Fiber/matrix interfacial bonding in fiber reinforced
polymer (FRP) composite materials is potentially sensitive to degradation in aqueous environments. Ultimate bond strength (UBS) in
carbon fiber/polysulfone (
CF/PSF) and
polyaramid/polysulfone (K49/PSF) was previously reported to be significantly decreased in two simulated in vivo environments. While UBS is a useful parameter, for orthopedic implant applications the
fatigue behavior of the interface is probably a more relevant
indicator of long-term composite material performance. In this article, the effects of simulated in vivo environments (saline, exudate) upon the
fatigue behavior of the interface of
CF/PSF and K49/PSF are reported. The
fatigue behavior of both material combinations was linearly dependent on the logarithm of
fatigue life in the dry (control), saline, and exudate environments. Testing either material in saline and exudate resulted in significantly lower
fatigue strength than in the dry environment; however, results in the two wet environments were indistinguishable. The
CF/PSF interface experienced
fatigue failure at approximately 10(5) load cycles at a maximum applied load level of only 15% of its ultimate dry bond strength without indication of an endurance limit being reached. These results raise some important questions regarding the durability of
CF/PSF composite in load bearing orthopedic applications.