POISSON'S RATIO FOR HONEYCOMB SANDWICH CORES,
RAND CORP SANTA MONICA CALIF
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An interesting mechanical property of honeycomb cores is their Poissons ratio it is very sensitive to cell geometry and can assume values from zero to about three. Large values may be observed when flexing some slabs of honeycomb with flat cell walls, while rippled wall honeycombs demonstrate zero Poissons ratio. The ratio of anticlastic curvatures is indicative of the value of Poissons ratio for axial loading in the plane of the slab. Equilateral hexagonal and square cells were considered here the doubled foil line the x-direction, and the cell width, a, the spacing between doubled foil lines see insert, Fig. 1. The angle d between the x-axis and an adjacent wall is 60 degrees for regular hexagonal cells, though in practice it may be much less the so-called under-expanded core, or well beyond 60 degrees over-expanded cores. Reducing the doubled foil line to a minimum, results in a nearly quadrilateral cell, herein assumed square. Conforming to common practice, the doubled foil line was assumed parallel or perpendicular to the loading or bend axis.