In-Plane Behavior of Auxetic Non-Woven Fabric Based on Rotating Square Unit Geometry under Tensile Load

Sensors Based on Auxetic Materials and Structures: A Review

Auxetic materials exhibit a negative Poisson's ratio under tension or compression, and such counter-intuitive behavior leads to enhanced mechanical properties such as shear resistance, impact resistance, and shape adaptability. Auxetic materials with these excellent properties show great potential applications in personal protection, medical health, sensing equipment, and other fields. However, there are still many limitations in them, from laboratory research to real applications. There have been many reported studies applying auxetic materials or structures to the development of sensing devices in anticipation of improving sensitivity. This review mainly focuses on the use of auxetic materials or auxetic structures in sensors, providing a broad review of auxetic-based sensing devices. The material selection, structure design, preparation method, sensing mechanism, and sensing performance are introduced. In addition, we explore the relationship between the auxetic mechanism and the sensing performance and summarize how the auxetic behavior enhances the sensitivity. Furthermore, potential applications of sensors based on the auxetic mechanism are discussed, and the remaining challenges and future research directions are suggested. This review may help to promote further research and application of auxetic sensing devices.

In-Plane Deformation Behavior and the Open Area of Rotating Squares in an Auxetic Compound Fabric

A conventional compound fabric was used to develop a modern, multifunctional material with an auxetic behaviour and a tailored open area for particle filtration. Such material was produced using traditional textile technology and laser cutting, to induce a rotating squares unit geometry. The behaviour was investigated of three different rotating unit cell sizes. The laser slit thickness and the length of the hinges were equal for all three-unit cells. The tensile properties, Poisson’s ratio and auxetic behaviour of the tested samples were investigated, especially the influence of longitudinal displacement on the fabric’s open area and the filtered particle sizes (average and maximum). Results show that the developed compound fabric possesses an average negative Poisson’s ratio of up to −1, depending on the applied auxetic geometry. The larger rotating cell size samples offer a higher average negative Poisson’s ratio and a higher breaking strength due to the induced slits. The findings highlight the usefulness of patterned cuts in conventional textile materials to develop advanced auxetic textile materials with tailored geometrical and mechanical properties.

Computational Fatigue Analysis of Auxetic Cellular Structures Made of SLM AlSi10Mg Alloy

In this study, a computational fatigue analysis of topology optimised auxetic cellular structures made of Selective Laser Melting (SLM) AlSi10Mg alloy is presented. Structures were selected from the Pareto front obtained by the multi-objective optimisation. Five structures with different negative Poisson’s ratios were considered for the parametric numerical analysis, where the fillet radius of cellular struts has been chosen as a parameter. The fatigue life of the analysed structures was determined by the strain–life approach using the Universal Slope method, where the needed material parameters were determined according to the experimental results obtained by quasi-static unidirectional tensile tests. The obtained computational results have shown that generally less auxetic structures tend to have a better fatigue life expectancy. Furthermore, the fillet radius has a significant impact on fatigue life. In general, the fatigue life decreases for smaller fillet radiuses (less than 0.3 mm) as a consequence of the high-stress concentrations, and also for larger fillet radiuses (more than 0.6 mm) due to the moving of the plastic zone away from the edge of the cell connections. The obtained computational results serve as a basis for further investigation, which should be focused on the experimental testing of the fabricated auxetic cellular structures made of SLM AlSi10Mg alloy under cyclic loading conditions.

Using Finite Element Approach for Crashworthiness Assessment of a Polymeric Auxetic Structure Subjected to the Axial Loading

Polyurethane foams are one of the most common auxetic structures regarding energy absorption enhancement. This present study evaluates the result reliability of two different numerical approaches, the H-method and the P-method, to obtain the best convergence solution. A polymeric re-entrant cell is created with a beam element and the results of the two different methods are compared. Additionally, the numerical results compare well with the analytical solution. The results show that there is a good agreement between converged FE models and the analytical solution. Regarding the computational cost, the P-method is more efficient for simulating the re-entrant structure subjected to axial loading. During the second part of this study, the re-entrant cell is used for generating a polymeric auxetic cellular tube. The mesh convergence study is performed on the cellular structures using the H- and P- methods. The cellular tube is subjected to tensional and compressive loading, the module of elasticity and Poisson’s ration to calculate different aspect ratios. A nonlinear analysis is performed to compare the dynamic response of a cellular tube versus a solid tube. The crashworthiness indicators are addressed and the results are compared with equivalent solid tubes. The results show that the auxetic cellular tubes have better responses against compressive loading. The primary outcome of this research is to assess a reliable FE approach for re-entrant structures under axial loading.

Comparison of ıncisional hernia models ın rats: an experimental study

PURPOSE

Incisional hernia repair is a frequently performed operation worldwide. In this experimental study, our aim is to present the incisional hernia model after creating midline laparotomy and several type of defects on abdominal wall of the rats. Thereby, the method determined here may be used in future experimental incisional hernia repair studies.

METHODS

After approval, 32 male rats were randomly seperated into 4 groups of 8 animals each, and were operated to form an incisional hernia; Sham group, 5 cm incision group, 5 cm incision plus capitonnage group, and 5 cm incision plus 2 × 4 cm muscle excision group, respectively. On the 28th postoperative day after killing, the abdominal anterior wall of rats were removed for histopathological and biomechanic examination.

RESULTS

The incisional hernia size was found to be statistically different in at least one group (p = 0.001). The incisional hernia size in Group 4 was found to be significantly higher than Group 2 (p = 0.001). When the tension and elongation values were examined, there was a difference in at least one group (p < 0.001 and p = 0.029, respectively). Histopathological examination shows that the degree of inflammation and fibrosis varies significantly (p = 0.001 and p = 0.002, respectively).

CONCLUSION

This study has lead us to believe that the rat model created by applying muscle excision from the midline of the abdomen is the ideal incisional hernia model that can be used in future experimental incisional hernia studies.