Study on fracture characteristics of A7N01S-T5 butt weld classified by hardness under different stress states

Conduct a detailed study on the ductile fracture characteristics of A7N01S-T5 arc welding butt weld. Firstly, the weld area was divided through hardness testing, and it was found that the base metal area (BM) of A7N01S-T5 butt weld had the highest hardness, while the weld nugget area (WM) had the lowest hardness. Except for a weak hardness section (HAZ II) in the heat-affected zone, the hardness of the other areas (HAZ I) was close to that of the base metal. A series of fracture tests were conducted in different regions, and information on stress state parameters and equivalent fracture strain of different tests was obtained based on DIC technology and finite element reverse engineering method. On this basis, constitutive and fracture models of materials in different regions were constructed using the Swfit-Voce joint hardening criterion, DF2014 criteria, and DF2016 criteria. Finally, two uniaxial tensile loads and one three-point bending load were tested and simulated for the welded joints. The results indicate that the material model constructed by partitioning can effectively characterize the ductile fracture behavior of butt weld under different loads. For weld-enhanced joints, HAZ II has the lowest tensile strength; For ground flat joints, WM has the lowest tensile strength. Under the action of a three-point bending load, the ultimate bearing load and fracture displacement of the joint have a certain degree of discreteness due to the existence of quasi-brittle zones in the joint and the differences in defects at different positions of the weld.