Dynamic Fatigue Crack propagation in tubular specimens

Gauging the fatigue performance of structures such as offshore jackets that are subject to cyclic loading is essential in the design and life extensions to ensure the suitability of the service. A novel fatigue rig that was developed at the Centre for Applied Dynamics Research in Aberdeen was recently modified to undertake
experimental tests on tubular specimens with a range of sizes and various cross-sections while monitoring dynamic forces applied to the specimen using two new load-cells. The crack initiation and propagation on tubular specimens with pre-cut grooves were investigated using an alternating current potential difference (ACPD) method. Crack length time histories have also been constructed. The mathematical model describing the rig behaviour with cracked specimens was formulated, and the stiffness of the plastic components in contact with the specimens was refined in the mathematical model. The mathematical model of the rig was further refined to implement the stiffnesses of different components. The results of the mathematical model were compared against the measurements from experimental data acquisition. Following the calibration of the mathematical model, it was observed that the model response is very close to that from experimental measurement. The validated mathematical model can predict the response of the fatigue rig, which enables the calibration of the experimental parameters in advance to achieve the desired response from the system.