Development of CFRP Hydrogen Pressure Vessels

The effects of CO2 emissions on the environment are widely acknowledged in science and politics, which is why the development of alternative propulsion systems has become a priority. Hydrogen-powered vehicles offer promising possibilities for reducing emissions from transport. The triple gravimetric energy density of hydrogen compared to gasoline makes it a good energy carrier without necessarily being associated with the same CO2 emissions from fossil fuels.

To achieve the desired volumetric storage density, hydrogen is generally stored in pressure vessels. Thanks to their high load capacity and excellent performance/weight ratio, Type IV pressure vessels are currently the focus of attention in the automotive industry. This type of pressure vessel consists of an internal thermoplastic liner for sealing the hydrogen and an enveloping composite structure for load absorption and impact protection. High-performance materials such as carbon fibres, glass fibres and matrix systems made of epoxy or various thermoplastics are used.

The main advantage of composite pressure vessels compared to the metallic variants is the lower weight. With an optimal exploitation of the lightweight design potential of this material group, a weight saving of up to 72% can be achieved compared to metallic tanks. Thus the operating costs of a vehicle and the transport costs can be reduced considerably. The improved fatigue behaviour and high corrosion resistance are additional arguments in favour of composite materials, which can thus ensure higher operational safety over the entire life cycle.

High-pressure vessels are constructed from a cylindrical part, which is closed at the fronts with domes on which the pole openings for the peripheral devices are positioned. Due to the different loads in axial and circumferential direction, isotropic materials are not optimally utilized, which is why fiber composite materials are used in the development. The freedom of design of the fibre orientations offers great flexibility in adapting the pressure vessels to the design space and the acting loads without impairing the functionality of the pressure vessels. Due to the direction-dependent properties of composite materials, the laminate can be specifically adapted to the acting load cases. In doing so, a low weight can be achieved while at the same time ensuring high performance of the structure.

A common manufacturing process in this context is filament winding, whereby the liner is wrapped with impregnated reinforcement fibers on a winding machine. This inevitably results in manufacturing effects that have a strong influence on the quality of the resulting laminate and must therefore be taken into account in the design. The aim of the design is to make full use of the material properties by means of an optimum laminate structure, which increases the safety against failure (leakage, bursting explosion) and further reduces the production and material costs. Meeting these sometimes conflicting requirements requires a high level of expertise in composite materials. At CIKONI we are happy to provide this expertise to our customers.

By combining multiple engineering approaches, CIKONI has been able to develop internal tools and methods and to enable a standardized development process for hydrogen vessels. During the step by step appoach, the single steps of the development cycle are coupled with each other, which guarantees a digital transfer of design relevant information. An expertise that is already used by various industries and international customers.

For example, the most efficient size for an available installation space can be determined and at the same time the dome contour can be optimized for the best material utilization. The selection of the materials to be used can be based on several aspects after a systematic evaluation. Significant properties in accordance with international standards are among others:

For the targeted utilization of the mechanical properties, the laminate structure is optimized with the help of analytical and numerical methods. CIKONI offers a continuous simulation process chain, in which FE-models with the desired level of detail can be built up by taking into account the manufacturing effects and the stress conditions arising under load. In order to determine the fibre orientations and laminate thicknesses of the individual layers, we accurately map the kinematics of the manufacturing process based on winding simulation. This enables us to predict the laminate that will be produced and to directly create programs to run the winding machine. We also carry out application-specific material characterizations as a prerequisite for achieving a high quality of prognosis.

In order to ensure the performance of the hydrogen container throughout its life cycle, the quality of production is crucial. For this reason, approaches for automation and quality assurance are decisive components of the holistic development of a hydrogen container. With the DrapeWatch system, CIKONI is able to implement automated quality monitoring during the winding process and to feed findings back into the design process.

CIKONI is able to support the development of fibre reinforced pressure tanks due to its expertise in various industries, which is in demand worldwide. As a highly specialized engineering team that has received several awards (AVK Innovation Award, ESAFORM Award, ThinkKing-Award, …), we are able to bundle comprehensive competences in hydrogen pressure tank development.