Characterization of the Graphite/Epoxy Interface with Various Surface Treatments under Cyclic Loading.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH
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The effects of graphite surface modification on fatigue crack growth resistance of the graphiteepoxy interface were examined using flexural peel specimens. Edge surfaces of pryolitic graphite were treated in an oxygen plasma for various lengths of time and subsequently bonded to a toughened epoxy to form flexural peel specimens. Fatigue crack growth rates were measured for the plasma treated and untreated specimens as a function of strain energy release rate. Fatigue crack growth resistance of plasma treated specimens was notably higher than that of untreated specimens, with the fatigue threshold doubled at an optimal treatment time. X-ray photoelectron spectroscopy, electron microscopy, and surface profilometry studies indicated that both surface chemistry and surface morphology of the graphite were changed by the plasma treatment. High temperature annealing was used to restore the original surface chemistry while retaining the etched surface morphology. Fatigue experiments were then performed on the heat treated specimens to separate the chemical and morphological effects on resistance to crack growth. Chemical modification turned out to be a secondary effect, contributing less than 13 to the overall fatigue crack growth resistance. A micro-mechanical model is proposed which explains the relative effects of surface chemistry and morphology on fatigue crack growth resistance along the graphiteepoxy interface.
- Laminates and Composite Materials