External compaction pressure over vacuum-bagged composite parts: effect on the quality of flax fiber/epoxy laminates

Vacuum bagging allows the removal of trapped air between fabrics layers, extraction of moisture and volatiles, and optimization of the fiber-to-resin ratio. However, during vacuum bagging the compaction pressure is limited to atmospheric pressure, preventing the composite reaching higher fiber volumetric contents and also allows surface porosity to arise, affecting the esthetical appearance of the composite and also its mechanical performance. While the autoclave process has shown to solve these problems, the cost of the equipment is too high for many applications. In the present work, a series of experiments are carried out by compressing unidirectional flax/epoxy vacuum-bagged laminates in a hydraulic press at different pressures. The quality of the laminates is analyzed in terms of surface finish, internal void content, and mechanical properties. The additional compaction from hydraulic pressure is shown to be very effective in improving considerably the overall quality of the composites.