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 offering the following topics. Topics other than those listed here can be discussed and assigned with the employees at short notice. Please contact Prof. Sören Ehlers or Prof. Alexander Düster for further information. It is also possible to find suitable thesis topics in cooperation with out national and international partners.

Bachelor and project theses:

Prediction of fatigue failure of welded joints based on machine learning algorithm 

Fatigue behaviour of welded joints depends on a number of factors, such as local weld geometry, macro-geometric misalignment, loading type, etc. Due to the complexity of this topic, machine learning techniques offer a possibility to assess the mutual influence of these aspects. In this study, different machine learning techniques, i.e. decision tree, boosted trees, and artificial neural network are utilised to to predict fracture locations and fatigue life of welded joints.

Please send an email to moritz.br(at)tuhh.de

Correlation between local weld geometry and fatigue strength of butt-welded joints 

It is a well-known fact that weld geometry influences fatigue resistance of welded connection, weld toe shape being of particular importance. Geometrical features of a weld can be generally described by size of weld toe undercut, radius and angle, as well as weld height and width.

Industry standards regulate size of some of these features and thereby define quality class of the weld and to ensure fatigue performance. Usually measurements of weld features are performed manually by means of templates. This method is not very efficient and obviously subject to individual inspector’s judgment. Many industries are more and more looking into 3D scanning as an inspection method which bears potential for automation and offers high repeatability. Scanned surfaces of welds can then be subject to geometric evaluation with regard to size of their features more reliably. Hence, this project deals with the correlation of local weld geometries and fatigue crack initiation locations.

Please send an email to moritz.br(at)tuhh.de

Fatigue strength of flush ground butt-welded joints

The post-weld treatment of butt-welded joints enables a significant increase in fatigue strength. Especially the use of high-strength steels allows a significant increase compared to the condition after welding. In many codes, the determination of fatigue strength of post-welded joints does not yet take into account the higher yield strength and the associated improved fatigue strength, although this is associated with design disadvantages.
Within the scope of this work, the fatigue strength behaviour of welded joints with optimised butt-welded joints is to be investigated and evaluated. For this purpose, literature data and test results from previous work are to be statistically evaluated.
The aim of this work is to improve the design of post-treated welded joints by highlighting the effect of post-treatment with regard to material strength and other influencing factors.

Please send an email to moritz.br(at)tuhh.de

Application of the strain energy density method to butt-welded joints

To this day many different local fatigue assessment methods have been proposed and are still being developed. Each of them has benefits and downsides for particular problems.

The most common local fatigue assessment method in ship and offshore industry is the structural hot-spot stress approach. One of the more sophisticated methods is based on the integration of the averaged strain energy density (SED) in a small volume surrounding for example the notch at a weld toe. In different studies the accuracy of the method has proven to be eminent; however, the computational effort is still high, due to particular requirements on the finite element mesh used for calculation of the SED.

In order to improve the applicability of the method for fatigue assessment of larger structures like ships or offshore structures it is necessary to decrease the computational effort of this method and to verify its accuracy based on different scenarios. Thus, this thesis aims at comparing different approaches for SED-based assessment of butt-welded joints.

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of steel specimens subjected to an accelerated corrosion test 

Steel structures exposed in maritime environments are highly susceptible to corrosion. To guarantee operational safety, the integrity of the structure has to be ensured. The remaining fatigue life of steel structures in a corrosive environment is difficult to predict. According to DNV, the service life can be verified with the nominal stress concept using S-N curves. Different curves considering the environmental condition can be applied, such as “air” or “free corrosion”.

Within the scope of this work, the S-N curves for round steel specimens are to be investigated and evaluated. In order to account for corrosion, an accelerated corrosion procedure has to be implemented – based on given literature – before testing the specimens.

The aim of this work is to determine the S-N curves for the given specimens and compare the results with respect to the corrosive media. Furthermore, the validity of the data obtained by the accelerated corrosion test has to evaluated.

