Large-scale hydrogen storage is a crucial part of the energy transition. The usage of salt caverns has a great potential in this process, but there are open questions regarding the construction’s lifetime which need to be investigated prior to their implementation. In this work, potential construction steels were studied. The conditions in a salt cavern were imitated on laboratory scale with an experimental high-pressure setup. Two steels, J55 and H2-ready X56, were systematically exposed to pressure/temperature cycles, gas (H2 and N2), water and brine. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques were used for the characterisation of the steels’ surface, focussing on corrosion effects and crack formation. For both steels, a significant impact of moisture and salt ions could be shown. However, only for J55, intensification of corrosion and cracking on the surface due to hydrogen gas exposure was found. Pronounced crack formation over the entire surface of J55 was revealed. For X56 significantly less crack formation could be observed. Overall, the results strongly indicate better resistance of X56 than J55 against the conditions in a salt cavern, used for hydrogen storage.

The two most common Post Consumer Recycled (PCR) plastics, isotactic polypropylene (iPP) and high density polyethylene (HDPE), differ in composition and mechanical behavior when compared to their virgin counterparts. This thesis focuses on understanding and modeling the mechanical performance of these two PCR plastics separately. Within this context, the present work implements three finite strain thermoelasto-viscoplastic constitutive models developed by Johnsen et al., Mirkhalaf et al. and Anand et al. proposed in the literature to predict the behavior of PCR-iPP and PCR-HDPE. The models are compared and further developed to take into account the effects of recycling. All the models depend on the fully implicit return mapping algorithm and associated state update procedures.

Given the complexity of the models, this thesis proposes the use of Bayesian optimization to facilitate the material parameter calibration when provided with the experimental data. A two-step procedure is proposed where first the models are calibrated for yielding, and then for post yielding behavior (strain softening and orientational hardening).

The models are assessed considering different experimental tests, including standardized specimens with different radius of curvature. A simple modification is suggested to capture the strain hardening response at large deformations accurately. This work concludes that the model developed by Mikhalaf et al. is capable of accurately reproducing the experimental results obtained in the validation experiments of PCR-PP where as the modified Anand model is capable of accurately reproducing the experimental results of PCR-PE.

Nuclear power is currently not a commonly used option in commercial marine applications, despite its potential for significant emission reductions. This thesis is an overview of what has been done before, and what the potential is of modern marine nuclear power applications considering the long-term goals of harmful emission reduction in the maritime industry.
The concept of nuclear power is discussed, followed by the current state of nuclear power in both the shore-based, naval and the mostly historic marine application. The regulations for the marine application are noted to be outdated and require significant work for a successful application. Finally, the societal aspect of nuclear power is highlighted, as societal acceptance is not self-evident for nuclear power applications.
Different developments in the field of nuclear power are addressed, with specific interest in the SMR (Small Modular Reactor), concepts that are part of the “generation IV” family, and concepts that can operate using thorium as fuel. Multiple options are considered, from the well-established PWR (Pressurized Water Reactor) to the gen IV concepts: the HTR/VHTR (high/very high temperature reactor), fast reactors in both gas-cooled, liquid-metal and sodium cooled varieties (GFR, LFR, SFR) and finally the MSR (Molten Salt Reactor). Of these the HTR/VHTR and MSR in small modular reactor form are considered the most attractive option for the marine application, due to their passive safety, high burnup, high operating temperatures, and possibilities for thorium use in the future.
Criteria are established that are of importance to a marine propulsion and power generation system, establishing a framework for an implementation. Focusing on topics as: efficiency, transient loading capabilities, environmental impact, economic viability, size, and weight.
For power conversion (linking the heat generation to power/electricity for the vessel) the open-cycle Brayton turbine with a heat exchanger is selected as most suitable, despite the steam turbine being more developed and projecting a possible higher efficiency. The choice for the open-cycle Brayton turbine stems from the system size and weight reduction, along with a relatively easily implementable heat rejection system for enhanced load following capabilities. The selected heat exchanger is of the helical coil type, as this is significantly more developed and proven than the PCHE.
The most suitable layout is determined to be an all-electric layout, as this will greatly improve reliability (enhancing safety by redundant arrangements) and make the implementation easier applicable to a host of vessels. The electric layout allows for the combination of additional system such as batteries and emergency power. This layout is then combined with the open Brayton turbine and its heat rejection capabilities to ensure a system that is both compact as well as highly capable in performance.
Finally, four suitable concept vessels were established that allowed for a like-for-like replacement with a nuclear propulsion and power generation system. This allowed for a comparison to the conventional fuel-based systems where it is shown that the implementation of nuclear power can provide very large CO2eq reductions (over 98%), while reducing size and weight if vessels of suitable size are selected. The trade-off to this reduction is the production of nuclear waste, alongside the increased upfront cost due to the high capital investment associated with nuclear power.

