PSI - Issue 39

Wei Song et al. / Procedia Structural Integrity 39 (2022) 214–221 Author name / Structural Integrity Procedia 00 (2020) 000–000

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structural characteristics, axial and angular misalignment are inevi t able flaws in welded components, especially for Load-carrying Cruciform Welded Joints (LCWJ) with higher accuracy requirements in welding process for engineering fields[1]. For these welded joints and components under cyclic loadings, fatigue strength will be significantly reduced, which exerts a great threat for the security of components [2, 3]. Although accep t able range of misalignments is allowed in some industry standards, it still blur to quantitatively study the misalignments in welded joints for fatigue assessment and structural design [4]. As a basic research technical approach, Finite Element Method (FEM) could effectively calculate the fatigue characteristic indicators of welded joints and components by comprehensive considerations of welding details and service conditions, such as loading conditions, geometric parameters, fracture properties and welding flaws. Relevant local approaches based on FEM include the Effective Notch Stress (ENS) [5], Hot Spot Stress (HS) [6], Notch Stress Intensity Factors (NSIF) [7], average Strain Energy Density (average SED) [8] and fracture mechanics method[9], which have a great potential for further explorations and applications of fatigue assessment and structural design. So far, researchers and fatigue design standards have proposed some relevant calculations data and commendations on the basis of above-mentioned methods considering the effect of misalignments. This paper aims to study the effects of varying misaligned LCWJs by experiments and FEM, then illustrates the fatigue strength and fatigue failure transition and combined with modified analysis formula. Firstly, it illustrates the stress distribution characteristics of weld roots and weld toes under two types misalignments based on notch mechanical theory, and further explain the influences on the analytical formula according to existing studies. Secondly, the multi-parameter equation fitting is carried out by using the FEM results of non-dislocation CLWJ, and the correction coefficient is introduced to valid the effectiveness of the fitting equation under different misalignments. Finally, the accuracy and application range of the equation are exhibited through experimental data.

Nomenclature SED

Strain energy density LCWJ Load-carrying Cruciform Welded Joints FEM Finite Element Method

2. Experimental procedures To explore the influence of fatigue life with various misalignments and verify the reliability of the analytical formulas, D32 and 907L low carbon steels were employed to obtain the test specimens of LCWJs. The geometrical details of the specimens were exhibited in the Fig. 1. In the processing of fatigue tests, the main plate was clamped by the fixture without limiting the position of the attachment plate, and axial or angular misalignments of LCWJs were observed in Fig. 3. For some specimens with incomplete penetration length at weld root, they were produced by wire electrode cutting technic. Before fatigue tests, the geometrical parameters of LCWJs were scanned by CAD software, which were summarized in Table 2. In Fig. 3(b), h i and v i represent the weld size in the horizonal and vertical directions, respectively. a and e stand for the distance of axis and angular misalignments, respectively. Fig. 3(c) shows fatigue test equipment for LCWJs. The high cycle fatigue experiments carried out on the MTS-810 electro-hydraulic servo test machine with the cyclic loading frequency of 5-10Hz and stress ratio R=0.1 in the nominal stress range from 150 to 300MPa.