Design, methodology development and production of composite cryogenic liquid oxygen tank for space applications

Abstract

The thesis focuses on the development of composite cryogenic liquid oxygen (LOX) tanks for sounding rocket propulsion systems, addressing challenges in aerospace engineering. Traditional composite materials used in these tanks are expensive and subject to various regulations in their supply chain. This thesis explores cost-effective alternatives, emphasizing affordable and sustainable aviation applications. This is the first study conducted in Turkey on cryogenic composite tank systems. Through this study, numerous infrastructures and laboratory systems were established, marking the first step towards indigenous development of these systems for research and development. All of these efforts will pave the way for structural advancements within Turkey's National Space Program. Cryogenic temperatures and LOX compatibility are the primary challenges for composite LOX tanks. To ensure the tank's operation in a cryogenic environment, various aspects need to be studied, including epoxy and fiber behavior in cryogenic conditions, thermal expansion coefficient compatibility between liner material and composite material, and LOX compatibility. Although properties of many materials under high and room temperatures are available in the literature, there is a lack of sufficient testing and information for cryogenic environments, especially for composite materials. For LOX compatibility, it's crucial that the composite structure doesn't trigger the combustive properties of liquid oxygen. The success in developing these innovative tanks relies on designing new materials specifically tailored to meet macro and micro-scale thermomechanical requirements. These materials must address long-term structural integrity, leakage due to microcracks, and contamination concerns in composite materials. The original contribution of this research is the detailed presentation of the entire process of developing a composite liquid oxygen fuel tank, including material screening, design, analysis methods, manufacturing processes, and quality controls. The thesis aims to deliver all phases of the reliable composite oxygen fuel tank development for use in sounding rockets. Although significant work on cryogenic composite tanks is currently underway, there is no consistent and comprehensive publication. This research aims to obtain conclusive results using numerical and experimental studies, demonstrating the advantages and disadvantages of using composite LOX tanks. The study focuses on the thermal and mechanical properties of different epoxy resins under cryogenic conditions and their compatibility with liquid oxygen. It also examines the fracture toughness of laminate-based testing under both room and cryogenic temperatures. Two types of tank structures were tested: tanks with a metal liner (Type-II) and linerless tanks (Type-V). A method that links micro and macro scales was developed to calculate real stresses on fiber and matrix components, providing insights into the composite structure's damage state. At the beginning of the study, the properties of epoxy resins were thoroughly examined to evaluate their mechanical performance and compatibility with liquid oxygen in cryogenic conditions. Collaboration with local manufacturers aimed to develop domestic formulations, promoting nationalization in aviation materials and supporting self-sufficiency. The study revealed that the Huntsman 1564-3474 epoxy system showed potential mechanical performance in a cryogenic environment and demonstrated compatibility with LOX. However, a Type-V tank system produced with this resin system suffered complete damage after a liquid nitrogen filling test, indicating its unsuitability for cryogenic environments. Fracture toughness tests on composite laminates produced by filament winding provided insights into mode-II damage types under room and cryogenic conditions, predicting and preventing critical information on damage. Fractographic analysis revealed differences in damage modes under room and cryogenic conditions. In particular, vacuum infusion and toughened resin systems exhibited similar mode-II fracture toughness values at room and cryogenic temperatures, while the behavior of the cold-curing resin system showed a significant decrease in cryogenic temperatures. Additionally, the study evaluated the negative effects of the wet filament winding method on production quality. These findings emphasized the importance of considering component interactions and production-related issues for cryogenic environment performance. During the study, a micro stress calculation tool was developed through literature assistance to predict actual stress values on components in composite structures. In this method, fiber and matrix components within the composite structure are modeled using a representative unit cell element, simulating the behavior of all components throughout the laminate with the help of periodic boundary conditions. This enables a connection between stress values on the composite layer modeled as an orthotropic material at the macro scale and stress values at the micro level. Python programming language, MATLAB, Abaqus, and ANSYS softwares were used to develop the calculation tool. The tool's added parameterization capability allowed evaluating the effect of temperature-dependent changes in material properties on micro-scale stress values. This provides foresight for determining the necessary material properties under cryogenic conditions. Additionally, the epoxy systems used in the tests were evaluated using this calculation tool. Considering Von Mises stress, Epotek 301-2 and 301-2FL emerged as a potential systems for cryogenic temperatures based on its temperature-dependent elastic modulus and thermal expansion coefficient. Similarly, the T7110 system stood out in minimizing maximum stress on the matrix but could not provide sufficient strength for pressurized tanks under room temperature conditions. Commercial epoxy systems and the proven cryogenic performance of the IM7-977-3 system were compared, evaluating their cryogenic performances. One of the main contributions of this study is revealing the effects of various tank geometries and epoxy materials on micro stresses, highlighting the emergence of constituent effects. Furthermore, the research emphasizes the importance of material selection and design parameters for cryogenic applications by revealing the limitations of specific tank systems. Design, production, and testing studies were carried out for Type-II and Type-V tank systems, and design evaluations were performed. It was determined that Type-II tank systems are unsuitable for cryogenic applications due to high thermal expansion differences between the metal liner and composite material in cryogenic temperatures. Under cryogenic conditions, the metal and composite shell experienced high delamination forces due to high thermal expansion differences. For the development of a low-cost cryogenic Type-V tank, innovative methods such as a liquefiable paraffin mandrel and wet filament winding were utilized. At the end of the studies, a successful prototype Type-V pressure tank was produced, capable of withstanding pressures up to 30 bars without any leaks. However, after a liquid nitrogen filling test, the same tank was observed to crack completely, losing its non-permeability. Throughout the thesis process, the aim was to work on each sub-problem, but due to the scale of the proposed study, some limitations were encountered. There are some recommendations to further expand the study, which include: Mechanical and thermal tests based on component and component interaction should be expanded to better assess material performance at different temperatures. The thermal and mechanical properties of each composite component should be determined as a function of temperature. Manufacturing using the wet filament winding method introduces uncertainties for composite materials. The production of such space systems is generally accomplished with prepreg materials and automated fiber placement systems. NDT measurement techniques for determining microcrack evolution on composite laminates could be researched and developed under cryogenic environments. Determining fiber/matrix interaction under cryogenic conditions is crucial for developing composite cryogenic pressure vessels. In conclusion, this thesis makes significant contributions to the development of cryogenic liquid oxygen tanks by exploring new materials, manufacturing techniques, and analytical methods. The findings not only extend the boundaries of cryogenic composite tank technology but also open doors to new possibilities for cost-effective and sustainable aviation applications. The results of the study are intended to provide a solid foundation for future advancements in this critical field.