Fatigue Behavior and Failure Assessment of Plate Connections in Ship Shaped Structures

Abstract

The complicated, welded plate connections are conventional details adopted in the design of ship shaped structures. If these plate connections are not adequately designed, significant fatigue cracking may initiate undetected in structures. Historically, little research has been conducted on full spectral fatigue analysis using both the hydrodynamic loading and associated refined solid finite element (FE) models with detailed weld representations. Moreover, experience has shown that the construction of a ship shaped structure, which can completely resist fatigue cracking, is economically infeasible. Thus flaw assessment on a fitness for purpose basis is needed to identify the limiting conditions for failure. In this study a fatigue analysis procedure based on MSC.Patran and Abaqus is proposed. The procedure is more convenient than the software package recommended by classification society because the supplementary development abilities are widely used in the proposed procedure. A linear hydrodynamic program with Green's function method is developed in Matlab and embedded into MSC.Patran PCL environment. More than 6000 FE analyses have been conducted using Abaqus/Standard. This research describes effects of weld strength mismatch on the elastic-plastic driving force of root crack resided in the cruciform joint, which is simplified from typical longitudinal connections. The presence of residual stresses may affect the fracture behavior significantly. In this study an eigenstrain approach is proposed to impose the residual stress fields to 3-D FE models. A method without crack propagation analysis is developed to calculate the applied crack driving force versus load for a particular cracked structure.