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Title: Study of 3D auxetic textile reinforced composites
Authors: Zhou, Lin
Degree: M.Phil.
Issue Date: 2018
Abstract: Auxetic materials are a novel type of materials with negative Poisson's ratio (NPR), which explore a new direction to improve mechanical properties and mechanisms of materials. Due to their unique performance, auxetic materials have shown enormous suitable applications in various industries. Auxetic composites are an important category of auxetic materials, which have been proven to have many enhanced properties compared with non-auxetic composites, such as enhanced impact resistance, increased energy absorption ability and improved mechanical indentation resistance. These properties have led to many interesting applications of auxetic composites including protective protection, aerospace industry and biomedical area. Although the auxetic laminates have been designed and developed in recent years, some limitations and gaps still exist. The concept of auxetic effect in composites is only studied in two-dimensional space. In addition, the developed 3D auxetic textile structure for composites reinforcement is still at a primary stage and has not further produced composites. So far systematic manufacture and investigations on the 3D auxetic textile reinforced composites are still missing. In this study, 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 behaviors 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 showed that the negative Poisson's ratio of composites could be obtained when suitable yarn arrangement in a 3D textile structure is adopted. The results also showed 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.
A further study on their mechanical properties under low velocity impact is presented. Both single-time and repeating impact tests were conducted under different impact energy levels ranging from 12.7 J to 25.5 J. Results showed that the 3D auxetic textile composite has better impact protective performance than the 3D non-auxetic textile composite because of better transmitted force reduction and higher energy absorption capacity under single-time impact and higher structural stability under repeating impacts. Moreover, the stress hardening effect under impact was observed for the auxetic composite, which could enhance its impact protection properties with increasing of impact velocity. This study systematically investigated 3D auxetic textile reinforced composite. The results of this study deepen the understanding of 3D auxetic textile reinforced composites against with non-auxetic ones under compression and impact loading, which will assist in the development of applications for 3D auxetic textile composites. This work has shown further potential applications for auxetic composites to be applied under low-velocity impact. In summary, this study brings a deeper understanding of 3D auxetic textile reinforced composites based on the previous study and provides a guidance for making 3D auxetic composites using non-auxetic materials. Overall, 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.
Subjects: Hong Kong Polytechnic University -- Dissertations
Materials -- Mechanical properties
Nanostructured materials -- Mechanical properties
Materials -- Elastic properties
Nanostructured materials -- Elastic properties
Pages: xviii, 144 pages : color illustrations
Appears in Collections:Thesis

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