Experimental investigation of fiber sizing-test fluid interaction for in-plane permeability measurements of continuous fibers
Many manufacturers are using liquid composite molding (LCM) to manufacture composites because of its simplicity and cost effectiveness. This generic process includes techniques such as vacuum assisted resin transfer molding (VARTM), resin transfer molding (RTM), and Seemann composite reaction infusion molding (SCRIM). VARTM is most commonly used due to its low tooling cost and ease of use. One of the most important factors that affect the manufacturability of composite parts is permeability. Permeability usually affects resin flow within fibers; hence, many researchers have placed importance on the measurement of this factor in various studies. Alternate test fluids such as corn syrup, silicon oil and motor oil are being used to calculate permeability, since they are cheaper, easy to clean, and are not volatile like resins. Permeability is generally affected by fiber sizing-test fluid interaction, fiber volume fraction, and fiber orientation. In the present study, permeability effects due to fiber chemical coating or sizing were investigated using VARTM. Experiments were conducted by inducing high- and low-viscosity corn syrup and silicon oil through uni-directional glass fibers, bi-axial glass fibers, and two types of uni-directional carbon fibers, with and without sizing. Darcy’s law was used to calculate permeability. Significant permeability differences found using fibers with and without sizing are reported. Separate saturated flow rate measurements for one of the uni-directional carbon fibers and uni-directional glass fibers, both sized and unsized, were carried out by infusing corn syrup and silicon oil with similar viscosities. It was found that, over time, corn syrup displayed a gradual decrease in flow rate for saturated fiber material for constant vacuum infusion. From previous research studies, the flow rate history in the RTM process showed two stages: initial rapid flow and steady-state flow. However, in the VARTM process, the cumulative mass vs. time plot was linear. The corresponding flow rate vs. time plot showed a high initial flow rate but was decreased with time when corn syrup was used for both uni-directional glass and carbon fibers, with and without sizing. This effect was not observed in the case of silicon oil. It was concluded that corn syrup should be used with caution as a test fluid for permeability measurements until further investigations can be made.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering