Fracture Mechanism and Gurson–Tvergaard–Needleman Damage Modeling of NbTi Alloy

In the multipass bundle-drawing process of multifilament composite wire of NbTi alloy, the cored wire is prone to damage and even fracture due to severe plastic deformation. Therefore, it is necessary to study the fracture mechanism of NbTi alloy in plastic deformation and conduct a model of the fracture process. A quasi-static uniaxial tensile test was conducted at room temperature, taking the Nb-47 wt.% Ti alloy as the experimental material. The fracture morphology and damage evolution were observed using scanning electron microscopy. The fracture morphology of the NbTi alloy presents a ‘cup-cone’ shape. The damage evolution shows the characteristics of microvoid nucleation and growth to microcrack formation, indicating that the fracture mechanism of the alloy is a typical microvoid coalescing ductile fracture. The Gurson–Tvergaard–Needleman (GTN) damage model is used in the finite element simulation for the uniaxial tensile process of NbTi alloy, and the microvoid volume fraction-related damage parameters in the model are determined by the reverse calibration method. The damage behavior in the multipass bundle-drawing process of the NbTi/Cu multifilament composite wire is predicted by the GTN damage model with calibrated damage parameters.