Sandwich cross sections

Last week we tested the capacity of a honeycomb sandwich to take impact energy up, and analysed how flax fibers keep the damaged laminate together preventing splintering.

Yesterday, I decided to make a cross section of the impact site to get a better picture:

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Two things are worth remarking:

  • as expected, most impact energy is absoved by the honeycomb core: The cells got crushed and absorved much of the energy by plastic deformation. Cell deformation extends about two to three cells beyond the recognizable external damage.
  • Though the saw was new and sharp, the edge is fluffly exposing mainly flax fibers. This shows that these fibers have a high impact resistance and a high energy absorption capacity. Properties similar to aramid.

 

Just for reference, here’s a picture of a broken carbon sandwich (bending failure):

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The edge is clean and sharp, and a cut-out of this sandwich has a perfectly clean edge.