Highly-loaded low-speed roller bearings are frequently used in equipment offshore e.g. slew bearings in crane, sheave bearings and FPSO turret bearings. Reducing maintenance costs, increasing productivity, ensuring safety of people and structural integrity and longevity assurance of equipment can be achieved by the condition monitoring of highly-loaded low-speed roller bearings.

Currently, very limited research is performed in the field of condition monitoring with acoustic emission (AE) monitoring for highly-loaded low-speed (<10 rpm) bearings with naturally developed damage. Acoustic emission monitoring has shown promising results in early stage and real time identification of defects according to literature. Furthermore, contamination of wear particles in lubricant shows an increase in AE activity according to literature.

In this research, the applicability of AE monitoring for damage assessment of highly-loaded low-speed roller bearings is investigated in a full scale duration test. Furthermore, the influence of contaminated lubricant with steel particles is investigated in the contamination test to study the feasibility of real-time detection of contaminated lubricant during operations and as a supporting technique for wear debris analysis in lubricant.

From the results, an increase in AE activity expressed in hit-rates is observed for a wide frequency band of 40 - 580 kHz during the duration test where the basic rating lifetime (L10) is consumed from 40% to 50%. Wear development in the bearing is observed during visual inspection and has been quantified with lubrication analysis.
A safety limit and a limit if the bearing is at risk for the AE activity has been defined with the results of the baseline and duration test. This research suggests that AE monitoring can be applied on highly-loaded low-speed bearings to assess the damage for representative operational conditions.

From the results of the lubricant contamination test, an increased AE activity with respect to higher lubricant contamination levels were observed. Furthermore, with a proper choice of the SNR-level, there is no masking effect of acoustic emission signals due to contaminated lubricant. The results of the contamination tests, indicates the possibility of detecting contaminated lubricant with AE monitoring.

The Static Recrystallization (SRX) phenomenon of austenite in C-Mn steels have a large impact on the final mechanical properties of the steel. However, the austenite recrystallization kinetics are difficult to investigate experimentally, due to solid-state phase transformations during cooling to room temperature. The best model alloys to examine SRX are those austenitic alloys such as, Ni-30Fe alloy, that do not experience undesirable phase transformation and that have similar stacking fault energy (SFE) as austenite in C-Mn steels. The hot-working of the Ni-30Fe alloy has been conducted at high deformation temperatures, followed by an uniaxial compression test at a low strain condition (ε = 0.2) with a strain rate of 1s^-1, and an annealing temperature of 900°C (above recrystallization start temperature). Thereafter, the alloy is experimentally investigated by Electron Backscatter Diffraction (EBSD), to characterize the austenite microstructure and to measure the crystallographic orientations. The experimental measurements from the EBSD technique are subsequently analyzed using MTEX software to study the SRX phenomenon that occurs during hot rolling of steels.The technique to separate recrystallized and deformed grains in this research has adopted the Kernal Average Misorientation (KAM) and Grain Average Misorientation (GAM) technique, rather than the previously utilized Grain Oriented Spread (GOS) technique which incidentally produced slower and inaccurate recrystallization kinetics. The initial and final grain size calculations have been conducted by consideration of the annealing twins, and the reported results are in close agreement with earlier conducted work of Sellars model. The EBSD scan which captures the Geometrically Necessary Dislocations (GND) have been experimentally measured after deformation to be approximately 4.5x10¹⁴m^-2, by utilizing the approach of KAM, curvature tensor and the Burgers vector with an estimated 13% error. Additionally, the effect of recovery has been captured with the continuous decrease in stored energy as a function of time, where the GND density is estimated to be 7.3x10¹²m^-2 after the annealing treatment.The GND density present in the deformed microstructure is significant to provide the net driving force necessary for nucleation, based on the validated strain-induced-boundary-migration (SIBM) mechanism. The initial nucleation site is observed at triple junctions, and the selected nucleation criterion factor for the captured GND densities, estimates the driving force for nucleation to favour single sub-grain SIBM. The minimum critical sub-grain size required for bulging is calculated to be 3.40 ± 0.44 μm after deformation, which is an increasing parameter with time, as a result of the recovery process. The number of recrystallized grains captured at different time intervals using the validated GAM technique assists in experimental nucleation rate calculations, that have been subsequently converted for a 3D microstructure, in order to compare with the nucleation framework of Rehman's model. The recrystallization nucleation process is experimentally observed to obtain peak values at 2s and continues until all the GNDs are annealed out of the specimen. There is a large discrepancy in the nucleation rate predicted by the model, which is much higher with respect to the experimental observations reported. Finally, the experimental recrystallization kinetics is observed to be in close agreement with the JMAK model during the initial phase of the annealing treatment, but deviates in the later phase of the recrystallization process.

