Fatigue crack tip opening behavior in particulate reinforced Al-alloy composites

Behavior of fatigue crack growth was examined in an Al2O3 particulate reinforced Al-Cu matrix composite and its matrix alloy, heat-treated to peak-aged and overaged conditions. The fatigue crack growth resistance of the composite was much better, especially at low growth rates, and depended on aging condition. Measurements of crack opening profiles have shown that crack tip in the composite remained closed at fairly high stress intensities and was opened to a much smaller displacement compared to the crack tip opening in the matrix alloy at the same stress intensity. Correlation of the fatigue crack growth rate with crack tip opening displacement (CTOD) revealed that both the composite and the matrix alloy obey the same fundamental relationship that the fatigue crack growth rate scales with the square of the CTOD.