Experimental, Analytical, and Computational Studies on the Fatigue Crack Growth Behavior of a Titanium Alloy under Cold-Turbistan Spectrum Loads

ABSTRACT The fatigue crack growth (FCG) behavior of Ti-6Al-4V alloy subjected to spectrum loads was experimentally determined and compared with predicted behavior by analytical and computational methods. In the experimental method, a compact tension (CT) specimen of Ti-6Al-4V was tested under standard cold-Turbistan spectrum loads to determine crack propagation behavior. Spectrum fatigue tests were conducted with triangular waveform at 2 Hz. In the analytical predictive method firstly, constant amplitude FCG tests were conducted at several stress ratios and a unified FCG law based on crack driving force, K* was derived for Ti-6Al-4V alloy. Then, the crack growth for every rainflow-counted fatigue load cycle in the cold-Turbistan sequence was determined using the derived FCG law. In the computational method, a global and a local model of the CT specimen of Ti-6Al-4V were created in HYPERMESH and FRANC3D, respectively. The FCG behavior under the cold-Turbistan spectrum was then predicted using FRANC3D and MSC NASTRAN. The required materials constants for the FCG law in the FRANC3D software were derived from the experimental constant amplitude FCG rate data of Ti-6Al-4V alloy. It was observed that both methods of FCG predictions, i.e., analytical and computational methods, although conservative, compared quite well with experimental results.