Crack Growth Behavior of Full-Scale Turbine Attachment Under Combined High and Low Cycle Fatigue

Abstract

Turbine attachments in the aero-engine are generally subjected to combined high and low cycle fatigue (CCF) loadings, i.e., low cycle fatigue (LCF) loading due to centrifugal and thermal loading stresses superimposed to the aerodynamically induced high cycle fatigue (HCF) loading. The primary focus of this study is to predict the crack growth life for the actual full-scale turbine attachment through experimentally examining the crack growth behavior under CCF loading at elevated temperature. The crack closure effect was first investigated by using the corner-notched (CN) specimen cut from the turbine attachment since the stress state of CN specimen is more similar to turbine attachment than compact tension (CT) specimen. Employing digital image correlation (DIC) technique, the level of crack closure of CN specimen was clarified under different stress ratios (R) for LCF loading. Afterward, a CCF crack growth model for the full-scale turbine attachment was proposed, which takes the crack closure effect, time-independent crack increment, and transient vibrational analysis into account. In order to verify the proposed method, a Ferris wheel system was established to conduct CCF test on the full-scale turbine attachment at elevated temperature. This study provides an effective methodology to predict the fatigue crack growth (FCG) life of full-scale turbine attachment under CCF loading.