Accession Number:

ADA256819

Title:

Some Observations on Stress Graphitization in Carbon-Carbon Composites

Descriptive Note:

Technical rept.

Corporate Author:

AEROSPACE CORP EL SEGUNDO CA MECHANICS AND MATERIALS TECHNOLOGY CENTER

Report Date:

1992-09-15

Pagination or Media Count:

35.0

Abstract:

The in situ stress graphitization behavior of hard carbons in unidirectionally aligned carbon-carbon CC composites was studied for three carbon fibers PAN-based T-50, pitch-based PX7, and rayon-based WCA and two carbon precursor resins phenol-formaldehyde SC1008, and polyarylacetylene PAA, a high-char-yielding, low-shrinkage resin. Graphitization was followed by measurements of density, transverse thermal expansion, d-spacing by x-ray diffraction XRD, and by scanning electron microscopy SEM. In conjunction with xenon-ion etching, the SEM technique was found to be particularly effective in identifying localized regions of graphitized matrix. Results reveal that the graphitization of the composite is significantly greater than graphitization of fiber or matrix alone to the same temperatures. SEM observations indicate that graphitization is confined to the matrix, usually as a sheathlike structure adjacent to the fiber and 1-3 micrometers thick. Such localized graphitization, usually termed stress graphitization, is believed to be the result of thermally induced tensile or compressive stresses acting at the fiber-matrix interface. Debonded regions, which are believed to either initiate at heatup or grow from preexisting cracks in the resin-matrix composite, show less stress graphitization than well-bonded regions, presumably because the debond gaps impede stress buildup at the fiber-matrix interface.

Subject Categories:

  • Polymer Chemistry
  • Laminates and Composite Materials
  • Plastics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE