The Effects of Processing on the Topology and Mechanical Properties of Negative Poisson’s Ratio Foams

Combined heat treatment and applied mechanical strains have been employed to modify the structure and properties of polyurethane (PU) foams. Consequently, foams with a range of pore sizes, shapes and orientations have been produced, including those possessing auxetic (negative Poisson’s ratio) behaviour. Four conversion conditions were employed: triaxial, biaxial and uniaxial compression (to linear compression ratios of 0.9, 0.8 and 0.7) and uniaxial tension to (linear extension ratios of 1.1 and 1.2). The converted foams were then observed by either SEM or optical microscopy, as appropriate, to determine the pore structure. Mechanical properties were measured using tensile testing in conjunction with videoextensometry, allowing the values of Young’s modulus and Poisson’s ratio to be ascertained. Increased anisotropy in the pore structure and elastic properties was observed. The biaxial as well as the triaxial conversion routes led to auxetic behaviour for the PU foams.Copyright © 2005 by ASME

[1]  K. Evans,et al.  Models for the elastic deformation of honeycombs , 1996 .

[2]  Roderic S. Lakes,et al.  Micromechanical Analysis of Dynamic Behavior of Conventional and Negative Poisson’s Ratio Foams , 1996 .

[3]  K. Evans,et al.  Auxetic Materials : Functional Materials and Structures from Lateral Thinking! , 2000 .

[4]  R. Lakes,et al.  Influence of Cell Size on Re-Entrant Transformation of Negative Poisson's Ratio Reticulated Polyurethane Foams , 2001 .

[5]  C. Smith,et al.  Quantitative analysis of the microscale of auxetic foams , 2005 .

[6]  A. Alderson,et al.  Expanding the range of auxetic polymeric products using a novel melt‐spinning route , 2005 .

[7]  R. S. Lakes,et al.  Negative Poisson's ratio foam as seat cushion material , 2000 .

[8]  Massimo Ruzzene,et al.  Auxetic compliant flexible PU foams: static and dynamic properties , 2005 .

[9]  Fabrizio Scarpa,et al.  Numerical and experimental uniaxial loading on in-plane auxetic honeycombs , 2000 .

[10]  Kenneth E. Evans,et al.  Auxetic two-dimensional polymer networks. An example of tailoring geometry for specific mechanical properties , 1995 .

[11]  Kenneth E. Evans,et al.  Fabrication methods for auxetic foams , 1997 .

[12]  A. Beltzer,et al.  Reexamination of dynamic problems of elasticity for negative Poisson’s ratio , 1988 .

[13]  Roderic S. Lakes,et al.  Viscoelastic behaviour of composite materials with conventional- or negative-Poisson's-ratio foam as one phase , 1993 .

[14]  M. Ashby,et al.  Cellular solids: Structure & properties , 1988 .

[15]  R. Lakes.  Foam Structures with a Negative Poisson's Ratio , 1987, Science.

[16]  Joseph N. Grima,et al.  Auxetic polymeric filters display enhanced de-fouling and pressure compensation properties , 2001 .

[17]  K. E. EVANS,et al.  Molecular network design , 1991, Nature.