- PublicationFracture mechanics simulation of welded joints at sub-zero temperatures considering the weld shape(2022-01-27)Welded joints are the most common method for connecting steel components, but they are also points of weakness, as they contain, among other things, initial cracks or are unwelded gaps. Most of the fatigue life of a welded joints takes place during the phase of macro crack growth, fracture mechanics models are therefore widely used method to predict the fatigue life. In this thesis, a procedure is developed how fracture mechanics simulations can be conducted automatically for a large number of welded joints with heterogeneous geometries. Therefore, an integrated procedure is developed in which parametric simulation models are generated, fracture mechanically analysed and the results together with their metadata are saved in a selectable master file. Then, the fatigue lives are calculated from the numerical results via the Paris-Erdogan equation and compared with the experimentally determined data. It is shown that by adapting the Paris-Erdogan parameters, high accuracy can be achieved in predicting fatigue lives under sub-zero temperatures. Moreover, a method is described in which a low effort verification of the Paris-Erdogan parameters C and m, separately from each other, by comparing numerical and experimental fatigue lives in a logarithmic space.
- PublicationA method for optimizing product architectures for the management of disturbance factorsThe demand for a better product and process quality is ever increasing in the globalized world. To satisfy this demand the management of disturbance factors in mechatronic systems is essential. The applicability and efficiency of strategies targeted at the management of these factors depend on the components, the source of the disturbance factors and the systems building structure. Therefore, a method is developed to derive a building structure of a system, which supports the management of disturbance factors, from an existing functional structure. This support lowers the effort, necessary to manage disturbance factors, and thereby aids in increasing the quality of the product and the associated process. Finally, the presented method is applied on to a sensor integrating timing belt to demonstrate its usability and practicality.
- PublicationProduction, scaling and application of nanostructured metal multilayers as post-weld treatmentCu/Ni Nanostructured Metal Multilayer coatings are introduced as a new post-weld treatment method. Steel specimen with a double V-groove butt-weld are coated with a Cu/Ni NMM coating with an overall thickness of 9 μm, consisting of a 1 μm Ni base layer, a nanolaminate structure with a bilayer thickness of 50 nm and Cu and Ni single layer thicknesses of 15 nm and 35 nm respectively. The coating is electroplated onto the steel substrate with a single bath method. The coated steel specimens are tested in tension-tension fatigue and the corresponding S-N curves are calculated from the fatigue results. SEM, TEM and EDX investigations provide insights into the material characterization of the nanolaminate structure and the understanding of NMM failure mechanisms.
- PublicationMeasurement and comparison of settling velocities of cohesive sediments from the German estuaries Weser and EmsSettling and sedimentation of fine-grained sediments is a physical phenomenon influenced by bio-geochemical processes that occurs in natural water bodies such as rivers, channels and estuaries. Of particular concern are estuaries maintained for navigation. The deepening of waterways to improve the navigability for ever larger container ships has the potential to intensify sedimentation and the accumulation of cohesive sediments, particularly within the estuarine turbidity maximum (ETM). For example, significant net sedimentation and accumulation are observed in the ETM of the Weser estuary even in the centre of the navigational channel, where high flow velocities favour sediment transport and erosion. Dredging is the main method of maintaining a channel, which requires large financial investment and also has potential negative environmental impacts. In engineering practice, numerical modelling of the ETM and accumulation zones is an important tool to improve channel maintenance. Knowledge of site-specific information on settling velocities is therefore essential, as underlying processes cannot be simulated universally valid yet and require sufficient local parametrisation. The research project FAUST (For An improved Understanding of estuarine Sediment Transport) addressed the challenge of net sedimentation and accumulation in the navigational channel by investigating the transport properties of cohesive sediments (mainly from the Weser estuary) in field and in laboratory studies. The conceptual design of the project FAUST has been presented in Patzke et al. (2019). Research on sediment erodibility, sediment fractions and density profiles has been published recently (Patzke et al. 2021; Patzke et al. 2022). The follow-up project ELMOD (Simulation and analysis of the hydrological and morphological development of the Tidal Elbe for the period from 2013 to 2018) focuses on sediment transport processes in the Elbe estuary. The findings and derived model parameterisations of the projects contribute to the development of large-scale 3D morphodynamical-numerical models. In this submission, laboratory-derived effective settling velocities of natural cohesive sediments from two German estuaries are examined.