Performance Analysis of Environmental Conditioning Effect on Crush Character of Hybrid Composite Pipes with Different Winding Angles

The effects of hydrothermal aging in distilled water (DW) and seawater (SW) environments on the water absorption behavior and crush characteristics of hybrid glass/carbon fiber-reinforced composite pipes with ±55° and ±70° winding angles were evaluated. Specimens were kept for 120 days at 30°C, and water absorption was analyzed experimentally and theoretically. Results revealed that distilled water-aged samples exhibited higher maximum water absorption rates (2.5% for DW55 and 2.62% for DW70) compared to seawater-aged samples (2.37% for SW55 and 2.44% for SW70), attributed to the inhibitory role of ionic components in seawater. Lower winding angles consistently showed greater water absorption due to increased microstructural voids, facilitating water diffusion. Quasi-static axial compression tests demonstrated significant degradation in crush performance after aging. Unconditioned samples with 70° winding angles achieved the highest initial peak load (56.9 kN) and specific energy absorption (28.89 J/g). However, aging reduced these values, with seawater-aged samples (SW55) showing a 12.32% decrease in specific energy absorption compared to unconditioned counterparts. Crushing force efficiency (CFE) also declined, correlating with matrix plasticization and fiber/matrix interface weakening. Notably, hybrid pipes with 55° winding angles exhibited superior energy absorption (30.44 J/g for U55), emphasizing the role of fiber orientation in load distribution.