Performance evaluation of peanut-shaped tubular auxetics with enhanced stiffness: a finite element study

Auxetic materials or structures possess a negative Poisson's ratio in contrast to conventional materials, and they shrink or expand transversely under uniaxial compression or tension, respectively. These unique deformation features leads to enhance the mechanical properties compared with the conventional materials. Auxetic tubular structures are of significant interest in the literature because of their superior mechanical qualities, applicability and extensive application. Various auxetic tubular structures with different geometries have been proposed and examined before including conventional peanut-shaped tubular structures. However, application of the peanut-shaped structures is limited due to their low stiffness. In this study, it is aimed to enhance the stiffness of the peanut-shaped tubular auxetic by either adding stiffener to the conventional structure or rotating the unit cell of the structure by a certain angle. Also, the effect of the above-mentioned modifications on the Poisson's ratio of the structure is investigated. A total of 12 different peanut-shaped auxetics are modelled and the elastic behaviour of these structures under uniaxial compression is compared numerically using finite element simulation. As a result of this analysis, it is observed that both the Poisson's ratio and stiffness values obtained from the models utilising stiffener were higher than the values obtained from their conventional counterparts. Besides, it is seen that the stiffness values increased while the Poisson's ratios decreased with the rotation of the unit cell in all of the peanut-shaped tubular auxetics.

Automated summary

Auxetic materials exhibit unique deformation features and have enhanced mechanical properties compared to conventional materials. Peanut-shaped auxetic tubular structures have been studied, but their application is limited due to low stiffness. This study aims to enhance the stiffness of peanut-shaped auxetic tubular structures by adding stiffeners or rotating the unit cell, and the effect on Poisson's ratio is investigated. Numerical simulations are conducted and show that both the Poisson's ratio and stiffness values are increased with the addition of stiffeners, and the stiffness values increase while the Poisson's ratio decreases with unit cell rotation.