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I'm considering doing some experiments with 3D-printed surfaces and sound transmission with constrained layer damping. I've also been thinking about using isogrid or honeycomb interior surfaces, which got me wondering:

Let's say I had a honeycomb sandwich that was cut through the middle back into two sandwich faces, each face having one side flat and the other side exposed honeycomb. If I then sandwiched the faces back together with a thin layer of viscoelastic polymer in between the honeycomb sides, would I expect more or less damping than with the same constrained layer between solid faces of equal thickness? Has there been any prior work on this?

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Currently, honeycomb cores are sometimes faced with an adhesive film between the Prepreg skin and the core. But you seem to be describing a viscoelastic midlayer.

This arrangement could be simulated parametrically with FEA and the polymer’s FEA Support Test Data. (Parametric FEA model: adjusting thickness and surrounding core/facesheet assembly material and geometry)

You could simulate the behavior you are interested in by performing a DMA temperature and frequency sweep on a viscous polymer you are interested in. Then, using time-temperature superposition principle, use WLF curve shifting to get the polymer’s dynamic properties in the acoustic frequency range.

Apply these properties to your FEA model and adjust (polymer thickness, core/facesheet geometry and material) as necessary to arrive at your desired design goal.

Drawback to this honeycomb modification: One drawback to breaking the out-of-plane cell wall direction with a viscous polymer is the loss of in-plane Shear stiffness that honeycomb cores are particularly good at providing. The interface at the “hard” outer walls would need to move in unison or risk delaminating the midlayer and compromising your engineered benefit.

Manufacturing alternative: I was thinking about a way to not detract from the core’s structural purpose and achieve something similar: What if “polymeric bubbles” were blown through hexagonal injectors into each cell. Blown in such a fashion to adhere to the cell walls and cure in place (likely with some inherent curvature).

Please contact me if you’d be interested in further research (toby_samples@ardl.com). I’m quite interested in this topic since reading your question.

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  • $\begingroup$ Thanks for the reply. Coming back to it after having let the idea sit for a while, I think what you're saying about losing the in-plane shear stiffness makes perfect sense. I'll shoot you an email and see where we can go with it... $\endgroup$ Jul 19 '18 at 16:21
  • $\begingroup$ Aaron, I did't get your e-mail, please resend. $\endgroup$ Jul 23 '18 at 15:26
  • $\begingroup$ OK, just resent from aaltmanpdx at gmail dot com. $\endgroup$ Jul 24 '18 at 15:39

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