An Assessment of the New LS-DYNA® Multi-Layered Solid Element: Basics, Patch Simulation and its Potential for Thick Composite Structural Analysis

Limitation of fossil fuels and global warming favor the introduction of new powertrain concepts for road vehicles with highest efficiency and low greenhouse gas emissions. Fuel cell vehicles offer the highest potential for sustainable mobility in the future. One major component of fuel cell vehicles is the hydrogen storage system. A promising and currently the most-used approach is to store hydrogen in wet-wound carbon fiber reinforced plastic (CFRP) vessels manufactured by a filament winding process with an operating pressure of up to 70 MPa (hereafter referred as H2 vessel). Due to the inherent complexity and the 3-dimensional nature, accurate behavior of such thick composite structures in impact simulations needs an adequate representation of the composite plies. Modeling thick composite structures with two-dimensional elements will produce inaccurate results in transverse normal direction. Therefore, 3D modeling should be used but the idealization of each ply with one solid element leads to undesirably large models and is impractical for large structures. Hence, representation of several plies in one solid element and more such elements across the thickness is aspired. An improved multi-layered solid element showing excellent efficiency of CPU time is implemented in the code of LS-DYNA® Version 971 R4. Like any brick element, it resolves the 3D stress state necessary for impact directions normal to the outer vessel surface. The element allows the definition of multiple integration points through the thickness in order to account for stacks of plies with arbitrary fiber orientation. By defining several layers with different material properties and ply orientations inside one multi-layered solid, the number of elements through the thickness is remarkably reduced and still, the result is close to the one obtained from the detailed finite element model of one brick element per layer. As depicted in Fig.1.2, a complex laminate configuration consisting of 18 different plies with varied fiber angles is represented by one multi-layered solid element with 18 integration points through the thickness. The above new element formulation is presented in this paper describing simulation results for both, different patches and for thick composite structures such as for hydrogen storage H2 vessels.