Crack growth in fillet welded steel joints subjected to membrane and bending loading modes

The present paper presents the results from extensive studies of the fatigue damage evolution in fillet welded steel joints subjected to Constant Amplitude (CA) stress under membrane and bending loading modes. The welded joints in question are F class details (category 71) with plate thicknesses ranging from 25 to 32 mm. The steel quality is a medium strength carbon manganese steel. Crack growth histories for the shallow semi-elliptical shaped cracks emanating from the weld toe are obtained by an Alternating Current Potential Drop (ACPD) technique. These growth histories are presented in detail and modelled by Linear Elastic Facture Mechanics (LEFM). The calculations follow the recent recommendations found in rules and regulations based on different formats of the Paris law. The uncertainties related to a multiple cracks situation and the variability in the weld toe geometry are discussed. The measured crack growth was modelled from an initial crack depth of 0.1 mm to final fracture. The recommended rule-based parametric formulas for the Stress Intensity Factor Range (SIFR) for small surface cracks at the weld notch are examined and supplemented by results from finite element modelling. Recommendations are given on how to make decision regarding uncertainties related to a correct characterization of the local weld toe geometry and the crack coalescence. Finally, an attempt is made to capture the influence of the applied stress ratio R and the applicability of a threshold value for the SIFR is discussed.