Please send an email to christian.woitzik(at)tuhh.de

Finite element modeling of the triaxial test

In this project, the triaxial test as one of the important characterizing tests for powder materials shall be simulated using the finite element method (FEM). This approach can help to study the behavior of discrete materials in two different ways. It may consider all particles together as a continuum and discretize it with finite elements. Here, some constitutive models like the Mohr-Coulomb or the Drucker-Prager model may be used. The other way is using the multi-particle finite element method (MPFEM) where each particle is modeled separately and discretized by finite elements. For this study, it is required to carry out a parametric study using the commercial software Ansys and prepare the corresponding macro scripts (APDL). Comparing the results of two above mentioned approaches and a scientific discussion is also expected.  

      Schematic view of the triaxial test

Interested applicants are asked to contact Dr. Amir Atrian: amir.atrian(at)tuhh.de

Simulation des Bruchverhaltens poröser Materialien mit der Diskrete-Elemente Methode

Im Rahmen des Graduiertenkollegs, Prozesse in natürlichen und technischen Partikel-Fluid-Systemen (PintPFS), werden zum Thema ”Identifikation von kontinuumsmechanischen Materialparametern granularer Materialien mit Hilfe von Partikelmethoden” Bachelor-, Projekt- und Masterarbeiten vergeben.

Der aktuelle Schwerpunkt des Projekts liegt in der Simulation und Auswertung verschiedener Experimente wie z.B. dem Oedometertest, mit deren Hilfe das Bruchverhalten von Partikeln untersucht werden kann. Die Simulationen werden mit einer Diskrete-Elemente Methode durchgeführt. Die Partikel werden dabei als Agglomeratebestehend aus Primärpatikeln und verbindenden Feststoffbrücken dargestellt. Durch das Versagen der Feststoffbrücken kann das Brechen der Partikel simuliert werden.

Weitere Informationen hier

Kontakt: sonja.kraus(at)tuhh.de

Master Theses:

Prediction of fatigue failure of welded joints based on machine learning algorithm 

Fatigue behaviour of welded joints depends on a number of factors, such as local weld geometry, macro-geometric misalignment, loading type, etc. Due to the complexity of this topic, machine learning techniques offer a possibility to assess the mutual influence of these aspects. In this study, different machine learning techniques, i.e. decision tree, boosted trees, and artificial neural network are utilised to to predict fracture locations and fatigue life of welded joints.

Please send an email to moritz.br(at)tuhh.de

Weld toe and root failure transition in load-carrying cruciform joints

It is well known that there is an inherent risk in load-carrying fillet welded joints for fatigue fracture from the weld root. This is usually avoided by large throat thicknesses, which reduced the nominal stress in the cross-section of the fillet weld. However, the reason for weld root failure is not only governed by throat thickness, but also by other parameters like loading type, leg length and so on. Assessment of the risk of root failure can be either empirically or numerically. For the later, different methods are permitted by industry standards and or are still under development.

In recent years, attempts have been made to simplify these approaches and to find a method that is most suitable for fatigue assessment based on finite element method. Although, differences between the different approaches have been proven, it is sometimes believed that some of the methods are directly comparable. However, recent studies found differences in the estimating whether cracks will initiate from the weld toe or root for different methods. Hence, this project is concerned with the investigation of weld toe or root transition for load-carrying cruciform joints. For this purpose, finite element simulations will be applied.

