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Item type:Publication, Access status: with files , Statistical correlation of 3D scanned weld geometry distributions and fatigue life for different welding methodsThe relationship between local weld geometry and fatigue life has been extensively studied over the past decades, driven by the need to enhance structural integrity and optimize costs throughout a structure’s service life. While numerous studies have explored the influence of weld geometry on fatigue strength, the comparative effect of different welding methods under comparable weld geometry quality remains largely unexplored. Furthermore, the influence of local geometric variations for each welding method has not been systematically evaluated. This study explores a large dataset of laser-scanned butt welds, analyzing key geometric parameters. The dataset is categorized by welding method (laser-hybrid welding, submerged arc welding, and flux core arc welding), and statistical distributions are examined to assess variations in weld geometry and compliance with ISO 5817 quality groups. The characteristic fatigue life for each quality group is estimated. The correlation between geometric factor and fatigue life is evaluated through the residual analysis of stress-life curve linear fitting. According to the findings, different geometry features dominate depending on the welding method. The fracture location is strongly influenced by angular misalignment, while fatigue strength is better explained by quantile-based analysis of local geometry. These results provide a basis for future predictive modeling and quality assessment in welded structures.Publicationtype: Journal Article28 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue behavior of thermal cut edges in normal- and high-strength steel: effect of defined post-processing treatment(Springer, 2025-09-08); ; ; ; Within ships or maritime structures, plate edges are an important detail for the strength and fatigue assessment. Large openings such as hatches on container vessels or windows on cruise ships lead to a stress concentration, which has to be considered for strength calculation. These openings within steel plates are generally manufactured by thermal cutting processes. The recommendations regarding fatigue design by the IIW and classification societies for the structural behavior of these details are limited to general design categories using the nominal stress approach. In addition, no strict differences in cutting technologies and edge treatments such as grinding are taken into account. The aim of this investigation is to present the potential of a defined edge treatment for thermal cut edges on the fatigue performance. Therefore, fatigue tests with constant amplitudes were carried out and the specimens are characterized by identifying important properties such as roughness and hardness. This paper describes the fatigue behavior of thermal cut edges made of structural steel plates with different thicknesses from 5 to 25 mm including steel grades from S235 up to S690. All specimens were manufactured in an acceptable and comparable quality range according to ISO 9013, quality level 2, and have been treated with a defined chamfer to compare the influences of cutting processes and yield levels. Previous studies already indicated a beneficial effect regarding fatigue strength of thermal cut edges using higher strength steels, but the results were not clearly in line to describe the behavior sufficiently. This study demonstrates and confirms that material effects and a targeted post-treatment have a beneficial impact on the fatigue behavior of thermal cut edges. A continuous increase in the achieved stress ranges was observed with increasing steel strength. Based on the observations made, an approach for predicting the achievable fatigue strength is presented, taking surface roughness and material strength into account.Publicationtype: Journal Article47 30 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fatigue behaviour of 12-month corroded offshore steel joints under accelerated salt spray exposure: an experimental and numerical analysis(Springer, 2025-06-14); ; ; The fatigue strength of steel structures can decrease significantly when corrosion occurs. Pitting corrosion, in particular, can lead to locally high stress concentrations and may interact with existing stress concentrations from weld seams. Particularly in the case of offshore support structures, which are exposed to a corrosive environment and include several welded connections, this issue becomes relevant. Hence, in this study, butt- and fillet-welded joints of structural steel were exposed to accelerated corrosion in a salt spray chamber and then tested for fatigue strength. In order to investigate the long-term behaviour, the specimens were stored for 12 months in a salt spray chamber. Base material specimens were investigated as reference. All specimens were clean blasted and 3D scanned prior to the fatigue tests. It was shown for all specimens that the fatigue strength decreased after 12 months compared to the uncorroded reference tests. However, the fatigue reduction was different for the different geometries. The greatest reduction was observed for the base material from 282 to 122 N/mm², followed by butt-welded joints from 215 to 147 N/mm², and fillet-welded joints from 168 to 144 N/mm². As the fatigue strengths showed only minor difference after 12 months, an equalization effect can be assumed. The results show that a generalized reduction of the fatigue strength, in accordance with the guidelines, is not appropriate and therefore should be revised for a more