Numerische Modellierungsstrategien von schalenmodellbasierten Schweißverbindungen
Research output: Thesis › Master's Thesis
In order to keep the modeling and calculation effort for large welded steel components, as commonly used in mining and metallurgy, in an economically justifiable amount, it is recommendable to use 2D shell elements. Therefore, the aim of this master thesis is to contribute to a methodical approach for a standard-compliant assessment of welded joints using finite element shell models. At first, a comprehensive numerical case-study on simple shell-models with different load- and boundary conditions as well as various mesh seeds has been conducted. In order to find a suitable concept, different node- and element- based stress evaluation strategies were taken into account. The developed concept “K1-NK-Center” is based on an evaluation of element center-stresses at the nearest, first adjacent element to the welded joint. The element size, which has to be used, corresponds to the sheet thickness of the connection plate. The evaluation occurs on basis of the nominal stress concept, whereby the analysis of the stress component on the weld side takes place as superposition of membrane- and bending stresses. This concept was compared with different structural hot-spot-stress concepts. Therefor methods for a punctual and extrapolating structural stress determination were considered. The evaluation of the results always yielded in conservative designs of the assessed fatigue strength, whereby the maximum deviation from the published structural stress concept is less than 10%. In addition, the influence of the sheet thickness was evaluated in all considered concepts, which can be used as an increasing factor for thin sheets implying sheet thicknesses smaller than 25mm. For thicker sheets, the effect always reduces the allowable fatigue strength. Taking into account the sheet thickness factor, the previously conservative results of up to 40% could be well matched to the tested mechanical strength properties. It should be emphasized, that the sheet thickness factor needs to be properly applied both for constant and multiaxial load conditions. As additional validation, comparative calculations were performed on multiaxial stressed samples and components. The multiaxial analysis tends to conservative results, whereas for the investigated components the calculation according to IIW is preferable to that of the FKM. Comparing the FKM-based method to the IIW guideline, the FKM is about a factor of two in life cycles more conservative. In the course of this work, a modeling and evaluation recommendation for shell-based structural spot fatigue strength assessment, efficiently applicable for large welded structures, was developed. This features a compliant, multiaxial component design utility for welded structures and provides an efficient engineering tool applicable for standards such as Eurocode 3 or the FKM guideline.
|Translated title of the contribution||Numerical modeling strategies of shell model based welded joints|
|Award date||12 Apr 2019|
|Publication status||Published - 2019|