| The objective of this study is to develop micromechanical models for predicting the stiffness and strength properties of textile composite materials. Micromechanical analysis of textile composites is possible due to the presence of a repeating unit-cell or representative volume element. The unit-cell is assumed to span the material continuously in all three dimensions. On the microscale--comparable to the scale of the unit-cell--the composite is heterogeneous due to the presence of the reinforcing yarn and the matrix. However, on the macroscale--comparable to the structural scale--the composite is assumed to be homogeneous and orthotropic. The homogeneous composite properties are then predicted from the constituent material properties and the yarn geometry.; The highlight of this study is a systematic analysis of issues involved in the finite element based micromechanics of textile composites. The unit-cell is discretized with three-dimensional finite elements, and periodic boundary conditions are imposed between opposite end-faces of the unit-cell. Six linearly independent deformations are applied to the unit-cell. From the forces acting on the unit-cell for each of the six deformations, the composite stiffness matrix is obtained. A similar procedure is followed to determine the composite coefficients of thermal expansion. The numerical procedure was tested by applying it for simple examples, for which the results are known. The numerical results were also compared with existing models for textile composites. In both cases, the results compare very favorably. The finite element procedure is extended to compute the thermal residual microstresses and to estimate the initial failure envelope for the textile composite.; An independent finite element micromechanical analysis, analogous to the above, is presented for thin textile composite structures with few unit-cells in the thickness direction. In that case, the composite is modeled as a homogeneous plate to predict the plate stiffness coefficients and plate coefficients of thermal expansion. It was shown the plate properties could not be predicted from the corresponding three-dimensional properties.; In addition, an approximate analytical procedure is presented to estimate the composite thermo-elastic constants. The procedure called the Selective Averaging Method is based on a judicious combination of stiffness and compliance averaging. The method is fast and easy to implement, and suitable for parametric studies. |
