Fatigue Damage Behavior in Composite Materials.
Interim rept. Jun 73-Jul 74,
UNITED AIRCRAFT CORP STRATFORD CONN SIKORSKY AIRCRAFT DIV
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Detection of early fatigue damage in composite materials by nondestructive inspection NDI techniques has been demonstrated for plus or minus 45 degrees GlassEpoxy, and plus or minus 45 degrees0 degrees GraphiteGlassEpoxy. Dynamic axial modulus and temperature were monitored continuously with a correlation between temperature rise and modulus decrease observed. The modulus decrease and temperature rise are indicative of irreversible damage in these materials. This is validated by observation of a rapid restoration of elevated temperature after reloading specimens which had been stopped and had cooled to ambient temperature. Torsional modulus measurements and coin tap tests were performed at 0, 1,000,000, 5 x 1,000,000, and 10 to the 7th power cycles, on all fatigue specimens. Other NDI procedures including holographic interferometry, ultrasonics, penetrant, and X-Ray radiography were performed on two specimens of each material to evaluate their effectiveness in detecting fatigue damage.
- Laminates and Composite Materials