Effect of debulking cycles on the fiber volume fraction of 3D fabrics for vacuum assisted resin infusion process

Liquid composite molding (LCM) processes are considered one of the cost-effective out-of-autoclave manufacturing techniques with the capability of producing medium to large size composite structures. The vacuum assisted resin transfer molding (VARTM) or the resin infusion process belongs to the LCM family, with the ability to produce largescale structures using only vacuum pressure. Due to high through thickness stiffness of 3D reinforcements, achieving desirable high fiber volume fraction using the VARTM process is challenging. De-bulking before resin infusion is a common process for 2D fabrics, however single de-bulking cycle may not have significant impact on improving fiber volume fraction of 3D fabrics. Multiple cycle compaction of 3D fabrics can improve fiber volume fraction significantly. In this study, we investigate the effect of cyclic loading on fiber volume fraction, internal fabric structure, and permeability of two different types of 3D fabrics. We have utilized X-ray micro computed tomography (XCT) technique to characterize the 3D reinforcements. An in-situ compaction fixture was used to compact the reinforcements to target thickness through cyclic loading. The internal reinforcement architecture changes were captured using 3D image slices obtained using the XCT machine. The permeability values were computed using the virtual voxel models generated from the XCT images. The results show that 5-10% increase in the fiber volume fraction of 3D reinforcements was achievable after multiple de-bulking cycles. The peak stresses decreased significantly after first few cycles and became repeatable after cycles greater than five. The peak stress after 15^th cycle was found to be approximately half the peak stress obtained after first cycle. The de-bulking cycles improved fiber volume fraction considerably, however the permeability decreased as the fiber volume fraction was increased.