Flow front measurements and model validation in the vacuum assisted resin transfer molding process

Abstract

Through‐thickness measurements were recorded to experimentally investigate the through thickness flow and to validate a closed form solution of the resin flow during the vacuum assisted resin transfer molding process (VARFM). During the VART'M process, a highly permeable distribution medium is incorporated into the preform as a surface layer and resin is inftised Into the mold, under vacuum. During Infusion, the resin flaws preferentially across the surface and simultaneously through the thickness of the preform, giving rise to a three dimensional‐flow front. The time to fill the mold and the shape of the flow front, which plays a key role in dry spot formation, are critical for the optimal manufacture of large composite parts. An analytical model predicts the flow times and flow front shapes as a function of the properties of the preform, distribution media and resin. It was found that the flow front profile reaches a parabolic steady state shape and the length of the region saturated by resin is proportional to the square root of the time elapsed. Experimental measurements of the flow front in the process were carried out using embedded sensors to detect the flow of resin through the thickness of the preform layer and the progression of flow along the length of the part. The time to fill the part, the length of flow front and its shapes show good agreement between experiments and the analytical model. The experimental study demonstrates the need for control and optimization of resin injection during the manufacture of large parts by VARTM.

Analysis of pressure profile and flow progression in the vacuum infusion process

“…The majority of VI-related experimental work reported in the literature is focused on either measuring the thickness variation due to the reinforcement compliance behaviour [9,10] or measuring the lead-lag distance in the VI process with a distribution medium on top i.e. in the SCRIMP T M process [11,12]. In fact, the only experimental effort to measure pressure profiles and fill-times was reported by Correia [6].…”

The Effect of Fiber Preform on the Mold Filling Stage of Resin Transfer Molding

“…FIGURE IV shows that the pressure versus distance from center of the circle. At the inlet boundary, the pressure is the largest, 6.16×10 5 Pa. At the outlet boundary, the pressure is 0 (relative to atmosphere pressure). From the figure, it also can be found pressure decrease slower when it is farther to the center of the circle plate.…”

“…For the permeability of 10 -10 m 2 , the pressure in the injection port require about 6.16×10 5 Pa to accomplish the filling.…”

“…The similar work also done by Bender et al [4], they investigated a flow rate control system. Mathur et al [5] did some experimental measurement on the through thickness flow, obtained the flow front evolution and gave a contrast with analytical model. The results obtained by analytical model agree well with experimental results.…”

Permeability characterization of stitched carbon fiber preforms by fiber optic sensors

“…In addition, several studies deal with the subject of transverse permeability [18][19][20][21], that needs to be characterized especially in the case of processes like as VARTM process or the resin film infusion (RFI) [22]. In fact, conversely to RTM, these processes exhibit significant through-the-thickness impregnation gradients [23,24] that may affect the total fiber impregnation, the filling time and, consequently, the dimensions and mechanical properties of the final composite part. In addition, due to the use of the flexible vacuum bag and, consequently, due to the variation of compaction pressure, the part thickness and local permeability of the fibre preform change during resin injection as function of time and space [25].…”