Research On Meso-mechanical Properties And Fatigue Strength Of Ti₂AlNb Alloy Electron Beam Welded Joints

The failure or fatigue behaviors of Ti₂ AlNb electron beam welded?EBW? joint, with the mechanical heterogeneity characteristics, is closely bound up with the mechanical properties in the micro zones of the welded joint. The nano-indentation technology and FEM technique and the digital image correlation?DIC? technique were used to study the mechanical heterogeneous of Ti₂ AlNb welded joints and to analyze the tensile and fatigue properties of Ti₂ AlNb welded joints.In order to obtain the mechanical properties of the micro zones of Ti₂ AlNb electron beam welded?EBW? joint, the finite element method was used to simulate the load-depth curve, in which the Ludwick hardening model was used, and the map form between the load-depth curve of nano-indentation and the Ludwick hardening model can be established. Furthermore, the constitutive relations of the micro zones of welded joint can be obtained by means of reverse analysis. In the process of establishing those relations, a multi-points fitting method was proposed to improve the robustness of the reverse analysis, in which the sensitivity of it was discussed. Based on the works above, the nano-indentation tests for the Ti₂ AlNb EBM joint were conducted and the map forms between the load-depth curves and constitutive relations?based on the Ludwick hardening model? for the micro zones of the joint were established, in which the multi-point fitting method was applied. The constitutive relations based on the Ludwick hardening models for the micro zones of Ti₂ AlNb EBM joint were obtained, and they were introduced into finite element model by means of the partition modeling method. The simulation for the tensile process of the joint were performed and compared with corresponding local deformation test results, and the simulation results of the mechanical behavior of the joint are in good agreement with the experimental results.For the sake of the researches on the low cycle fatigue behavior of the Ti₂ AlNb EBM joint, the fatigue parameters of Manson-Coffin equation were obtained by means of the B?umel-Seeger method and, on the basis of the FEM simulation above, Morrow's mean stress correction of Manson-Coffin equation and SWT model were used to evaluate the low cycle fatigue life of the joint. The results show that SWT model works better in the evaluation of the low cycle fatigue life and failure zone of the joint.