Development of composite auxetic structures for civil engineering application

Auxetic materials are a class of non-conventional materials having negative Poisson's ratio. They expand laterally when axially loaded or laterally shrink when compressed. Due to its counterintuitive behaviour, auxetic materials possess enhanced properties that could be beneficial for many specific applications. This thesis aimed to develop such a class of auxetic materials from braided composite rods which can be beneficial for civil engineering applications as a strengthening materials. The developed auxetic structures can be reinforced into either for existing structural elements or for newly built one. Novel macro auxetic structures were developed from core fibre reinforced braided composite rods based on missing rib or lozenge grid and re-entrant hexagon or bow-tie auxetic structural design. The developed structures tested under tensile loading to study their tensile and auxetic behaviour. The auxetic behaviour was studied thorough images taken during tensile loading. Also, the auxetic and tensile behaviour of the developed structures were studied by varying their structural and material parameters. Developed auxetic structures exhibits negative Poisson's ratio and it is mainly depends up on structural parameters. The Poisson's ratio of the developed auxetic structures were studied by suitable analytical model either by existing model or by using newly developed model. These analytical models could be useful to predict the Poisson's ratio of the developed auxetic structures accurately. In addition to analytical model, the FE solver DIANA was used to develop a numerical modelling to predict the tensile and auxetic behaviour. The developed numerical model was accurate to predict the tensile and Poisson's ratio of the structures. In addition, the auxetic structures were reinforced into the masonry wall specimens, which is built by cement hollow bricks. The reinforced masonry wall specimens were tested under three point flexural loading and the results were compared with plain grid (commercial design) reinforced masonry wall. The auxetic structures strengthened walls performed well under flexural load compared to plain grid reinforced wall, but the crack level was more for auxetic structures reinforced wall due to its lateral expansion. This research works opened novel opportunity to use auxetic materials in the civil engineering field and created huge scope to do more research work in this area.