Analytical modeling of deformed plain woven thermoplastic composites

This research addressed the deformation predictability of post-manufactured, plain weave architecture composite panels. Often times during the production of deep drawn composite parts, a fabric preform experiences various defects ranging from local buckling, interply slip, intraply shear, delamination, overheating and thickness variations. Minimizing these defects is of utmost importance for mass produceability in a practical manufacturing process. Considering intraply shear as the enabler for panel alteration, characterization of the local trellis angles can lead to better understanding of defects. The approach is analogous to forming limit diagrams used as a design tool in the sheet metal industry when developing new products to predict draw depth based upon the strain characteristics of the material. There were two broad objectives of this research. The first objective was to adapt a grid strain analysis technique to characterize surface deformations. These deformations were related to the extent of local trellis shearing and were used as a validation tool. The second objective was to generate a predictive model with the use of a bilinearly blended Coons patch to predict formability for the top surface of a composite panel. This model was generated independently of the results obtained from the grid strain analysis. By implementing this analytical, predictive model, it was possible to characterize formability of a composite part using nothing more than geometry of tooling, material thickness and imposed boundary conditions.