Abstract:
This study develops a high-fidelity analytical methodology using Finite Element Analysis to predict the high cycle fatigue life of a problematic deck truss-to-bulkhead flooring connection detail on U.S. Navy DDG-51 class destroyers. A detailed, three-dimensional global/local Finite Element modeling technique was employed using the ABAQUS software to accurately determine the stress state at the crack initiation site. A global FEA model, composed primarily of shell elements, represented a large section of the ship's deck structure to capture the overall load paths and stiffness. The displacements from this global model were then applied as boundary conditions to a highly refined, local solid-element submodel of the specific flooring connection detail. This local submodel, which utilized 20-noded quadratic brick and 15-noded wedge elements, allowed for a precise stress analysis in the complex geometry of the connection. To simulate crack propagation, the local stress analysis results were integrated with the fracture mechanics software ZENCRACK, which automatically updated the local FEA mesh to include a semi-elliptical surface crack using specialized quarter-point, 20-noded brick elements at the crack tip. Stress intensity factors were calculated along the crack front using the M-integral method and used in a fatigue crack growth analysis with the NASGRO life prediction equation to determine the number of cycles for the crack to grow to a critical size. The Finite Element based analysis successfully predicted fatigue lives that were consistent with shipboard observations of cracking, validating the global/local FEA and fracture mechanics approach as a powerful tool for evaluating complex naval structural details and potential design modifications.
