Bachelor-, project- and master theses

We always appreciate your interest in executing a bachelor’s, project or master’s theses at our institute. As part of our ongoing research, we are offing the following topics:

Bachelor and project theses:

Topics other than those listed here can be discussed and assigned with the employees at short notice.

Fatigue testing of additive manufactured specimen made from Inconel 718

Powder bed fusion based additively manufactured components are known to have poor surface quality after production. These surfaces can contain defects, from which fatigue cracks can be initiated. However, the fatigue strength can be significantly increased by post-production methods like heat treatment or machining of the surface. In this work the notched fatigue behavior of Inconel 718 specimens produced by selective laser melting are investigated. It is well known that the fatigue strength of notched components consist of crack initiation and propagation depending on different factors like defects and general shape of the notch. So far the focus of such tests was the interaction of surface defects and fatigue crack initiation from those defects. In order to overcome this problem, three different geometries are tested, with different amount of notch acuities.

Investigation of weld toe and root failure transition

It is well known that the fatigue strength of notched components cannot be determined solely by calculating the stress peak σmax in the notch by the theory of elasticity and using the fatigue strength or endurance limit σR derived from unnotched specimens. In order to overcome this problem a variety of different methods have been suggest, which take the stress gradient or so-called notch effect in the vicinity of a local stress raiser into account.

Investigation of temperature effect on fatigue crack growth in welded structures

The fatigue life of structures can be divided in two stages. While the crack initiation stages can occupy up to 90% of the lifetime of smooth specimen (Clark and Knott, 1975), the fatigue life of welded structures is generally propagation-dominated. Crack growth is usually influenced by temperature effects and since more ship and offshore structures are employed in arctic environments these effects need to be analysed.

Investigation of strain rate effects on the fracture toughness at low temperatures

Fracture mechanics is the study of materials with “pre-existing flaws”, and can be used to predict structural failures due to the many cracks and flaws that are commonly found in all engineering materials.

There are generally two possible fracture modes for engineering materials that can lead to failure: ductile and brittle fracture. A mix of the two can be found within the Ductile-to-Brittle Transition (DBT) region. Whether a material is ductile or brittle is governed by the ability of the material to initiate and sustain plastic deformation.

Die mittragende Breite gekrümmter Gurte – ein Vergleich

Es ist eine bekannte Tatsache, dass gekrümmte Gurtungen eine sog. mittragende Breite (MB) besitzen, die von der Krümmung des Gurtes abhängt. Die praktische Anwendung auf gekrümmte Spanten (UBoote) oder Kimmaussteifungen und Rahmenträgern erfordert daher eine entsprechende Berücksichtigung. Meist werden diese MB in Abhängigkeit einer dimensionslosen Kennzahl

anschaulich dargestellt.

Master Theses:

Topics other than those listed here can be discussed and assigned with the employees at short notice.

Fatigue testing of additive manufactured specimen made from Inconel 718

Powder bed fusion based additively manufactured components are known to have poor surface quality after production. These surfaces can contain defects, from which fatigue cracks can be initiated. However, the fatigue strength can be significantly increased by post-production methods like heat treatment or machining of the surface. In this work the notched fatigue behavior of Inconel 718 specimens produced by selective laser melting are investigated. It is well known that the fatigue strength of notched components consist of crack initiation and propagation depending on different factors like defects and general shape of the notch. So far the focus of such tests was the interaction of surface defects and fatigue crack initiation from those defects. In order to overcome this problem, three different geometries are tested, with different amount of notch acuities.

Investigation of weld toe and root failure transition

It is well known that the fatigue strength of notched components cannot be determined solely by calculating the stress peak σmax in the notch by the theory of elasticity and using the fatigue strength or endurance limit σR derived from unnotched specimens. In order to overcome this problem a variety of different methods have been suggest, which take the stress gradient or so-called notch effect in the vicinity of a local stress raiser into account.

Investigation of temperature effect on fatigue crack growth in welded structures

The fatigue life of structures can be divided in two stages. While the crack initiation stages can occupy up to 90% of the lifetime of smooth specimen (Clark and Knott, 1975), the fatigue life of welded structures is generally propagation-dominated. Crack growth is usually influenced by temperature effects and since more ship and offshore structures are employed in arctic environments these effects need to be analysed.

Assessment of the differences between model-scale ice and sea ice and their impact on the performance of ships

Simulation or calculation methods are not yet sufficiently mature to evaluate the resistance and performance of ships in ice. Model-scale testing is the most used performance prediction method and plays a very important role in Arctic ship design. However, some of the most important properties in model-scale (bending strength, crushing strength, compressive strength and elastic modulus) differ significantly from full-scale.

Strukturnachweise für Offshorebauwerke

Für Bauwerke der Offshorewindindustrie ist in Deutschland der BSH Standard Konstruktion anzuwenden. Der BSH Standard sieht generell eine Konstruktion nach den Eurocode-Standards vor, gängige Offshoreregelwerke können nur ergänzend zur Anwendung kommen. Aus dieser Forderung ergeben sich für die Industrie zwei Probleme: Zum einen ergeben sich aus den unterschiedlichen Regelwerken unterschiedliche Sicherheitsniveaus. Zum anderen gibt es bei Anwendung der Eurocodes immer noch offene Fragen zu offshorespezifischen Problemen, wie der Bestimmung der anzusetzenden Lasten und der Durchfüh- rung des Betriebsfestigkeitsnachweises.

Assessment of the influence of process parameter on the local stress state in laser shock peened metallic alloys

Residual stresses of yield stress magnitude are normally found to be present in welded structures. The stresses are created as a result of the thermal expansion and contractions during the welding process. These local stresses are strongest a few centimetres from the weld. The presence of residual stresses of yield stress magnitude alters the local stress condition when superimposed by external loads. The local stress at the weld toe consequently fluctuates from the yield stress down by an amount equal to the stress range, which has a detrimental effect on the fatigue strength of welded structures. Several methods for post weld improvement are currently available which either improve the weld geometry or introduce compressive residual stresses. One fairly new method is laser shock peening (LSP). By means of high magnitude pulsed laser shots surface areas at or near the weld toe are mechanical deformed.

Parallelisierung von FEM Simulationen mit Hilfe von OpenMP

Die im Bauingenieurwesen, Maschinenbau und Schiffbau anzutreffende Komplexität der strukturmechanischen Problemstellungen (Größe der Modelle, Nichtlinearitäten, Dynamik, Fluid-Struktur Interaktion) stellt sehr hohe Anforderungen an die Simulation. Um dieser Problematik entgegenzuwirken, soll die aktuelle Entwicklung der Hardwarearchitektur genutzt werden.

Simulation des superplastischen Umformens mit Hilfe der FEM

Mit Superplastizität wird die Eigenschaft von metallischen Legierungen und keramischen Werkstoffen bezeichnet, eine plastische Formänderung durch Korngrenzengleiten anstatt von Wanderung von Versetzungen zu erzielen. Dabei sind Formänderungen von weit über 200% ohne Bruch erreichbar.

Fluid-Struktur-Interaktion

Die Interaktion von Fluid und Struktur spielt insbesondere im Schiffbau eine bedeutende Rolle, da die Belastung, Bewegung und Deformation des Schiffes ganz wesentlich von dem umgebenden Fluid beinflusst wird. Für beide Teilbereiche (Fluid und Struktur) existieren bereits problemangepasste Simulationscodes, die speziell für die jeweilige Aufgabenstellung (Fluid oder Struktur) entwickelt wurden.