Effects of loading waveform on fatigue crack growth of Udimet 720 Li superalloy

The influence of loading waveform, including constant load tests, on fatigue crack growth rate (FCGR) of the Ni-base superalloy Udimet 720 Li has been investigated in air at the temperature of 700 °C, using corner crack specimens. The fatigue crack growth is controlled by oxidation mechanisms and the mode of fracture is completely intergranular. The loading ramp has the same effect on crack growth rate as the unloading ramp. The time spent at maximum load produces higher crack growth rate than the same time consumed during loading or unloading ramp. High strain rate due to high loading ramp of about 300 kN/s followed by slow unloading leads to considerable increase in crack growth rate, which is attributed to interaction between crack tip plasticity, creep and oxidation.

[1]  H. Ghonem,et al.  OXIDATION‐ASSISTED FATIGUE CRACK GROWTH BEHAVIOR IN ALLOY 718‐PART I. QUANTITATIVE MODELING , 1991 .

[2]  A. Pineau,et al.  ELEVATED TEMPERATURE FATIGUE CRACK GROWTH IN ALLOY 718—PART I: EFFECTS OF MECHANICAL VARIABLES , 1993 .

[3]  H. Solomon.  Frequency dependent low cycle fatigue crack propagation , 1973 .

[4]  Hermann Riedel,et al.  Fracture at high temperatures , 1987 .

[5]  J. Martin,et al.  Crack tip plasticity and crack growth in a single-crystal superalloy at elevated temperatures , 1984 .

[6]  G. Osinkolu,et al.  Fatigue crack growth of UDIMET 720 Li superalloy at elevated temperature , 2001 .

[7]  Byrne,et al.  Effects of frequency on fatigue crack growth at elevated temperature , 1999 .

[8]  Robert P. Wei,et al.  MECHANISM FOR OXYGEN ENHANCED CRACK GROWTH IN INCONEL 718 , 2001 .

[9]  H. D. Solomon,et al.  Low Cycle Fatigue , 1988 .

[10]  P. Reed,et al.  Anomalous crack shape development (tear drop cracking) in turbine disc material Udimet 720 , 2000 .

[11]  W. Schmitt,et al.  Numerical Methods in Fracture Mechanics , 1987 .

[12]  A. Pineau.  Mechanisms of Creep-Fatigue Interactions , 1989 .

[13]  J. Knott,et al.  Fundamentals of Fracture Mechanics , 2008 .

[14]  Eric Andrieu,et al.  Oxidation effects on the fatigue crack growth behaviour of alloy 718 at high temperature , 1997 .

[15]  Mark Hardy,et al.  Creep, fatigue and oxidation in crack growth in advanced nickel base superalloys , 2001 .

[16]  R. Raj,et al.  Mechanisms of creep-fatigue interaction , 1982 .

[17]  A. Pineau,et al.  Frequency and wave-form effects on the fatigue crack growth behavior of alloy 718 at 298 K and 823 K , 1978 .