اتصالات رشته ای در سازه های هواپیما
Abstract
1-Introduction
2-Cyclic fatigue tests
3-Stress analysis
4-Conclusions
Acknowledgements
References
Abstract
Tie-rods are connecting elements used in an aircraft and they basically consist of a straight tube and two screwed in adapter ends. In order to optimize the tie-rod in terms of weight reduction a detailed knowledge of its fatigue strength is important. However, the complex load and contact distribution within the threaded connection between tube and adapter end make a secure and efficient fatigue design challenging. Moreover, the connection is realized with a thread insert to assure smooth adjustability of the adapter ends, which further increases the complexity of a fatigue strength assessment. Thus, cyclic fatigue tests with a load ratio of R = 0.01 are performed to investigate the influences of thread insert length and position on the fatigue life of three different configurations. The experimental results are explained by Finite Element analyses using a detailed Finite Element model of the threaded connection. Finally microscopic examinations as well as the Finite Element analyses are utilized to further optimize the threaded connection in terms of reduced weight and high fatigue strength.
Introduction
Tie-rods are commonly used connecting elements in an aircraft and attach, e.g., galleys, lavatories or storage bins to the fuselage structure. The specific design of tie-rods varies depending on the installation purpose and manufacturer. In this paper the threaded connection of interior tie-rods from RO-RA Aviation Systems is investigated. Fig. 1 shows a schematic sketch of such tie-rods with a straight tube and two adapter ends, which are screwed into the tube in order to adjust the length of the complete assembly. The threaded connection between the tube and the adapter end consists of two parts: a threaded sleeve and a screw insert in order to maintain a smooth-running connection to the adapter end. The sleeve is firmly attached to the tube. Such tie-rods are subjected to tension and compression loads with variable amplitude and must meet the high requirements of the aeronautic industry. Structural components in aircrafts in general have to be designed for a certain service life and therefore a detailed knowledge of their fatigue behavior is of great importance [1]. Furthermore, tie-rods have to meet weight requirements because of their large number in an aircraft. Previous fatigue tests carried out in the test facilities of the Institute of Structural Lightweight Design have shown that the threaded connection between tube and adapter end is a critical failure location.