A Simplified Strategy to Address Effects of the Drop of Temperature on the Gurson-Tvergaard-Needleman Model for G20Mn5QT Cast Steels

Abstract

G20Mn5QT cast steels have been widely used in cast steel connections, which may suffer from ductile fracture at ambient temperature. Northern climates make the problem even worse because the ductility of the cast steels deteriorates with the drop of temperature. For ductile fracture analysis of cast steel connections working at low temperatures, Gurson-Tvergaard-Needleman (GTN) models were calibrated and validated for G20Mn5QT cast steels at 20°C, −20°C, −40°C, and −60°C based on previous test results. The effects of the drop of temperature on material parameters in GTN models of G20Mn5QT cast steels were determined. A simplified strategy was proposed to address the effects of the drop of temperature by two GTN parameters, the void nucleation strain εN and the critical void volume fraction fc. It was found that εN decreased almost linearly with the drop of temperature, and fc had a similar relationship with the drop of temperature as the Charpy impact energy. The relationships between these two parameters and the drop of temperature were presented for the establishment of GTN models for G20Mn5QT cast steels at any possible low temperatures. Scanning electron microscope (SEM) micrographs indicated that the dimple-based ductile fracture mechanism was dominant in the fracture of G20Mn5QT cast steels, which was accompanied by possible quasi-cleavage fracture at low temperatures.