Low Cycle Fatigue Life Evaluation of Notched Specimens Considering Strain Gradient

Abstract

An improved model based on the Chaboche constitutive model is proposed for cyclic plastic behavior of metal and low cycle fatigue of notched specimens under cyclic loading, considering the effect of strain gradient on nonlinear kinematic hardening and hysteresis behavior. The new model is imported into the user material subroutine (UMAT) of the finite element computing software ABAQUS, and the strain gradient parameters required for model calculation are obtained by calling the user element subroutine (UEL). The effectiveness of the new model is tested by the torsion test of thin copper wire. Furthermore, the calibration method of strain gradient influence parameters of constitutive model is discussed by taking the notch specimen of Q235 steel as an example. The hysteresis behavior, strain distribution and fatigue failure of notched specimens under cyclic loading were simulated and analyzed with the new model. The results prove the rationality of the new model.

Determination of Local Stresses and Strains within the Notch Strain Approach: The Efficient and Accurate Calculation of Notch Root Strains Using Finite Element Analysis

“…This is also the reason why the standard use of FEA with elastic-plastic material behaviour to determine local stresses and strains has not yet found its way into regulations for the assessment of fatigue strength. Rather, this sort of finite element analysis is only used in individual cases [34][35][36][37][38][39][40], in which the calculation time only plays a subordinate role, or for the development of notch root approximations themselves [7,14,15,41,42], where the stresses and strains determined in this way are used as a reference for those estimated with notch root approximations. Recommendations for the efficient design of finite element analyses with which input data for strain-based strength assessments can be generated can only be found in rudimentary form-see, e.g., [43].…”