An investigation of defect evolution in foam core sandwich structures produced using vacuum assisted resin transfer moulding

In this work, a resin infusion process used by Flight Dynamics Corp. was investigated for the fabrication of low-cost composite sandwich structures. Trials were performed to establish a complete set of potential defects that could develop during the manufacture of E-glass epoxy vinyl ester sandwich panels. A series of non-destructive evaluation techniques were examined for their potential to identify two representative defects. It was found that thermography and bondline analysis were effective at detecting defects such as dry spots and incomplete resin infiltration. However, due to technical limitations of these methods visual inspection of high quality digital images proved to be the most accurate method for evaluating the specimens. The effect of these defects was also evaluated through a selection of compression tests. These tests showed that the sensitivity of this test to the presence of defects is low. A parametric study of the infusion process was performed to evaluate the potential of defect evolution under controlled conditions. The evolution of defects was most affected by the vacuum pressure level and the method for distributing resin through the thickness of the sandwich panel. As part of this study, the resin flow front was evaluated to determine the effect on the evolution of defects. A series of defect metrics were developed for a variety of resin distribution methods. In general, it was found that defect evolution due to a single variable was limited and that further evaluation of the interaction of process parameters would be useful to optimize the process