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Welded hollow sections are typical in different industries. A database of fatigue life data of welded hollow section joints covering sequence effects and the accuracy of the linear damage accumulation is presented. The effects of the shape of the applied load spectra, sequence effects of different amplitudes have been investigated using two high-strength steels. This document covers thin-walled tubes of 2-mm thickness made of low-carbon or mild steel 1.8849 (S460MH) and austenitic TWIP-steel 1.4678 + CP700 (X30MnCrN16-14). Constant amplitude and two-level load spectra are presented to check the linear damage accumulation. Using stress concentration factors from finite element analysis, typical FAT classes for the structural and the effective notch stress concepts are checked as well. Both structures show much higher strength compared IIW recommendations by structural stress approach and DVS 0905 by effective notch stress approach. Typical maximum linear damage sums taken from recommendations and codes of 0.2 or 0.5 are exceeded for all spectra investigated and in some of the cases even significantly above 1.0. Transferability of the recommendations to component type structures like those tubular joints made of high-strength steel needs revision to lift its lightweight potential but this will require additional data.

The effective notch stress approach to estimate fatigue strength of welded components requires stress concentration factors of an idealized weld geometry using fictitious notch radii. This paper covers the estimation of those stress concentration factors for welded T-joints in different configurations. In comparison with different existing estimations, new methods using metamodeling by (a) the response surface method based on polynomial regression using coupling terms and (b) based on artificial neural networks are presented. The methods were trained by a large database of reference results obtained by finite element analysis. Besides higher quality of prognosis, the new metamodels enhance the range of allowable parameters of the T-joints compared to existing ones. The resulting methods provide means of obtaining stress concentration factors fast and of sufficient quality which could also be embedded in more complex applications as programmed solutions.

This paper presents the influences of the irregularity “insufficient penetration welding” on the fatigue strength based on experimental and numerical investigations. For this purpose, the fatigue strength of partial penetration butt welds of mild steel (S355) with different non-welded gaps were subjected to fatigue loading. Three different planned gap dimensions (h = 4, 6, 8 mm) at one-sided (Y-seam) and two-sided (DY-seam) partial penetration butt welds were analysed. The results were obtained on a small-scale test specimen with a steel plate thickness of t = 20 mm, without axial and angular misalignment. For the numerical effective notch stress approach, regression formula for efficient analysis of stress concentration factors was determined. The results show that butt joints which are not fully penetrated on one or both sides, and which were previously not permissible for welded joints subject to fatigue loading, can be evaluated in the future on the basis of these investigations.

Stress concentration factors (SCFs) at weld toes and weld roots as required for the effective notch stress concept (see [1, 2]) are usually computed using finite element analysis (FEA) which requires a certain amount of effort for model generation, the solving process, and postprocessing. Regression functions of many FEAs within given parameter bounds provide the possibility of a fast prediction of SCFs. This paper provides new and accurate regression formulae for the estimation of notch stresses at idealized weld geometries on the basis of multiple linear-elastic FEAs for the transverse stiffener (non-load carrying T-joint) under tension and bending of the load carrying slab. Regression of sampled finite element results has been performed using (a) second-order polynomial regression with coupling terms (PRC) and (b) artificial neural networks (ANN). The presented formulae are compared with several existing estimations of stress concentration factors. The new methods appear to show a higher quality of prognosis as well as apply to significant larger ranges of the geometrical parameters of the weld joint. The formulae presented here for the transverse stiffener add another welded joint to a series of similar surrogate models presented from Munich University of Applied Sciences in earlier publications and made available for use by the web-based tool SCF-Predictor.

Fatigue evaluation based on the effective notch stress approach requires stress concentration factors for idealized notch geometries. In this paper, stress concentration factors are calculated numerically for different idealizations of the weld geometry. The joints covered here are one-sided Y-butt joints and two-sided DY-butt joints, each with partial and full penetration. The variable parameters of the finite element models are the weld flank angle, the notch radius, the sheet thickness, the ratio of weld seam width to sheet thickness, and the ratio of height of non-fused root face to sheet thickness. Existing estimation formulae for stress concentration factors will be compared with new methods for stress concentration factor estimation: (a) polynomial regression using mixed terms and (b) artificial neural networks. These two methods show similar or superior quality compared with the existing estimations which is expressed through lower estimation errors with respect to the numerically calculated stress concentration factors. The database for the regression analysis using methods (a) and (b) consists of a total of 11,871 design alternatives obtained by finite element analysis. In addition to the improved quality of prognosis, the range of allowable geometrical parameters is significantly increased compared with the existing formulae. The methods (a) and (b) provide a possibility to a fast estimation of stress concentration factors of sufficient quality for a large range of geometrical weld seam parameters. The presented formulae could also be part of a programmed solution.

The main aim of the project was to evaluate the influence of combined effects of fatigue loading and exposure to cyclic corrosion testing on the corrosion and the fatigue resistances of coated thin sheet steel joined by spot welding. Seven types of steel including cold rolled mild steels, high-strength steels, and press-hardened steels (PHS) were selected and provided by steel suppliers for fatigue strength evaluation of resistance spot welding (RSW) assemblies. Panels were joined using conventional resistance spot welding in both lap-shear and T-peel designs. Joined samples were painted by e-coating following the industrial process. Metallographic characterization of the steels revealed that microstructures and metallic coating composition and thickness were as expected. Cross-section of spot welds showed good quality and typical evolutions of hardness. Tensile tests performed on reference samples (non-exposed to corrosion) showed tensile which were obviously configuration and material dependent. For each configuration, three replicates were tested and did not show significant scatter. The results were and will be used to evaluate the influence of corrosion on tensile strength of the joined samples. Fatigue tests were performed “in air”, meaning without corrosion exposition, leading to typical SN-lines. The results will be used to evaluate the influence of corrosion on the fatigue resistance of the joined samples.

The main aim of the project was to evaluate the influence of combined effects of fatigue loading and exposure to cyclic corrosion testing on the corrosion and the fatigue resistances of coated thin ...

The aim of this study is to evaluate fatigue performance of joined assemblies (spot weld and/or adhesive bonding) in corrosive environment. Various assemblies have been tested in alternated and simultaneous fatigue-corrosion modes. Adhesive joints are strongly affected by simultaneous fatigue-corrosion with a large drop of the fatigue life compared to results in air. By alternating fatigue and corrosion, the reduction of fatigue life is important. For spot welding, fatigue life is decreased at higher load amplitudes and increased at lower amplitudes. These results are strongly linked to the opening of the gap near the spot weld at high load amplitudes. At low amplitudes, corrosion might limit the local stress at the notch root of the weld.

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