Damage of Turbojet Engine Disks in a Function of Cyclic Material Properties and the Type of Engine Start-Stop Cycle

 

Strain Posavljak

Miodrag Janković

Katarina Maksimović

 

The damage of one turbojet engine disk, dominantly exposed to centrifugal forces of blades and its own centrifugal forces, was discussed in this paper. It was assumed that 23H11N2V2MF steel in delivered and heat treatment state would be used for disk manufacturing. One blade and a critical disk area were observed as separated ideal elastic bodies. Their stress response at maximum rotation frequency was determined using the finite element method. Equivalent stress at the critical point of disk was brought in relation to equivalent stress at the corresponding point of disk when observed as a blisk reduced to an axisymmetrical problem. The so-called equivalent stress concentration factor was thus obtained. This factor was used for defining Sonsino-Birger’s curve which, in a combination with cyclic stress-strain and Masing’s curves, was used for determining spectra of real (elastic-plastic) strain amplitudes at the disk critical point for three different start-stop cycles. These start-stop cycles, defined as blocks of rotation frequency, were decomposed at simple cycles. Spectra of real strain amplitudes, used for that purpose, were brought in relation to Morrow’s curves of low cycle fatigue life. Both states of the above mentioned steel of known cyclic properties were taken into account

Key words: aircraft engine, turbojet engine, disk, material fatigue, cyclic stress-strain,  stress concentration, centrifugal force, finite element method.