Integrated local/global analysis and fracture assessment of pipelines with defects

The present study addresses nonlinear finite element analysis of pipelines subjected to e.g. large curvatures. Cracks are accounted for by means of a newly developed line spring finite element formulation. Linking these elements to shell elements, and further linking the shell elements to beam elements, one has a global model of the pipeline that also accounts for local flexibilities and fractures due to defects (in the welds). This has obvious practical advantages, e.g. related to easy meshing/preprocessing, in addition to having a tool that directly provides fracture mechanics quantities, such as J-integral/CTOD etc, that is compared to the fracture toughness of the material. A recent development in this respect is the notion of two-parameter fracture assessment. This means that both the crack tip stress tri-axiality (constraint) and the corresponding fracture toughness is employed in the assessment, giving a much more realistic capacity of cracked structures. The above simulations are carried out using a developers version of the software USFOS, accounting for large displacements and plasticity.