To decrease vehicle emissions, automotive manufacturers aim to decrease materials usage. Dual-phase (DP) steels are used in safety critical locations of a vehicle and with stronger DP steels, less material is needed. However, DP steels are known to be affected by hydrogen embrittlement (HE), which decreases the ductility and is thus of significant concern.

This work investigates the effect of heat treatment on the microstructure and HE of DP steel. Heat treatments are developed and conducted using dilatometry, with obtained microstructures characterized using scanning electron microscopy (SEM), optical microscopy (OM), electron backscatter diffraction (EBSD) and hardness measurements. Tensile specimens are heat treated using a Gleeble 3800-GTC thermo-mechanical simulator, before evaluating the HE effect by measuring the total absorbed hydrogen content using thermal desorption spectroscopy (TDS), and determining the static mechanical properties using slow strain-rate tensile (SSRT) testing. The fracture micromechanisms are investigated with fractography using SEM and EBSD with interrupted SSRT and fractured specimens.

The critical transformation temperatures are determined at 686±1 ⁰C and 571±10 ⁰C for Ar3 and Ar1 respectively. Intercritical annealing at 590 ⁰C, 630 ⁰C, and 670 ⁰C result in a martensite content of 24.97±6.43 %, 40.41±4.21 %, and 77.63±6.97 %, respectively. Hardness values of 240±31, 300±9, and 380±20 HV1 are obtained for the respective intercritical annealing conditions and are an accurate method for comparing the martensite content and microstructure of dilatometry and Gleeble specimen. The martensite distribution changes from a discontinuous network of lath martensite with small martensite islands at 590 ⁰C, to a continuous network of lath martensite without martensite islands at 670 ⁰C.

TDS yield an increase in the total absorbed hydrogen content of 1.16±0.11 wppm, 1.29±0.13 wppm, and 1.58±0.27 wppm at increasing intercritical annealing temperature, which is attributed to an increase in the ferrite/martensite interphase.

Through SSTT the optimal combination of ultimate tensile strength (UTS) and elongation is found at 630 ⁰C, with UTS of 1025±8 MPa and elongation of 12.6±0.6 %. For all specimens significant HE is observed, with an embrittlement index of 58.9±7.1 %, 89.2±1.1 %, and 85.8±2.5 % for increasing intercritical annealing temperature. The highest embrittlement at 630 ⁰C is attributed to dislocation pile-up around martensite islands, severely increasing embrittlement.

Fractographic investigation revealed the presence of quasi-cleavage fracture bands across the specimen cross-section. This is attributed to preferred crack propagation along martensite bands in the cross-section, with preferred crack nucleation at the martensite surface layer of the specimen short edge. EBSD of the fractured specimen revealed an increase in the kernel average misorientation (KAM) surrounding the ferrite/martensite interface and martensite islands, indicating an increased HE action due to the HEDE and HELP mechanisms.

It is concluded that there is considerable embrittlement of the heat-treated DP steel, which is significantly influenced by the martensite content and distribution. Since DP steels are used in safety critical components, controlling the distribution of martensite in the microstructure is vital, and avoiding surface layer martensite and martensite bands can reduce the HE effect.

The growing amount of plastic waste generated by the consumer goods industry has led to excessive landfilling and increased greenhouse gas emissions, contributing significantly to the greenhouse effect. Government initiatives have identified the potential for a more sustainable approach to managing this homogeneous plastic waste stream. The Netherlands Circular Economy Program 2023-2030 (NCEP) envisions the MEGA project as a solution to repurpose plastic waste by replacing aging pedestrian infrastructure. Polypropylene (PP), known for its chemical stability and weather resistance, can be reinforced with glass fibers (rPP-G) to meet the requirements of such applications. Additionally, 3D printing is recognized as a promising method to reduce plastic waste during production, making it a valuable component of this initiative.

Nevertheless, outdoor infrastructural applications are subjected to load and temperature cycling due to their exposure to varying weather conditions, static loads, and pedestrians walking at different frequencies. This study aimed to assess and evaluate the effects of hygrothermal aging on the mechanical behavior of rPP-G. Three conditions were studied: a control condition not subjected to the aging environment, an extreme condition subjected to 95 % relative humidity (R.H.) and 80 ◦C, and a condition that approximated real application humidity levels of 77 % R.H. at the same temperature.