Carbon dioxide emissions from the transportation sector account for roughly one-third of world-wide CO2 emissions. Governmental pressure to tackle this problem has forced the industry to adapt with regard to material development. One such adaption is the development and application of advanced high-strength steels (AHSS), offering high specific strength combined with improved ductility. This enables lightweighting of consumer cars, as well as improving the overall occupant safety and crashworthiness. Despite these apparent advantages of AHSS, sheet metal forming operations can cause unexpected edge-cracking. In this research the occurrence of edge-cracking is investigated and rationalized with fracture toughness testing. The Essential Work of Fracture (EWF) methodology is applied on double-edge notched (DENT) specimens, an increasingly applied method to characterize the crack propagation resistance of thin sheet metal. A novel sample preparation method is evaluated here, based on sheared notches instead of fatigue pre-cracked specimens. The obtained fracture toughness parameters are validated against laboratory-scale deep-drawing experiments to estimate its predictive capabilities. Scanning electron microscopy (SEM) was employed to examine the fractured surfaces and to identify the relevant micro-mechanisms of fracture. It was found that the obtained EWF results are in good agreement with the observed cracking behaviour during deep-drawing. Both the established method (fatigue pre-cracking) as well as the novel method of sheared notches were able to reveal the intrinsically low fracture toughness, otherwise undetected with conventional tensile testing. From the fractured surfaces of the EWF samples the relevant micro-mechanisms of failure were identified that govern the fracture toughness properties. Transgranular cleavage fracture was responsible for brittle behaviour while failure ductile failure occurred via microvoid coalescence.
Although the fatigue pre-cracking method for EWF testing seems to show a higher accuracy in predicting the cracking susceptibility, the shearing method can be employed as a rapid routine test to identify deterioration of fracture toughness properties early on.

On the railway line between Zutphen and Hengelo in the Netherlands, rolling contact fatigue (RCF) defects are found at the surface of the rail. RCF is a known hazard to the safe operation of railways, the cracks can cause transverse rail fracture, which may result in derailment. Contrary to convention, the traffic on this particular railway is bidirectional. In literature, little is known about the effects of bidirectional traffic on the rail material and the formation of RCF defects. In this study, the effects of the bidirectional traffic on the rail material and RCF defects are investigated by performing a metallographic examination of the rail surface and microstructure of rail material specimens taken from the actual track. The metallographic examination is supported by the analysis of the wheel-rail contact, which is simulated with multibody wheel-rail contact simulation software.

In longitudinal direction, optical microscopy revealed the absence of plastic strain in the surface layer of the rail. This plastic strain, which is the result of tangential surface traction, is always observed on rails subjected to uni-directional traffic and is considered the leading cause of fatigue crack initiation. However, the simulated wheel-rail contact stresses exceed the yield limit, so plastic deformation is expected. It is concluded that the frequent direction reversal of the tangential surface traction causes cyclic plasticity without the accumulation of strain, detectable with optical microscopy. Despite the absence of accumulated plastic strain in longitudinal direction, RCF cracks of varying sizes are observed on the rail surface. Although developed as a result of bidirectional traffic, the observed crack morphology shows similarities to the 'squat' RCF defect.

