Fatigue crack growth in tubulars caused by nonlinear dynamic loading

The fatigue performance of offshore structures in the oil and gas industry is vital to the reliability and integrity during service life, and there are very few studies on fatigue cracks induced dynamically to tubulars. Capability of a unique experimental fatigue rig designed to test single-edge notched beams [1] was in this work expanded allowing to obtain for new insights into fatigue crack growth in tubular specimens. Fatigue cracks were initiated in pre-cut grooves in aluminium tubular specimens and then under dynamic loading propagated in the direction of the groove. The alternating current potential difference (ACPD) method was adopted to monitor the crack propagation in time histories. Three specimen types featuring different groove depths were made and tested in fifteen individual experiments. And for each specimen type, a three-dimensional finite element model was created to calculate the stress concentration factor (SCF). Experimental measurements of specimen accelerations and forces generated were used to develop a novel calibrated dynamic model, for which dynamic responses were computed. The predictions obtained from a mathematical model were compared with the experimental results and a close correlation was observed.