Consider the animation below of such a material, and study how a negative value for Poisson’s ratio is possible with this material. As can be seen here, a compressive axial load produces contraction ...

P. M. O'Leary, Viscoelastic Rayleigh Waves for Constant Poisson's Ratio, Proceedings of the Royal Irish Academy. Section A: Mathematical and Physical Sciences, Vol. 81A, No. 2 (1981), pp. 147-155 ...