This paper presents a practical method to evaluate the stress intensity factor (SIF) for welded plate joints with a semi-elliptical surface crack, based on the 2D weight function. According to the expression initially proposed by Wang & Glinka (2009), an improved 2D weight function for surface cracks in finite thickness plate is firstly developed. In order to overcome the limitation of reference solutions, three-dimensional finite element (FE) models have been created to calculate the SIFs for surface cracks with aspect ratio a/c=0.05∼1.0 and crack-depth to platethickness ratio a/T=0.01∼0.8. Subsequently, the effectiveness of the proposed weight functions has been verified by the SIFs given by FE models under several two-dimensional stress distributions. Finally, it is demonstrated that the 2D weight function is suitable to evaluate the SIFs of weld-toe surface cracks in different types of welded plate joints of ship structures.

INTRODUCTION

Welded plate joints are widely used in ships and marine structures. The weld defects or crack-like flaws usually initiate at the weld toe region and gradually grow as semi-elliptical surface cracks. Accurate stress intensity factor (SIF) solutions of theses surface cracks are needed for reliable fatigue crack growth prediction and fracture assessment for welded structures.

One of the most common methods to analyze surface cracks is the finite element (FE) method. Newman and Raju (1981) proposed the empirical formula of stress intensity factors for a semi-elliptical surface crack in finite thickness plate under remote tension and bending loading. As for welded joints, the SIF of a weld toe surface crack can be predicted from the weld toe magnification factor Mk and Newman-Raju solution. By means of FE analysis, Bowness and Lee (2000) presented empirical formula for estimating Mk factors for surface cracks in fillet welded Tbutt joints. However, the values of Mk-factor are influenced by many aspects including the profile parameters of weld bead, the size of mainplate and attachment, and the geometry parameters of surface cracks, etc. It is still a tough task to obtain the Mk formulae for geometrically complex welded plate joints, such as fillet welded cruciform joint and web gusset joint.

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