Vibration fatigue analysis of equipments used in aerospace

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Mechanical Engineering, Turkey

Approval Date: 2005




Metal Fatigue of dynamically loaded structures is a very common phenomenon in engineering practice. As the loading is dynamic one cannot neglect the dynamics of the structure. When the loading frequency has a wide bandwidth then there is high probability that the resonance frequencies of the structure will be excited. When this happens then one cannot assume that the structures response to the loading will remain linear in the frequency domain. Thus to overcome such situations frequency domain fatigue analysis methods exist which include the dynamics of the structure. In this thesis, a Helicopters Self-Defensive System̕s Chaff/Flare Dispenser Bracket is analyzed by Vibration Fatigue Method as a part of an ASELSAN project. To obtain the loading (boundary conditions), operational flight tests with accelerometers were performed. The obtained acceleration versus time signals are analyzed and converted to Power Spectral Densities (PSD), which are functions of frequency. In order to obtain the stresses for fatigue analysis, a finite element model of the bracket has been created. The dynamics of the finite element model was verified by performing experimental modal tests on a prototype. From the verified model, stress transfer functions have been obtained and combined with the loading PSD̕s to get the response stress PSD̕s. The fatigue analysis results are verified by accelerated life tests on the prototype. Also in this study, the effect of single axis shaker testing for fatigue on the specimen is obtained.