Folded sheet outperforms honeycomb

Tom Shelley reports a novel space filling structure for composite panels that can also be reinforced.

Doubly periodic folded sheet is stronger than corrugated construction and has potential applications in aerospace for structures, cars for impact absorption and lighter weight and more effective packaging.

The technology is the invention of Dr. Daniel Kling, proprietor of Folded Structures Company in New Jersey in the USA, which has received two NASA grants to develop the technology for use in aerospace. This has enabled the refinement of automated software to generate folding patterns and finite element test and optimise the resulting structures, and also to permit the purchase and adaptation of composite manufacturing equipment to produce parts for test and evaluation. The folding patterns now exist in many variations, although the most immediate large scale commercial application for them would appear to be weight saving packaging.

Says Dr Kling: "I am a former sculptor. Somebody one day gave me a chunk of a door. I looked at the material used for the core and decided I could do better." He particularly noted that structural foams in general are not very efficient compared with structures where all parts are designed to perform load-carrying tasks. Rather than create more optimal constructions by traditional sculpting and model making methods, he immediately set about devising a software algorithm to automatically generate folding patterns.

Called 'Foldstar', the software is fully functional, but is not at the present time being offered commercially to the rest of the engineering world, although it is planned to do this later. Dr Kling did reveal to us that the software generated a, "Triangular wave described by four parameters", and that it was possible to use it to generate curved structures by, "By designing the patterns with a small offset" but was unwilling to reveal further details. It should be pointed out that at the present time, the patents are still, "Applied for" rather than granted, and since there have been various other patents applied for and granted for different methods of producing folded structures, it would make no sense to release all details publicly until the Folded Structures patents are finalised, granted and enter the public domain.

Nonetheless, Dr Kling was willing to reveal that he is able to design and manufacture multi-laminate components using a batch press with a "die with articulated components", as well as having a roll press to produce folded material continuously.

Applications are seen in paper cores superior to corrugated cardboard, multi-layer blocks to replace Styrofoam for shock absorbing and a replacement for honeycomb in cores in aircraft floors and airframe. Doubly-folded steel sheets are stronger than corrugated structures and it should be possible to use the technique in light weight aluminium and steel truck beds and car floors to add resilient strength to the frame and well as produce novel energy absorbing structures. When we suggested the structure might lend itself to blast absorption, Dr. Kling responded that this was indeed one of the target applications. Filled with a suitable cementitious material, one configuration provides a means of reinforcing rubbish bins, so that if a bomb were to be left in one, and the explosion were large enough to burst the containment, the reinforcement would be reduced to powder. If this is the case, it might now be considered safe to once more install litter bins in railway and underground stations and other public places in the UK.

Author
Tom Shelley

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