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A novel mechanism for generating auxetic behaviour in reticulated foams: missing rib foam model

“…the auxetic specimen, which is typical of this particular foam material [3,18]. Both the hexagonal and missing rib models predict a higher value of E for the conventional foam than the auxetic.…”

“…4 and ϭ E s b(t/l) 3 , E s being the intrinsic Young's modulus (the cell is also shown following a small hinging deformation). Experimental evidence suggests that flexure is the dominant deformation mechanism in auxetic foams and in conventional foams with relatively thick ribs such as the foams used in the present study [3,12]. This honeycomb model was further developed by Masters and Evans [13] for hexagonal cell honeycombs, which may deform concurrently by hinging, flexure and stretching of ribs.…”

“…Foam materials with negative Poisson's ratios were first produced by Lakes [1] and have since been examined by several others [2][3][4][5][6]. Lakes described a process by which conventional, reticulated, positive Poisson's ratio foams could be converted into auxetic, i.e., negative Poisson's ratio foams.…”

Stiffness of Auxetic Foams

“…The * corresponding author; e-mail: ftkwiece@prz.edu.pl auxetic foams have negative the Poisson ratio values from -0.1 to -0.7 [1]. Foam materials with negative the Poisson were first produced by Lakes [2] and then by several others [3][4][5][6][7].…”

“…Sample dimensions a×b×c after compressions were 0.714a × 0.714b × 0.714c according to the recommended literature [2][3][4][5][6][7]. The stiffness k of a body is a measure of the resistance offered by an elastic body to deformation k = F ∆l where F is the force applied on the body, ∆l is the displacement.…”