Center section’s lower side

Today, the mold of the center section’s lower side was finally ready to start with the first step in producing the shell, namely the paint job.

The last days we applied several coats of SE 700 release wax (Bacuplast Faserverbundtechnik GmbH), one coat of priming wax and a finishing coat of PVA release film (R&G Faserverbundwerkstoffe GmbH):

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After the PVA dried, it was time to spray the paint. To reduce weight and obtain a better surface, I decided to use in mold coating (IMC). This means essentially that you spray on the release film and laminate on the paint, in contrast to the old fashioned approach where you laminate everything and then at the end spray the final part. Thus, you have to choose very early the background color, which in my case is RAL 9001:

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I decided to use a polyurethane based paint that binds very well to most resins even weeks after having cured (HP-Textiles GmbH).

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In a couple of days we will start with the external face-sheet of the sandwich. The aramid honeycomb core is already trimmed and waiting for the face-sheet:

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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.