A CDM-based constitutive model for structural steel considering ULCF damage accumulation

Steel structures typically exhibit the degradation in mechanical properties under large strain cyclic loads , such as the decrease of capacity and stiffness, which form the failure mode dominated by ductile fracture . However, existing methods for assessing such damage mainly focus on the ultra-low cycle fatigue (ULCF) life prediction, while neglecting the mechanical evolution of materials during the damage process. To this end, this paper proposes a novel constitutive model for structural steels considering the damage accumulation of ULCF. Firstly, a damage index for accounting the ULCF damage was developed based on the continuous damage mechanics. And based on the proposed damage index, the stiffness and the yield stress of the commonly used Chaboche constitutive model were improved. Cyclic loading tests on coupon specimens and circular notched specimens were conducted to explore and fit the relationship between the constitutive parameters and the damage index. Finally, the accuracy of the proposed constitutive model was verified through detailed comparisons between finite element analyses and tests. Results show that the proposed model can be used to describe the cyclic behavior of structural steels during the development process of ULCF with high accuracy. • A new damage index for assessing the ductile damage was proposed. • A novel constitutive model that can consider the mechanical degradation under large strain cyclic loads was proposed. • The accuracy of the proposed constitutive model was verified by tests. • The mechanism of ductile damage accumulation affected by stress triaxiality was discussed.