Assessment of constraint independence and temperature dependence of critical fracture energy, Gfr

Characterisation of ductile fracture is a major problem, especially in the nuclear industry where the material behaviour needs to be characterized over a wide range of temperature considering the embrittlement of the material due to irradiation.. Use of the J-Δa curve for stable crack growth is useful, but transfer of crack growth curve from specimen to component is difficult due to dependence on constraint (geometry, a/W).A new fracture parameter critical fracture energy, Gfr, based on segregation of fracture energy from total energy is explored to simulate ductile crack growth during ductile tearing test by Marie and Chapuliot. The present work aims in estimating Gfr for the material 20MnMoNi55 steel for different initial a/W ratio, different crack growth and the independence of Gfr on these parameters is verified. As ductile material starts behaving in a brittle manner at low temperature so it is expected that the estimated Gfr will decrease with the decrease in temperature. In this work Gfr is also measured at different low temperatures (200C to -80°C) and is observed to be decreasing with temperature.