The tensile properties were evaluated by applying the load at a speed of 1 mm/min. The dynamic mechanical response was investigated at frequencies of 1 Hz and 2 Hz to simulate a crowd walking and a crowd brisk-walking on the material. The creep response was examined through short-term creep tests at elevated temperatures, and a methodology was derived based on the Time-Temperature Superposition (TTS) principle to extrapolate the behavior at ambient temperatures for stress levels of 8 and 10 MPa. For further analysis of the results, Scanning electron microscopy (SEM) captures were acquired, and the IR spectrum and diffraction pattern of rPP-G under different aging conditions was measured. The tensile properties suggested increasing degradation with hygrothermal effects, leading to a 14.3 % reduction in ultimate tensile strength (UTS), a 16 % reduction in Young’s modulus, and a 93.3 % increase in strain at break. This indicated weakening of the fiber/matrix interface, verified by increased fiber pull-out. However, no hydrolytic degradation was observed, as no differences in chemical compounds and crystallinity were detected. The dynamic mechanical response suggested the existence of two mechanisms: water acting as a stiffener at cryogenic temperatures, and induced plasticization and fiber/matrix weakening from the hygrothermal effects. However, fiber/matrix weakening dominated under extreme aging conditions, hindering the stiffening effects of water on the molecular structure of rPP-G. This effect was more pronounced under median aging conditions for the 1 Hz loading, as more time allowed for molecular relaxation. Increasing frequencies appeared to shift the glass transition temperature (Tg) to higher temperatures, highlighting the material’s elastic character. The creep response of rPP-G revealed an exponential relationship between temperature and time to fracture, allowing the use of Time-Temperature Superposition (TTS) with the Arrhenius equation to predict its behavior at ambient temperatures. The derived methodology suggested that hygrothermal effects leading to the degradation of tensile properties are significantly more apparent under long-term load applications, revealing a 282.6% reduction of time to fracture at 8 MPa under extreme conditions.

This thesis demonstrated the significance of dynamic mechanical analysis in understanding the effects of degradation on reinforced thermoplastic polymers. Additionally, it highlighted the importance of creep testing for such applications, revealing crucial insights into the long-term load application effects on the service life of thermoplastic polymers.

The Ba3MoNb1-xVxO8.5 family exhibits significant oxide ion conductivity, and is thus interesting in the potential use of solid oxide fuel cells as an electrolyte. Its structure contains palmierite-like layers consisting of metallic cations forming octahedral and tetrahedral polyhedra, through which the oxide ions can be conducted. Furthermore, the cationic vacancies present in the structure lead to complex stacking configurations beneficial to the conductivity. In this work the Ba3MoNb1-xVxO8.5 family, with x = 0.0, 0.1, 0.2, 0.3, 0.4, have been synthesised and analysed with the use of X-ray diffraction and subsequent refinement of their structures. The synthesis for each sample was performed successfully, and the first calcination step was further identified to bring a higher yield under higher temperature and longer time of the calcination. From the LeBail refinement the a lattice parameter was shown to correlate with Vegard's law, decreasing with an increase of substitution of Nb5+ with V5+, whilst the c parameter expands upon substitution of the smaller cation. This is hypothesised to be caused by repulsion, either coming from distortions caused by second-order Jahn Teller effect, or due to more tetrahedral coordination. Finally, the Rietveld refinement has given insight into the location and occupation of the metallic cations. V5+ has been incorporated into the solid solution, and sits on the same crystallographic sites as the other metallic cations, choosing to split off to either one of the two sites, thereby contradicting earlier literature. Furthermore, the vanadium doping also seems to move the overall concentration of Mo6+ and Nb5+ to one site in particular. These results have thereby given new insight into this family of solid electrolytes.

