Research On Redundancy And Tolerance Damage Designs For APU Installation System

At present, China's large domestic commercial aircraft is under development stage. APU(Auxiliary Power Unit), as one of the most indispensable components in large and medium-sized planes, its safety and reliability should be considered during its matching selection and the design for its installation system. In this paper, the redundancy and damage tolerance design techniques of APU installation system were studied based on engineering practice, which provided technical support for preliminary selection scheme of APU installation system, installation structure validation and APU's types and suppliers.Through researches at home and abroad on the use and installation of APU, based on the principle of redundancy design, typical APU installation system and the influences of redundancy design on its installation structure were studied. From the perspective of design, combining with engineering application requirements, ANSYS parametric modeling APDL language was used to analysis and calculate the FEM of both hollow and solid APU rod. By the circular setting of APDL program, appropriate crack shape parameters could be automatically obtained and stress intensity factor in varied state could be calculated. Based on Forman crack propagation model, an application software for estimating the service life of APU installation tension rod was programmed out called LifeEst. In a given geometry, material parameter and load spectrum, the service life of the APU tension rod containing initial cracks could be efficiently estimated by using this software. The results of this study can be applied in damage tolerance analysis for the APU install tension rod, but having certain universality to analyze other hollow or solid round tension rod under the load of pressure or tension.Since there are already lots of researches in the first phase at home and abroad, this paper studied the crack's expansion in the second phase, Analyzed the influence of crack shape parameters on the distribution of stress intensity factor, and also the influences of initial cracks and material parameters on service life, and relevant results were obtained by calculation.