In this study, new insights are generated by considering the implications of bidirectional traffic and the rolling direction reversal on existing theories about the rail squat formation mechanism. Directions are formulated for further research on cyclic plasticity without the accumulation of plastic strain.

The fuel consumption of cars has become an important issue in the development of new materials and. These developments resulted in the generation of new grades of steel for the automotive industry. In particular, new advanced high strength steels (AHSS) have been developed for the automotive industry to lower fuel consumption (with weight reduction) by combining strength with formability. Especially, quenching and partitioning (Q&P) steels from 3rd generation AHSS can exhibit significant strength and ductility balance by combining martensite with retained austenite. Recently, there has been a new interest in applying the Q&P treatment to stainless steels, in particular martensitic stainless steel. For the automotive industry, the development in Q&P treated martensitic stainless steel can be a game-changer. The mechanical properties of Q&P treated commercial martensitic stainless steels have been widely researched. Unlike mechanical behaviour, the corrosion behaviour of Q&P treated martensitic stainless steel has not been investigated deeply. The effect of environmental factors or the effect of microstructure on the corrosion performance of Q&P processed martensitic stainless steel needs to be studied. This master thesis aims to identify the effect of microstructural constituents (retained austenite, primary and fresh martensite) on the corrosion response of Q&P treated martensitic stainless steels. To this end, an experimental approach is taken for this project. This work aims to create a relationship between heat treatment, microstructure, and the resulting corrosion properties. As an experimental path, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and Mott-Schottky experiments were carried out in 3.5 wt.% NaCl solution to reveal the corrosion response and passive film properties of the Q&P microstructures. In addition, X-ray photoelectron spectroscopy (XPS) was performed to analyze the chemical composition and fractions of oxide layers in the passive layer. Results demonstrate a phase dependency for the corrosion performance of Q&P treated martensitic stainless steels.

Literature reports a great deal of contradictory results concerning the effect of microstructure on the corrosion and passivity behaviour of advanced high strength steels. The difficulty in identifying the controlling cause of corrosion results from the inability of disentangling the coupled effects of individual microstructural features in a scientifically rigorous manner, thereby attributing the core behaviour to the wrong sources.
The aim of this thesis is to isolate and identify the effect of phases on the electrochemical response of high strength steels. To this end, a combined computational and experimental approach is taken. This work starts by analysing the connection between heat treatment, microstructure, and the resulting corrosion properties. After clarification of this interdependence, a finite element electrochemical model illuminates the corrosion behaviour of idealised two phase ferrite-martensite and ferrite-pearlite systems for different phase volume fraction combinations. The results from the simulations guide the microstructure creation for electrochemical experiments, where employed heat treatments result in ferrite-martensite and ferrite-pearlite microstructures with similar ferrite volume fractions. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) experiments in 0.1M and 0.01M H₂SO₄ solutions; potentiostatic polarisation, EIS and Mott-Schottky analysis in 0.1M NaOH solutions reveal the corrosion response and passive film barrier properties of the microstructures. Results demonstrate a clear phase dependency for both active and passive conditions, and are further discussed in light of microstructural features of secondary martensite and pearlite phases.

Microstructure-corrosion property correlation is an open question in the field of materials science. The microstructure of metals and alloys consists of several features with different individual corrosion response. The corrosion behavior of the macroscopic system is an outcome of the complex interaction of the components of microstructure. Hence, a definitive understanding of the corrosion response of the microstructural features is needed for improving the material durability and design.In the present work, the effect of grain size  on the active corrosion behavior of pure iron is investigated. Samples with different grain sizes are obtained by annealing heat-treatment. The microstructure of samples is characterized by optical microscopy, electron backscatter diffraction and X-ray diffraction. Electrochemical characterization using potentiodynamic polarization and electrochemical impedance spectroscopy are performed on the samples in deaerated 0.1 M and 0.01 M H₂SO₄ solutions. The surface topography of the corroded sample surface is characterized by atomic force microscopy. Following the experiments, a numerical corrosion model is attempted to replicate the observations. The results reveal an aggregate effect of grain size and crystallographic orientation of grains on the corrosion behavior of the samples.

