Chapter III: Part III: Publications of the United States Government on

the mechanical properties of wood, and timber
testing

ILLUSTRATIONS

Frontispiece Photomicrograph of a small block of western
hemlock
1. Stress-strain diagrams of two longleaf pine beams
2. Compression across the grain
3. Side view of failures in compression across the
grain
4. End view of failures in compression across the
grain
5. Testing a buggy-spoke in endwise compression
6. Unequal distribution of stress in a long column due
to lateral bending
7. Endwise compression of a short column
8. Failures of a short column of green spruce
9. Failures of short columns of dry chestnut
10. Example of shear along the grain
11. Failures of test specimens in shear along the
grain
12. Horizontal shear in a beam
13. Oblique shear in a short column
14. Failure of a short column by oblique shear
15. Diagram of a simple beam
16. Three common forms of beams--(1) simple,
(2) cantilever, (3) continuous
17. Characteristic failures of simple beams
18. Failure of a large beam by horizontal shear
19. Torsion of a shaft
20. Effect of torsion on different grades of hickory
21. Cleavage of highly elastic wood
22. Cross-sections of white ash, red gum, and eastern
hemlock
23. Cross-section of longleaf pine
24. Relation of the moisture content to the various
strength values of spruce
25. Cross-section of the wood of western larch showing
fissures in the thick-walled cells of the late
wood
26. Progress of drying throughout the length of a
chestnut beam
27. Excessive season checking
28. Control of season checking by the use of S-irons
29. Static bending test on a large beam
30. Two methods of loading a beam
31. Static bending test on a small beam
32. Sample log sheet, giving full details of a
transverse bending test on a small pine beam
33. Endwise compression test
34. Sample log sheet of an endwise compression test on
a short pine column
35. Compression across the grain
36. Vertical section of shearing tool
37. Front view of shearing tool
38. Two forms of shear test specimens
39. Making a shearing test
40. Impact testing machine
41. Drum record of impact bending test
42. Abrasion machine for testing the wearing qualities
of woods
43. Design of tool for testing the hardness of woods
by indentation
44. Design of tool for cleavage test
45. Design of cleavage test specimen
46. Designs of tension test specimens used in United
States
47. Design of tension test specimen used in New South
Wales
48. Design of tool and specimen for testing tension at
right angles to the grain
49. Making a torsion test on hickory
50. Method of cutting and marking test specimens
51. Diagram of specific gravity apparatus

TABLES

I. Comparative strength of iron, steel, and wood
II. Ratio of strength of wood in tension and in
compression
III. Right-angled tensile strength of small clear
pieces of 25 woods in green condition
IV. Results of compression tests across the grain on
51 woods in green condition, and comparison with
white oak
V. Relation of fibre stress at elastic limit in
bending to the crushing strength of blocks cut
therefrom in pounds per square inch
VI. Results of endwise compression tests on small
clear pieces of 40 woods in green condition
VII. Shearing strength along the grain of small clear
pieces of 41 woods in green condition
VIII. Shearing strength across the grain of various
American woods
IX. Results of static bending tests on small clear
beams of 49 woods in green condition
X. Results of impact bending tests on small clear
beams of 34 woods in green condition
XI. Manner of first failure of large beams
XII. Hardness of 32 woods in green condition, as
indicated by the load required to imbed a
0.444-inch steel ball to one-half its diameter
XIII. Cleavage strength of small clear pieces of 32
woods in green condition
XIV. Specific gravity, and shrinkage of 51 American
woods
XV. Effect of drying on the mechanical properties of
wood, shown in ratio of increase due to reducing
moisture content from the green condition to
kiln-dry
XVI. Effect of steaming on the strength of green
loblolly pine
XVII. Speed-strength moduli, and relative increase in
strength at rates of fibre strain increasing in
geometric ratio
XVIII. Results of bending tests on green structural
timbers
XIX. Results of compression and shear tests on green
structural timbers
XX. Results of bending tests on air-seasoned
structural timbers
XXI. Results of compression and shear tests on
air-seasoned structural timbers
XXII. Working unit stresses for structural timber
expressed in pounds per square inch

PART I THE MECHANICAL PROPERTIES OF WOOD