This study explores the potential of metal oxide fluorides as cathode materials for solid-state fluoride-ion batteries (FIBs), aiming to combine the stability of intercalation-based electrode materials with the high energy density of conversion-based materials. Through comprehensive experimental investigations using techniques such as electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), linear sweep voltammetry (LSV), and X-ray diffraction (XRD), the compatibility and electrochemical performance of transition metal oxides (Cu₂O, FeO, and Mn₂O₃) with CsPb_0.9K_0.1F_2.9 (PK10) solid electrolyte and Pb/PbF₂ composite anode are evaluated. Results indicate negligible room temperature capacity for Cu₂O, FeO, and Mn₂O₃, suggesting potential limitations related to the cathode fluorination reaction. Additionally, PK10 electrolyte displays slight instability at room temperature, indicating potential electrochemical activity. Symmetric cell testing using Pb/PbF₂ composite electrodes confirms the suitability of the Pb/PbF₂ composite as both counter and reference electrodes. Notably, Cu₂O full cells show enhanced specific capacity at elevated temperatures (60 °C), reaching 310.24 mAh/g during the first cycle, equivalent to 82.96% of the theoretical specific capacity. This considerable increase in capacity due to only a slightly higher temperature is attributed to reduced overpotential and enhanced fluoride ions diffusion rates. However, observation of capacity fade between cycles for the Cu₂O cell at 60 °C suggests irreversible reactions, necessitating further investigation. In conclusion, this study highlights the potential of metal oxide cathode materials in solid-state FIBs, emphasizing the importance of understanding electrolyte stability and cathode compatibility for battery performance enhancement.

Thin film solar cells are devices that make use of thin layers to generate electricity from solar energy. Among various layers present in a thin film solar cell architecture, transparent conductive oxide (TCO) is crucial. TCOs are a set of materials with a unique set of properties. As a front contact, TCOs are required to offer high transparency to allow photons to reach the absorber layer to generate charge carriers. At the same time, TCOs need to be conductive as well to transport charge carriers from absorber to the metal electrode. However, there exists a trade-off where improvement to one property often comprises the other.
The concept of a bi-layer TCO configuration is explored in this project which makes use of two single layer TCOs: one with superior electrical properties and the other with superior optical properties. Hydrogenated indium oxide (IOH) is investigated as the conductive layer while the intrinsic zinc oxide (i-ZnO) as the transparent layer. Various other conductive layers are also tried in combination with i-ZnO, those being - Cerium doped indium oxide (ICO) and Cerium and hydrogen co-doped indium oxide (ICOH).
The first step to produce highly conductive bi-layer films is optimise post-deposition annealing parameters. Emphasis is placed on optimising annealing time, which tracing out the behavior of change in opto-electrical properties of the bi-layer after every 10 min increment in annealing time. 140 minutes is found as the optimum annealing time for IOH/i-ZnO bi-layers on both flat glass and textured glass substrates.
Novel highly conductive IOH/i-ZnO bi-layer were deposited demonstrating mobility of 143 𝑐𝑚^2/𝑉 𝑠 and carrier concentration of 1.05𝑥10^19 𝑐𝑚^−3 on flat glass. The bi-layer has the ability to not only retain individual constituent TCO properties and also to surpass the limitations of their individual TCOs. This attributes to the fact that the free charge carriers transport takes place a t the interface between TCO layer in the bi-layer stack. The ICO/i-ZnO and ICOH/i-ZnO structures were deposited, both bi-layers demonstrated mobility below 100 𝑐𝑚^2/𝑉 𝑠, however they outperformed their layers both electrically and optically.
IOH/i-ZnO bi-layer construction was also deposited on textured glass substrates. Best sample demonstrates mobility as high as 110 𝑐𝑚^2/𝑉 𝑠 with a carrier concentration of 3.63𝑥10^19 𝑐𝑚^−3. The reason for slightly lower mobilities is attributed to the inconsistency in shape and size of the textures present on the substrate, which leads to non-uniform deposition of IOH across the entire surface. Further investigation will lead to understanding hydrogen’s role in the IOH/i-ZnO bi-layer and the extent to which bi-layer performance on textured substrates can be improved.

