Materials with negative Poisson ratios are known to have high shear ri
gidities - a useful property for many types of structural and function
al materials. To improve upon relatively low Young's modulus of existi
ng auxetics, one may consider embedding such components in an elastic
material with sufficiently high modulus. We show theoretically that su
ch composite materials do exhibit auxeticity when the inclusion volume
fraction exceeds a critical value and the ratio of Young's modulus of
inclusion to that of a matrix falls within a definite interval. The e
xistence of these auxeticity windows, once verified experimentally, op
ens up a new avenue of auxetics research. (C) 1998 Elsevier Science B.
V. All rights reserved.