Effects of the curing process on natural frequencies and damping ratio of composite tubes

Cylindrical polymer composites are commonly used in aerospace and defense components like rocket motor casings, fuselage sections, drive shafts, and pressure vessels. These components often face dynamic loads. Ensuring good vibration characteristics is important to avoid resonance and structural fatigue. Among the manufacturing steps, the curing process significantly affects the amount of polymer cross-linking and the residual stresses at the fiber–matrix interface. This, in turn, influences how the composite responds dynamically. This study focuses on the joint effect of curing temperature, curing duration, and filament winding angle on the vibration and damping properties of intact and delaminated glass-fiber/epoxy cylindrical composites made by the filament winding method. Specimens were cured at 90°C, 120°C (as recommended by the manufacturer), and 140°C, and were wound at angles of 55°, 75°, and 85°. Controlled delamination defects were introduced during production. The vibration behavior was assessed using impact hammer modal testing. Natural frequencies were obtained through Fourier Transform of accelerometer signals, and damping ratios were calculated from the exponential decay of the response envelope. The results indicate that natural frequency rises with winding angle because of increased hoop stiffness. The introduction of edge delamination resulted in a major drop in the fundamental frequency of the structure. The most severe degradation was observed at 55 o filament angle, where the first natural frequency decreases approximately by 13%. The most substantial variation in the damping ratio was observed at 85 o filament angle and 120°C curing temperature, where edge delamination caused a sharp 521% increase compared to the pristine state cured at 90°C. These findings show that curing, layup, and defect parameters are interconnected and impact the dynamic performance of filament-wound cylinders. By optimizing these factors together, we can design lightweight, vibration-resistant composite structures that are suitable for aerospace and defense applications.