Simulations of Ductile Tearing at Large Strains of Biaxially Loaded Pipes

The purpose of the present paper is to present results from analyses of ductile tearing of biaxially loaded pipes subjected to large scale yielding. The paper deals with three dimensional finite element modelling of pipes with a circumferentially orientated surface crack, where the analyses aim to reproduce the crack propagation behaviour of six full scale bend tests of x-65 seamless pipes with different levels of internal overpressure. The tests were performed as a part of the joint industry project Fracture Control - Offshore Pipelines. Ductile tearing is taken into account by using the Gurson-Tvergaard-Needleman formulation, where calibration of the material model parameters is done by reproducing the fracture toughness test of a SENT-specimen of the same material with finite element modelling. The following simulations of the pipes show a good correspondence with the full scale test results, where both the global response and the ductile tearing from the crack are captured. One important result of the study is that the Gurson-Tvergaard-Needleman parameters that were calibrated against the SENT-specimen could successfully be used for the ductile tearing simulation of the full scale pipes.