For many engineering applications, the energy-absorption capacity has become one of the major concerns in the selection of materials and the design of structures. It is of particular importance for materials and structures subjected to collision or impact loads during service. In this thesis, based on an extensive literature review on the large deformation and energy-absorption capacity of composite materials, a new class of cellular textile composites with high energy-absorption capacity is developed and studied experimentally and theoretically....[ Read more ]

For many engineering applications, the energy-absorption capacity has become one of the major concerns in the selection of materials and the design of structures. It is of particular importance for materials and structures subjected to collision or impact loads during service. In this thesis, based on an extensive literature review on the large deformation and energy-absorption capacity of composite materials, a new class of cellular textile composites with high energy-absorption capacity is developed and studied experimentally and theoretically.

Fabrication and formability of thermoset and thermoplastic textile composites, including corresponding 3D grid-domed cellular structures, have been studied. The processing parameters have been optimized in terms of the energy absorption capacity of the material. For thermoplastic textile composites, two impregnation methods (by PET/PP co-knitted and PET/PP sandwiched structures, respectively) have been implemented and compared.

The mechanical properties and the large deformation mesoscopic mechanisms of the textile composites with thermoset and thermoplastic matrix have been investigated and compared. It is shown that nylon/polyester thermoset textile composites display an ideal bi-linear stress-strain relationship, whilst the PET/PP co-knitted thermoplastic textile composites display strong non-linear and anisotropic characteristics. The effects of the fabric structure, fiber content, the fiber surface treatment and the thickness of the composite panel on the mechanical properties have been investigated. By in-situ observations of large deformation mechanisms, it is identified that the nonlinear property mainly comes from the change in the configuration of the fabric architecture during elongation for the nylon/polyester textile composite samples. For the PET/PP co-knitted textile composite samples, however, the inelastic property is attributed to the damage evolution in the matrix, the relative displacement between wales and/or courses and the sliding between wales, as well as the change in the configuration of the fabric architecture during loading. The correlation between the change in fabric architecture, the matrix damage and the material properties has also been described.

The energy-absorption behavior and mechanisms of grid-domed textile composites with two cell-configurations have been studied. In Configuration 1, the membrane-dominated large plastic deformation of truncated conical shells contributes most to the energy-absorption capacity of the grid-domed composite, as revealed by a theoretical model. Therefore, a new cell configuration, Configuration 2, has been proposed, in which each cell consists of a truncated conical shell only. Comparing with Configuration 1, the grid-domed textile composite with Configuration 2 displays a considerably higher energy-absorbing capacity, more stable deformation mode, lower peak force and almost constant magnitude of force during its large deformation process. The collapse process of a flat-topped conical shell under axial compression has been experimentally investigated. Based on the experimentally observed deformation features, an elastic deformation model and a rigid-plastic deformation model are proposed and formulated. The predictions of these models on the load-displacement and energy-absorption characteristics are in good agreement with the experimental results. The numerical results also indicate that most of the energy dissipation is resulted from the membrane deformation and its proportion increases as the deformation progresses. The effects of the parameters, such as cell height, diameter ratio of cell-top to cell-bottom, semi-apical angle of the truncated conical shell, cell wall area and cell density have been experimentally studied, leading to an optimal design of the cell geometry.

It has been demonstrated that the cellular textile composites studied in this thesis possess higher specific energy-absorption capacity and better impact performance compared to polymer foams, so that they will serve as ideal candidates for energy absorption purpose.