The Effects of a Low Areal Weight Inter-layer Tackifier on Saturated Permeability of Carbon Fabrics

Accurate preform permeability characterization for liquid composite molding is paramount for producing process models, an understanding of resin saturation, and injection and outlet port placement. While, recent advances in computational tools have improved predictive methods for defining permeability, these techniques still lack robustness due to the complexity of advanced fiber reinforcements and the variables induced throughout the manufacturing process. Experimental techniques offer accurate methods for characterization and can detect trends in preforms that employ specific processing additives like tougheners or various types of preimpregnation. These additives have been shown to significantly alter resin flow, surface chemistry, and ultimately bulk reinforcement permeability. In this study, the saturated permeability of low areal weight inter-layer tackified preforms constructed with a four-harness satin IM7 carbon fabric were investigated. Both in-plane and through-thickness permeability measurements were made with different layups of the carbon fabric with and without the inter-layer tackifier. Additionally, the effects of a heated debulking cycle was explored through both compaction and permeability measurements. In general, the addition of tackifier was seen to reduce permeability by blocking the inter-tow flow channels. Interestingly, tackified preforms that underwent the debulking cycle showed a strong resistance to compaction and nesting, and this subsequently produced higher bulk permeability values compared to tackified preforms processed at room temperature. The debulking alleviated nesting enough to maintain inter-tow flow channels, and measurably higher permeability. Other results showed that the addition of tackifier produced a more consistent and isotropic measured permeability compared to their non-tackified counterparts. Ultimately, the study shows that preform properties may be tailored for specific liquid molding considerations by altering both tackifier content, and pre-processing.