Quantitative Fractography for Evaluating Fatigue Crack Growth Behavior of Aerospace Aluminum and Titanium Alloys

To introduce competing manufacturing technologies and to achieve accurate prediction of new fatigue life for components of long-service life civil and military aircrafts, the determination of fatigue crack growth behavior by quantitative fractography is highly useful. To this end, fracture analyses of round bar fatigue tests for mill annealed wrought Ti-6Al-4V plate specimens and a service fracture in a Al 2024-T3 skin panel are reviewed. For the Ti-6Al-4V, inherent variations in the fatigue life data are observed, which relate to both surface and microstructural features. These data are discussed in terms of potential fatigue failure modes suggested by literature, to provide a deeper understanding of uncertainty. Some precautions are offered regarding the criticality of crack initiation information and Methods of improving quantitative fractography analysis are suggested. On the contrary, a plot of crack length versus number of cycles was successfully obtained for aluminum alloy which leads to more effective durability and damage tolerance assessments.

Keywords: Ti alloys, Al Alloys, fatigue crack initiation, crack growth, fatigue life prediction