Fatigue life assessment of welded joints under sequences of bending and torsion loading blocks of different lengths

Abstract

In this work, the nominal stress concept, the notch stress approach and two critical plane approaches are used to analyse the fatigue endurance of a pipeto-plate welded joint subjected to complex loading histories. Both the pipe and the plate were made of S355JR steel. Starting from already known fatigue endurance curves obtained for the same specimens under pure bending and pure torsion, a first series of tests was conducted, in which specimens were loaded in bending for a given fraction of the estimated life and then in torsion until failure. A similar series of tests was then carried out by changing the loading order: specimens were firstly loaded in torsion for a given fraction of the estimated endurance and then in bending until failure. The whole test campaign was repeated for two different fractions of the estimated life, that is, 0.3 and 0.45, respectively. After that, additional three series of tests were carried out, in which the specimens were subjected to consecutive sequences of bending and torsion blocks of different lengths (short, medium and long, respectively); the relative length of the bending and torsion block in each series was determined in order to produce the same damage. The experimental results, in terms of total damage at failure, were analysed using the Palmgren-Miner hypothesis. For all the assessment methods, the characteristic endurance curves were firstly calibrated on the basis of finite element (FE) analyses and of the experimental results obtained under pure bending and pure torsion loadings. The observed damage at failure resulted always greater than 0.5 for all the employed methods and greater than 1 for most of the tests. The different methods gave similar results, with the critical plane methods giving a slightly more stable damage at failure and a correct determination of the failure location. For all the methods, the damage at failure slightly reduces as the block length shortens. K E Y W O R D Scritical plane, loading blocks, multiaxial fatigue, nominal stress, notch stress, welded joints

Multiaxial fatigue life prediction by equivalent energy‐based critical plane damage parameter under variable amplitude loading

“…38 Finally, by combining the multiaxial constitutive relationship with multiaxial notch correction approach, the proposed multiaxial fatigue damage models can be extended to the case of fatigue life prediction for notched components. 39 The applicability of the proposed methodology in dealing with actual engineering components under more complicated loading conditions including three-dimensional stress state is a future task.…”

“…In order to evaluate the fatigue life by the proposed multiaxial fatigue damage models, a multiaxial constitutive relationship can be employed to calculate the stress responses according to the experimentally measured strains 38 . Finally, by combining the multiaxial constitutive relationship with multiaxial notch correction approach, the proposed multiaxial fatigue damage models can be extended to the case of fatigue life prediction for notched components 39 . The applicability of the proposed methodology in dealing with actual engineering components under more complicated loading conditions including three‐dimensional stress state is a future task.…”

Closed‐form solution for the Fatemi‐Socie extended critical plane parameter in case of linear elasticity and proportional loading

“…The seam weld of interest for this work was the one between the tube and the base plate. The welded joint was previously studied by the same authors examining its fatigue endurance under different loading conditions and in the presence of residual stresses 4‐6,42‐45 . For all the cases, FE‐analyses were conducted using the second release of Ansys© 2021 software.…”

“…The welded joint was previously studied by the same authors examining its fatigue endurance under different loading conditions and in the presence of residual stresses. [4][5][6][42][43][44][45] For all the cases, FE-analyses were conducted using the second release of Ansys© 2021 software. Static structural analyses were performed assuming small displacements; structural steel S355 was considered as the material for all three case studies with linear elastic behavior, E ¼ 210GPa and ν ¼ 0:3.…”

“…2 Especially in such circumstances, finite element analysis (FEA) provides a valuable tool able to account for the complex features mentioned above. [3][4][5][6][7][8] The standard way to approach fatigue analysis consists of investigating the component's critical regions (i.e., considering stress/ strain gradients and multiaxiality) and applying the correct loading history (i.e., accounting for variable amplitude or randomness). However, given the wide variety of geometries, loading conditions, and damage parameters to be considered, the solution of such models can be time-consuming during both the solution and postprocessing phases.…”