Isothermal compaction-creep-recovery behavior and statistical void analysis of prepregs under various process parameters

Abstract

In this study, the compaction-creep and permanent deformations of multi-layered (4, 8 and 12) glass/epoxy prepreg specimens have been investigated at different temperatures and compaction pressures, and at a constant compaction speed of 1 mm/min. The complete deformation history of specimens during compaction has been recorded from the stress-free state to the fully consolidated condition. It is noted that under similar pressure conditions, increasing the number of prepreg layers resulted in a decrease in the degree of compaction and associated creep response. At 90 °C, higher percentages of reinforcement compaction and permanent deformation were observed, due to low resin viscosity and increased resin bleed-out. X-ray computed tomography (XCT) aided geometrical models were developed to analyze the level of voiding as well as the microstructural changes in uncured specimens following the compaction-creep process. A decrease in the number of interlaminar voids and an increase in the level of intralaminar voiding was observed at higher compaction pressures and temperatures. Also, the void content in cured specimens were studied analytically. The lowest void volume fraction (VVF) was measured at 65 °C and 0.3 MPa compared to other temperatures in all layer specimens. More importantly, lower VVF was measured in 8-layer specimens than 4- and 12-layer specimens. The results highlight the importance of understanding the thermo-mechanical compaction-creep stage during the processing cycle and its effect on determining the overall void content in the resulting manufactured part.