Evaluation of low cycle fatigue based on the use of Coffin-Manson dependence under zero-to-“soft” loading cycle

Abstract

To calculate the durability of gas turbine engine parts damaged by low-cycle fatigue (LCF), according to the Structural codes of turbine engine strength it is necessary to test specimens cut from respective parts (or test coupons) under hard loading. Hard here means there is a fixed strain cycle. The tests are conducted with different asymmetry coefficients of the strain cycle and with different exposure time at the maximum cycle strain (to take into account the effect of creep at high temperatures). The tests carried out are to provide sufficient statistics to ensure the reliability of the calculation. We suggest a method of assessing the durability of gas turbine engine parts based on testing standard specimens at zero-to-soft loading cycle using modified Manson-Coffins equation. The results of the work confirm the possibility of achieving the required adequacy of assessing the durability of parts damaged by the LCF mechanism with the use of a modified Manson-Coffin equation. Some recommendations concerning its application are given.

Keywords

• gas turbine engines
• low cycle fatigue
• fatigue tests
• cyclic durability
• manson-coffin equation
• soft loading
• hard loading