A MICROMECHANICAL STUDY ON DP600 STEEL UNDER EXTREMELY LOW-CYCLE FATIGUE

M. Aghaei, S. Ziaei-Rad, N. Saeidi and E. Ahmadi

International Journal for Multiscale Computational Engineering, Volume 21, Issue 1, January 2023, Pages 43-58

ABSTRACT

Extremely low-cycle fatigue (ELCF) is a cyclic loading in which loads are large; in the plastic region, strain-controlled and specimen life is less than 1000 cycles (in some definitions less than 100 cycles). Experiments and finite element simulations were performed to obtain a suitable material model (elastic-plastic and damage model) for investigating ELCF behavior of dual-phase (DP) steel. Then it was possible to determine the hysteresis diagram, strain-life diagram, and damage initiation and propagation mechanisms. Experiments include ELCF tests to achieve the specimen life, hysteresis, and strain-life diagrams. After that, fracture surfaces of test specimens were investigated with a scanning electron microscopy (SEM) device to evaluate the involved damage mechanisms. Simulation was performed in ABAQUS software through writing a user subroutine VUMAT. In this way, after choosing an appropriate representative volume element (RVE), hardening behavior of the martensite phase was defined by means of Rodriguez equations and a combined hardening coupled with a modified Lemaitre damage model, used for the ferrite phase defined in VUMAT code, while loading and meshing were defined on a 2-D plane strain model. For verification of the modeling, two RVEs were chosen, and their results were compared with each other. Finally, hysteresis diagrams and damage mechanisms obtained from the simulation were compared with experimental results. A good agreement was observed between the simulation and experiment results.

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