3D Crack Growth Analysis and Its Correlation With Experiments for Critical Turbine Components Under an International Collaborative Program

Abstract

Following a reanalysis of the original material data plus supplementary Low Cycle Fatigue (LCF) specimen testing, an Original Equipment Manufacturer (OEM) reduced the low cycle fatigue life limits for a number of turbine components. To ascertain the validity of the new life limits, an international collaborative spin rig test program was initiated to provide more accurate low cycle fatigue life limits. The program covered a broad range of activities including, Finite Element (FE) stress analyses, cyclic spin rig testing, fractographic assessment and fatigue crack growth (FCG) analyses. This paper describes the 2D and 3D crack growth analyses of critical turbine components in a turboprop gas turbine engine, comparison of predicted results obtained using different software and also correlations with spin test results from the program. First, FE stress analyses of selected turbine components were carried out under both engine operating conditions and spin-rig test configurations in order to determine the maximum and minimum operating speeds required to match the stress ranges at the critical location specified by the OEM under engine operating conditions. Second, 2D and 3D crack growth analyses were performed independently by three organisations for a disk bolthole using the state-of-the-art software. Third, the predictions from different software were compared, and the relative technical merits of each software were evaluated. Finally, the predicted results were correlated against the striation counts determined by the OEM from the results of spin rig tests.

Prediction of fatigue crack propagation lives of turbine discs with forging-induced initial cracks

“…Prior to this investigation, a 2D axisymmetric FE model of the turbine section generated and correlated under a collaborative program on Turbine Rotor Life Analysis [4,17] was available and used for the purpose of this study. As shown in…”

“…In general, common failure locations for turbine discs under normal operating conditions are often at the critical design features such as bolt holes and disc firtrees [4,5] and the design stress and life limits are calculated based on these locations. There are a number of investigations devoted to both failure analyses and life assessment of turbine discs in literature.…”

“…Consequently, most turbine discs are failure-critical components and their design life limits are often determined by the accumulation of low cycle fatigue (LCF) damage during service [1,2]. Therefore, prediction of fatigue damage and the associated crack growth rates are very important in determining either the likely failure modes or the component replacement intervals to prevent failures under normal operating conditions [3,4].…”