ORAL/POSTER REFERENCE: ICF100398OR CYCLIC PLASTIC DEFORMATION OF PIPELINE

In the oil and gas industry, one way of laying pipes on the seafloor is by the reeling process. In this process the pipe is subjected to a cyclic plastic deformation. Due to this plastic deformation the mechanical properties of the material are changed. In this study cyclic plastic deformations are applied to laboratory specimens and alongside these experiments finite element calculations are performed to see if the material behaviour can be predicted. The specimens were subjected to 1 % and 2.5 % strain amplitude during several cycles. The experiments show that the material exhibits a lowering of the yield strength and an apparent slow transition from elastic to fully plastic behaviour after the first half cycle. To describe this in the finite element calculations three hardening models were tested: isotropic hardening, kinematic hardening and the fraction model. In the fraction model several material fractions are loaded in parallel, which allows for more complex material responses. From the calculations it followed that the isotropic and kinematic hardening models can not describe the cyclic plastic deformation of pipeline steel. Both failed to predict the lowering of the yield strength and the slow transition from elastic to fully plastic behaviour. The fraction model on the other hand can describe both phenomena