In order to meet the shipping industry's emissions reduction goals, it is imperative to explore and adopt alternative marine fuels. Methanol (or methyl alcohol) is expected to play a large role in the future. However, current regulations limit the attractiveness of methanol as marine fuel due to the inability to use the space around a venting point on deck. Hazardous area zones are installed around fuel tank vapour outlets due to the flammability and toxicity of methanol vapour. Consequently, these areas become very impractical. This thesis investigates the ventilation of the fuel tank vapour below the waterline instead on deck in order to be able to limit/eliminate these areas. Therefore, the main research question is:

"What is the concentration of methanol at deck level when methanol is vented below the waterline?"

An Eulerian based CFD model and a simple integral model are used to predict the methanol concentration above the waterline. The integral model predicts the gas concentration above the waterline based on the gas flow rate reaching the surface and the radial inflow rate of air. The CFD model tracks parcels (group of bubbles with the same properties) using the force balance in the discrete phase model. Both of the models are successfully validated against experimental data from the "Rotvoll experiment" wherein methane was released at the bottom of a water basin. The CFD model showed strong superiority over the integral model, o.a. due to the lack of gas dissolution in the integral model.

The numerical models are applied to the case wherein a mixture of methanol and nitrogen is vented due to an overpressure. The overpressure could be caused by for example the failure of the vapour return line when bunkering or a fire. The bunker tanks are protected by a pressure relief valve, which reduces the overpressure by directing the gases in the bunker tank towards the venting location below the waterline. The flow rate characteristic (pressure - flow rate) of the pressure relief valve determines the rate at which the gases are injected in the water. The gas dissolution showed strong dependence on the departure bubble diameter and the venting depth. Different cases with different initial bubble sizes and different venting depths were simulated. The CFD model showed that in the most critical case (lowest venting depth 0.5m and largest initial bubble size 0.08m) the gas dissolution is large enough such that no methanol vapour reaches the deck of the ship and barge. The subsea venting of methanol-nitrogen vapour proved to be a safe alternative compared to the venting above deck.

Studies on the impact of Hydrogen on the electrochemical and mechanical behaviour of Iron-based materials have been increasingly conducted in the past few years. This is mainly due to the ever-growing demand for sustainable energy sources, which involve Hydrogen and to meet the high structural and economic demands from the automobile sector and other industrial demands for which high strength steels like dual-phase steels have been developed. Steels may absorb hydrogen both throughout the production process and during different phases of use. High-strength steels (particularly dual phase steels) and martensitic stainless steels are highly susceptible to hydrogen embrittlement. Moreover, hydrogen embrittlement is already possible at quantities as low as 0.1 ppm[1]. Therefore, understanding Metal-hydrogen interactions is essential.

This thesis aims to study the effect of Hydrogen charging on three different
iron-based materials and the possible effect on the electrochemical/corrosion performance. The Iron-based materials used in the study are Pure Iron, DP1000 and AISI 420. The methodology involves using an electrochemical procedure based on potentiostatic Hydrogen charging and Cyclic Voltammetry (CV), applied on these Iron-based materials having different phases to monitor H-uptake in the materials. The materials are charged with Hydrogen both on the active and passive surfaces. The electrochemical method is capable of measuring the diffusible H concentration (including mobile Hydrogen) for the steel alloys under H-charging conditions. Using X-Ray Diffraction (XRD) Technique, microstructural analysis is carried out on Pure Iron, DP1000 and AISI 420 stainless steel to identify the different phases interacting with Hydrogen. To gain additional insights relating to the electrochemical/corrosion performance of the investigated materials and into the H-related findings, potentiostatic polarization techniques, Electrochemical Impedance Spectroscopy (EIS) and Scanning Kelvin Probe (SKP) are carried out.

As a result, it was discovered that Pure Iron had the maximum amount of diffusible Hydrogen under the charging conditions tested, followed by DP1000 and then AISI 420 Steel with the lowest amount. EIS technique was useful in identifying a trend between the barrier properties of the passive layer and the H desorption values for the three materials. The results also revealed that materials charged with Hydrogen on active and passive surfaces behaved differently with respect to the amount of Hydrogen desorption. The microstructural features of the active surface and the passive oxide film that formed on the materials are further discussed in relation to this.

