Accession Number : ADA324903

Title :   Characterization of the Graphite/Epoxy Interface with Various Surface Treatments under Cyclic Loading.

Descriptive Note : Master's thesis,

Corporate Author : AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH

Personal Author(s) : Ryan, James P.

PDF Url : ADA324903

Report Date : 12 MAY 1997

Pagination or Media Count : 101

Abstract : The effects of graphite surface modification on fatigue crack growth resistance of the graphite/epoxy 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 graphite/epoxy interface.

Descriptors :   *INTERFACES, *MORPHOLOGY, *HEAT TREATMENT, *CRACK PROPAGATION, *SURFACE CHEMISTRY, RESISTANCE, THESES, GRAPHITE, ETCHING, PROFILOMETERS, ELECTRON MICROSCOPY, X RAY PHOTOELECTRON SPECTROSCOPY, FATIGUE(MECHANICS), EPOXY COMPOUNDS, PEEL STRENGTH.

Subject Categories : Laminates and Composite Materials
      Mechanics
      Thermodynamics

Distribution Statement : APPROVED FOR PUBLIC RELEASE