Research On Influence Factors Of Micromechanical Fracture Model Parameters Of Q460D Steel Base Metal And ER55-G Welding Material

Micromechanical fracture models make it possible to predict the ductile fracture of steel structures,which provide the basis and prerequisite for controlling or even preventing the ductile fracture of steel structures under strong earthquakes.In order to study the influencing factors of parameters in micromechanical fracture models for Q460D steel base metal and ER55-G welding material,the following work was carried out in this paper:(1)In the case of combing the development history and application research situation of micromechanical fracture models,the advantages and limitations of existing micromechanical fracture models were summarized.Micromechanical fracture models under monotonic loading,i.e.Stress Modified Critical Strain model(SMCS)and Void Growth Model(VGM),and micromechanical models under extremely low cycle fatigue,i.e.Degraded Significant Plastic Strain model(DSPS)and Cyclic Void Growth Model(CVGM)were selected for further study in this paper.(2)Uniaxial tensile tests on the smooth round bar specimens of the Q460D base metal and ER55-G welding material were conducted to obtain the fundamental material behaviors which were needed in finite element analyses.It was found that there is some difference between the mechanical properties of ER55-G welding materials when along and vertical to weld length direction.(3)The Smooth-notched tensile specimens were sampled from Q460D base metal,ER55-G welding material along and vertical to weld length direction respectively.Two samples for each material with three different notch radii were performed(six for Q460D steel base metal,and six for ER55-G welding material along and vertical to weld seam respectively).Then,the smooth notched tensile(SNT)tests and finite element analyses(FMA)based on the test results were conducted.Combining the micromechanical fracture model criterion formulas and the critical stress and strain data,which were obtained by finite element analysis when crack initiates in notch area,the parameters of the micromechanical fracture models under monotonic tensile loads were calibrated.What's more,the scanning electron microscope tests on fracture surfaces of SNT specimens were performed to obtain the characteristic length7)~*.The calibration results of the parameters in micromechanical fracture models were compared and the influencing factors of the parameters under monotonic load were analyzed.(4)Similar to the monotonic tensile specimens,smooth-notched cyclic specimens were sampled from Q460D base metal,ER55-G welding materials along and vertical to weld length direction respectively,and twelve samples for each material with three different notch radii were performed(a total of one hundred and eight smooth notched round bar specimens).Then,the low-cycle reversed loading tests under six kinds of loading processes on the specimens and corresponding finite element analyses were conducted.Through combining the test results with ABAQUS finite element analyses,the micromechanical fracture model parameters of the Q460D steel base metal and ER55-G welding materials along and vertical to weld length direction were calibrated.The influencing factors of parameters in micromechanical fracture models under extremely low cycle fatigue loading were studied in comparison of the parameter calibration results.