Browsing by Author "Brätz, Oliver"

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Open Access
Heat management and tensile strength of 3 mm mixed and matched connections of butt joints of S355J2+N, S460MC and S700MC
(2023) Eichler, Stefan; Arnim, Mareike von; Brätz, Oliver; Hildebrand, Jörg; Gericke, Andreas; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth‐Michael
High-strength structural steels are beneficial in terms of the sustainability of constructions due to the possible reduction of weight and overall material needs. Nevertheless, high-strength steels have a smaller processing parameter range in regarding the specific heat input and resulting cooling rate. Especially the cooling time t8/5 characterizing the time span to cool down from 800 to 500 °C is an important indicator. Single layer butt-welded gas metal arc welding (GMAW) connections of 3 mm plates between normal strength (S355J2+N, S460MC) and high-strength steels (S700MC) as well as matched connections (S460MC, S700MC) are carried out. Hereby, the influence of the energy input, melting rate, joint preparation, filler metal (matching and undermatching) and backing methods are observed. Spatially resolved IR-thermal observation shows variations within the welds of up to 50 % in the cooling time t8/5 depending on those parameters. These fluctuations lead to significant changes of the microstructure within the melting and heat-affected zone. UCI hardness mappings show the softening and microstructural change within these zones. Those soft zones can be the region of failure for butt welded connections as shown by transverse tensile tests with spatially resolved optical strain measurements. The results obtained can be used to define more precise welding procedures of these types of connections and also are used to develop design rules for mixed connections made of normal strength and high-strength steel.
Open Access
Load‐carrying capacity of MAG butt and fillet welded joints on high‐strength structural steels of grade S960QL and S960MC
(2023) Brätz, Oliver; Arnim, Mareike von; Eichler, Stefan; Gericke, Andreas; Henkel, Knuth‐Michael; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike
The use of high-strength structural steels brings great advantages in constructions regarding material requirements, weight reduction and productivity. Different steel grades within the S960 range are commercially available but not yet represented in Eurocode 3. The weldability of these steels is limited to smaller process windows to ensure the high material properties. In contrast to steels with moderate strength, there is a considerable risk of softening in the heat-affected zone causing a strength reduction of the connection. By now, the current EN 1993-1-12 only extends the design rules to cover steel grades up to S700. Therefore, the potential of these high-strength steels cannot be used to its full extent in structural engineering. This study, made within a steel application research project (FOSTA P 1507), deals with the weldability and load-carrying capacity of butt and fillet welded joints of S960QL and S960MC produced by gas-shielded metal arc welding. The influence of different bevel geometry, filler metal, and plate thicknesses was investigated. To extend the design rules up to S960, a need of an amendment was found for some combinations.
Open Access
Mechanical properties of MAG butt welded dissimilar structural steel joints with varying strength from grade S355 up to S960
(2023) Brätz, Oliver; Arnim, Mareike von; Eichler, Stefan; Gericke, Andreas; Hildebrand, Jörg; Bergmann, Jean Pierre; Kuhlmann, Ulrike; Henkel, Knuth-Michael
Mixed connections made of normal-strength and high-strength structural steels allow for optimized material usage and production effort in applications where, as a result of different mechanical effects on materials of the same type, it would otherwise be necessary to adjust the plate thickness. Reduced material consumption and smaller weld geometries can thus generate ecological and economic advantages. When welding high-strength structural steels, however, significant softening can occur in the heat-affected zone, which can influence the load-carrying behavior of the overall joint. Since there are currently no appropriate standards for butt welds made of steels with different strengths up to S960, a separate design concept is required. In this paper, the weldability and load-carrying capacity of multilayer MAG welded butt joints designed as mixed connections of a normal-strength structural steel S355 and a high-strength structural steel in the range S690 to S960 are investigated. Extensive experimental investigations are carried out, in which other influencing variables such as the filler metal used, the heat input, the plate thickness, and the weld geometry are varied in order to identify their effects on the load-carrying capacity of the welded joints. Among other things, the results form the basis for an empirically based design model for mixed connections.
Open Access
Study on load‐carrying capacity of MAG butt‐welded mixed connections with different steel strengths
(2023) Arnim, Mareike von; Eichler, Stefan; Brätz, Oliver; Hildebrand, Jörg; Kuhlmann, Ulrike; Bergmann, Jean Pierre; Flügge, Wilko
Mixed connections of normal-strength steel and high-strength steel can enable an optimum resource-saving use of materials by adapting the material strength to the forces acting on them. But the design and calculation of butt-welded mixed connections is not clearly regulated in the currently valid standards EN 1993-1-8 and EN 1993-1-12. In the research project Effective design concepts for mixed connections in steel structures an extensive experimental program with 180 mixed connections has been conducted to investigate the load-carrying capacity and behaviour of these connections. The weld joint specimens were made with normal-strength steel S355J2+N and different high-strength steels S690QL, S700MC or S960QL. Varying parameters were also the filler metals, plate thicknesses, weld bevels and the heat input during welding. The influence of these parameters on the load-carrying capacity and the deformation behaviour of mixed connections was investigated. Moreover, high-resolution microhardness mappings (UCI) on the welded specimens were carried out to examine the formation of the soft zone in the heat-affected zone of the high-strength steels.