Coupled continuum damage mechanics and porous plasticity approaches for modeling temperature driven ductile to brittle transition fracture in metals

Fracture in metals is generally characterized in two different categories. Named as ductile and brittle, these fracture types heavily depend on environmental conditions such as, temperature, strain rate and stress triaxiality. Increasing temperature increases the degree of ductility while increasing strain rates and stress triaxiality ratios increase the degree of brittleness. Depending on these conditions, the mode of fracture changes from ductile to brittle and vice versa, which is called the ductile to brittle transition phenomenon. Within the context of this work, two different theoretical constitutive models for temperature driven ductile to brittle transition fracture have been developed. In both of these approaches, Gurson-Tvergaard-Needleman porous plasticity model has been employed to represent void-growth and coalescence dependent ductile fracture. Void-Volume ratio has been utilized as main ductile fracture indicator for GTN model. For brittle fracture, two different models have been proposed. Leckie-Hayhurst creep model has been modified to represent principal stress effects on microcrack initiation and growth prior to brittle fracture. Another brittle damage model has been chosen as Lemaitre-type continuous damage model, which also represents microcrack growth driven brittle failure, while representing softening effects due to crack initiation and growth. Ductile and brittle damage effects have been coupled over classical effective stress framework.First transition fracture model has been developed based on hypoelasticity of continuum mechanics. Developed model has been implemented in ABAQUS as a user defined material model. Single element tests have been performed to validate implementation. Later, small punch fracture tests performed by Turba et.al. (2011) has been modeled and its experimental results have been compared with developed models numerical results. Second approach to transition fracture has been developed based on hyperelastic framework of continuum mechanics. This approach not only serves as a basis to further extend the brittle fracture considering anisotropy of microcracks.