Mechanical analysis of the auxetic behavior of novel braided tubular structures by the finite element method

Abstract

Auxetic materials are characterized with counter intuitive mechanical behavior, that is, a negative Poisson's ratio, in which the material expands in the direction perpendicular to the elongation direction. This intriguing property can be used to engineer structures with various porosity for ‘smart filters’ where the permeability changes in response to exterior force. In this research, the mechanical behavior of braided tubular structures that comprise helical auxetic yarns (HAYs) has been investigated. The permeability of the structure can be altered with the application of different levels of tensile force. Both HAYs and biaxial structures are fabricated on a Maypole braiding machine. The novelty of this braided tubular structure is that its open area decreases when stretched due to the local auxetic effect. A multi-scale finite element model is established to analyze the auxetic effect and the relationship between tensile force and the open area. The open area of the biaxial structure is measured by a camera system that is installed next to an Instron machine while the sample is subjected to tension. The experimental results show that the open area in the biaxial structure is reduced due to the auxetic effect of each HAY. The model gives a reasonable prediction compared to the experimental data, even though deviation exists, which is probably due to the nonlinear behavior from contact and large deformation.