Numerical and experimental investigations of thick-wall composite hydrogen tanks

Kurzfassung

Hydrogen-powered fuel cells have established as one of the main emission-free alternatives to combustion engines in a broad range of transportation systems. This technology is however limited by the lower energy content of hydrogen on a volume basis compared to fossil fuels. For the mass market, high-pressure tanks have to be further developed so that costs fall while maintaining high performances. Type IV composite pressure vessels are submitted to high internal mechanical loading at 700 bars and require the manufacturing of thick-wall laminates. To achieve optimal sizing and save weight, predictive numerical solutions need to be developed to simulate the complex failure mechanisms in thick-walled laminates under various loading scenarios. Moreover, the in-situ laminate layup and quality are strongly dependent on the manufacturing processes (i.e. winding technology) and can influence the mechanical potential of the vessel. It is therefore necessary to first investigate local fibre architecture in pressure vessels and determine the local material properties. In the presented work, carbon fibre reinforced thermoset pressure vessels have been provided by Mercedes-Benz AG to be investigated at the DLR test facility. Local fibre layups are first investigated with the Computer Tomography (CT) technology on small in-situ cylindrical specimens and used as input for the simulation. In a second step, failure mechanisms are investigated with the Digital Image Correlation (DIC) technique with special focus on delamination effects. Impact tests are finally performed in the DLR drop tower facility in Stuttgart on several energy levels to estimate the impact performances of tank segments. Simulating the behaviour of thick-wall composites necessitates the use of special modelling methods compared to classical thin-walled laminates. In this work, a stacked-layer approach with TSHELL elements and a cohesive contact formulation is investigated. Digital twins of every experimental tests with their precise boundary conditions are built up with this approach and first ran in a predictive manner. With the developed numerical approach, the simulated mechanical behaviour is in good agreement with the experimentally observed failure patterns and load curves (Figure 1). Furthermore, delamination effects have been accurately reproduced in simulation. Prediction capabilities still have to be improved through the consideration of strain-rate effects in the layers and at the interfaces.