Please send an email to moritz.br(at)tuhh.de

Topics related to fatigue strength of 3D printed materials

Additive manufacturing as a new production process offers great advantageous for certain applications compared to classical processes; however, additively manufactured components are known to have poor surface quality after production. These surfaces can contain defects, from which fatigue cracks can be initiated. Possibilities to improve the fatigue strength included post-production methods like heat treatment or hybrid production processes (e.g. machining of the surface). In current projects the fatigue behavior of 316L specimens produced by selective laser melting and wire and arc additive manufactured are investigated. Topics for project and master thesis include:

• Fatigue strength of welded 3D printed materials
• Fatigue strength of wire and arc additive manufactured (WAAM) materials
• Hybrid additive manufacturing

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of welded joints under consideration of notch acuity, material strength, and crack initiation behaviour

In recent years there has been a trend towards steels of higher and higher strength in various industrial sectors. In order to be able to use the advantages of greater strength constructively, high demands are placed on the quality of weld seams. The estimation of the fatigue strength according to the classification regulations of DNV GL etc. As a result, no high-strength materials are currently being considered in welded joints. Within the scope of this thesis, the fatigue strength behavior of butt weld joints shall be investigated and evaluated. For this purpose, fatigue strength evaluations are to be carried out under consideration of notch acuity, material strength, and crack initiation behaviour. The aim of this study is an estimation of the fatigue strength based on the aforementioned properties and an estimation of the constructional possibilities by the use of high-strength steels in shipbuilding.

Please send an email to moritz.br(at)tuhh.de

Fatigue assessment of post-weld treated joints for high-speed sailing yachts

The keels of high-performance sailing yachts are increasingly made of high-strength steels with yield strengths above the usual strengths of ship structural steel. The constructions of these keels consist of both milled profiles and welded hollow chamber profiles which are often post-weld treated. However, the assessment of the fatigue strength according to the DNV GL regulations does not currently include consideration for high-strength materials in welded joints and the effect of post-weld treatment. Within the scope of this project thesis, the fatigue behaviour of high-strength steels will be investigated and evaluated. For this purpose, fatigue tests are carried out for different steel grades and production methods. Herein welded joints in as-welded state and after grinding are considered. In addition, the effect of notches in the base material due to milling of the structure will be investigated. To secure and validate the test results, the sample series should be analysed with the aid of the finite element method.

Please send an email to moritz.br(at)tuhh.de

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.

The thesis work has to analyze the differences in mechanical properties between full-scale and model-scale. Furthermore, the possible impact on the performance prediction of ships is to be addressed, especially with regard to vertical ship motions.

Please send an email to Franz.vonbock@tuhh.de
Instructor: D.Sc. (Tech.) Franz von Bock und Polach

A comparative study of deformation and crushing behavior of particles using DEM and MPFEM

The Poraver expanded glass granules may be used as filler material in the void spaces between two walls in double hull vessels. Recent studies demonstrated that this filler material has improved crashworthiness and energy absorption of ship structures during collision.

To model discrete materials like powder, sand, soil, rock, etc., two techniques, i.e. the finite element method (FEM) and the discrete element method (DEM) are mainly used. In DEM, for each particle the equation of motion is solved, considering contact with its neighbors. On the other hand, FEM considers all particles together as a continuum and discretizes it with finite elements. Now, if each particle is modeled separately and discretized by finite elements, we have the multi-particle finite element method (MPFEM). Both DEM and MPFEM may be used for modeling of breakage and crushing behavior of Poraver granules. For DEM, an open source code is available, and for MPFEM, the commercial software Ansys may be employed. In this project, the Poraver particles are under quasi-static compressive loading, and the particles crushing behavior is investigated using these two techniques. It is also expected to have a comparative study on the theory and different aspects of each technique.

Interested applicants are asked to contact DR. Amir Atrian: amir.atrian(at)tuhh.de

Simulation des Bruchverhaltens poröser Materialien mit der Diskrete-Elemente Methode

Im Rahmen des Graduiertenkollegs, Prozesse in natürlichen und technischen Partikel-Fluid-Systemen (PintPFS), werden zum Thema ”Identifikation von kontinuumsmechanischen Materialparametern granularer Materialien mit Hilfe von Partikelmethoden” Bachelor-, Projekt- und Masterarbeiten vergeben.

