Low-cycle fatigue analysis based on linear hardening structural strain method

Low-cycle fatigue analysis of welded structures is particularly important for rail vehicles. To effectively evaluate the low-cycle fatigue of welded structures, a numerical calculation method for structural strain based on a linear hardening constitutive model was proposed. This method is based on classical plate-shell theory and elastoplastic mechanics. By considering the strain hardening behavior of materials, the true stressstrain relationship of materials was simplified into a linear hardening constitutive model. The structural stress at the welding toe position of the welded structure was calculated using finite element analysis software ABAQUS and Fe-safe. The linear hardening constitutive model with plasticity correction was presented based on the radial mapping algorithm. The structural stress was plastically corrected using a structural strain numerical calculation program written in MATLAB, and the structural strain was calculated. Based on this structural strain, the calculation formula of the equivalent structural strain range considering the plate thickness effects and load mode was provided, and low-cycle fatigue data were analyzed using the main strain-life curve. The finite element models of three welded joints made of Q450 high-strength weather-resistant steel material widely used in rail vehicles were established. The fatigue data obtained from tests were analyzed using both the main stress-life curve of the structural stress method and the main strain-life curve of the numerical calculation method for structural strain. The equivalent structural strain ranges calculated by the two methods were compared. The results show that the test data for each welded joint are distributed within a linear narrow band of the main strainlife curve, which verifies the feasibility of the numerical calculation method for structural strain. Compared to the structural stress method, the numerical calculation method for structural strain can better reflect the strain hardening phenomenon during low-cycle fatigue and be more suitable for evaluating the low-cycle fatigue of welded structures. This method has research value for the low-cycle fatigue evaluation of welded plate structures in rail vehicles. Compared to the traditional method of calculating structural stress and structural strain parameters by extracting node forces, the numerical calculation program for structural strain written by MATLAB greatly improves the efficiency of calculating structural strain parameters. © 2024, Central South University Press. All rights reserved.