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

Paper Number: 121952

121952 - Research on Effects of Surface Finishing and Mean Stress on Fatigue Lives of Notched Specimens -Application of Elastic-Plastic Fe Analyzes for Notched Specimens of Low Alloy Steel- 

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 this paper, application of elastic-plastic Finite-Element Analysis, FEA, for fatigue evaluation of notched specimens of low alloy steel were researched.
In load-controlled fatigue tests with positive mean stress (stress ratio, R>-1) for notched specimens, local stress-strain behavior at notch root should be focused on in order to evaluate the effect of notch and mean stress on fatigue strength. Because of difficulty of direct measurement of the local stress-strain during fatigue tests, estimation of stress-strain behavior by FEA, are necessary. 
In this study, elastic-plastic FEA were performed simulating fatigue tests for notched specimen of low alloy steel, JIS-SQV2A. Stress concentration factors of simulated specimens were 1.5 or 1.8. In analyses, cyclic stress-strain curve was applied, which is based on fatigue test results of smooth specimens performed in another research. Cyclic loadings were applied to be objective nominal stress amplitudes and mean stresses. Local stress-strain behaviors at notch root and mean stress changes with increasing number of fatigue cycles were investigated by these analyses.
As a result of FEA, in the case of lower stress amplitude, plastic deformation occurred only in the first cycle and local mean stress was constant. On the other hand, in the case of higher stress amplitude, cyclic plastic deformation occurred throughout all cycles and local mean stress became lower with increasing fatigue cycles. After sufficient numbers of fatigue cycles were applied, local mean stress at notch root became almost zero. These results were consistent with fatigue test results of SQV2A in another research, in which mean stress had little effect on fatigue lives of notched specimens. Also, it was confirmed that fatigue lives of notched specimens could be arranged on identical S-N curve based on fatigue lives of smooth specimens by using equivalent strain amplitude, ε_a^eq estimated by FEA. From these results, it is concluded that FEA is applicable for evaluation of fatigue lives of notched specimens.

Presenting Author: Daiki Takagoshi Mitsubishi Heavy Industry, Ltd.

Presenting Author Biography: I am currently affiliated with Mitsubishi Heavy Industry, Ltd. for 8 years.
I have been involved in research on environmental fatigue, irradiation embrittlement and Hydrogen embrittlement in Pressurized Water Reactors.
In my work, I conduct material testing and Finite Element Method (FEM) analysis.

Authors:

Daiki Takagoshi Mitsubishi Heavy Industry, Ltd.
Yuichiro Nomura Mitsubishi Heavy Industries, Ltd.
Seiji Asada Mitsubishi Heavy Industries, Ltd.
Yoshihide Kitamura The Kansai Electric Power Co., Inc.