Perovskite materials gain a huge interest in the photovoltaic (PV) community due to its unique characteristics, including long carrier diffusion length, widely tunable bandgap, light absorption potential, and low processing cost. Nowadays, most perovskite fabrication methods employ a solution-based process due to its simplicity and production speed. However, this deposition method provides a non-uniform structure and uses highly toxic solvents, posing the risk of contamination and adverse effects on the environment. On the other hand, a solvent-free method like thermal evaporation can produce a uniform and conformal layer. This method can be used to produce not only the perovskite absorber layer but also the contact layers and transport layers. Depending on the deposition parameters, the resulting morphological properties also change. Therefore, it becomes interesting to understand the detailed knowledge of the film growth and the effects of the deposition parameters on the exact kinetics and the optical properties. Hence, the first objective of this study focuses on developing C60 electron transport layers (ETL) for application in all-evaporated perovskite solar cells (PSCs). The C60 thin film was deposited with different thicknesses of 20, 30, 40 nm and deposition rates 0.3, 0.5, and 1 Å/s on top of the silicon wafer substrate. The resulting surface morphology is obtained from scanning electron microscopy (SEM) and atomic force microscopy (AFM). It indicates that C60 with 40 nm thickness and 0.3 Å/s deposition rate shows a pinhole-free layer with an average surface roughness of 1.05 nm and thickness uniformity of more than 94%. The X-ray diffraction (XRD) measurement shows that decrease of peak intensity as the thickness is reduced from 40 to 20 nm. Moreover, with different deposition rates, 1 Å/s of deposition rate exhibits an asymmetric broadening peak which attributes to the small grain size and the presence of a planar defect in the structure of C60.
The optical analysis has also been performed to get the complex refractive index C60 and identify the effect of deposition rates and layer thicknesses on optical constants. A procedure to extract optical constant for the perovskite absorber layer has been developed during this thesis project using a combination approach of b-spline and Tauc-Lorentz dispersion model. The obtained results were found to be in excellent agreement with experimental work and literature data.
Furthermore, the complete solar cells with p-i-n configuration and semi-transparent perovskite solar cells (ST-PSCs) were optically simulated using GenPro4 software. This simulation aims to identify both the photocurrent density of the perovskite absorber layer and the optical losses caused by parasitic absorption in the supporting layers. In the p-i-n structure, ITO and MoOx layer located on the illuminated side contribute to the main portion of optical loss. Simulations suggest that 40-nm-thick ITO and 10-nm-thick MoOx is an ideal layer stack to deliver high implied photocurrent (22.14 mA/cm2). On the other hand, the optical loss in semi-transparent perovskite solar cells is investigated in two different wavelength regions (i) 300 – 800 nm and (ii) 800 – 1200 nm. In this investigation, the metal back contact is replaced with ITO and cells illuminated from the ETL side. The results show that, in the first wavelength range, the main optical losses are due to reflection, parasitic absorption in the C60 and top ITO layer. These losses are reduced by applying 120-nm-thick anti-reflective coating MgF2 and decreasing the thickness of C60 to 10 nm. Moreover, in the wavelength region of 800 – 1200 nm, the optical losses are mainly affected by the top and bottom ITO, MoOx layer, and reflected light. After optimizing top ITO and MgF2 thickness to 50 and 120 nm, respectively, a 17.07 mA/cm2 of photocurrent transmitted through the cells can be achieved. The light transmittance is ~88%, indicating the potential of semi-transparent perovskite solar cells to be applied in perovskite/silicon tandem devices.

