Fatigue crack growth and crack closure of P/M aluminum alloys.

Fatigue crack growth tests were carried out on P/M (Powder Metallurgy) aluminum alloys, 7090-T7, Al-12Si-5Fe, Al-15Zn and Al-2C, in air under ΔK-increasing and-decreasing conditions. Crack growth rates and crack closure behavior were investigated in detail by using the unloading elastic compliance method. The crack opening ratio U was found to depend on the roughness of the fracture surface. The fracture ductility of material εf was found to exert a considerable effect on the fatigue crack growth rate of the intermediate region, and the following empirical equation was proposed to account for the effect of material properties on the crack growth rate ; da/dn = 4.87×103(ΔKeff)/(Eε0.2f))2.7 The fracture toughness of the materials was hoped to be increased to obtain the improved fatigue crack growth resistance in the high growth rate regime.