T. Mooney, K. Wepfer, GE Aviation, Lynn, MA
Current methods to determine low cycle fatigue (LCF) damage in gas turbine engines rely on algorithms to approximate LCF usage. Current algorithms are based on combinations of operating time and/or speed counts to estimate LCF usage. Variation inherent in these approximation methods forces conservatism in the establishment of safe part and engine life limits. This conservatism limits combat readiness, reduces time-on-wing and increases operating and support costs.
GE developed an approach to accurately determine LCF usage for each part by calculating the cyclical stresses on each part after each flight. The calculation is based on measured data recorded during each flight. The data is processed through an aero-thermal engine model to calculate the parameter suite needed for the stress calculations. Direct calculation of cyclical stresses provides a more accurate determination of LCF. Furthermore, flight-to-flight evaluation of LCF provides insight useful for part, module and engine prognosis for estimating remaining time-on-wing. The improved estimate of life usage enables optimal part life entitlement, improves asset utilization and reduces the risk of overflying cyclical limits.
This paper describes a cooperative program funded by DARPA and the US Navy to develop and demonstrate a ground based system for determining LCF damage after each mission. This system is being developed for the T700-GE-401C engine in the H60R/S helicopter.
Summary: Current methods to determine low cycle fatigue (LCF) damage in gas turbine engines rely on algorithms to approximate LCF usage.
