| High strength structural steels have been widely applied in building structure,bridge project,tower and mast structure,which have excellent performance of structural strength,easy connection and mechanical manufacturing.The fracture of structural steel can lead to serious social problems,so the fracture of steel has become a hot topic in the construction industry.To explore the ductile fracture property of Q460 D HSLA steel under different stress triaxiality and Lode parameter,and obtain fracture parameters in many ductile fracture criteria,the test of axial symmetry round bar specimens and notched round bar specimens tensile,axisymmetric cylindrical compression,flat notched specimens tensile and flat grooved specimens tensile are conducted.The fracture is analysed by SEM and microstructure metallography technicals.The ABAQUS finite element simulation analysis is used to study the sample.The Q460 D structural steel is calibrated by experiment and the ABAQUS finite element simulation analysis including stress modified critical strain model?,void growth model?,and Rice-Tracey ductile fracture criterion which widely used in fracture prediction analysis of steel structure.According to the stress triaxiality,the Lode angle parameter and the fracture strain data collected by ABAQUS finite element method,the iMPact in fracture process of Q460 D structural steel is studied.And equivalent fracture strainf?-stress triaxiality ? two-dimensional fracture path and equivalent fracture strainf?-stress triaxiality ?-Lode angle parameters ?three-dimensional fracture path are displayed.The result show:(1)The yield stress and ultimate stress of notched round bar specimens and flat grooved specimens increase with increasing notch sharpness,the toughness of theQ460 D steel is not sensitive to the strain rate at the given loading rate,which shows that the effect of strain rate on steel can not be considered.(2)The microstructures of notched round bar specimens under high stress triaxiality are typical microporous polymerized ductile fracture,and the microstructure is transgranular fracture.The fracture form of flat notched specimen under pure shear is brittle and transcrystalline cleavage fracture.The fracture of flat notched specimen with pull-shear stress in the low stress triaxiality state is compound micropore fracture,microstructure was tearing dimple.The fracture surface in the plane strain is uneven,and the incision at the fracture and ditch makes the fracture appear along the ductile ductile fracture.(3)The round tensile fracture of ferrite and pearlite polymerization deformation is a parabola.Pure shear fracture tissue into strip,deformation occurred in the ferrite and pearlite boundary.The ferrite becomes coarse and abnormal when the tensile shear fracture,and the pearlite becomes fine.The whole structure is elongated under plane strain condition fracture.(4)The SMCS fracture model parameter and the VGM fracture model parameter of Q460 D structural steel were calibrated.With the increase of the toughness of the steel structure,the fracture parameters will be increased.at the same time,calibration of the Rice-Tracey fracture criterion,when structural steel at different Lode angles the fracture strain trend would be changed.(5)The initial stress of the Q460 D structural steel increases with the decrease of the cutting radius of the stress triaxiality.Under the same Lode angle parameters,the fracture strain of the steel decreases with the increase of thestress triaxiality,and the ductility of Q460 D steel has a certain dependence on the Lode angle.The results obtained in this paper can be used to calibrate a series of micromechanism fracture models of Q460 D structural steel.The calibrated fracture model can be applied to the fracture prediction and failure analysis of the actual steel structure. |
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