accurate design of offshore support structures. Finally, numerical analysis based on 3D scans of the specimens was conducted and compared with the test results.Publicationtype: Journal Article30 16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Round-robin study on the determination of weld geometry parameters—part B: analysis of welded specimenThe local geometry of the weld toe or the weld seam has a high influence on the fatigue strength of welded joints. Two main parameters for the geometrical description of the weld toe are the weld toe radius and the weld toe angle. Currently, there is no uniform definition or standardized measurement approach for the assessment of these parameters. For this reason, the presented extensive round-robin (RR) study focusses on the influence of different evaluation techniques and measurement systems regarding the mentioned parameters based on 3D surface scans. In total, 20 participants take part in this two stage RR (19 participants in the second part). In this work, the results of the second part (part B) of the RR, namely the evaluation of weld toe radius and weld toe angle on real welded joints, are presented, where the actual weld toe geometry is not known a priori. For this, 22 data sets were evaluated. The data sets consist of measured values for the radius and angle of the weld toe in relation to the position along the weld seam. In general, significant variations are determined for the evaluated weld geometry parameters, especially for the weld toe radius. It is also shown that the condition of the weld toe transition has a high influence on the parameter. Particularly for weld seams with a low weld toe angle, the measurement results for the radius of the individual participants show high variations. For small weld toe radii, the results are quite comparable between the participants. The results for the weld toe angle are comparable for flat welds, but a wide range of results is observed for sharp weld toes. The degree of automation of the measurement method also has a high influence on the results. The most accurate results are expected from manual measurements, while the fully automatic and semi-automatic methods show larger deviations.Publicationtype: Journal Article19 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Results of the JaCo project: fatigue strength of robot-welded tubular joints for offshore wind energy converters(Springer, 2025); ; ; Nielsen, L. P.Jacket foundations are lattice-like structures, whose assembly requires the welding of a large number of tubular joints. Such foundations type is suitable to support wind energy converters in deeper water with large turbine size. In order to increase the production speed and its quality, robot systems were developed to produce tubular joints. As fatigue is dominating the design of these structures, an assessment of the performance of tubular joints produced by four different robots was performed and compared with the performance of manually welded joints. In total, 18 large-scale tests were performed on joints with dimensions representative for offshore structures, which were produced in industrial environment. Almost all breakthrough cracks occurred through the chord, with cracks initiated at the weld toe, although in some cases cracks were also initiated and propagated between weld beads. Strain measurements have demonstrated that when multiple cracks are present in one specimen, they interact only in the last phase of the fatigue life, when they are so large that they affect the stiffness of the tubular components. The measured fatigue strengths of joints produced by robot were similar or higher than the T-curve of DNV-RP-C203. Two fabricators delivered components of which the fatigue strength was more than 20% higher than the standard curve. These results emphasize that mastering the welding process with robots is necessary to achieve superior levels of fatigue strength.Publicationtype: Journal Article34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A statistical assessment of the fatigue strength improvement of butt joints by flush grinding(Springer, 2023-10); ; ; ; All major rules and guidelines include fatigue design (FAT) classes for flush ground butt-welded joints. These FAT classes vary between FAT110 and FAT155; however, in the majority of cases, the underlying database and specimen-related details are unclear or unknown. This study evaluates 1003 fatigue test results gathered from various literature sources and tries to relate the fatigue strength improvement to typical specimen types and test conditions. To this goal, statistical methods based on correlation analysis are employed. Next, proposals for updates of rules and guidelines for flush ground butt-welded joints made of steel are established by determining new FAT classes and a suitable slope exponent. In addition, an overview of design standards and recommendations is given and main influencing factors are discussed.Publicationtype: Journal ArticleScopus© Citations 3 84 86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Statistical analysis of sub-zero temperature effects on fatigue strength of welded jointsShips and offshore structures in Arctic environments are exposed to severe environmental actions and sub-zero temperatures. Thus, the design of such structures has to account for the Arctic environment and must be cost-efficient at the same time. A vital part of the design process is to ensure that fatigue-induced failure does not occur in the lifetime of the structure. While effects of high temperatures on material behavior are well covered in international standards and guidelines, there is no comprehensive guidance