Numerical Investigation of Structural Design of Torsion links in a Landing gear retraction mechanism

Torsion links are components which couple inner and outer cylinders of a landing gear mechanism. They prevent torsion or twisting between the cylinder and piston components in the structure. The integrity of this component is essential to prevent shimmy vibrations in an aircraft landing gear. Failure of this component is thus catastrophic for the aircraft. The typical geometry of torsion link of a medium sized aircraft is shown in figure 1. In this paper, an attempt is made to study stress contours and maximum bending stress on the torsion link and the effect of changing the holegeometry and hole patterns on it, from this the best optimised model is selected and modal analysis is done on it. The upper torsion link is the component on which the analysis is done. This component behaves as a simply supported beam with a moment on one end. It is seen that maximum bending stresses occur on the top surface of the upper torsion link on the ends near the flanges. This analysis is done on MotionView and HyperMesh tools. It is required to minimize the stresses by changing hole positions and geometry. It is to be noted that changing hole geometry affects total volume of the component and that volume of aircraft components is to be maintained at minimum. So a balance between reducing stress and volume needs to be achieved. These stresses increase with increasing distance between holes. The effects of giving multiple holes and combining holes are also studied. The optimised model from stress analysis is further analysed through modal analysis. The model is analysed in free - free run using ANSYS. From this six natural frequencies of the optimised model is obtained and further discussion on the mode shape is done.