Statistical characterization of fiber permeability for composite manufacturing

Resin transfer molding (RTM) is considered one of the most promising composite fabrication techniques because of its relatively low equipment and tooling costs, short cycle times, and excellent design flexibility. Yet several technical issues impede wider application for this process. One of those issues is the measurement and characterization of fiber preform permeability, which plays a key role in process design and control. In this study, an automatic permeability measurement apparatus with automatic data acquisition and processing capabilities has been developed to improve measurement accuracy and reliability. Four major factors and their effects on permeability for a knitted and a woven fabric preforms are investigated. Design of experiments, ANOVA analysis, and distribution characterization techniques are used to analyze the permeability-influencing factors and statistical properties of fiber preform permeability. It is found that the fiber preform permeability values vary significantly for different mold shapes and fiber handling conditions. It is also revealed that permeability values for both fabrics follow normal distributions, even though their means and variances are different. These results can be used to better understand the behavior of the RTM process and to improve process design and control.