Fatigue assessment of high strength welded joints through the strain energy density method

Abstract

The main aim of the present work is to investigate, through the strain energy density method, the fatigue behaviour of high strength welded joints realised employed in hydraulic runner blades. The geometries, found in literature, present the welding bead machined in order to have no geometrical discontinuities in the specimen realising a wide fitting radius between the two welded plates; the only critical geometrical discontinuity in the specimen is given by the lack of penetration that leads to an internal crack-like defect. The specimens presented failure both from the weld toe and from the weld root depending on the amount of welding penetration. The results, summarised in this work with the strain energy density method, show clearly the possibility to consider a unique master curve for this kind of joints regardless of the failure initiation point. Acquiring, through a finite element model, the strain energy density value both at the weld toe and at the weld root and comparing them, the method is proved to be adequate to detect the most critical area of the joint. A first fatigue master curve in terms of cyclic averaged strain energy density value is provided for the fatigue design of high strength welded joints.

Resource‐efficient joint fabrication by welding metal 3D‐printed parts to conventional steel: A structural integrity study

“…However, a specific modelling of fatigue‐life for additive manufactured metals is still missing; thus, we applied the method used for ‘traditional’ welded joints that better suited our hybrid problem 56 . The fatigue resistance of welded joints is usually evaluated by using global fatigue damage criterions, and some of the most suitable for our joint were the effective notch stress method (ENS), 36,37 peak stress method (PSM), 38,39 and the more recent strain energy density (SED) approach 40–42 …”

“…The SED approach 40–42 is based on local strain energy density evaluations in a pre‐defined control volume around the notch. The SED approach can provide accurate results for complex structures with coarse mesh definition, 40,41,57 and it is mainly defined by geometrical parameters. The method defines a SED critical value W C , which identify the fracture conditions.…”

“…The fatigue life assessment with the SED approach began with the weld geometrical modelling according to Meneghetti et al 38 The V‐notch angle 2 α was set to 135°, and being greater than 102.6°, the mode II stress distribution was considered not singular, 38 and the fatigue assessment was performed considering only mode I singularity. Concerning the critical volume, it was characterised according to Berto and Lazzarin 41 . The critical radius R 0 assumed the value 0.28 mm, as engineering approximation for structural steels 41 .…”

“…The fatigue life and crack locations largely depend on the surface finishing, the material defects and the load magnitude 34,35 . For this reason, we compared the global fatigue damage criterions 36–42 that are usually used for the fatigue life assessment of welded joints, and chose the most suitable one for our problem. For this study, we used the strain energy density (SED) approach 40–42 to define the fatigue life of the welded hybrid joint, because the SED approach ensures great accuracy with little calibration information and coarse meshing 40,43,44 …”

A frequency‐domain approach for damage detection in welded structures

“…However, as is well‐known, the fatigue strength of a welded component in presence of multiaxial cyclic loading is significantly lower than that of an unwelded one (even if the components are made of the same material) 2 . In particular, the factors causing the above strength reduction 3–5 are residual stresses, 6–9 thermal distortions, 10 defects caused by partial penetration, 11 and material microstructural imperfections 12 …”