Fatigue life estimation of notched specimens of modified 9Cr-1Mo steel under uniaxial cyclic loading

Abstract

Accuracy in the estimation of low cycle fatigue life of modified 9Cr-1Mo steel notched specimen by different analytical methods such as linear rule, Neuber’s rule, strain energy density method and numerical method such as finite element analysis have been studied in this investigation. The fatigue tests on notched specimens having notch radius of 1.25 mm, 2.5 mm and 5.0 mm were carried out at 823 K with net stress amplitudes of 250 MPa, 300 MPa and 350 MPa. The fatigue tests on smooth specimens were carried out with strain amplitudes ranging from ±0.3% to ±0.8% with a strain rate of 3 × 10⁻³ s⁻¹ at 823 K to evaluate the fatigue life of notched specimen through strain-life approach. In order to predict the cyclic stress response of the material, Chaboche non-linear hardening model was employed considering two back stress components. Predicted hysteresis loops for smooth specimen were well in agreement with experimental results. Estimated fatigue lives of notched specimens by analytical methods and finite element analysis were within a factor ±16 and ±2.5 of the experimental lives respectively.

Keywords:

• Low cycle fatigue
• modified 9Cr-1Mo steel
• notched specimen
• chaboche model
• life prediction
• analytical methods

Acknowledgements

The authors are thankful to Dr A. K. Bhaduri, Director, IGCAR, Kalpakkam for his keen interest and support in this investigation. The authors also thank to Dr C. R. Das, MTD, IGCAR for the help in SEM investigation.