Just to bring up a random thought, are you talking about just resting the metal against the wood/polyethylene to support it against impact perpendicular to the metal, or are you thinking of gluing them together as a laminate (which would work better against shearing forces likely to buckle the metal)?

Speaking from absolutely no personal experience, I was wondering if the ability to repair armour is considered a factor these days. Obviously if you get a gash in solid steel, youve got a good chance of fixing it (given a while with a MIG and a big hammer). It strikes me that repairing a laminate is pretty much a throw-it-out-and-start-again job - although I guess if you used a hot glue gun to stick the parts together it might be possible to heat them and re-separate them.

Neither a new sheet of thin steel nor a new lump of wood is going to break the bank, and obviously repairing the wood (to its original strength) is getting on for a non-starter anyway, but I guess its relevant with thicker and more expensive (e.g. titanium) armour.

On the topic of strengthening wood, some model builders on Discovery Home & Leisure were swearing by the idea of liberally coating wood (especially balsa, to be fair) with superglue as a way of strengthening it without adding much weight. Gluing on a thin strip of carbon fibre seemed to help, too. I dont know how well model aircraft techniques translate to combat robotics, but it might be worth an experiment. :-)

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Fluppet