Permeability Modeling for Single Scale and Dual Scale Fabrics and its implementation to Fabrics Undergoing Shear
Composites have found applications, right from high-end aerospace structures to naval and land-based structures. These structures are realized by manufacturing processes like, autoclave and vacuum assisted resin transfer molding (VARTM). For any composite product development, process modeling is essential that requires input of fabric permeability. Present work focusses on the permeability modeling for fabric and the effect of fabric in-plane deformation on permeability. For this, a bottom to top approach is adopted starting from fiber tow permeability to fabric layup permeability determination involving different length scales. Thus, to start with, for transverse tow permeability estimation, a semi-analytical model is proposed based on a control volume (CV) approach. Model parameters are determined from the microstructural analysis of tow through SEM. In addition, a new experimental method is proposed for transverse tow permeability determination that shows good comparison with model results. The results of this study indicate that a CV approach is more appropriate than a unit cell method due to filaments being randomly arranged in a tow. For longitudinal tow permeability determination, a 1D linear flow experimental methodology is established. Furthermore, two semi-analytical permeability models are proposed for single scale fabric ply and multiple fabric plies respectively that accounts for fabric level inter-tow and inter-ply gaps. The permeability model results are validated with experimental and numerical results that shows contribution of inter-tow and inter-ply gaps to overall permeability. Once, the tow permeability models are established, the thesis focusses on the permeability modeling for dual scale fabric characterized by saturated and wetting flow fronts due to inter-tow gaps being of the order of ply thickness (mm). The fluid flow takes place at two length scales; micro-flow at tow level and macro-flow at inter-tow gap level and for this description, requires specification of two permeability; tow and inter-tow gap permeability. For this, analytical permeability model is first proposed for dual scale UD fabric which is then extended for dual scale BD fabric by incorporating the effect of weft tow saturation. Once, the permeability model for BD fabric is established in terms of fabric architecture and processing parameters, effect of fabric in-plane deformation on permeability is studied by shearing the fabric at pre-determined shear angles. The model parameters required for permeability estimation are determined by studying the sheared fabric architecture. The model results are then compared with analytical results.