The most commonly used material in the automotive industry is steel. Steel used in making Body-In-White (BIW) for cars are broadly classified as Advanced High Strength Steels (AHSS). These AHSS are produced by a well-defined alloying and specific annealing procedure. However, external oxidation of the constituent alloying elements from the steel is observed the annealing step . This selective oxidation of alloying elements on the steel surface affects the adhesion of the Zinc to the steel which is essential for corrosion protection. The main goals of this research work were to define the optimal parametric windows for the Electrolytic Plasma Cleaning technique to form a plasma capable of cleaning a steel surface by removing external oxides formed during the annealing process. Electrolytic Plasma Cleaning uses the traditional electrochemical cell that consists of an anode, a cathode, an external potential and an electrolyte but at higher input potentials. An experimental setup was developed with the aim of finding the ideal working parameters, establishing the groundwork for future large-scale experimentation.

Coating deposition by Physical Vapour Deposition (PVD) on high strength steels is an important research project at TATA Steel - IJmuiden. The research is aimed at replacing the conventional hot-dip galvanisation process to obtain a defect-free coating without affecting their well-engineered properties. However, the annealing treatment of the steel, performed to obtain these properties, affects the coating adhesion properties. This is a result of the selective oxidation process, which forms external oxides of alloying elements at the surface. Therefore, a pre-treatment process is required to remove these surface oxides from the steel strips before they are coated. Plasma sputtering is currently being
used for the pre-treatment to remove any contaminants and surface oxides from the steel. To obtain a good coating adhesion, a relatively large amount of surface oxides needs to be removed by sputtering. Also, the removed material is known to contaminate the vacuum chamber in the PVD deposition line, for which frequent maintenance of the chamber might be necessary. Thus, an additional
surface pre-treatment step was investigated in this study to reduce the sputtering process inside the vacuum as much as possible. In the present work, the effect of both direct current electrolytic alkaline cleaning and sulphuric acid etching on the surface of DP800 steel was investigated. Two different baths were considered for this purpose; a 27 g/L NaOH bath with some additive at 60°C and a 50 g/L H₂SO₄ bath at 25°C and 50°C. A current density of 1.5 A/dm² was applied during the electrolytic cleaning for which both cathodic and anodic polarisation methods were investigated. Also, a range of acid etching times (10s to 120s) was investigated for the given concentration and temperatures of the acid bath to study its effect on the surface. The effect of adding a corrosion inhibitor into the acid bath on the rest of the coating deposition process was also investigated. Various surface characterisation techniques and wettability tests were performed to study the changes in morphology and composition of the surface and their effect on the coating adhesion properties of the treated samples. Finally, coating adhesion tests were performed after zinc deposition to investigate the adhesion performance of the steel after the pre-treatment steps. Initial surface analysis during electrolytic alkaline cleaning showed that the anodic polarisation was more effective than cathodic polarisation of the sample, as the latter tends to reduce the surface wettability by additional deposits of iron fines over the surface. A subsequent acid etching provided a reduction in the minimum required sputter intensity to obtain a good adhesion from 2300 kJ/m² to about 800 kJ/m². A further reduction was achieved to a sputter intensity of only 214 kJ/m² after retarding the effects of surface reoxidation by vacuum sealing the samples. Acid etching at 25°C provided bad coating adhesion at lower etching times, attributed to the partial dissolution of surface oxides and absence of an initial grain roughening. Good coating adhesion was either obtained at higher etching times or by increasing the temperature of the acid bath to 50°C. Addition of a corrosion inhibitor was considered impractical as high sputter intensities (> 321 kJ/m²) was required to remove the adsorbed inhibitor molecules from the surface. Thus, a reduction in the required sputter intensity was achieved by more than a factor of 10 after acid etching, only if the effects of surface reoxidation during the transfer time between acid etching and entering the PVD installation can be minimized.