Der aktuelle Schwerpunkt des Projekts liegt in der Simulation und Auswertung verschiedener Experimente wie z.B. dem Oedometertest, mit deren Hilfe das Bruchverhalten von Partikeln untersucht werden kann. Die Simulationen werden mit einer Diskrete-Elemente Methode durchgeführt. Die Partikel werden dabei als Agglomeratebestehend aus Primärpatikeln und verbindenden Feststoffbrücken dargestellt. Durch das Versagen der Feststoffbrücken kann das Brechen der Partikel simuliert werden.expected.

Weitere Informationen hier

Kontakt: sonja.kraus(at)tuhh.de

Fluid-structure interaction

Fluid-structure interaction of ships and offshore structures

Coupled simulation of a floating offshore windturbine.

Fluid-structure interaction plays an important role, especially in marine applications, where the loads acting on possibly deformable structures are mainly determined by the fluid around them.
In the past, we have considered several applications, such as ships in sea waves in order to simulate the landing maneuver of service ships to an offshore wind turbine plant as shown in the figure below.
It also includes snapshots of simulations of flexible marine propellers and floating offshore wind turbine plants.

In all of these applications, the interaction of fluid and structure must be considered to predict the structural integrity or the performance accurately.
This leads to a coupled problem, where loads have to be transferred from the fluid subproblem to the structural subproblem and where displacements of the structure have to be sent in the other direction.
For both subproblems, dedicated solvers already exist. It is therefore desired to reuse existing software and modify it such that coupling can be realized between two solvers instead of developing a new code that can handle both problems simultaneously.

Accordingly, we pursue a partitioned approach to solve the coupled problem rather than a monolithic approach. Through a third software, a coupling manager, the data exchange between the fluid and the structural solver (and possibly between any number of solvers for a variety of different problem types) is managed. A major field of research in our group is the development of new coupling algorithms and so-called convergence acceleration schemes inside our coupling manager comana. You can find below a list of publications around these topics.

In your thesis, you may work more on the application side and participate in one of our research projects, e.g. the acoustic behavior of flexible marine propellers or the simulation of a wave energy converter. Alternatively, topics which are less related to applications (e.g. about coupling algorithms and novel discretization schemes) are available.

Interested applicants are asked to contact:

Dr.-Ing. Lars Radtke, Prof. Alexander Düster

Cardiovascular fluid-structure interaction

Coupled simulation of the hemodynamics in an end-to-side anastomosis.

The simulation of blood flow (hemodynamics) requires the simulation of a fluid-structure interaction problem such that it is very possible for this biomedical application to join forces with the simulation of flexible marine structures.
One of the main applications for blood flow simulations is the optimization of implants like stents, bypass-grafts or stent-grafts as well as external cardiovascular devices.
In recent years, we have developed a simulation approach that allows for investigations, e.g. of the hemodynamic in the connection by arteries and bypass-grafts, so-called anastomoses, as shown in the figure below.

In order to solve the coupled fluid-structure interaction problem, we reuse existing software for the structure and the fluid subproblem and couple them using a third software, our coupling manager comana.
In such a partitioned solution approach for coupled problems, the so-called added mass effect can lead to instabilities in the simulations. In biomedical applications, where the density of the fluid and the structure are almost equal this effect is especially problematic (as opposed to engineering applications considering, e.g. steel and water). While we can achieve stable simulations with novel stabilization methods from literature, we constantly work on improving and fine-tuning these. Theses focusing on these rather theoretical aspects may only perform larger simulations in an exemplary spirit and mainly work with academic test cases.

In an active research project, we currently use mathematical shape optimization methods in combination with the coupled simulation approach. Using the so-called adjoint method, our goal is to find optimal shapes. e.g. for anastomoses, that minimize or maximize clinically relevant hemodynamic factors associated, e.g. with the development of atherosclerosis or hemolysis.

Interested applicants are asked to contact:

Dr.-Ing. Lars Radtke, Prof. Alexander Düster