Elastoplastic Design of a Dome Structure for Water Impact Loads

Dome structures of re-entry modules are generally subjected to very high impact loads during landing. Design of such structures is governed by the displacement limits imposed by envelope constraints and high strains developed during impact. The constraints in payload mass too pose challenges in the design and calls for adopting an elasto-plastic design methodology, wherein significant yielding needs to be permitted under the ultimate loads. This paper discusses the design methodology of the dome structure subjected to water impact loads. The impact loads are estimated by simulating the worst-case conditions at touchdown of the structure, considering dynamic amplification imparted due to excitation of the fundamental mode of the structure. Finite Element (FE) simulations with material and geometric non-linearities are employed to estimate the plastic strains and displacements on the structure. Loading and unloading curves are used to study the residual displacements and to assess the integrity of the structure. FE based optimization is carried out with constraints on plastic strain as well as total displacements on the structure to arrive at a minimum mass configuration for the dome.