Viscoelastic–plastic cyclic compaction response and microstructural normalization of single-layer woven fabrics in vacuum infusion

In Vacuum Infusion (VI), cyclic compaction before infusion enhances fiber volume fraction by driving the microstructural normalization of the fabrics. Because mechanical testing machines cannot replicate flexible tooling mechanics, this study characterizes the in-situ viscoelastic–plastic cyclic compaction response of a single-layer 2/2 twill glass woven fabric and optimizes key cyclic compaction parameters. Using an automated VI workstation equipped with a high-resolution thickness measurement system (1μm resolution), we subjected the dry fabric to 15 compaction cycles at 2 kPa/s and 4 kPa/s, followed by a 20-min degassing phase. Minimum compaction and maximum relaxation thicknesses exhibited exponential decay across cycles, and no statistically significant overall between-rate difference was detected for either thickness measure. The 4 kPa/s rate induced higher elastic and lower time-dependent deformation during compaction than the 2 kPa/s rate, while creep and relaxation deformations stabilized rapidly without significant rate dependence. To improve efficiency while maintaining normalization, 15 cycles at 4 kPa/s are recommended. Under ideal control, optimizing compaction holding durations (40 s for cycles 1–10; 30 s for cycles 11–15) and pairing them with a constant 10 s relaxation hold is projected to save 660.3 ± 11.1 s. Ultimately, cyclic compaction and degassing yield a fully normalized fabric architecture suitable for subsequent resin infusion, establishing a robust characterization methodology for diverse reinforcements.