The peak stress method to calculate residual notch stress intensity factors in welded joints

Abstract

According to the recent literature, the intensity of linear elastic residual stress\ud fields near the toe region of a welded joint can be quantified by the residual\ud notch stress intensity factors (R‐NSIFs). The computational effort required to\ud compute the R‐NSIFs implies strong limitations of applicability in practice,\ud owing to the very refined meshes needed and to the non‐linear transient nature\ud of welding process simulations, especially in 3‐dimensional numerical models\ud of large structures. The peak stress method (PSM) is a design approach that\ud takes care of the industrial needs of rapidity and ease of use. According to the\ud PSM, it is possible to evaluate the R‐NSIFs by using the peak stress calculated\ud at the point of singularity with coarse finite element (FE) models. While the\ud PSM was originally calibrated by using the Ansys FE code, in the present contribution,\ud the PSM has been calibrated to rapidly estimate the R‐NSIFs in the\ud Sysweld FE environment

Rapid Calculation of Residual Notch Stress Intensity Factors (R- NSIFs) by Means of the Peak Stress Method

“…A mesh pattern having element size equal to 0.29 mm was adopted near the weld toe, which corresponds to a mesh density ratio a/d =1 0≥ 4, according to the PSM calibration in Sysweld ® [43]. Results are summarized in Table 3, where it is possible to notice a good agreement between the K 1 value obtained from the local stress field computed with a very fine mesh and the one estimated by means of the coarse PSM mesh.…”

“…The PSM has been recently calibrated in Sysweld ® finite element environment, to rapidly evaluate the linear elastic notch stress intensity factor (NSIF) under mode I loading [43]. According to such calibration, the mode I NSIF is proportional to a constant K* FE , which is equal to 1.64 in case of V-notches with opening angle ranging from 90 to 135 and equal to 1.90 in case of cracks (0 opening angle).…”

Residual Notch Stress Intensity Factors in Welded Joints Evaluated by 3D Numerical Simulations of Arc Welding Processes

“…To represent the whole residual stress distribution, including in regions far from the singularity point, higher order nonsingular stress terms beyond K 1 are necessary. By postprocessing the results of Figure 7 according to Equation (1) [25], a value of R-NSIF equal to 68.2 MPa•mm 0.326 was obtained in [40]. Comparison between thermal results from 2D and 3D models: snapshots captured when the heat source is traveling over the cross-section (a) or the welding line (b); the fusion zone shapes (in red) obtained by 2D and 3D FE models, respectively, are highlighted; and (c) temperature history at node A as a function of the adopted element type and average element size d. (Figure 5b-d); the results of 3D models refer to the half-width longitudinal section, where the plane strain conditions are better matched and therefore comparable to those of the 2D model.…”

“…• Three-dimensional 8-node brick elements ( Figure 5c): The R-NSIF was estimated by adopting the values of K * FE = 1.64 [40,42] and average element size d = 0.28 mm, as shown in Equation 7, which highlights that, in the case of 3D FE models, a distribution of the R-NSIF K I can be calculated as a function of the y-coordinate.…”

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

“…On the other hand, the so‐called local approaches allow a more realistic evaluation of the expected fatigue life 10–16 . In particular, among them, the authors consider in the present work the strain energy density (SED) method that, unlike other local approaches, like the notch stress intensity factor (NSIF) method, that allows to estimate the failure modes like, for example, weld root failure or weld toe failure 17 .…”