | .41 | 1,800,000 | | 8,800 | 14,500 | | Pignut hickory, | | | | | | | 3.5% moisture (U.S.) | .86 | 2,370,000 | | 11,130 | 24,000 | |-----------------------------------------------------------
-------------------| | NOTE.--Great variation may be found in different samples of metals as well | | as of wood. The examples given represent reasonable values. | |-----------------------------------------------------------
-------------------|
TENSILE STRENGTH
Tension results when a pulling force is applied to opposite ends of a body. This external pull is communicated to the interior, so that any portion of the material exerts a pull or tensile force upon the remainder, the ability to do so depending upon the property of cohesion. The result is an elongation or stretching of the material in the direction of the applied force. The action is the opposite of compression.
