Abstract :
In theDuctile-Brittle Transition Temperature (DBTT) region, it is not realistic to
take unique fracture stress or fracture strain as the fracture criterion to investigate the fracture
properties. In this paper, an updated continuum damage model was proposed, in which the
fracture energy density, a function of the stress triaxiality, temperature and strain rate in the
transition region was taken as the critical damage factor. Uniaxial tension tests were carried
out to get the basic material properties at different temperatures, to calibrate the fracture
model constants and verify the validity of the damage model. The fracture behaviour of pipes
with penetrating cracks under the internal pressure was experimentally investigated with the
load-deflection curves and the crack propagation length captured from tests. The J-R curves
were obtained from the testing results for different temperatures. Based on the Finite Element
Analyses (FEA) with the proposed fracture criterion of the updated continuum damage
model, the loading level of pipes with penetrating cracks were estimated and compared with
the experimental results. Meanwhile the fracture processes of the pipeline structures in the
transition region were reproduced. The experimental and numerical results agreed very well
in present calculations. It has been shown that the fracture process in the transition region
strongly depends on both the stress and strain states, and could be effectively predicted using
the continuum damage model.