for sub-zero temperature fatigue strength assessment. Additionally, stress-life (S–N) test data of welded joints at sub-zero temperatures is particularly scarce. Hence, this study presents an extensive review of recent test results of various weld details tested in the range of − 50 to 20 °C. This data could build the basis for future considerations of temperature effects in fatigue design guidelines and recommendations. For this purpose, the fatigue test results are submitted to a rigorous statistically assessment—including a summary of the limitations of current design guidelines with respect to sub-zero temperature effects.Publicationtype: Journal ArticleScopus© Citations 8 74 228 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of the optical measurement technique and evaluation approach on the determination of local weld geometry parameters for different weld types(2020-02-01); ; ; ; The joining by welding processes of components is usually related to the creation of additional notches and geometrical peculiarities. Multiple investigations have shown that a clear correlation between the local weld geometry and the fatigue life of welded joints exist. Thereby, the local increase of the local stress can be expressed by a stress concentration factor at the transition from the base material to the filler material, the so-called weld toe. The stress concentration factor can be determined for the most weld types if the geometric parameters such as plate thickness weld toe radius and flank angle are known. However, no standardized method for the determination of these parameters exists. Beside the well-established 2D-measurement methods on cross sections with weld impression analysis, new 3D-methods based on contactless, optical measurement were applied in the last years for the geometrical analysis of welded joints. With these methods, long length of welds can be analyzed in a very short time and with low effort. However, the influence of the measurement system (geometrical accuracy, lateral resolution) was not quantified yet. Additionally, in all known cases of application different evaluation algorithms were used. This does not allow for a straightforward comparison of the investigated parameters and results. In this round robin study, the determination of weld toe radii and flank angles by different evaluation algorithms and 3D-measurement systems and by different institutes are compared. Furthermore, an approach for the direct determination of the stress concentration factors of fillet welds by translating the complex weld shape in a 2D-finite element simulation was implemented. The results of this direct approach are compared to the stress concentration factors determined indirectly using the geometric parameters and those calculated by established approximation formulas.Publicationtype: Journal Article146 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Fatigue strength of high-strength steel after shipyard production process of plasma cutting, grinding, and sandblasting(2018-11-01); ; ; ; This paper investigates experimentally the fatigue strength of high-strength steel, which has undergone the normal shipyard production process of plasma cutting, grinding, and sandblasting. The study includes steels with the yield strength of 355 and 690 MPa. The tested specimens are of dog-bone shape and represent the large-scale situation of a cruise ship balcony opening corner, loaded in shear or tension. The influence of surface roughness, internal inclusions, hardness, and residual stress on the fatigue strength are studied and discussed. Compared to the design curve as well as to the untreated surfaces, the results show significantly improved fatigue strength under constant amplitude loading at a load ratio of R = 0.1. However, very flat or even rising slope of the S-N curve indicates variations in the material and surface quality as well as in the residual stress. Surprisingly, internal defects even up to 100 μm in size did not decrease the fatigue strength.Publicationtype: Journal Article194 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Influence of aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of metal-composite single-lap joints(2017-11-01); ; The use of frictional heat for joining thermoplastic-based materials to metals has grown in importance in recent years. Friction spot joining is a relatively new joining technology suitable to join metal-polymer and composite overlap structures. In this work, the influence of various aluminum surface pre-treatments on the bonding mechanisms and mechanical performance of single-lap shear and cross-tensile joints was studied. Mechanical, chemical, and electrochemical pre-treatments were applied to the aluminum surface prior to the joining process. All surface pre-treatments increased the joint strength to some extent, compared with specimens without surface pre-treatments. Some of the treatments (chemical and electrochemical) led to the formation of strong chemical bonding between the aluminum and composite. Phosphoric acid anodizing with additional primer layer showed the best performance in increasing the joint’s strength. The reason was the strong bond formation between the primer layer and the matrix of the composite during the joining cycle. Moreover, the morphology and chemical composition of the aluminum after surface pre-treatments were analyzed in detail to study the correlation between bonding mechanisms and the mechanical performance of the joints. Finally, fracture surface of the joints was analyzed optically and by SEM, demonstrating parts of the composite remained attached to the aluminum after failure.Publicationtype: Journal Article118