Skip to main content
Engineering LibreTexts

16.9: Questions

  • Page ID
    31623
  • 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!

    How does elastic deformation of a honeycomb with hexagonal cells with some faces aligned parallel to the loading axis take place?

    a By elastic compression of the vertical faces
    b By elastic buckling of the vertical faces
    c By elastic bending of the diagonal faces
    Answer

    C.

    What is the criterion for the onset of yielding in a honeycomb?

    a That somewhere the stress should exceed the flow stress through the thickness of the film
    b That the maximum stress in the face exceeds the material flow stress
    c That the stress at the centre of the face should exceed the material flow stress
    Answer

    A.

    Deeper questions

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

    How might elongating the cells of a hexagonal honeycomb in the direction of loading change E/ES for a given relative density?

    a Decrease it
    b Have no effect
    c Increase it
    Answer

    C. Increase it. The length of the beam that must bend is decreased whilst the original length of the cell is increased.

    For a highly porous structure E/ES is proportional to (ρ/ρS)n. In which case will the structure show an increased bending stiffness? Hence explain why many porous materials are often used as the core in sandwich structures.

    a n > 2
    b n = 2
    c n < 2
    Answer

    In many open-cell structures n = 2, so that there is no benefit in using the porous structure alone. However advantage can be obtained if the surfaces of the material are covered with a stiff, strong material.

    The structure will be stiffer in bending if n < 2. In this case the relative second moment of area will increase as the density is reduced faster than the Young modulus will decrease.

    Consider a honeycomb loaded with some faces parallel to the compressive loading direction, in which the shape of the hexagonal cell is such that θ < 0, how would the material deform elastically in the transverse direction?

    a contract inwards
    b no tranverse movement
    c expands outwards
    Answer

    A. contract inwards, in other words the material has a negative Poisson ratio.

    • Was this article helpful?