| Woven composites have showed great potentials as a valuable alternative to sheet metals for high-strength and low-weight products. However, wide applications of these materials have been hampered due to the lack of low-cost fabrication methods. As the first necessary step to numerically analyze and then optimize feasible manufacturing processes, material characterization of woven composites is studied here. The key challenges of modeling this class of materials are: (a) various scales in length involved, (b) shear dominated deformation, and (c) the resulting anisotropic material behavior. This dissertation presents a framework for the material characterization of woven composites by defining the equivalent material properties in a local non-orthogonal coordinate system and by providing a transformation from this local non-orthogonal coordinate system to the global orthogonal coordinate system. The material properties in the constitutive law can be obtained through a pure numerical approach or an experimental fit. For the pure numerical approach, the homogenization method is employed to investigate the meso-microscopic material behavior of the composite, and the finite element method is applied for characterizing the macro-scale material behavior. In the experimental approach, the equivalent material properties are directly obtained by fitting some experimental data such as uni-axial tensile test and bias extension test.; The presented material characterization framework is validated by comparing numerical results of bias extension and trellising simulations with experimental data. Very good agreements have been obtained. The normalization for trellising test is then investigated from the energy point of view and by using the developed non-orthogonal constitutive model. Thermo-forming simulation of a plain weave composite further demonstrates the feasibility and efficiency of this framework. By using the contact status between the tooling and the composite blank as a switch for material properties under high or low temperatures, the complicated thermo-displacement coupled analysis is greatly simplified.; The proposed material characterization framework can capture the anisotropic material behavior of woven composites under various deformation modes. It builds up a solid foundation for the future work on the optimization of the thermo-forming process, which can lead to a complete set of design tools for the thermoforming of woven composites, and greatly expand their applications. |
