A survey of biaxial (bending or tension and torsion) constant amplitude fatigue of welded connections is presented. Re‐analysis of 233 experimental results from eight different studies has been performed based on hot spot stresses and three potential damage parameters: maximum principal stress range; maximum shear stress range; and a modified critical plane model for welds. Of the three methods, the critical plane model was most successful in resolving the data to a single S–N line. The design curve for all toe failures based on the critical plane model was FAT 97 with a slope of 3. By excluding butt welds and including only fillet welds that failed at the weld toe, the design curve was increased to FAT 114 with a slope of 3. However, observed scatter was 70–100% larger than that observed in uniaxial loaded specimens analysed using the hot spot approach.
A B S T R A C T Multiaxial fatigue data from 233 welded test specimens taken from eight different studies have been evaluated based on three published interaction equations for normal and shear stress. The interaction equations were obtained from SFS 2378, Eurocode 3 and International Institute of Welding (IIW) recommendations. Fatigue classes for normal and shear stress were obtained directly from the design guidance documents. Additionally, mean fatigue strengths were determined by regression analysis of bending only and torsion only data for different specimen types. In some cases, the S-N slopes assumed by the different standards were not appropriate for the test data. Specimens that showed significantly different cracking locations or cracking mode between bending and torsion were not easily correlated by the interaction equations. Interaction equations work best in cases where both the normal stress and the shear stress tend to produce crack initiation and growth in the same location and in the same direction. The use of a damage summation of 0.5 for non-proportional loading as recommended by IIW was consistent with experimental observations for tube-to-plate specimens. Other codes used a damage sum of unity.Keywords biaxial fatigue; fatigue of welds; interaction equations; multiaxial fatigue.
N O M E N C L A T U R ED = Palmgren-Miner damage sum D σ ,D τ = partial damage sum for normal or shear (D σ = n σ /N fσ , D τ = n τ /N fτ ) m, m τ = S-N curve slope for normal and shear stress n σ , n τ = number of applied normal stress or shear stress cycles N f = cycles to failure sN = standard error of estimation ρ = regression coefficient σ C , τ C = characteristic fatigue strength based on design recommendations. Normal and shear stress range at N f = 2 × 10 6 and 95% survival probability σ m , τ m = mean fatigue strength based on experimental data. Normal and shear stress range at N f = 2 × 10 6 and 50% survival probability σ , τ = applied range of normal and shear stress
The main purpose of this study is to have an overview of critical crack size and growth, and their influence on the remaining fatigue life of door corner and associated bulkhead in order to set proper period for repair and service of structural components. Growth of cracks is calculated by using the fracture mechanics for two cases: the first assessment is made for a passenger ship's door corner where no visible cracks have been detected and the second assessment is conducted for the structure where cracks have been detected during inspections. The analysed door corner is situated in area of maximum shear forces of the ship hull. Loading of the door corner is generated by applying the measured nominal shear stresses of the associated bulkhead. Measured stresses correspond to 1500-hr data of a passenger ship's normal operation in different wave conditions.
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