Design optimization of bellow joint which is used liquidpropellant rocket engines

Bellows joints are parts that are frequently used in hydraulic lines, constructions and various areas such as nuclear stations to absorb the energy caused by flow and external forces, to provide flexibility to the lines, and thus to prevent damages such as cracking and deterioration in the flow lines. There are various types of bellows joints, which allow axial, lateral and angular movements, such as axial type, gimbal type, hinge type, etc. Bellows joints that assist thrust vector control in liquid propellant rocket engines prevent the hydraulic lines from being damaged during the orientation movements of the missile. While providing this flexibility to the lines in rocket engines, they create additional force against the linear actuators that move the liquid motor nozzle. This additional force causes the need for larger actuators and thus more weight and volume envelope. Fatigue and pressure resistance studies of bellows joints operating under pressure are frequently studied subjects in the literature. Bending moment and movement-induced strength studies are the subjects that are rarely studied and difficult to examine. In this study, the design of the bellows operating under internal pressure has been made to minimize the force to be transferred to the actuators, that is, the bending moment of the bellows joint resulting from this movement. As a result of the optimization study, it is found that the bending moment for the bellow joint could be reduced by a significant rate of 75% without violating the stress constraints (that is, without compromising the structural integrity of the bellow joint). The analytical results calculated with the design parameters obtained after the optimization studies were compared with the finite element methods. In the finite element method, different methods and models using boundary conditions for pressure and motion analysis are examined separately.