Issue 38

L. Cui et alii, Frattura ed Integrità Strutturale, 38 (2016) 26-35; DOI: 10.3221/IGF-ESIS.38.04 26 Focussed on Multiaxial Fatigue and Fracture Crack initiation behavior of notched specimens on heat resistant steel under service type loading at high temperature Lu Cui School of mechanical Engineering, Xi’an Shiyou UniversityUniversity Institut für Werkstoffkunde, Technische Universität Darmstadt cuiluxa@hotmail.com Peng Wang BorgWarner Turbo Systems Engineering GmbH Institut für Werkstoffkunde, Technische Universität Darmstadt Wp168@hotmail.com A BSTRACT . Cracks at notches deserve special consideration in the design of steam turbine components. This work is addressed to investigate the crack initiation behavior a 10%Cr rotor steel with the help of notched specimens under service-type loading. A significant drifting down of the peak-values of axial deformation under constant amplitude load was observed. Crack initiation was evaluated with the help of the relationship between irreversible deformation energy and cycle number. Further, metallographic examinations were employed to characterize the superposition of creep and fatigue damage mechanisms. Both Neuber-hypothesis and von Mises equivalent strain at notch root were applied for lifetime prediction. Finally, the effectiveness of both methods is validated by comparing with experimental results. K EYWORDS . 10%Cr steel; Notched; Lifetime; Neuber; von Mises. Citation: Cui, L., Wang, P., Crack initiation behavior of notched specimens on heat resistant steel under service type loading at high temperature, Frattura ed Integrità Strutturale, 38 (2016) 26-35. Received: 14.05.2016 Accepted: 20.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION team turbine components are subjected to quasi-static primary loading due to steam pressure superimposed by variable secondary loading due to temperature transients in start-up and shut-down processes. The difference between the surface temperature and the average core temperature leads to compression strains during start-up and tension strains during shut-down (Fig. 1). At stationary service, the turbine temperature reaches quasi-balance, and the compression and tension stresses relax during the hold time. Due to stress concentration, notches lead to a further decrease of lifetime [1]. S