Towards a manufacturing signature for unstiffened flow formed thin-walled shell structures

Abstract

Thin-walled shell structures such as those used for space launch vehicles are highly sensitive to various kinds of imperfections. This imperfection sensitivity makes it challenging to predict the load carrying capacity of these structures. A correlation between the manufacturing process and the load carrying capacity, called manufacturing signature, would facilitate the design of these structures. Therefore, in this paper, a step towards a manufacturing signature of flow formed unstiffened isotropic shell structures is made. For this purpose, the investigated shell structures and their manufacturing process are introduced in detail in this work. Afterwards, the geometric and thickness imperfections of these shell structures are measured using an in-house developed measurement system. The measurement results are evaluated in detail and the buckling loads of the measured shell structures are calculated numerically. The results show that all six shell structures have similar knock down factors (ρi≈0.74), which indicates a correlation between the manufacturing process and the load carrying capacity. Subsequently, experimental buckling tests are carried out for three shell structures. The discrepancies between the numerically calculated and the experimentally measured buckling loads are tracked back to load imperfections. Finally, the impact of load imperfections is studied briefly.