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Abstract:
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Size effects in out -of -plane bending stiffness of honeycomb cellular materials were studied using analytical mechanics of solids modeling , fabrication of samples and mechanical testing . Analysis predicts a positive size -effect relative to continuum model predictions in the flexure stiffness of a honeycombed beam loaded in out -of -plane bending . A method of determining the magnitude of that effect for several different methods of constructing or assembling square -celled and hexagonal -celled materials , using both single -walled and doubled -walled construction methods is presented . Hexagonal and square -celled honeycombs , with varying volume fractions were fabricated in Nylon 12 using Selective Laser Sintering . The samples were mechanically tested in three -point and four point -bending to measure flexure stiffness . The results from standard three -point flexure tests , did not agree with predictions based on a mechanics of solids model for either square or hexagonal -celled samples . Results for four -point bending agreed with the mechanics of solids model for the square -celled geometries but not for the hexagonal -celled geometries . A closed form solution of an elasticity model for the response of the four -point bending configuration was developed , which allows interpretation of recorded displacement data at two points and allows separation the elastic bending from the localized , elastic /plastic deformation that occurs between the loading rollers and the specimen’s surface . This localized deformation was significant in the materials tested . With this analysis , the four -point bending data agreed well with the mechanics of solids predictions . |