Multi-scale analysis of mechanical properties of high-strength steel with heterogeneous characteristics after pre-fatigue damage

Abstract

This study investigates the residual mechanical behavior of Q690 high-strength steel after pre-fatigue damage by explicitly considering the non-homogeneous characteristics of the initial material. A framework combining experiments, molecular dynamics (MD) simulations, and finite element (FE) modeling is established. Monotonic tensile tests and fatigue experiments are first conducted to characterize the initial mechanical properties and the S–N relationship. Tensile tests on specimens subjected to different levels of pre-fatigue damage are then performed to quantify the degradation of elastic modulus, yield strength, ultimate strength, and ultimate strain. At the microscopic level, MD simulations are employed to reveal the damage evolution mechanisms and the atomic-scale origins of residual property degradation under cyclic loading. The obtained degradation laws are further incorporated into FE models with non-homogeneous initial material properties to simulate the fracture process and post-fatigue mechanical response. The results show that pre-fatigue damage has a negligible effect on the elastic modulus. A moderate strengthening effect on yield strength is observed at low damage levels, followed by a clear reduction with increasing fatigue damage. In contrast, ultimate strength and ultimate strain decrease monotonically, with the ultimate strain being more sensitive to fatigue damage. The proposed non-homogeneous multiscale modeling framework provides a more realistic description of fracture behavior and residual performance degradation in high-strength steels subjected to fatigue loading.