Research On The Fracture Behavior Of High-strength Circular Steel Tube Materials Based On Micromechanical Damage Models

High-strength circular steel tube has become one of the mainly selected section types of the key members in large-span space steel structures.The material properties of finished steel pipe are affected by rolling process and are discrete greatly.Additionally,the fracture properties of welded joints are also complicated.Therefore,based on microscopic damage fracture mechanisms,fracture behaviors of Q460 high-strength hot-rolled circular hollow section(CHS)steel members and their corresponding weld-deposited metal material are studied in this paper.Both experiments and finite element simulation research methods are adopted to distinguish the differences among the base metal,heat-affected zone and weld metal.From material to member two levels,fracture performance of the high-strength CHS member and its welding joint are systemly investigated.Main contents and research results of this paper are as follows:(1)Considering differences of sampling location and stress state,92 experimental specimens extracted from base material,heat-affected area and weld metal of high-strength CHS members have been designed and loaded to obtain material properties of steels respectively.The test results show that the mechanical properties of different batches of domestic high-strength hot-rolled round steel pipes are more discrete,even though the mechanical properties of the same steel pipe base material,heat-affected zone and welded deposited metal materials are also quite different.Among them,the strength of the weld metal is the highest,and the ductility is worse than that of the heat affected zone and the base metal;the heat affected zone is close to the strength of the base metal,and the ductility is comparable to the base metal,but the test data is more discrete,so special attention should be paid to this area in fracture analysis.(2)Based on the material test data,unidirectional tensile constitutive models of the base material,heat-affected area and weld deposited metal of various Q460 CHS members have been established.Based on three microscopic damage and fracture mechanisms,ABAQUS software is employed for numerical simulation,parameter identification and fracture prediction.The simulation results show that the stress state parameters have significantly influence on the ductility of steel.Generally speaking,LOU model’s fracture prediction results are better than those of VGM model and SWDM model.The applicability of SWDM model is slightly better than VGM model,but its prediction results are more discrete.(3)Three tensile fracture tests of Q460 high-strength CHS members are carried out.Furthermore,refined finite element model of steel pipe specimens has been established by ABAQUS software.Three kinds of microscopic damage and fracture models are used to predict the fracture behavior of each specimen.Research results show that although the ductile fracture failure are happened in all these CHS specimens,but the fracture of the axial-loaded pipe is a typical fracture mechanism of hole polymerization and growth,while the fracture of the eccentric-loaded pipe is a composite fracture mechanism of hole polymerization and growth as well as shear.LOU,VGM and SWDM models are all effective and applicable for fracture prediction of high-strength steel components.