With fossil fuels being phased out and growing global interest in a hydrogen economy, there is demand for re-purposing existing pipelines for transportation of hydrogen gas. However, hydrogen is known to have adverse affects on the properties of steels. Hydrogen will dissolve in the steel matrix and contribute to a reduction of mechanical properties, causing Hydrogen Embrittlement (HE). There is currently a knowledge gap about the behaviour of pipeline steels and their welds in a gaseous hydrogen environment that prevents re-purposing of pipelines for hydrogen transport. In this work, a combined approach of modelling and in-situ mechanical testing was used to assess the HE susceptibility of X60 pipeline steel and its girth welds. To this end, a novel tensile setup featuring in-situ charging with high pressure H2 gas and a sample geometry representing miniature pipelines was developed and validated. To our best knowledge, this setup design has not been reported elsewhere, making this a breakthrough design. An FEA modelling approach was used to estimate the pre-charging duration as well as to gain an insight into the stress states inside the notched samples. It was found that both the base and weld metals lose ductility when subjected to gaseous H2. The base metal showed 27% loss of ductility when subjected to 100 bar H2, which further increased to 40% in notched samples. A trend of increasing loss of ductility was found with increasing pressure for the weld metal, which showed up to 14% loss of ductility at 100 bar H2. The weld metal also retained more of its reduction in cross-sectional area after fracture in H2 as compared to N2 than the base metal. Other characteristics like yield strength and UTS were not affected by the hydrogen gas. The fracture mechanism in the both metals was found to change from microvoid coalescence (MVC) fracture to quasi-cleavage (QC) fracture. The base metal fracture mechanism changed to QC completely, while the weld metal only showed partial QC fracture. In the base metal, ductile fracture mechanisms like HELP and possibly AIDE were found to be dominant even in the QC fracture mode. It was concluded that the weld metal is less susceptible to HE than the base metal in a gaseous hydrogen environment. For both metals, HE effects were only observed at high amounts of plastic strain, which is outside of the operating conditions of a pipeline. However, before pipelines can be repurposed for hydrogen transport, fatigue testing should be performed to assess the influence of existing defects and cyclic loading conditions on the HE performance of both steels.

Fossil fuels have been the primary source of rising energy requirements for humankind. However, the extensive use of fossil fuels has led to an increase in Earth's surface temperature. To tackle rising energy demands and the increase in Earth's surface temperature, various organizations like Inter-governmental Panel for Climate Change and the European Environmental Agency have suggested the use of renewable energy as an alternative energy supply. E.g., the use of hydrogen as an alternative fuel in transportation will reduce greenhouse gas emissions. Besides, converting CO2 and N2 to fuels and industrial feedstock like CO or NH¬3 can curb the Earth's increasing surface temperature. As a result of this, in this thesis, the catalysts for the synthesis of hydrogen from water-splitting (hydrogen evolution reaction- HER), conversion of CO2 to CO via carbon dioxide reduction reaction (CO2RR), and reduction of N2 from air to NH3 (Nitrogen reduction reaction-N2RR) are studied. The conventional catalysts used for these reactions are Pt for HER, Cu for CO2RR Cu, and Ru for N2RR. Although these catalysts are active and exhibit a high yield of products, they have some disadvantages, such as the long-term availability and cost of Pt and Ru. On the other hand, Cu suffers from the low selectivity for the conversion from CO2 to CO. To overcome these disadvantages; scientists have developed a new kind of catalyst with a higher specific activity, known as the Single-Atom Catalysts (SAC). The SACs use fewer precious elements than the conventional bulk catalysts without compromising the activity. The use of binding energy (EB) as a descriptor for the reactions mentioned has been proven in the literature. Therefore, EB is used in this thesis to predict novel SACs through high-throughput DFT calculations using 3-N doped graphene as the substrate. The descriptor for HER is the EB of H atom, for CO2RR is EB of CO, and that of N2RR is EB of N on the respective catalyst surfaces. These calculated binding energies are compared against the descriptor EB on the conventional catalysts to obtain the novel SACs. With EB as the descriptor, the candidate catalysts for HER are B, Cr, Mn, Fe, Co, Ni, Ge, Ru, In, Sb, La, and Pb. The candidate catalysts for N2RR are Ru, Mo, and Cr. The candidate catalysts for CO2RR are Mg, Al, Ca, Zn and Se,. In addition to this, the charge dissipation of the adsorbent species on the SAC and the effect of atomic size on the EB is studied. It was seen that the computational predictions go hand in hand with the predictions of existing experiments for HER and CO2RR.

