Angle‐Dependent Compressive Failure Transition of CFRP Tubes After Accelerated Seawater Aging

ABSTRACT Fiber‐reinforced polymer (FRP) tubes with tailored winding angles are widely applied in marine structures, such as deep‐water risers and offshore pipelines. However, seawater ingress caused by coating degradation significantly affects their long‐term durability. This study investigated the axial compressive behavior of CFRP tubes with different winding angles (0°–90°) after 12 months of accelerated seawater aging. The results reveal that the aging response strongly depends on winding angle due to the different contributions of fibers, resin, and interfaces. Low‐angle specimens exhibited improved ultimate compressive capacity, while high‐angle specimens showed degradation, with maximum changes of +39.5% and −27.2%, respectively. For angles ≤ 60°, exposure generally increased peak load but caused stiffness reduction at certain angles, demonstrating a decoupling between strength and stiffness evolution. The 45° specimen achieved a 20.1% increase in peak load, whereas the 75° specimen showed a 47.9% stiffness loss. SEM, FTIR, moisture uptake, and DMA provided complementary evidence of moisture‐induced matrix plasticization and the associated change in failure response. A Hashin‐based finite element model, calibrated and evaluated only against the air‐exposed group, reproduced the main winding‐angle trends with a mean peak‐load error of 9.1%. These findings provide insights into the durability design of CFRP tubular composites in marine environments.