Dynamic mechanical analysis of a uniaxial continuous carbon fiber-thermoplastic composite subjected to anodic and cathodic currents

The dynamic mechanical properties of a uniaxial continuous carbon fiber-thermoplastic composite were found to degrade significantly when subjected to anodic and cathodic currents in the presence of seawater. The composite tested was made of PAN-based graphite fibers (50 vol%) in Du Pont s J-2 thermoplastic resin (nylonbased). The shear storage modulus, G′, and the shear loss modulus, G", of the composite were measured by subjecting a rod-shaped sample to small amplitude torsional oscillations. The moduli remained constant over time when the sample was in air and when it was submerged in seawater in the absence of applied currents. Both moduli decreased to ∼45% of their initial values when a constant anodic current of density 0.414 $μ$A/cm2 was applied for 2 h. A cathodic current of the same density and duration caused the moduli to decrease to ∼63% of their initial values. The moduli remained at these low levels after the current had been turned off. Inspection, under a scanning electron microscope, of the sample exposed to the anodic current revealed numerous cracks in the polymer matrix. In the sample exposed to the cathodic current, the fibers separated from the matrix of the composite.