The comfort assessment of ships is based on several criteria. There are for example criteria for motions, noise and vibrations. The criteria for motions are nowadays often defined as comfort limits on the accelerations in the ship motions. However, from other industries it followed that the rate of change of the accelerations, the jerk, can also have an influence on the sense of comfort of passengers and crew. The goal of this thesis is to investigate whether it would be useful to add jerk criteria to the comfort assessment of ships. Jerk cannot be measured directly (yet), so it has to be obtained from acceleration measurements or calculations. For this goal filter and processing procedures are defined. To be able to make comparisons different ways of quantifying the jerk are established. One is aimed at peak values, since these are often determining the limit for comfort and operability. The other is focused on quantifying the non-linearity of the response. Research is performed on what the physics behind jerk are, and what phenomena are likely to cause large jerk values. The prime cause is found in slamming. The jerk following from slamming is influenced mostly by the shape of the bow and the speed of immersion in the water. Using the measurement data of two different hulls from other research the effect of varying conditions on the jerk is investigated. From this research it follows that there can be a difference in seakeeping behaviour when looking at jerk instead of accelerations. Since jerk is the third derivative of displacement to time, the non-linearity in this response is relatively high. Therefore non-linear codes are required to calculate the jerk response correctly. The use of a Reynolds Averaged Navier Stokes (RANS) code proves to be able to predict the jerk behaviour correctly. In this thesis only model test measurements and calculations are used. The scaling of jerk to full scale, and difficulties that it might impose, are only discussed theoretically. The general conclusion is that jerk is worth investigating to compare the seakeeping behaviour of ships. Until quantitative limits are available only qualitative comparisons are possible, but these can already give additional insight.

The effects of precipitates in the microstructure of an AA7075 aluminium alloy on: the dislocation behaviour, dislocation structure and dislocation structure evolution during plastic deformation were investigated using the physical yield criterion model by van Liempt and Sietsma. The model was in fact applied for the first time to aluminium and an AA7075 aluminium alloy. By constructing an extended Kocks-Mecking plot from the measured tensile and interrupted tensile data the dislocation density, average dislocation segment length and physical yield stress were determined.

The aim of the present study was to get a better understanding of the role of precipitates in the evolution of the dislocation structure during plastic deformation. The recovery of anelastic strain during loading and subsequent unloading after plastic deformation was investigated as well. The yield criterion was used to study the anelastic loading, while a constitutive unloading model by Torkabadi et al. was used to study the unloading behaviour. The models were combined to define the fraction of unrecoverable anelastic strain. The anelastic strain is related to springback. Therefore a better understanding of the anelastic strain could be useful for making better predictions of springback after metal forming. The physical yield criterion was further extended by incorporating a continuous uniform dislocation segment length distribution. Insight on the dislocation segment length distribution, and the evolution thereof during plastic deformation, could help to better understand the mechanical behaviour of metals.

The evolution of the dislocation structure during plastic deformation is impeded by the presence of precipitates in the microstructure. Therefore, the physical interpretation of α in the Taylor equation which quantifies the dislocation structure, proposed by Arachebelata et al., was modified to incorporate the effects of precipitates in the microstructure. The dislocation structure parameter α should remain constant. However, the average dislocation segment length obtained from the extended Kocks-Mecking plot does not decrease sufficiently to accommodate a constant α. The introduction of the length between precipitates, which is independent from work hardening, into the Taylor equation ensures that α does remain constant, whilst in addition it provides an estimate of the distance between the precipitates.

Anelastic strain, caused by reversible glide of dislocations in the pre-yield regime, is introduced into or recovered from the metal during loading and unloading respectively. The anelastic unloading strain determined from the interrupted tensile tests was found to be smaller than what was expected according to the model. Three possible causes were identified: not all Frank-Read sources are at their critical state when unloading is initiated, dislocation loops propagating through the crystal undo portions of the anelastic unloading strain and the retracting dislocations remain stuck behind obstacles whilst retracting under the reducing applied stress. The constitutive model was found to be not suitable for studying the dislocation behaviour during unloading because the change of dislocation segment length with plastic deformation is not accounted for. The development of a physical unloading model is therefore recommended.

The distribution of the dislocation segment lengths could explain the non-zero value of the work hardening rate Θ at the abrupt change of slope between the pre and post-yield regime in the extended Kocks-Mecking plot. The value of Θ at this point could be an indication of the distribution width. The continuous uniform distribution is a rather unrealistic description of the dislocation segment length distribution. Therefore, other distribution types are proposed for the further development of the dislocation segment length distribution model of the physical yield criterion.