Wood - Mechanical Properties

Quiz Questions

 1. Wood may be described as an orthotropic material; that is, it has unique and independent mechanical properties in the directions of three mutually perpendicular axes: longitudinal, radial, and tangential. True False 2. Modulus of rupture is an accepted criterion of strength, al- though it is not a true stress because the formula by which it is computed is valid only to the elastic limit. True False 3. The modulus of rigidity, also called shear modulus, indicates the resistance to deflection of a member caused by shear stresses. True False 4. The modulus of rigidity, also called shear modulus, indicates the resistance to deflection of a member caused by shear stresses. True False 5. Resistance to twisting about a longitudinal axis is called toughness. For solid wood members, toughness shear strength may be taken as shear strength parallel to grain. True False 6. If the load is sufficiently high and the duration of load is long, failure (creep-rupture) will eventually occur. The time required to reach rupture is commonly called duration of load. True False 7. Resistance to failure under specific combinations of cyclic loading conditions: frequency and number of cycles, maximum stress, ratio of maximum to minimum stress, and other less-important factors is called fatigue. True False 8. Measurement of fracture toughness helps identify the length of critical flaws that initiate failure in materials. True False 9. What does figure 4-2 illustrate about? (Refer Pg 4-25) Possible crack propagation systems for wood Average toughness values Average coefficients of variation for some mechanical properties None of the above 10. The vibration properties of primary interest in structural materials are speed of sound and internal friction (damping capacity). True False 11. The speed of sound increases with increasing temperature or moisture content in proportion to the influence of these variables on modulus of elasticity and density. True False 12. Internal friction is the term used to denote the mechanism that causes this energy dissipation. The internal friction mechanism in wood is a complex function of temperature and moisture content. True False 13. The influence of knots depends on their size, location, shape, and soundness; attendant local slope of grain; and type of stress to which the wood member is subjected. True False 14. Mechanical and physical properties as measured and reported often reflect not only the characteristics of the wood but also the influence of the shape and size of the test specimen and the test mode. True False 15. Knots in round timbers, such as poles and piles, have high effect on strength than knots in sawn timbers. True False 16. What does figure 4-3 illustrate about? (Refer Pg 4-29) Types of knots Effect of grain angle on mechanical property Functions relating mechanical properties to specific gravity of clear, straight-grained wood None of the above 17. Strength properties in directions ranging from parallel to perpendicular to the fibers can be approximated using a Hankinson-type formula. (Refer Pg 4-29) WhereN is strength at angle ? from fiber direction,Q strength perpendicular to grain, and n an empirically determined constantWhat does P stand for? Strength parallel to grain Power of the grain Property ratio None of the above 18. Juvenile wood is the wood produced near the pith of the tree; for softwoods, it is usually defined as the material 5 to 20 rings from the pith depending on species. True False 19. In relatively dry and moderate temperature conditions where wood is protected from deteriorating influences such as decay, the mechanical properties of wood show little change with time. True False 20. What does ASTM stand for? American Standard for Testing and Materials American Society for Testing and Materials American Standard for Transportation and Materials None of the above