Tubular joints subjected to cyclic wave loads are prone to fatigue cracks. It is generally considered the most critical failure mode in mechanical and structural systems. Most of the jacket structures in the offshore industry run more than the service life due to existing oil and gas reserves, and it leads to ensuring structural integrity is maintained. Evaluation of crack propagation using the Fracture Mechanics (FM) approach (Paris law) is commonly adopted for simple geometry. However, the application of Paris law and SIF based method is not feasible to reflect the complex geometry in tubular joints, including initial defects becoming impossible. Hence a Finite Element (FE) analysis-based method is adopted in the present study to investigate the crack propagation in tubular joints. The simulation was carried out using ZENCRACK software for local crack propagation together with the FE analysis program Abaqus. The numerical simulation of crack propagation in a joint with an initial crack depth and thickness ratio of 0.2 at the crown has been carried out and the results are compared with that obtained from experiments. Experimental studies using a scale model (1: 13) of the joint with an initial crack has been conducted under axial cyclic loading with a loading ratio and frequency of 0.1 & 1.2Hz, respectively. The relationship between applied stress and the number of cycles till failure (S-N curve) has been generated based on the recorded time history of strain measurements. The crack growth pattern at the brace-chord intersection has been presented and discussed.
Keywords: Fracture mechanics, SIF, Finite element method, Semi-elliptical crack, Crack growth, Paris Law.