CONTENTS

[PREFACE]
[PART I
THE MECHANICAL PROPERTIES OF WOOD]
[Introduction]
[Fundamental considerations and definitions]
[Tensile strength]
[Compressive or crushing strength]
[Shearing strength]
[Transverse or bending strength: Beams]
[Toughness: Torsion]
[Hardness]
[Cleavability]
[PART II
FACTORS AFFECTING THE MECHANICAL PROPERTIES OF WOOD]
[Introduction]
[Rate of growth]
[Heartwood and sapwood]
[Weight, density, and specific gravity]
[Color]
[Cross grain]
[Knots]
[Frost splits]
[Shakes, galls, pitch pockets]
[Insect injuries]
[Marine wood-borer injuries]
[Fungous injuries]
[Parasitic plant injuries]
[Locality of growth]
[Season of cutting]
[Water content]
[Temperature]
[Preservatives]
[PART III
TIMBER TESTING]
[Working plan]
[Forms of material tested]
[Size of test specimens]
[Moisture determination]
[Machine for static tests]
[Speed of testing machine]
[Bending large beams]
[Bending small beams]
[Endwise compression]
[Compression across the grain]
[Shear along the grain]
[Impact test]
[Hardness test: Abrasion and indentation]
[Cleavage test]
[Tension test parallel to the grain]
[Tension test at right angles to the grain]
[Torsion test]
[Special tests]
[Spike pulling test]
[Packing boxes]
[Vehicle and implement woods]
[Cross-arms]
[Other tests]
[APPENDIX]
[Sample working plan of United States Forest Service]
[Strength values for structural timbers]
[BIBLIOGRAPHY]
[Part I: Some general works on mechanics, materials of construction, and testing of materials]
[Part II: Publications and articles on the mechanical properties of wood, and timber testing]
[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]
[INDEX]
[FOOTNOTES]

PART ITHE MECHANICAL PROPERTIES OF WOOD

PART I
THE MECHANICAL PROPERTIES OF WOOD