Most materials can be expected to have a positive Poisson's ratio, i.e. to shrink in x- and y-direction when they are stretched in z-direction and vice versa. Some materials and constructions, however, show a negative Poisson's ratio - starting from crystals, ceramics etc. to foams or man-made structures. Besides the basis interest in these structures, they can offer other interesting properties, such as shear resistance or sound absorption, allowing for their use in different fields of application.
A recent article by Z. Wang and H. Hu gives an overview of the principles of auxetic materials, focusing on textile structures mimicking macroscopically the principals which are well-known from microscopic auxetic materials, allowing for understanding these effects easily ... and leading to novel textile applications.
Z. Wang and H. Hu
Auxetic materials and their potential applications in textiles
Textile Research Journal 84, 1600 (2014)
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