Fracture behavior of seawater-absorbed carbon/epoxy laminated composites in the hydrostatic pressure condition

It was shown in the previous study that the fracture toughness of dried carbon/epoxy composites increased 38% as the applied hydrostatic pressure increased from 0.1 to 200 MPa. However, no research has been conducted on the fracture behavior of seawater-absorbed carbon/epoxy composites in a hydrostatic pressure environment. This work investigates the compressive fracture behavior of seawater-absorbed carbon/epoxy composites subjected to various hydrostatic pressures. Compressive fracture tests were performed under four hydrostatic pressure levels, 0.1 (atmospheric pressure), 100, 200, and 270 MPa. The compliance and fracture loads were determined from load-displacement curves as a function of hydrostatic pressure. Fracture toughness was determined from the elastic work factor approach. The results showed that compliance decreases but fracture load increases as the applied hydrostatic pressure increases. Fracture toughness increased with increasing pressure. Specifically, fracture toughness increased from 2.66 to 4.44 kJ/m², a 67% increase, as hydrostatic pressure increased from 0.1 to 270 MPa. Optical microscope examination of the fractured surface showed that local delaminations and microcracks are suppressed with increasing hydrostatic pressure. SEM examination showed that seawater-absorbed specimen shows a lot more epoxy fracture than the dried specimen.