Ductile Fracture Analysis of Welded Hollow Spherical Joints Subjecting Axial Forces with Micromechanical Fracture Models

Two micromechanical fracture models, void growth model (VGM) and stress modified critical strain (SMCS) model, were adopted to distinguish the failure mechanism of welded hollow spherical (WHS) joints under axial load based on FE analysis. Ductile fracture was successfully predicted for WHS joints under axial tension. The predicted fracture location is at the weld toe between WHS joints and circular hollow section members, which is consistent with corresponding test results. The predicted fracture load is lower than the peak load on the load-displacement curve, which indicates that the failure mechanism of WHS joints under axial tension is fracture due to inadequate strength and the fracture load should be taken as the ultimate load bearing capacity of the joints. A simplified SMCS model was proposed and verified for ductile fracture prediction of WHS joints under axial tension. Micromechanical fracture analysis was also conducted on WHS joints under axial compression. It was obtained by both VGM and SMCS model that no fracture would occur before the load reached its peak value, the reason of which was discussed by tracing the variation of the equivalent plastic stain and stress triaxiality at the potential location of fracture. Therefore, the failure mechanism of WHS joints under axial compression is losing stability with the depression of the sphere cap and the peak load on the load-displacement curve should be taken as the ultimate load bearing capacity of WHS joints.