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.
Highlights
Due to the requirements of functional design, weight reduction, and component connection, many engineering load bearing components usually have notches or holes
18.InInthe thefigure, figure,the themeasured measurednominal nominal considering the effect stress-strain hysteresis curves of the specimens with a notch radius of mm are compared withthe the stress-strain hysteresis curves of the specimens with a notch radius of 2 mm are compared with calculated hysteresis curves considering the effect of strain gradient, which basically coincide
By observing the change of the marker line on the surface of the notched specimen before and after the tensile test under an optical microscope, it is confirmed that the constitutive relationship of the material is affected by the strain gradient
Summary
Due to the requirements of functional design, weight reduction, and component connection, many engineering load bearing components usually have notches or holes. If the effect of strain gradient on the constitutive behavior of materials is considered, the evaluation of fatigue of notch specimens will change. Xiong et al believe that the strain gradient causes strain hardening of material near notch, which increases the initial yield strength of the material in the high strain gradient region, which will change the local strain of the notch [8] They found that the fatigue life assessment of notched specimens according to this mechanism was more reasonable. Gao and Huang (1999, 2000) proposed a strain gradient plasticity theory based on mesoscopic dislocation mechanism, namely MSG theory, which combined macroscopic plasticity theory and dislocation mechanism by establishing a multi-scale and hierarchical theoretical framework [24,25] These types of theoretical formulas introduce high-order stress, and the equilibrium equations and boundary conditions are relatively complicated.
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