Session: DA-03-02 Fatigue 2-Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens

Paper Number: 123111

123111 - Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens -Definition of Fatigue Life of Notched Specimen Using Crack Growth Analysis - 

   DFC and DFC2 subcommittees in the Japan Welding Engineering Society developed a new approach of fatigue analysis method. This fatigue analysis method has been made several modifications and incorporated into the JSME Environmental Fatigue Evaluation Method 2022 Edition (JSME S NF1-2022). Research on effects of surface finishing and mean stress on fatigue lives of notched specimens have been followed by DFC3 and DFC4 subcommittees.

   In the DFC4 subcommittee, it was investigated the evaluation method of combined effects of stress concentration, and surface finish and stress concentration and mean stress on the fatigue properties of ferritic steels. Load controlled fatigue tests were conducted using notched round bar specimens in the DFC4 subcommittee. The fatigue tests were finished when the displacement over notch mouth exceeded the prescribed value and crack depth was measured on the facture surface of specimens. Since the crack depths are different among the specimens when the fatigue test finished, fatigue lives of specimen should be compared based on the same crack depth. To compare the fatigue lives based on the same standard life among the specimens, the fatigue crack growth analysis was conducted. The stress intensity factor of surface crack in notched round bar was investigated first. Next, the suitable fatigue crack growth rate (FCGR) for tested material was investigated among the existing FCGR equations and determined. The crack depth for fatigue life evaluation was determined to be 2mm and influence of FCGR and stress concentration factor Kt on N_2mm were investigated by case studies.

  It was found that the effects of crack growth rate and stress concentration factor Kt on the N_2mm were relatively smaller for low-alloy steel than carbon steel because the tested stress amplitude were higher for low-alloy steel than carbon steel.

Presenting Author: Masao Itatani Toshiba Energy Systems & Solutions Corporation

Presenting Author Biography: Graduated doctoral coase of Mechanical Engineering, Osaka University in 1991 and then joined to Toshiba Corporation. The main field is structural integrity assessment of nuclear power components such asn fatigue, crack growth and fracture.

Authors:

Masao Itatani Toshiba Energy Systems & Solutions Corporation
Takuya Ogawa Toshiba Energy Systems & Solutions Corporation
Masahiro Takanashi IHI Corporation
Yun Wang Hitachi, Ltd.
Yuichiro Nomura Mitsubishi Heavy Industries, Ltd.
Yoshihide Kitamura The Kansai Electric Power Co., Inc.