Modelling concurrent deformation mechanisms in auxetic microporous polymers

A 2D model for the deformation of auxetic microporous polymers (those with a negative Poisson’s ratio) has been previously developed, consisting of a network of rigid rectangular nodules interconnected by fibrils. This model has now been extended to describe the deformation of the network via concurrent fibril hinging and stretching mechanisms. Expressions for the strain-dependent Poisson’s ratios and Young’s moduli are derived and fully investigated with respect to their dependence on the model parameters. These expressions are compared with the experimental strain-dependent data for auxetic microporous polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE). The use of concurrent deformation mechanisms makes a very significant improvement in the agreement of theory with experiment for both cases. Slight discrepancies are discussed in terms of the use of the assumptions of a 2D network of regular, rectangular nodules and a constant force coefficient ratio governing the two deformation mechanisms.

[1]  D. O. Stalnaker,et al.  The Poisson Function of Finite Elasticity , 1986 .

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

[3]  J. Parise,et al.  Elasticity of α-Cristobalite: A Silicon Dioxide with a Negative Poisson's Ratio , 1992, Science.

[4]  K. Evans,et al.  The fabrication of microporous polyethylene having a negative Poisson's ratio , 1992 .

[5]  K. Evans.  Auxetic polymers: a new range of materials , 1991 .

[6]  B. D. Caddock,et al.  Microporous materials with negative Poisson's ratios. I. Microstructure and mechanical properties , 1989 .

[7]  Kenneth E. Evans,et al.  Microstructural modelling of auxetic microporous polymers , 1995, Journal of Materials Science.

[8]  Kenneth E. Evans,et al.  Auxetic polyethylene: The effect of a negative poisson's ratio on hardness , 1994 .

[9]  B. D. Caddock,et al.  Microporous materials with negative Poisson's ratios. II. Mechanisms and interpretation , 1989 .

[10]  K. Evans,et al.  Strain-dependent behaviour of microporous polyethylene with a negative Poisson's ratio , 1993, Journal of Materials Science.

[11]  Joseph Edward Shigley.  Applied mechanics of materials , 1976 .

[12]  Kenneth E. Evans,et al.  The effects of powder morphology on the processing of auxetic polypropylene (PP of negative Poisson's ratio) , 1996 .

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

[14]  Kenneth E. Evans,et al.  Tensile network microstructures exhibiting negative Poisson's ratios , 1989 .

[15]  James R. Chelikowsky,et al.  Negative Poisson ratios in crystalline SiO2 from first-principles calculations , 1992, Nature.

[16]  K. Evans,et al.  Negative Poisson's ratio of microporous polyethylene in compression , 1993, Journal of Materials Science Letters.

[17]  Kenneth E. Evans,et al.  Auxetic foams: Modelling negative Poisson's ratios , 1994 .