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.

Auxetic materials have attracted significant interest due to their exceptional mechanical characteristics and distinctive deformation modes. Nevertheless, the practical use of these materials in engineering is constrained by their limited ability to absorb energy. Thus, enhancing the energy absorption (EA) capabilities of auxetic materials is crucial to expand their range of potential applications. In this study, the EA capabilities of auxetic tubular structures with rotating deformation mechanisms are examined, with a specific emphasis on three different perforation shapes: elliptic, peanut, and square, along with their modified versions incorporating stiffeners. The study employs a combination of experimental testing and numerical modelling, utilising ANSYS/LS-DYNA to evaluate various crashworthiness parameters. These parameters include total EA, specific EA, maximum crushing force, and crushing force efficiency, all of which are assessed under quasi-static compression conditions. The research highlights the importance of perforation shape and stiffener incorporation in enhancing crashworthiness. Results show that elliptic perforations exhibit superior EA and stiffened auxetic models outperform conventional ones in terms of crash absorber performance. The presence of stiffeners significantly improves the ability of tubular structures to withstand crushing forces. Furthermore, the study validates the numerical model against experimental findings, demonstrating a high level of agreement in terms of crushing force–displacement, EA, and failure modes. The research provides valuable insights into the design and performance of crashworthy structures and offers potential applications in various fields where impact resistance and EA are critical.

Concrete-filled steel columns (CFSCs) are of great interest in the literature as they are capable of carrying higher loads by combining the exceptional qualities of steel and concrete. With auxetic materials being introduced to civil engineering applications, the influence of these materials on CFSCs remains a matter of curiosity. The current study implements a nonlinear finite element analysis to evaluate the performance of circular CFSCs with six auxetic tubes under axial compression and the proposed numerical model was validated using published experimental data. The effect of the auxetic steel tube’s porosity and Poisson’s ratio on CFSCs was examined parametrically in terms of ultimate strength using the confined concrete model. Moreover, the stress distributions of the concrete and the auxetic steel tubes were also thoroughly examined. Based on the findings of the analysis, the ultimate load of CFSCs, utilising auxetic tubes with the same density and porosity but different Poisson’s ratio, increased proportionally with the increase of auxetic behaviour. When it comes to auxetic tubes with different densities and porosities, the influence of the Poisson’s ratio of the tubes diminished and the stiffness of tubes became more dominant over the mechanical characteristics of columns as the density of the auxetic steel tubes increased or decreased. The stiffness of the auxetic tubes reduced as porosity increased, as did the ultimate load of the columns. Additionally, the ultimate loads of the auxetic steel tube columns are found to be lower than those of bare steel tube columns filled with concrete due to perforations.

This study investigates the effects of processing parameters and testing temperatures on the mechanical properties of auxetic structures fabricated from Ti6Al4V-ELI using Laser Powder Bed Fusion. Three distinct sets of process parameters (Set 1: 50 W–400 mm s ⁻¹ , Set 2: 75 W–800 mm s ⁻¹ , and Set 3: 100 W–1200 mm s ⁻¹ ) were employed to fabricate peanut-shaped auxetic structures, which were subsequently tested at temperatures of −20 °C, 25 °C, 100 °C, and 200 °C. Digital image correlation was employed for detailed strain analysis, while the fabricated auxetic structures were further characterized using x-ray diffraction, scanning electron microscopy, and Vickers hardness testing. The experimental results were validated through thermomechanical finite element simulations, followed by a parametric study to examine the influence of geometric parameters and testing temperature on the mechanical performance of the auxetic structures. According to the test results, Set 3 exhibited the highest peak force, whereas Set 1 demonstrated the lowest. Furthermore, Set 2 achieved maximum elongation at 200 °C. The investigated structures exhibited auxetic behavior under varying testing temperatures and processing parameters. The structure fabricated with Set 1 parameters demonstrated the highest auxetic response, whereas that produced with Set 3 parameters exhibited the lowest. The parametric study revealed that the mechanical properties of auxetic structures are influenced by the auxetic unit cell dimensions, pattern distribution, and testing temperature while also being sensitive to processing parameters, thus offering the potential for tailored optimization and guiding future material design.