Dissemination of IT for the Promotion of Materials Science (DoITPoMS)

DoITPoMS Teaching & Learning Packages The Structure and Mechanical Behaviour of Wood Questions
The Structure and Mechanical Behaviour of Wood AimsBefore you startIntroductionThe structure of wood (I)The structure of wood (II)The structure of wood (III)Stiffness of woodStrength of woodWater's effect on the mechanical behaviour of woodWood as an engineering materialSummaryQuestionsGoing further
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Questions

Quick questions

You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!

  1. What is the main difference between hardwoods and softwoods?

    a Hardwoods are harder than softwoods.
    b Softwoods have areas of tension and compression in their tree trunks.
    c Hardwoods have vessels and fibre cells.
    d Softwoods contain cellulose, lignin and hemicellulose.

  2. How do wood's materials properties change when wet?

    a Wood gets stiffer.
    b Wood gets weaker.
    c Wood gets stronger.
    d Wood shrinks.

  3. What deformation characteristic does wood show on three-point bend testing?

    a Fibre pull-out.
    b Hookean elasticity.
    c Crack propagation.
    d Viscoelasticity.

  4. By what mechanism does wood fail on loading during three-point bend testing?

    a Fibre pull-out.
    b Brittle fracture.
    c Ductile fracture.
    d Elastic yielding.

  5. Which of the following is not present in a plant cell?

    a Vacuole.
    b Hemicellulose.
    c Chloroplast.
    d Mitochondrion.

  6. Which region of the yew tree is used to make longbows?

    a The cambium.
    b The region bordering both the bark and the cambium.
    c The region bordering both the sapwood and the heartwood.
    d The region bordering both the cambium and the sapwood.

Deeper questions

The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.

  1. Below is shown a 3D model of the trunk interior of balsa made from slides taken in the tangential, radial and transverse directions. Identify the key features on this 3D balsa wood sample:

  2. Calculate the percentage of elastic strain energy that is stored in a loading-unloading cycle for a wood sample.

  3. Calculate the stiffness of this wood sample given the previous graph of loading and unloading for Scots pine.

  4. (…continued from previous question) Now calculate the strength of the wood sample using the following results:

    L (cm)

    9.0 ± 0.1

    w (mm)

    3.20

    h (mm)

    3.30

    mass (kg)

    1.7 ± 0.05

    Use g = 9.81 m s-2

  5. (...continued from previous question) What are the errors in your calculated values of stiffness and strength?

  6. What wood, out of the following, would be used to make a cricket bat blade?

    a     Willow: Tough, light and resilient

    b     Cane: Light and springy.

    c     Birch:  Inexpensive, tough and heavy.

    d     Elm: Very easy to bend, good durability and easy to work.

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