Study On Fracture Performance Of High Strength Steel And T-shape Welded Connections Based On Shear Modified GTN Model

ABSTRACT:The popularization and application of high strength steel structure is the inevitable trend of the development of architecture science and technology,but the deformation ability of high strength steel is worse than that of ordinary steel,and the brittle change tendency of welding connection is more serious.Therefore,based on the Gurson-Tvergaard-Needleman(GTN)micro damage fracture prediction model,the fracture properties of domestic Q460 high strength steel and T shaped butt welded joint are systematically studied in this paper,so as to provide scientific basis and technical support for the study of the mechanical properties of complex high-strength steel joints and systems.The specific research contents are as follows:(1)39 smooth and notched round bar specimens were machined from the parent material,weld and heat affected zone of the domestic Q460C steel plate and 24 smooth flat plate,groove plate and rectangular notched specimens were processed from domestic Q460D steel sheet metal.So a total of 33 uniaxial tensile and 30 ultra-low cycle fatigue tests were conducted.The results show that the tensile elongation of the Q460 high strength steel is more than 25.1%and the hysteretic fracture strain is about 6%;The tensile elongation of weld and heat affected zone is 23.7%and 26.6%respectively,while the hysteretic fracture strain is only 3.2%and 4.4%respectively;When the Lode angle parameter is the same,the strength of the steel increases and the fracture displacement decreases with the increase of the stress triaxiality;When the Lode angle parameter approaches 0,the micro-mechanism failure of steel is different from that of "nucleation,growth and coalescence of micropores".(2)10 T-shape welded connections with different thickness and angle were machined by one-sided forming full penetration welding technology.Then 5 uniaxial tensile and 5 ultra-low cycle fatigue tests were completed respectively.The results show that the "stress-strain" curve of welded connections has no yield platform,and the plastic deformation ability is significantly lower than that of base metal,heat affected zone and weld.The fracture "elongation" of the 5 uniaxial tensile specimens varies between 7.6%?11.7%and the strain of hysteretic fracture is as low as 2.6%.The ductility of the thin T-shape welded connections is the worst,but the ductility of the thick T-shape welded connections with obtuse angle increased significantly.(3)The traditional GTN model is used to make a fine numerical analysis of the uniaxial tensile specimens.The damage parameters of the GTN model of the Q460 high strength steel base metal,the weld and the heat affected zone are identified respectively.It is found that the traditional GTN model can accurately predict the fracture time of the steel at the middle and high stress triaxiality,but for the specimens with Lode angle parameter approaching 0,the prediction results are poor.(4)The VUMAT user material subroutine is written and the shear modified GTN model is embedded in the ABAQUS.The fracture simulation of the T-shape welded connections is realized,and the suitable shear damage parameters for the welded joint are given.