Vacuum-assisted resin transfer molding is a promising technique for making large and complex composite structures. However, void formation remains a problem. Two primary contributors to void formation, nonuniform resin flow and continuous evaporation of resin under low pressure, were experimentally studied. Improved pressure control at the vent is proposed to reduce the void content of the manufactured composite material: at the start of the resin infusion, the pressure at the vent is set to the full vacuum of the equipment, while after the resin has saturated all of the reinforcements, the pressure at the vent is increased slightly. The full vacuum at the start of infusion avoids air entrapment, and the slightly higher pressure later in the process restrains the resin evaporation. A lower void content is obtained. POLYM. COMPOS., 36:1629-1637

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