Session: DA-03-01 Fatigue 1-Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens

Paper Number: 122843

122843 - Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens -Mean Stress Effect for Notched Specimens of Carbon Steel- 

  DFC3 and DFC4 subcommittees in the Japan Welding Engineering Society have investigated the mean stress effect and its correction methods on fatigue analysis for carbon steel STPT370 (equivalent to SA-106 Gr.A) in consideration of stress concentration.

  The Modified Goodman approach has been widely applied for mean stress correction. However, according to the investigation results from polished smooth specimens, the Smith-Watson-Topper approach showed higher rationality for mean stress correction. Therefore, in this study the applicability of Smith-Watson-Topper approach was discussed for notched specimens.

  2 types of polished notched specimens with stress concentration factors K_t of 1.5 and 1.8 were prepared for fatigue tests. Firstly, the regression curves of both types of notched specimens were obtained from fully reversed fatigue tests under nominal stress amplitude control. Secondly, mean stress fatigue tests for notched specimens were conducted at several loading conditions. For both stress concentration factors, the data of mean stress fatigue tests dispersed below the regression curves, indicating that the fatigue strength of notched specimen could be reduced by the mean stress effect for this material. The elastoplastic analysis of Finite Element Method (FEM) was conducted for estimating Mises stress amplitude, Mises strain amplitude, Mises mean stress and Mises mean strain at the bottom of notch. With these parameters, the equivalent stress amplitude S_eq of Smith-Watson-Topper approach was calculated. For comparison purpose, S_eq was also calculated by correcting the nominal stress amplitude and mean stress directly with the stress concentration factors K_t. Finally, the applicability of Smith-Watson-Topper approach for notched specimens was discussed by comparing the equivalent stress amplitude S_eq to the fictitious elastic stress amplitude S_a of the regression curves of smooth specimens.

  The results showed that the equivalent stress amplitude S_eq of Smith-Watson-Topper approach was available to mean stress correction for the notched specimens of STPT370.

Presenting Author: Yun Wang Hitachi, Ltd.

Presenting Author Biography: The author Yun Wang was born on November 22, 1976 in Shanghai, China. He received the Ph.D at Nagoya University (Japan) in 2007. The topic of his doctoral dissertation was “Microscopic Research on Plastic Deformation and Initial Fatigue Damage of Austenitic Stainless Steel”. He is currently working as a chief researcher for Hitachi, Ltd. His main research is related to residual stress measurement, fatigue behavior evaluation and countermeasures against stress corrosion cracking.

Authors:

Yun Wang Hitachi, Ltd.
Motoki Nakane Hitachi-GE Nuclear Energy, Ltd.
Akihiko Hirano Hitachi-GE Nuclear Energy, Ltd.
Masahiro Takanashi IHI Corporation
Yoshihide Kitamura The Kansai Electric Power Co., Inc.