Metal halide perovskites have attracted a lot of attention over the last decade as a potential low cost alternative to traditional silicon based photovoltaics. Solar cells based on these materials have already achieved power conversion efficiency (PCE) of 22%. However, these high performing compositions are lead containing which is regarded as a potential risk for humans as well as the environment. A lot of research effort has been put into completely replacing lead with other group-14 elements such as tin and germanium, due to their similar sizes and electronic configuration. These kinds of perovskites have shown promising optoelectronic properties but are highly unstable due to the easy oxidation of tin and germanium.
In this thesis an alternative approach of mixing lead with other smaller divalent metal cations is explored. MAPbI3 is synthesized using lead acetate due to the facile removal of byproducts and its tolerance for mixing with other metal salts. The alternate metal salts were selected on the basis of their solubility in commonly used solvents and the suitability of the crystal structure of the precursor compound for perovskite structure formation. We found manganese to be a suitable substituent of lead and the upper limit for these mixed metal perovskites after geometrical calculations as well as experimental verification is found to be around 30%. Though the mixed metal compositions maintain the tetragonal crystal structure of lead based perovskites, a secondary crystalline phase is observed with increased lead substitution. Efforts are made to identify its composition and to remove it by optimizing the thermal treatment as well as the ratio between the other precursors. The optimized recipe for 30% lead substituted showed phase purity as well as good optical and electronic properties. Detailed compositional analysis revealed that, unlike MAPbI3 synthesized using chloride based precursors, in these mixed metal compositions chlorine is also incorporated in the films containing manganese especially near the substrate interface. This suggests that the smaller metal cation has an affinity for the smaller halide anion and that it plays a key role in the initiation of nucleation in such mixed metal (Pb:Mn) compositions. Finally, solar cells were made as a proof of concept incorporating these mixed metal perovskites and devices with up to 1.45% PCE were obtained.

The tie rods in the Duomo are structural elements, subject to monotonic loading and cyclic loading. Non-destructive testing is used to find cracks and determine their geometry. Lamb waves are applied to determine the presence of cracks in the tie rod and to estimate their positions. The cracks are located using eddy current testing. Finally the geometries of the cracks are determined using active infrared thermography. Experimental testing in the field of fracture mechanics is done to determine the fracture toughness of wrought iron. Combining the geometry of the crack with the fracture toughness of the material, leads to an estimation of the critical crack size.

The tie rods are made of wrought iron. The material properties are very heterogeneous. A tie rod is made out of multiple wrought iron bars of 1-1.5 meters. These bars are welded together under an angle of 27°. Cracks of two damaged tie rods are found to be under such an angle. The search for cracks will be concentrated on inclined cracks with a repetition of 1-1.5 meters.
Lamb waves is the first technique applied. An ultrasonic tomograph A1040 MIRA is used for testing. The modelling of Lamb waves travelling in tie rods and the signal processing are based on the possibilities of the MIRA. The dispersion behaviour of Lamb waves is modelled to understand the wave propagation in tie rods and the influence it has on the testing done with the MIRA. Using this knowledge, proper testing settings are found. Subsequently, signal processing is considered. The main objective of this part is to be able to identify cracks present in the tie rods.

The position of the cracks in the tie rod is determined using eddy current testing. Commercial eddy current probes are too sensitive to discontinuities to be applied to tie rods. Therefore, new probes are developed to overcome this drawback. Two probes are designed, both for the horizontal face and for the vertical face of the tie rod. The vertical face of the tie rods are best accessible. Therefore, on-site testing is done with the probe specially designed for that face.

Active infrared thermography is implemented to establish the geometry of the crack. A finite element analysis has been performed to model the propagation of heat through a tie rod. This is followed by experimental testing in the laboratory carried out on a broken tie rod. Finally, the results of the modelling and of the experimental testing are compared.

The last part has a fracture mechanical nature. The fracture toughness of the material is determined assuming both linear-elastic and elastic-plastic material behaviour. Also the fatigue behaviour is evaluated. The values obtained from experimental testing have been applied to a simplified model of the crack geometry to determine the critical crack size of the tie rod, for monotonic loading, and the threshold crack size, for cyclic loading. Fatigue life is predicted taking the threshold crack size as the initial crack size and the critical crack size as the final crack size.