Probability evaluation for exhaustion of the operating capacity of gas-turbine-engine disks with low-cycle fatigue

Evaluation of the probability of LCF cracks developing in disks is based on comparing the range of strains Δε*, determined by a Manson equation taking account of the scatter of material mechanical properties, and Δɛ at a critical point of the disk with overspeeding of rotor rotation and temperature during operation. The probability evaluation is based on the method of linearizing functions of random arguments. The sequence of calculations in determining the probability of cracks occurring depending on the number of loading cycles is demonstrated on the example of a specific turbine disk.

In the example considered the probability of a crack developing is governed mainly by the difference in average values for the range of strains and by the mean deviation for the range of strains determined by the Manson equation, i.e., scatter of material mechanical properties. The value for endurance N=3.3·10⁴ cycles, determined using mechanical properties according to the technical specification at loads with a nominal engine operating schedule, corresponds to the probability of forming a crack in a disk P_fail=10⁻⁵.