Research And Application On Fracture Toughness Of Q460D High Strength Steel Base Metal And ER55-G Welding Material

With the application of Q460 high strength steel in engineering,its fracture problems occurred occasionally.Therefore,it is particularly necessary to study the fracture toughness of Q460 high strength steel and its weld.In order to study the fracture toughness of Q460D high-strength steel base material and corresponding ER55-G welding material and its application in steel frame beam-column connections,the following work was carried out in this paper:（1）Fracture mechanics,micromechanical fracture models and other related theories were reviewed.The research status of steel fracture toughness and steel frame beam-column connections at home and abroad was summarized.Fracture mechanics-J integral and micromechanical fracture models VGM and SMCS were selected to study the fracture toughness of Q460D high-strength steel base metal and corresponding ER55-G welding material and the fracture performance of steel frame beam-column connection under monotonic load.（2）Compact tensile tests were carried out on CT and BN test specimens taken from Q460D high-strength steel base metal and ER55-G welding material to obtain the fracture toughness J_IC value of Q460D high-strength steel base metal and ER55-G welding material,and the fracture elongation₁)of each BN test specimen.（3）The elastoplastic finite element analyses（FEA）of CT specimens were performed using the Contour integral method in ABAQUS,and the accuracy of the method was verified by comparing the FEA results and the test results.The thickness of the specimen model was changed to analyze the influence of the thickness on the stress field at the crack tip of the compact tensile specimen.The fracture toughness of other strength steels was collected and studied,and the effect of strength on the fracture toughness of the material was studied.（4）The compact tensile test specimens（CT and BN test specimens）of Q460D high-strength steel base metal and ER55-G welding material were analyzed by using micromechanical fracture models VGM and SMCS combined with ABAQUS finite element software,and the applicability of micromechanical fracture models in compact tensile tests was discussed.（5）A finite element model was established for the local specimens of Q460C high strength steel joints,the J-integral based fracture mechanics approach was used to predict its fracture,and the prediction results are compared with the prediction results of the micromechanics fracture model VGM and SMCS,as well as the test results,to verify the accuracy of the finite element model and the traditional fracture mechanics J integral for predicting the fracture of local joint specimens,at the same time,to explore the applicability of the micromechanics fracture model in the research of local joint specimens with initial defects.（6）The J-integral based fracture mechanics approach and micromechanics fracture model VGM and SMCS were used to perform finite element analysis on the cross-shaped Q460D high-strength steel frame beam-column joints of three types of welding holes.The effects of initial defect location,initial defect length,notch radius and welding hole form on the fracture index were studied,and the effect of welding hole form on the ultimate bearing capacity and critical fracture displacement of the joint specimen was further studied.