NUMERICAL AND EXPERIMENTAL STUDY OF AUXETIC CLOSED-CELL FOAMS
Mechanics of Adaptive Materials and Biomechanics Department
V. Belyi Metal-Polymer Research Institute
National Academy of Sciences of Belarus, 246050 Gomel, Belarus
Received:
Rec. 6 October 2004
DOI: 10.12921/cmst.2004.10.02.197-202
OAI: oai:lib.psnc.pl:571
Abstract:
The procedures of fabrication and testing of auxetic foams with closed cells based on foaming a liquid substance and by joining microspheres are discussed. Physically , to obtain an auxetic structure, bending rigidity of elastic rods, plates and shells should strongly depend on the initial curvature. The cells of small size are found mostly to hold their original shape. Large ones show relatively low rigidity , and would get deformed similarly to thin-walled shells when compressed with a possibility of losing stability. Thus, the volumetric compression of a foamed material is mainly realized at the expense of decreased free volume of large cells. Separation of cells according to deformation levels is found to cause auxetic elastic behavior in converted closed cells foams. Technologically, to obtain this auxetics we proposed a two-stage process. It includes the formation of concave cell structure by a permanent volumetric compression of the initial material just after foaming in the solidification state under the action of a liquid or gas. High plasticity of foam materials in this stage allow s us to obtain the re-entrant structure of cells. To obtain a material with non-convex cells we used mostly a gas or liquid under pressure as a forming instrument. After cooling the foam material shows the property of elastic (reversible) deformation. I he homogeneity and isotropy of Poisson’s ratio of obtained auxetics are caused by a uniform distribution of the gas or liquid pressure on the sample surface. Some problems of Poisson’s ratio minimization for foam materials we have solved by the finite element analysis.
References:
[1] K. E. Evans. Auxetic polymers: a new range of materials. Endeavour. New series (4) 170-174 (1991).
[2] D. A. Konyok. K. W. Wojciechowski. Yu. M. Pleskachevsky. and S. V. Shilko. Materials with
negative Poisson ‘s ratio (review). Mechanics of composite materials and structures. 10(1) 35-69 (2004) (in Russian).
[3] R. Lakes. Foam structure with a negative Poisson s ratio. Science. 235 1038-1040 (1987).
[4] Pat. WO 00/53830. D 01 D 5/08. Auxetic materials. Alderson K. L.. Simkins V. R. (2000).
[5] K. L. Alderson and K. E. Evans. The fabrication of microporous polyethylene having a negative Poisson’s ratio. Polymer. 33(20) 4435-4438 (1992).
[6] S. V. Shilko. S. V. Stelmakh. D. A. Chernous. and Yu. M. Pleskatchevskii. Structural simulation of supercompressible materials. J. Theor. Appl. Mech. 28(1) 87-96 (1998).
[7] Y. C. Wang. R. S. Lakes, and A. Butenhoff. Influence of cell size on re-entrant transformation of negative Poisson’s ratio reticulated polyurethane foams. Cell. Polym. 20. 373-385 (2001).
[8] Pat. R B 6242. B 29 C. The fabrication of material with a negative Poisson’s ratio. Shilko S. V.. Konyok D. A.. Bodrunos N. N. (2002) (in Russian)
[9] Yu. M. Pleskachevsky and S. V. Shilko. Auxetic foams and composites. Poly mer Processing Simposia: Abstr. Int. Conf. Antalya. 22-24 Oct. 2001. Polymer Processing Society, Antalya. 417 (2001).
The procedures of fabrication and testing of auxetic foams with closed cells based on foaming a liquid substance and by joining microspheres are discussed. Physically , to obtain an auxetic structure, bending rigidity of elastic rods, plates and shells should strongly depend on the initial curvature. The cells of small size are found mostly to hold their original shape. Large ones show relatively low rigidity , and would get deformed similarly to thin-walled shells when compressed with a possibility of losing stability. Thus, the volumetric compression of a foamed material is mainly realized at the expense of decreased free volume of large cells. Separation of cells according to deformation levels is found to cause auxetic elastic behavior in converted closed cells foams. Technologically, to obtain this auxetics we proposed a two-stage process. It includes the formation of concave cell structure by a permanent volumetric compression of the initial material just after foaming in the solidification state under the action of a liquid or gas. High plasticity of foam materials in this stage allow s us to obtain the re-entrant structure of cells. To obtain a material with non-convex cells we used mostly a gas or liquid under pressure as a forming instrument. After cooling the foam material shows the property of elastic (reversible) deformation. I he homogeneity and isotropy of Poisson’s ratio of obtained auxetics are caused by a uniform distribution of the gas or liquid pressure on the sample surface. Some problems of Poisson’s ratio minimization for foam materials we have solved by the finite element analysis.
[1] K. E. Evans. Auxetic polymers: a new range of materials. Endeavour. New series (4) 170-174 (1991).
[2] D. A. Konyok. K. W. Wojciechowski. Yu. M. Pleskachevsky. and S. V. Shilko. Materials with
negative Poisson ‘s ratio (review). Mechanics of composite materials and structures. 10(1) 35-69 (2004) (in Russian).
[3] R. Lakes. Foam structure with a negative Poisson s ratio. Science. 235 1038-1040 (1987).
[4] Pat. WO 00/53830. D 01 D 5/08. Auxetic materials. Alderson K. L.. Simkins V. R. (2000).
[5] K. L. Alderson and K. E. Evans. The fabrication of microporous polyethylene having a negative Poisson’s ratio. Polymer. 33(20) 4435-4438 (1992).
[6] S. V. Shilko. S. V. Stelmakh. D. A. Chernous. and Yu. M. Pleskatchevskii. Structural simulation of supercompressible materials. J. Theor. Appl. Mech. 28(1) 87-96 (1998).
[7] Y. C. Wang. R. S. Lakes, and A. Butenhoff. Influence of cell size on re-entrant transformation of negative Poisson’s ratio reticulated polyurethane foams. Cell. Polym. 20. 373-385 (2001).
[8] Pat. R B 6242. B 29 C. The fabrication of material with a negative Poisson’s ratio. Shilko S. V.. Konyok D. A.. Bodrunos N. N. (2002) (in Russian)
[9] Yu. M. Pleskachevsky and S. V. Shilko. Auxetic foams and composites. Poly mer Processing Simposia: Abstr. Int. Conf. Antalya. 22-24 Oct. 2001. Polymer Processing Society, Antalya. 417 (2001).
