Effect of Double-Vacuum-Bag Process on the Void Evolution in Composite Laminates

Voids are a common defect in the manufacturing process of composite materials, which can reduce the mechanical properties of components. As an out-of-autoclave (OoA) technology, double-vacuum-bag (DVB) process can achieve low-cost manufacturing of composite materials with low void content. This paper investigated the effect of DVB process on void evolution and laminate properties during the curing process of composites. Different dwelling temperatures were applied, and a single-vacuum-bag (SVB) process was designed as the experimental control group. The curing cycles were completed and the laminates were rapidly cooled at selected time points. This work used a microscope to take cross-sectional images of samples, for statistical analysis of void morphology and void growth behavior. Besides, the density and fiber volume fraction of composite materials were measured by Archimedes method and combustion method. The experimental results show that as the curing cycle progressed, the void content of laminate produced by DVB process continued to decrease. Compared with the SVB process, the dual vacuum environment of the DVB process can timely discharge the stagnant air in the prepregs, thereby reducing the void content, which is at the same level of the composite materials manufactured by hot press with 0.6 MPa.