Analysis Of The Structural Fatigue Life Of The Antenna For Helicopters

Based on the theory of mechanical vibration and finite element method, static analysis, modal analysis and random vibration analysis of an antenna on a helicopter are made with the help of ANSYS. Then the fatigue life of the antenna is calculated using the Power Spectrum Density (PSD) method.The key issue is the estimation of the fatigue life of structures. In order to overcome the limitation that a power function with two parameters can only express middle cycle range of S ? N curve, a power function with three parameters and two power functions with two parameters are utilized individually to express middle and high cycle ranges of S ? N curve. Further based on random process, Miner's linear damage cumulative theory and P ? S ? N curve of components, the formulas are derived to evaluate fatigue life of high cycles with a certain probability for both narrowband and broadband cases.The key method is studied for calculating fatigue life of structures by integrating ANSYS. The reliability of the analysis using ANSYS is shown with an example for a beam to be analyzed for both static analysis and random vibration analysis. Macro files compiled with Parametric Design Language are used for calculating fatigue life considering the disadvantage of the fatigue-calculating function of ANSYS owned.Finally, the finite element models of an antenna on a helicopter are built for both subsection with screw thread and whole without screw thread. The structure of the antenna is analyzed for both modal analysis and static analysis considering all kinds of loads. The results indicate that subsection structure with screw thread has stress constentation at the screw thread and it can't fit for the checking of static intensity while the whole structure without screw thread can fit for the checking of static intensity. Then the whole structure without screw thread is analyzed for random vibration considering a random power spectrum of acceleration and the fatigue life of the structure is calculated by finding the PSD values on the dangerous point and dealing by math analysis.