The present work is a detailed study of the parameters that are involved in the characterization of fabric systems. These fabric systems are used as reinforcements in composite structures. Processes such as Resin Transfer Molding and Resin Film Infusion Molding that are used to manufacture composite structures, depend heavily on the responses of these reinforcements for their success. Fabric systems have undergone rapid changes over the years and have reached extremely advanced and complex forms. Near net shape preforms have become popular, and techniques such as multi-axial warp knitting and 3-D braiding are used to accomplish this. Further, the combination of these preforms with manufacturing processes such as Resin Transfer Molding and Resin Film Infusion Molding have resulted in the fabrication of complex composite components. The viability of these techniques for mass production has resulted in wide spread attention over recent years.

The problem of estimating the resistance of a given textile preform to the flow of resin or any fluid medium is characterized by its permeability. This quantity is dependent on the pore architecture and is therefore system dependent. The permeability of a preform changes with fiber volume fraction due to the changes in pore architecture. It is therefore critical to understand this quantity apriori, in order to ensure efficient fabrication of composite structures.

The complex nature of the pore architecture, makes permeability assessment an extremely difficult issue. Repeatability of test runs can become a difficult task as small inherent changes in the preform, can result in differences in pore structure and therefore result in different permeabilities. This study therefore tries to address this issue by incorporating a special study on the effects of statistics in permeability measurements. High costs of material handled, leads to limited testing and therefore small data bases. It is therefore important to take care while selecting the descriptive population distribution. The Student’s t Test was used in this study to generate 50% confidence bands around the steady-state permeability data obtained on tests run using Type 162 E-glass fabric. The results were then compared with a similar advancing front permeability test. The results were found to be extremely encouraging.

The following work also involves the detailed study of compaction behavior of both multi-axial warp knit and braided preforms. Power law regression fit curves were obtained on the data in order to describe the change in fiber volume fraction with respect to applied external pressure, over a range of fiber volume fractions. Since the advent of composites, weak interfacial properties such as delamination and impact resistance have caused considerable concern in the community. Recently, through the thickness reinforcing techniques such as stitching have gained importance as being an inexpensive solution to this apparent problem. The present work involves the study of the effects of stitching density on compaction and permeability. Preforms with four stitching densities were tested along with a similar batch of unstitched preform, and regression curves were fitted to the data obtained. The effects of braiding angle in 2-D, triaxially braided preforms was also studied as a part of trying to understand this ancient yet extremely interesting form textile manufacturing. Effects of thickness in 2-D, triaxially braided preforms was also examined. A small amount of work was also done to study the effects of sizing/finishing on compaction and permeability. Both, 7781, E-glass and AS4 Graphite fabric were tested.