Forecasting low-cycle fatigue life of gas-turbine engine parts by the method of equivalent tests for specimens with stress concentrator under extension-compression

Abstract

A method of low-cycle fatigue equivalent tests based on the application of test specimens whose stress-strain state shall be similar to the stress-strain state of the part to be investigated is proposed in the paper. The stiffness ratio of the stressed state is used as the similarity criterion of stress and strain state of the specimens and the part. The method was successfully applied on the low-pressure compressor disk of a gas turbine engine. Specimens with a circular cross section and a V-concentrator were used as equivalent specimens. The tests were carried out as follows: the specimens were tested under stretching and compression for the zero-to-compression stress cycle; the disks were tested on a dedicated test bench with the spin-up of up to 5000 rpm. The proposed method of equivalent tests makes it possible to forecast low-cycle fatigue life of large-sized critical parts whose full-scale tests cannot be carried out. The method can also be used to assess the high-cycle fatigue life of parts and to forecast their long-term strength. The obtained equations make it possible to design and optimize the construction of aviation parts: the permissible value of strain rate in the most strained area of the part can be determined by the specified fatigue life.

Keywords

• low-cycle fatigue
• equivalent endurance tests
• full-scale tests
• strain state stiffness
• specimens with stress concentrator
• conformity factor