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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)
Wood - Mechanical Properties
Where
N is strength at angle ? from fiber direction,
Q strength perpendicular to grain, and
n an empirically determined constant
What 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