Effect of seawater on the interfacial strength and durability of polymer composites

The effect of absorbed moisture on the fiber/matrix interfacial strength and 90° ply strength have been studied for E-glass and carbon fiber reinforced epoxy. In-situ observations of fracture in an environmental scanning electron microscope with associated calculations indicating reductions in ply stress at debonding ranging from 0% to 30%, with 70% at the reduction attributed to a weaker interface and the balance due to changes in the residual thermal stresses. Burst tests and low-cycle fatigue tests using internal pressure in filament wound tubes gave only a 6% reduction in burst strength for seawater saturated specimens compared to unaged specimens, but a more significant reduction in the low-cycle fatigue behavior was noted. The effect of moisture was apparently to plasticize the matrix, giving more viscoelastic deformation and to reduce the strain to failure in the glass fibers.