Study On Extremely Low Cycle Fatigue Ductility Fracture Of Q460 Steel And Weld Zone

Steel will undergo fatigue fracture with obvious plastic deformation under the action of earthquake.It is called extremely low cycle fatigue ductile fracture of steel.In recent years,scholars at home and abroad have conducted a large number of researches on ordinary steel based on the micro-damage and fracture mechanism,and proposed a series of micro-damage fracture prediction models,with achieved good prediction results.However,the study of extremely low cycle fatigue ductile fractures is not yet mature.Based on the previous research,this paper comprehensively considers the behavioral characteristics of the mixed hardening model of steel,and proposes the fracture prediction model VMX concerning the relevant physical factors such as stress triaxiality and Rode angle,considering the nonlinear loading process for steel,and the impact of the damage accumulation,as well as the softening behavior of the steel during the fracture process.The VUMAT material subroutine for ABAQUS was compiled by"Fortran language",and the extremely low cycle fatigue state constitutive model and fracture prediction analysis of Q460 steel and weld metal were performed.This paper introduces the theoretical basis of the microdamage fracture model,compares and analyzes the characteristics of the VMX model and other models,and derives the realization theory of the Voce-Chaboche nonlinear hybrid hardening model with the VMX fracture prediction model in the material subroutine VUMAT.The program compiled by "Fortran language" is embedded into the ABAQUS explicit analysis module,and the constitutive simulations are performed on twenty five Q460 steel extremely low cycle fatigue specimens and nineteen weld metal extremely low cycle fatigue specimens of different types and different loading systems.The fracture predictions of six Q460 steel extremely low cycle fatigue specimens and six weld metal extremely low cycle fatigue specimens of the augmented loading system were analyzed,and the influence of the VMX model parameters was analyzed.The analysis results show that the Voce-Chaboche nonlinear mixed hardening model has good applicability to the mixed hardening behavior of Q460 steel and weld metal during cyclic loading.When extremely low cycle fatigue ductility of VMX model used to Q460 steel and welded metal,the result of fracture prediction has good applicability.The loading circle and crack development position are in good agreement with the test results.Using unit cell deletion technology,the trend of crack development of the specimens was successfully simulated.