Life Estimation of Circumferentially Notch Round Bars Using J Integral
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Nuclear reactor’s structural components are subjected to high-temperature gradients at the time of shutdowns and start ups. These temperature gradients lead to loading conditions leading to low-cycle fatigue. Additionally, the presence of flaws, defects, and welds results in areas of stress concentration in the components. Therefore, the procedure of estimating the life of such components should consider the effects of stress concentration and temperature. In the present work, the low-cycle fatigue (LCF) life of specimens with circumferential notch is estimated when subjected to strain-controlled loading condition. Notched specimens mimic the multi-axial stress conditions which are results of defects present in the component and LCF conditions are at high temperature mimic the loading conditions due to temperature gradients. In order to study the effect of notches on the life of specimen, LCF were first conducted on plain or smooth specimens, i.e., specimens with notch and then on notched specimens at the same loading condition. The specimens were made of 316 LN austenitic stainless steel and the tests were done in strain control mode at room temperature and at 873 K. LCF loading conditions are conditions when stresses and strains are beyond the elastic limit, and hence, the elasto-plastic fracture mechanics approach was applied for life estimation using principles of fracture mechanics. In the present investigation for fatigue life, the J integral for the geometry is calculated to find out the root stress strain magnitude. The fatigue life is then estimated using the local strain-life method. The predicted life when compared with the experimental results was found to be within a factor of 1.2.
KeywordsFatigue Life Notch Fracture
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