Micromechanics of two-dimensional woven composites

The overall objective of this research was to develop a robust computational micromechanics strategy that allows reliable prediction of the hygrothermal and mechanical behaviors of two-dimensional woven composites, and to address the characteristic behaviors by comparative studies among the various weaves.; A finite element based computational micromechanics strategy was developed by addressing the specific challenges pertaining to the micromechanics analysis of 2D woven composites. The strategy consists of (1) a basic building block technique for parametrically generating 3D finite element meshes for various weaves, including plain, satin, twill and uni-weave, and (2) concise formulas derived using the “equivalent sub-cell” concept for specifying complex boundary conditions for the full or partial unit cell of different weaves.; A comparative study of the characteristic behaviors of plain, satin and twill weaves was conducted. The effects of woven tow architecture on the effective moduli were studied. Supported by extensive computational micromechanics analyses, simple formulas based on the “rule of mixtures” analysis were proposed for the effective moduli. Various investigative techniques were used to identify the dominant characteristics that determine specific effective properties.; Elastic progressive failure behavior was modeled and compared for different weaves. Comparisons of the damage mechanisms in the plain and satin weaves indicated significant similarities of damage behaviors in the comparable regions for the two weaves. Plasticity-induced nonlinearity was studied for the plain weave to understand the effect of tow architecture on the development of local plastic deformations. The results showed that plastic deformation in the polymer matrix woven composite can develop early in the load history at the interlaced region even for low waviness weaves.; Transient moisture diffusion was modeled to examine the effects of the woven microstructure on the diffusion behaviors. The effect of the irregularity of fiber distribution in the matrix on the effective diffusivity was modeled using a simple “bi-zone” approach. Simulations of moisture diffusion tests were made for 3-ply satin/uni-weave hybrid composites using fiber volume fraction values determined from image analysis. Good agreement was found between the analysis results and the experimental results.