A triaxiality and Lode parameter dependent ductile fracture criterion

• Micromechanics based approach to determine the transition triaxiality at which the damage mechanism changes is provided.
• Factors that influence transition triaxiality are discussed.
• Qualitative computational failure locus is developed using micromechanics.
• A calibrated fracture locus for ASTM A992 steels is provided.
• Calibrated fracture locus is used to predict fracture in ASTM A992 specimens.

A computational fracture locus is developed and used to predict the ductile fracture in ATSM A992 steels in this study. The fracture locus is obtained by performing micromechanical analyses on the computational cells by deforming computational cells along paths of predefined stress states described by two dimensionless stress-state parameters: stress triaxiality (Tσ) and Lode parameter (L). The microscopic damage mechanisms at different stress-states are demonstrated. The microscopic damage mechanism is observed to change from predominantly microvoid elongation to microvoid dilation at transition triaxiality of Tσ = 0.75 for ASTM A992 steels. This transition stress triaxiality is found to be dependent on hardening and microstructural properties of the matrix. Also, at low triaxiality, the Lode parameter is found to have a significant effect on the microvoid elongation and dilation for ASTM A992 steels. The computational fracture locus which is a function of triaxiality and Lode parameter proposed for ASTM A992 steels is implemented in the finite element program ABAQUS® as a ductile fracture criterion. This fracture model is validated using the existing experimental data on axisymmetrically notched specimens and new data on plate with holes and notches made of ASTM A992 steels. The procedure prescribed to develop the fracture criterion in this manuscript is generic and can be used for other metals whose hardening and microstructural properties are known.