Low-velocity impact on thick-wall wound composites for the sizing of hydrogen storage tanks

Kurzfassung

Global climate changes and more recently energy crisis raise challenges on the society which can be partially tackled by technological breakthrough. For some decades, energy systems for air, maritime or rail transportation are evolving towards the use of hydrogen as an emission free and renewable fuel. Before the hydrogen is converted in fuel cells to water the storage is realised either in composite tank structures under high pressure, under cryogenic conditions at low pressure or in chemical reaction systems. In the present study, linerless tank structures of type V made exclusively of composite material are investigated under operational pressure of 700 bar for railway transportation systems. To improve the sizing of wound composite tanks and optimize their lightweight potential, particular risks (tool drop, tank drop according to R134e, hail and stone impact) are considered and simulated additionally to sizing criteria such as burst pressure. As a first step towards complete structure simulation, the wound material is characterized in split-disk, tensile and bending tests. The damage mechanisms during impact events are investigated on segments with various thicknesses and winding sequences impacted at low velocity in the drop tower at DLR Institute of Structures and Design. Numerical models are developed along the building block approach to validate the material behaviour on the coupon level and predict the tank failure under various load cases. In simulation, a thick-thick shell element formulation is investigated in LS-DYNA to reproduce accurately failure mechanisms in the material thickness. The numerical approach is based on a physically-based continuum damage model for composite materials, whose mechanical properties are calculated virtually using microscopic unit cells. Delaminations are predicted with cohesive zone model and a tri-linear traction-separation law. The present paper highlights the main building blocks of the numerical toolchain and their potential to reproduce complex failure mechanisms under impact loading. Key results of the preliminary experimental test campaign are presented.