Evaluation of component‐similar rotor steel specimens with a local probabilistic approach for LCF

• Published in: Fatigue & fracture of engineering materials & structures Vol. 43; no. 5; pp. 932 - 946
• Main Authors: Mäde, Lucas, Kumar, Kiran, Schmitz, Sebastian, Gundavarapu, Sesha, Beck, Tilmann
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01.05.2020
• Subjects: Boreholes; Chromium molybdenum vanadium steels; Crack initiation; Cracks; Flaw detection; Heat resistant steels; heavy duty forged rotor discs; LCF; Life prediction; Modelling; notch support; Parameter estimation; probabilistic; Probabilistic models; size effect; Size effects
• ISSN: 8756-758X; 1460-2695
• DOI: 10.1111/ffe.13166

Lately, a successful validation of a combined size and gradient effect modelling approach in a local probabilistic framework for LCF was published. A second validation study is here presented using LCF data of component‐similar specimens made of forged X12CrMoWVNbN10‐1‐1. It is found that a reasonable LCF crack initiation life prediction can be achieved by the local probabilistic model using single batch material parameters. However, the material parameters obtained from mixed batch LCF test data overestimate the actual material inherent LCF life scatter. Consequently, the size effect shift is pronounced too much, and the LCF life is predicted beyond crack initiation. Estimating the material parameters from a single batch data set instead results in a much less dispersed LCF life distribution and an approximately correct size effect shift. The predicted median Wöhler curve then corresponds to borehole‐specimen lives for initial cracks at the detection threshold. A reasonable prediction of technically relevant crack sizes in such inhomogeneous components requires additional modelling of stress gradient effects.