Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Youqi Wang / Textile composites are made from textile fabric and resin. Depending on the weaving pattern, composite reinforcements can be characterized into two groups: uniform fabric and near-net shape fabric. Uniform fabric can be treated as an assembly of its smallest repeating pattern also called a unit cell; the latter is a single component with complex structure. Due to advantages of cost savings and inherent toughness, near-net shape fabric has gained great success in composite industries, for application such as turbine blades. Mechanical properties of textile composites are mainly determined by the geometry of the composite reinforcements. The study of a composite needs a computational tool to link fabric micro- and macro-geometry with the textile weaving process and composite manufacturing process. A textile fabric consists of a number of yarns or tows, and each yarn is a bundle of fibers. In this research, a fiber-level approach known as the digital element approach (DEA) is adopted to model the micro- and macro-geometry of fabric and fabric reinforced composites. This approach determines fabric geometry based on textile weaving mechanics. A solver with a dynamic explicit algorithm is employed in the DEA. In modeling a uniform fabric, the topology of the fabric unit cell is first established based on the weaving pattern, followed by yarn discretization. An explicit algorithm with a periodic boundary condition is then employed during the simulation. After its detailed geometry is obtained, the unit cell is then assembled to yield a fabric micro-geometry. Fabric micro-geometry can be expressed at both fiber- and yarn-levels. In modeling a near-net shape fabric component, all theories used in simulating the uniform fabric are kept except the periodic boundary condition. Since simulating the entire component at the fiber-level requires a large amount of time and memory, parallel program is used during the simulation. In modeling a net-shape composite, a dynamic molding process is simulated. The near-net shape fabric is modeled using the DEA. Mold surfaces are modeled by standard meshes. Long vertical elements that only take compressive forces are proposed. Finally, micro- and macro-geometry of a fabric reinforced net-shape composite component is obtained.

So far the theoretical approach to weaving resistance and fabric geometry and the factors affecting it have been made for such weaves as plain, hop-sack and warp and weft faced ribs. In this work theoretical models were adopted to determine the fabric geometry and weaving resistance. Experimental and theoretical findings are in agreement. The trends of the effects on values of weaving resistance of such factors as warp elastic constant, weft tension, warp tension, the coefficient of friction of yarn against. yarn agree with the trends obtained by other workers by showing that weaving resistance increases with these factors. The results-also show that-the fabric geometry depends on warp and weft tension at-the moment of beat-up. Additionally, the change of fabric geometry across the fabric, the effect of two different let-off mechanisms,, Hattersley and WIRA/Poole, and the beaming CO processes on weaving resistance and fabric geometry were investigated. It was found that the fabric width-depends on the dynamics of fabric formation before and at the moment of beat-up.

So far the theoretical approach to weaving resistance and fabric geometry and the factors affecting it have been made for such weaves as plain, hop-sack and warp and weft faced ribs. In this work theoretical models were adopted to determine the fabric geometry and weaving resistance. Experimental and theoretical findings are in agreement. The trends of the effects on values of weaving resistance of such factors as warp elastic constant, weft tension, warp tension, the coefficient of friction of yarn against. yarn agree with the trends obtained by other workers by showing that weaving resistance increases with these factors. The results-also show that-the fabric geometry depends on warp and weft tension at-the moment of beat-up. Additionally, the change of fabric geometry across the fabric, the effect of two different let-off mechanisms,, Hattersley and WIRA/Poole, and the beaming CO processes on weaving resistance and fabric geometry were investigated. It was found that the fabric width-depends on the dynamics of fabric formation before and at the moment of beat-up. / Wool Industries Research Association