PSI - Issue 17

Michał Kwietniewski et al. / Procedia Structural Integrity 17 (2019) 154 – 161 Michał Kwietniewski / Structural Integrity Procedia 00 (2019) 000 – 000

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methyl caproate, LDI). The physicochemical properties of these unique series of polyurethanes were investigated. It was found that the PEO containing polyurethanes were generally weak, tacky amorphous materials. In contrast, the PCL polyurethanes were relatively strong, elastomeric materials which ranged from completely amorphous to semicrystalline as noted by differential scanning calorimetry. The PCL containing polyurethanes exhibited increasing tensile strength, modulus, and ultimate strain with increasing PCL molecular weight because of increasing phase separation and increasing soft segment crystallinity. The observed diversity in material properties showed that these polyurethanes may be useful for a wide range of applications. In the paper by Prisacariu and Scortanu (2011) the influence of ethylene glycol, triethanol amine and a rigid polyol on the tensile strength, elongation at break and tear resistance of a microcellular elastomer (used in RIM technology), was studied using multiple linear regression analysis. It was found that the moulded density has the biggest influence on the tensile strength; so that the tensile strength is increased by the ethylene glycol and rigid polyol content, while triethanol amine reduces it. All the chain extenders studied have a negative influence on the elongation at break. Similarly, the moulded density and the ethylene glycol content have a beneficial effect on the tear resistance, while triethanol amine and the rigid polyol reduce this property. In addition, also polymers themselves with special microstructures and special inorganic crystals like silicon dioxide, zeolites, and elemental metals are the auxetic molecules. It is a simple molecular design approach based on site-connectivity driven rod reorientation in main chain liquid crystalline polymers to achieve auxetic behaviour (Fig. 9). Under a tensile force, the extension of the flexible spacers in the polymer main chain will force the laterally attached rods from a position roughly parallel to the tensile axis to a position normal to it and push the neighbouring chains further apart what has been described in Mir et. al. (2014).

Fig. 9. Arrangement of laterally attached rods in a main chain liquid crystalline polymer; Yang et. al (2004)

4. Summary

As it can be found in paper by Peel (2007) elastomer ‐ matrix composites show promise for high Poisson's ratio and negative Poisson's ratio (auxetic) applications due to high orthotropy. Especially auxetic composites have attracted considerable attention in recent years and have demonstrated a high potential of applications in different areas due to their wonderful properties as compared to non-auxetic composites. In the paper by Zhou (2016) a three dimensional (3D) auxetic textile structure previously developed was used as reinforcement to fabricate auxetic composites with conventional polyurethane (PU) foam. Both the deformation behavior and mechanical properties of the auxetic composites under compression were analyzed and compared with those of the pure PU foam and non auxetic composites made with the same materials and structural parameters but with different yarn arrangement. The results show that the negative Poisson's ratio of composites can be obtained when suitable yarn arrangement in a 3D textile structure is adopted. The results also show that the auxetic composites and non-auxetic composites have different mechanical behaviors due to different yarn arrangements in 3D textile structure. While the auxetic composites behave more like damping material with lower compression stress, the non-auxetic composite behaves more like stiffer material with higher compression stress. It is expected that this study could pave a way to the development of innovative 3D auxetic textile composites for different potential applications such as impact protection. As it was shown different elastomeric (even foamed) materials can be applied in various composite structures. Different types of polymer chain structure and the influence of the chemical structure of these macromolecules on the strength properties of polymeric materials were presented in the paper. These features are extremely important in the process of selecting or designing the polymer constituting the warp of the auxetic fabric.