Polymers--Deterioration

Degradation of the critical components of polymer matrix composites in marine
environments had been experimentally investigated. Water absorption behavior of neat
resin and composite specimens was examined. The tensile strength of fibers was
monitored using the single filament test. The mechanical properties of the resins were
monitored by tensile, flexure, and dynamic-mechanical tests. In addition, matrix
shrinkage during cure and matrix swelling after immersion in water were monitored. The
integrity of the fiber/matrix (F/M) interface of the composite systems was studied using
the single fiber fragmentation test (SFFT). Macroscopic composites were examined using
transverse tensile and transverse flexure tests to study the influence of the integrity of the
matrix and F/M interface on the macroscopic response. In addition, for characterization
of F/M debonding in the SFFT, a fracture mechanics model and modified test procedure
were developed.

This research evaluated the applicability of electrochemical impedance spectroscopy (EIS) as a non-destructive technique to predict and characterize the degradation of carbon fiber reinforced polymer (CFRP) composites exposed to aqueous environments at ambient and 6.2 $\pm$ 0.3 MPa. Changes in EIS data were related to water uptake into the composite material as a function of exposure time. Electrochemically induced damage (both anodic and cathodic) were also evaluated using impedance measurements. Three point flexure tests with concurrent EIS measurements were employed to study the effect of stresses on water uptake and mechanical degradation. Visual observation of the extent of damage (i.e., fiber-matrix debonding) was made using scanning electron microscopy (SEM) and correlated with EIS observation.