Study On Ductile Fracture Of Steel And Weld Metal Based On Micro-Mechanism

The use of steel is very extensive,it will have serious consequences once it is damaged.The ductile fracture is a very important fracture method,therefore,the analysis and prediction of the ductile fracture of steel is a very important issue which has the importance of protecting people's lives and property.Many scholars at home and abroad have conducted a series of studies and achieved fruitful results who developed ductile fracture criterion based on the micro damage mechanism from the traditional stress intensity factor criterion,J-integral criterion,crack tip open displacement criterion etc,besides,a series of fracture prediction models were proposed and good fracture prediction results were obtained.The stress triaxiality and Lode angle become two important parameters to describe the stress state and are the main variables in the current fracture models.The ductile fracture process of steel includes the elastic stage,the hardening stage and the softening stage,for the first two stages,people have studied quite well,but for the last,there are few studies.Based on previous research results,this article adopts the VMX model which combines the isotropic hardening,stress triaxiality,Lode angle and softening stage.This paper studies the problem of uniaxial tension and introduces the basic theory of micro damage mechanisms and related parameters.The Swift and Voce mixed model is used to fit the true stress-plastic strain relationship after necking to improve accuracy.The VUMAT subroutine was written in Fortran language,the various stages of the development of ductile fracture were realized by programs and calculated in the ABAQUS display analysis module.In this paper,fracture prediction and analysis are performed on 9 base metal specimens and 9 weld metal specimens,the results show that the isotropic hardening criterion is applicable to the monotonic loading,and the Swift and Voce mixed model is true to the after necking,the true stress-plastic strain relationship is well fitted,and the VMX model has good applicability to monotonic loading.