Book Description

Experimental work on the fatigue crack growth characteristics of high strength P/M (Powder Metallurgy) aluminum alloys has been extended, with particular attention given to crack closure in the near threshold region as a function of R. It has been conclusively shown that the R-dependence of the threshold level is directly related to closure. In the absence of closure as in ultra-fine grained material the threshold level is independent of the R-ratio. Experimental work has been initiated on the growth of fatigue cracks under variable amplitude loading conditions. An approach to deal with topics such as the anomalous growth of short cracks, the non-propagation of cracks from notches, fatigue notch sensitivity, and the notch size-effect in fatigue has been developed. A comparison of the fatigue behavior of powder metallurgy and ingot metallurgy products has been initiated. Thus far out work indicates that P/M products can be produced which are free from manufacturing defects which might degrade fatigue properties of these high strength aluminum alloys. The fatigue properties are responsive to grain size, fracture toughness, and the degree of closure developed.