Numerical Analysis on the Local Stress-strain Response of U75V Notched Bar Considering Ratchetting
The ratchetting-fatigue interaction of engineering materials has been extensively investiga-ted in the recent decades.However,as an essential engineering problem,the fatigue failure of notched components with ratchetting has not yet been well touched.It is known that the local stress/strain field at the notch root is a prerequisite for further fatigue life assessment.Neuber's rule is a widely used semi-ana-lytical method for predicting the local stress/strain at the notch root,but its feasibility is not verified when remarkable ratchetting occurs at the root.Therefore,in this work,the cyclic deformation of a notched bar made of U75V steel under asymmetrically uniaxial stress-controlled cyclic loading is simulated using the fi-nite element method.A cyclic elasto-plastic constitutive model is selected and verified according to the ex-perimental results of U75V steel.A UMAT subroutine is developed and implanted into the finite element software Abaqus.Based on the simulation,the stress/strain distributions and corresponding stress/strain concentration coefficients at the notch root,as well as their evolutions during cyclic deformation,are stud-ied.Then,the applicability of Neuber's rule to analyze the local stress-strain response at the notch root of notched components is discussed,taking ratchetting into consideration.The results show that during cy-clic deformation,the local stress at the notch root is relaxed,and the stress concentration coefficient de-creases accordingly.Meanwhile,the ratchetting strain becomes concentrated at the notch root,and the strain concentration coefficient increases with the number of cycles.The geometric mean of stress and strain concentration coefficients also gradually increases with the number of cycles,significantly differing from the theoretical stress concentration coefficients.This suggests that Neuber's rule cannot accurately describe the stress-strain response at the notch root of notched components when significant ratchetting be-havior occurs.Therefore,modifications should be made to Neuber's rule to expand its application scope.
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