Design optimization of bellow joints used in liquid propellant rocket engines

Bellow joints are frequently used in hydraulic lines, constructions, and various areas such as nuclear stations to absorb the energy caused by flow and external forces, provide flexibility to the lines, and prevent damages such as cracking and deterioration in the flow lines. There exist various types of bellow joints (e.g., axial type, gimbal type, and hinge type) that allow axial, lateral, and angular movements. Bellow 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, resulting in more weight and volume. In this study, design optimization of the bellow joint used in liquid propellant rocket engines is conducted to minimize the force transferred to the actuators by minimizing the bending moment developed in the bellow joint. It is found that the bending moment developed in the bellow joint could be reduced by a significant rate of 75 % without compromising the structural integrity of the bellow joint.