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Thermo-mechanical behavior of a Plain Woven Textile Composite Material: Experimental and Numerical Studies

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Title
Thermo-mechanical behavior of a Plain Woven Textile Composite Material: Experimental and Numerical Studies
Author
Choi, Heeyoung
Advisor
Ji, Wooseok
Issue Date
2017-02
Publisher
Graduate School of UNIST
Abstract
This thesis is concerned with a combined experimental and numerical investigation of the thermal and mechanical response of a plain woven textile composite material. In order to experimentally investigate the thermo-mechanical behavior of the textile composite, panels are first made using the vacuum assisted resign transfer molding (VARTM) process. Then, specimens are cut from the panels according to the ASTM standard. Tensile tests are performed on the specimens at various temperatures with the directions of fiber tows aligned at 0 and 45 degrees with respect to the loading direction, respectively. Digital image correlation (DIC) technique is employed to obtain real-time full-field strain and deformation data. From the stress-strain data obtained at room temperature, basic mechanical properties of the textile composite such as stiffnesses and strengths are identified. Different failure modes are observed when the fiber tows are aligned with the loading direction and they are oriented at 45 degrees. It is imparted, from the tests results with different ranges of temperature, that the thermo-mechanical behavior of the composite is greatly influenced by the thermal degradation of the matrix material. Numerical analysis is also performed using a finite element-based representative volume element (RVE) model to have an in-depth understanding of the thermo-mechanical behavior of the composite material. Optical images are taken at various sections and geometrical data of in situ fabric architecture in the composite are extensively measured to create the RVE model. Matrix properties are also measured per ASTM standard at various temperatures and it is found that the matrix exhibits strong nonlinear stress-strain response and its mechanical properties are degraded as the temperature increases. Special homogenization technique for fiber tows are employed in order to account for directionally-dependent non-linearities of the tows. In the RVE model, fiber tows are considered as a nonlinear transversely isotropic continuum. Mechanical behavior of the fiber tows in the direction transverse to the fibers is greatly influenced by the matrix material but the property in the fiber direction is mostly determined by the strong fibers. Periodic boundary conditions are applied to the RVE model to apply tensile and shear loading to the textile composite model. Using thermally degraded matrix properties, thermo-mechanical response of the plain woven textile composite material are obtained from finite element analysis (FEA) and the results agree very well with the experimental data. Different stresses and strain distributions on the fiber tows and matrix under tensile and shear loading cases are also be obtained and regions where stresses are significantly accumulated or mechanical performances are weakened are identified.
Description
Department of Mechanical Engineering
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