Experimental and FEA Investigations on the Fracture Properties of Pipe Structures Under Internal Pressure in DBTT Region

The fracture behavior of pipes with penetrating cracks was experimentally investigated with the results of the load-deflection curves and crack length. $J-R$ curves were obtained from the testing results for different temperatures. With the decrement in temperature, the critical $J$ integral decreases and the tearing modulus increases. An updated continuum damage model was proposed, in which the fracture energy density as a function of the stress triaxiality, temperature and strain rate in the transition region was taken as the critical damage factor. The uni-axial tension experiments at different temperatures were carried out to obtain the basic material properties and the critical fracture energy density, to verify the validity of the damage model. Based on detailed finite element analyses with the proposed updated continuum damage model, the loading level of pipes with penetrating cracks was estimated and compared with the experimental results, meanwhile the fracture processes of the pipeline structure in the ductile-brittle-transition-temperature region were reproduced. It has been shown that the fracture process in the transition region strongly depends on both the stress and strain state, and can be effectively predicted using the continuum damage models incorporating with the stress state effect.