Fatigue crack growth behaviour of a nickel base super alloy GTM720 under cold-TURBISTAN spectrum load sequence

[Display omitted] •Constant amplitude FCGR determined at various stress ratios in GTM720 alloy.•The material constants for two parameter crack driving force, K* is determined.•Fatigue crack growth under cold-TURBISTAN spectrum load is predicted using crack driving force, K*.•Experimental fatigue crack growth behavior is determined under cold-TURBISTAN load sequence.•A fairly good correlation was obtained between predicted and experimental results. Damage tolerance concept is widely used in aerospace industry for designing structural components against fatigue. In this study, an attempt is made to predict fatigue crack growth behavior in an aero-engine material under a standard spectrum load sequence using a closure independent crack driving force parameter, K* and compare with experimental results. Initially, constant amplitude (CA) fatigue crack growth rate (FCGR) behavior of GTM720, a nickel based super alloy was determined at stress ratios, R = σmin/σmax ranging from R = 0.1 to 0.7. Then, empirical fatigue crack growth law was derived from this CA-FCGR data in terms of two parameter crack driving force, K*. Further, the fatigue crack growth behavior was predicted through cycle-by cycle approach in a pre-cracked compact tension (CT) specimen of GTM720 alloy under standard cold-TURBISTAN spectrum load sequence using K* as the crack driving force. Also, experimental fatigue crack growth behavior under the same load sequence was determined in a CT specimen and compared with predicted results. A fairly good correlation was observed with predicted and experimental results. Predicted fatigue crack growth life was conservative and the fatigue crack growth life ratio, Npred/Nexpt was about 0.92.