The recent drive towards carbon-neutral transportation has led the automotive industry to the development of fuel cell electric vehicles (FCEVs). These are especially convenient in the trucking industry, where the required long ranges and the slow recharging capabilities of battery electric vehicles (BEVs) make this alternative not suitable at this time. A crucial component of any fuel cell system is the hydrogen storage solution. This is most often a type IV composite pressure vessel (CPV), where gaseous hydrogen is compressed and stored at 70 MPa. CPVs are sophisticated structural components and the full understanding of their mechanical behaviour is yet to be achieved. This study presents a modelling framework for the prediction of the mechanical response of CPVs during pressurization. The framework begins with an analytical adjustment of the vessel geometry and material composition to match the properties of the filament-wound tank. Then, the analysis is solved numerically. The model takes into account damage progression to simulate the vessel’s deformational behavior and estimate the burst pressure. The modelling strategy is highly replicable, it reduces significantly the computational time of the analysis with respect to the previous benchmark, and it is able to predict burst with reasonable accuracy both in the cylinder and in the dome region of the vessel. The numerical results are correlated to the experimental data collected during burst testing at cellcentric GmbH in Stuttgart, Germany.

The combination of a relatively recent emissions scandal and the ever growing incentive to provide sustainable transportation solutions, led to the fact that the transition to electrically propelled land-based vehicles is more prominent than ever. All prominent European car-makers announced diverse fully and partially electric product portfolios for 2021 and beyond with strong indication that the era of the Internal Combustion Engine (ICE) is slowly fading into history. While Battery Electric Vehicles (BEVs) are already well on their way in establishing a strong market share in the personal vehicle domain, the field of long haul transport is left to search for solutions elsewhere as battery technology does not present an efficient solution at this time. Fuel-Cell Electric Vehicles (FCEVs) pose a solid performance base to close the gap that batteries cannot
and provide sustainable, zero emissions solutions, for all heavy transport sectors - automotive, aviation and maritime. Within fuel cell systems, a component whose criticality is often overlooked or even understated is the hydrogen storage tank. Current state of the art uses type IV composite pressure vessels (CPVs) with a plastic liner and Carbon Fiber Reinforced Plastics (CFRP) composite overwrap to ensure structural integrity. Recognizing the complexity of a CPV is crucial in order to allow for the development of robust and worthwhile
design processes that could yield a significant decrease in material use, making FCEVs more cost effective and an attractive long-term solution. This thesis aims to provide some detail on the behavior of CPVs and their depth through the development of an automated numerical analysis framework and the execution of a focused experimental study that examines the impact of laminate stacking sequence as well as manufacturability factors on overall CPV behavior and, in particular the cylinder-dome transition of the vessels. The details and experimental correlation of the developed numerical analysis framework are shown and discussed. The framework heavily utilizes the outputs of an industry standard filament winding software, Composicad, which is used as a basis that is then further refined in order to generate a satisfactory geometric description of the vessel and its laminate composition. Major emphasis is placed on the discussion of processes made for the geometry correction and attention is placed on particular factors that were also tested in the experimental study - hoop ply drop-off and stacking sequence. The framework is correlated to experimental results and laminate configurations from previous and current experimental results to showcase its versatility and potential for future optimization studies given the high level of automation involved. Two Finite Element (FE) models are investigated within the scope of the developed framework - a solid and shell element model. The performance and predictive ability for each are presented and discussed. The experimental study presents data on the impact of stacking sequence effects and hoop ply drop-off
on CPV behavior - in particular, the cylinder-dome transition. The influence of both parameters are discussed and contextualized with previous studies in order to identify relevant trends. Novel results were obtained for the relationship between hoop layer placement and burst performance. The results further indicate a delicate interaction between vessel stacking sequence, burst strength and manufacturing robustness. The results of this study highlight important factors for future numerical studies of CPVs and showcase the development of an analysis approach with low computational cost while retaining acceptable accuracy. Furthermore, the experimental study helps put focus on future areas in need for further investigations in order to identify design-critical performance trends.

Type IV composite pressure vessels (CPVs) are used commercially for the gaseous storage of hydrogen in fuel cell electric vehicles (FCEVs). However, their economic implementation requires material optimization and a reliable prediction of the vessel strength. In this regard, their burst when loaded under internal pressure is impacted by the combined effect of the stacking sequence design and the variability of mechanical properties resulting from the manufacturing process. This work shows a framework for analysis that accounts for some of these manufacturing-induced characteristics in the mechanical response, namely the relation between the vessel stacking sequence, its final geometry, and the material properties. Furthermore, vessel burst pressures are alternatively estimated from the failure criteria evaluation in constitutively elastic analyses and the modeling of damage progression. Predictions are reasonably accurate when the collapse occurs in the cylinder (+2.2 %), although a more considerable discrepancy exists with experimental results when vessels fail in the dome transition region (+12.3 %).

The current needs of sustainable mobility lead to the electrification of transport industries, which require innovative products. The use of fuel cell electric vehicles (FCEVs) on a commercial basis depends on the development of hydrogen storage devices, which must be reliable and cost-effective. For the design of high safety composite pressure vessels (CPVs), it is necessary to have in-depth knowledge on the structural mechanics of these components. When internally pressurized for the first time, interfiber fracture (IFF) takes place within the structure of CPVs. The aim of the current investigation is to gain insights into the characteristic damage pattern and mechanisms that take place during CPV pressurization by analyzing the acoustic emissions and comparing the results to analytical and numerical solutions. Hence, a predefined number of vessels is manufactured and hydraulically pressurized in a specially designed test chamber up to burst. An array of 120 sound pressure sensors installed within the test chamber is responsible for recording the occurring acoustic events. By using a delay-and-sum beamforming algorithm, the events are localized. Their position and corresponding pressure level are analyzed and compared to analytical solutions calculated using classical lamination theory and 3D elasticity theory. Furthermore, a comparison to a finite element analysis is established. Therefore, insights are given into the application and correlation of these calculations to the experiments. Finally, the solutions are validated through damage observations using microsections and computer tomography. The findings contribute to a deeper understanding of the occurring damage mechanisms, the accuracy of the experimental method used and the damage progression due to different loading conditions of the CPVs under investigation.