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Usually I see composite as a laminate wrapped around the core of a sandwich structure. Usually in loading such as bending the bending stress is the highest furthest away from the neutral axis, while usually the maximum transverse shear appears at the outer surface of a structure. I believe this is why laminate is orientated differently as it's orthotropic + wrapped around the outer surface of the structure.

I've also seen people making sandwich core e.g. 2d extruded lattice, by using composite. I suppose they are the same as the conventional laminate in terms of manufacturing and material properties (layers of lamina), the only difference is probably that in order to take the shape of a 2d extruded lattice, it's cut from layers of rectangular lamina? Why would people do this though, are they better than traditional material? Is it because people make them quasi-isotropic?

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    $\begingroup$ Kai, your terminology is very confusing. A sandwhich structure is a casual way to refer to a high load-bearing skin applied to a cheaper, usually lighter, core. The reason is to improve stiffness without a lot of weight, expense, and complexity. The core still has to be carefully engineered. It has to adhere to and support the skins and resist buckling in the skin and support the skin against point loads. It may be isotropic or not. Please post a picture or two so we understand what you are talking about as far as the 2D extruded lattice is concerned.. $\endgroup$ – Phil Sweet Jan 28 at 23:04
  • $\begingroup$ e.g. carbon fiber nomex honeycomb panels $\endgroup$ – Kai Jan 29 at 2:44
  • $\begingroup$ See en.wikipedia.org/wiki/Sandwich_theory to get a feel for what goes on in sandwich composites. $\endgroup$ – Biswajit Banerjee Jan 29 at 21:07
  • $\begingroup$ Most honeycomb panels are not isotropic. They are made by bonding sheets of material together along lines with gaps between them, and then pulling the stack of sheets apart to open up the gaps and form the honeycomb shape. This means there is more thickness of the honeycomb walls in the direction of the bonds (where two layers are bonded together) than at right angles to it. The data sheets for the panels give the mechanical properties in both directions. $\endgroup$ – alephzero Jan 30 at 11:16
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Structured composites are often designed with multiple loading directions/conditions, and something being "better" has to be defined by the application.

Honeycomb structures may be used in a panel that needs to resist crushing as well as bending. With material being at 90° to the surface it can provide more protection against forces normal to the panel surface than say a soft foam core with the same density.

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