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Material and Geometric Analysis of Structures Subjected to Large Deformation
AuthorFerranto, Justin Sequoia
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The two major focuses of this dissertation are: (1) Studying the structural behaviors of hyper-elastic membranes subjected to extremely large deformation. These membranes are used in a reconfigurable tooling system (RTS) which was under development during the course of this study. (2) Establishing a continuum constitutive model for fabric materials under in-plane large deformation through theoretical and numerical analyses. This model may also be applied to study a class of materials which involve significant internal structure reconfiguration during deformation.The RTS allows quick onsite fabrication of high temperature composite parts. RTS applications include rapid onsite repair of aircraft components. The RTS uses a hyperelastic membrane as an interface between the state-change material and model. This membrane may be subjected to 800% engineering strain during operation. In this part of the study, material properties of the membranes have been characterized through three tests: simple tension, equal biaxial tension and planar tension. Nine-term Money-Rivlin constants are obtained through data regression. Finite element simulations have been conducted to simulate the deformed shapes of a membrane around several representative geometries under various vacuum pressure and constraint conditions. Experimental results have been compared with predictions from finite element simulations. This study contributes to understanding the behavior of membrane structures under large deformations in general; the results are used to generate design guidelines for RTS applicability.Fabric materials are widely used in industry for numerous applications. They exhibit a meso-scale complexity and involve significant internal structure reconfiguration during large deformation, which prohibits the direct application of the theory of continuum mechanics when studying these materials. In the second part of this work, a unique meso-scale FEA model, utilizing new modeling techniques and boundary conditions, is developed. This model can be used to simulate the weaving/loom process, and to predict the mechanical behaviors of a representative unit of fabric subjected to multi-axial large deformations. This model has also been used to examine the mechanism of fabric internal structure reconfiguration during deformation under various load paths. An energy based continuum model for plain weave fabric is developed, where a sinusoidal shape function is used to describe the yarn waviness before and after deformation. Castigliano's theorem is applied to determine the interactions between yarns. The model presented has been validated with the FEA model, and compared with third party experiments. Favorable agreements have been found. This model has the potential for developing a general constitutive relationship for a broad class of materials which involve significant internal structure reconfiguration during deformation