Numerical and analytical calculations of the energy release rate or J- integral indicate that extremely low energies are involved in microcrack formation due to moisture absorption in graphite/epoxy materials. This suggests that moisture weakens the fiber-matrix interface by reducing the adhesion between graphite and epoxy. Additionally, since tensile stresses at the fiber-matrix interface were calculated to be substantially less than the matrix ultimate strength, it is concluded that moisture, and not any mechanical cause, creates damage around fibers when graphite/epoxy composites are exposed to humid environments.
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