Abstract

Large diameter steel pipelines for gas transportation may experience extreme overloads due to external actions such as soil sliding, faults movements, third part interactions. In these scenarios the material undergoes severe plastic strains which locally may reach the fracture limits. Due to the manufacturing process, the steels used in such applications have an anisotropic behavior both for plasticity and fracture. In this paper two steel grades have been characterized in view of anisotropic plastic fracture. Fracture tests have been planned to characterize the fracture behavior under different stress states and in different directions to define the anisotropic sensitivity. Finite element modelling, incorporating an anisotropic plasticity formulation, has been used to calculate the local fracture parameters in the specimens and to define the complete ductile fracture locus. An uncoupled damage evolution law has been finally used to evaluate the fracture limits on real pipelines failed in full scale laboratory tests. The strain to fracture prediction has been verified by local strain measurements on the fractured pipes. The model robustness has been also verified on global parameter predictions, such us the burst pressure.

Abstract

A hybrid experimental-numerical approach to characterize plasticity and ductile fracture properties of aluminum 6061-T4 sheet is presented. The anisotropic elasto-plastic behavior is characterized by a Barlat89 model and the ductile fracture behavior by a GISSMO model in combination with the Xue-Wierzbicki model. We discuss then the validation procedure and the results related to a deep-drawing case where the simulation is carried out in a commercial FE-solver LS-DYNA. The drawing depth at fracture, as an exemplary result, shows a very good agreement between simulation and experiment.