Poisson’s ratio negative

Ycganch-Hacri, A Wcidncr, D.J., and J.B. Parise Elasticity of Alpha-Cristobalitc A Silicon Dioxide with a Negative Poisson s Ratio, Science, 650 (July 31, 1992). Yun, W, and R.T. Howe Recent Developments in Silicon Micro-accclcromctcrs, ... 

A polyester foam with a negative Poisson s ratio has been reported by Lakes. Its cells consist of reentrant faces. Figure 19.4 shows a cell with 24 faces. When the cell is extended its sides are moved inward and when it is compressed the walls move outward. The negativity of v increases with 9. 

A cell structure with a negative Poisson s ratio. If it is compressed, the sides will move inward. 

Murray, C. J., Foam Exhibits Negative Poisson s Ratio, DN, Dec. 1989. 

By the properties of bonds h and (h/g < 6), a Poisson s ratio of < vp < 1 can be obtained. If such configurations constitute the principal contribution to the microscopic properties of the system, then this can lead to negative Poisson s ratio. 

Assuming that Eq. (333) is fulfilled also at the percolation threshold for random lattices with Z replaced by the average coordination number (Z,) (where Z, means the coordination number of the th lattice site), one can obtain negative Poisson s ratios from percolation systems of particles—for example, polymer molecules, which can be due to a sufficiently large number of neighbors, < Z > > Ad. 

K. W. Wojciechowski, Isotropic systems of negative Poisson s ratios, in Proceedings of the 2nd Tohwa International Meeting, M. Tokuyama and I. Oppenheim, eds., World Scientific, Singapore, 1998. 

Hirotsu S (1991) Softening of bulk modulus and negative Poisson s ratio near the volume phase transition of polymer gels. J Chem Phys 94 3949-3957 Hirotsu S, Flirokawa Y, Tanaka T (1987) Volume-phase transitions of ionized N-isopropylacry-lamide gels. J Chem Phys 87 1392-1395... 

The negative sign is to ensure that the numerical value of Poisson s ratio is positive. For isotropic materials, the theoretical value of u is Most metals show values in the range 0.25-0.35. Some materials, counterintuitively, have a negative Poisson s ratio, and get thicker when under tension. They are discussed later in this chapter. Representative values of Poisson s ratio are given in Table 10.1. 

In the families of cordierite, yS-eucryptite, /3-cordierite and NZP, a mechanism similar to that giving rise to auxetic (negative Poisson s ratio) materials seems to occur (Section 10.3.2). The stmcture is built from inflexible layers, similar to those found in clay minerals (see Sub-section... 

Xu, T. and Li, G. (2011) A shape memory polymer based syntactic foam with negative Poisson s ratio. Materials Science and Engineering A, 528, 6804—6811. 

Yageneh-Haeri A, Weidner DJ, Parise JB (1992) Elasticity of a-cristobahte A sihcon dioxide with negative Poisson s ratio. Science 257 650-652... 

Lakes RS (1987) Foam structures with a negative Poisson s ratio. Science 235 1038 Nye JF (1972) Physical properties of crystals, 6th edn. Clarendon Press, Oxford Petililka V, Slavik JB, Sole I, Taraba O, Tichy J, Zelenka J (1960) Piezoelectricity and its technical applications, (in Czech) Academia, Prague... 

Although the possibility of materials with a negative Poisson s ratio had been recognized theoretically it is only comparatively recently, since the mid 1980s, that examples of such materials have become available. These materials expand laterally when stretched and contract laterally when compressed, and are called auxetic from the classical Greek word auxetos, meaning to increase. 

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