Experimental and theoretical fatigue analysis of avionic unit mounting brackets integrated on an unmanned aerial vehicle under random vibration environment

In air platforms, structures encountered many types of loadings. During the design stage, all these loadings have to be considered very carefully in order to avoid catastrophic failures. One of the major concerns for engineers is the loadings that alter the structures' life and cause fatigue failure. Random vibration can be considered the main source of fatigue type of failures in air platforms. In this thesis, the fatigue life of aluminum brackets, which are used to integrate an avionic unit to an unmanned aerial vehicle, is investigated in the frequency domain. The finite element model of the structure is constructed and the model is verified with experiments. In order to analyze the real environmental conditions, flight data is obtained by operational flight tests. Time domain signals are converted to the frequency domain and acceleration Power Spectral Density functions are obtained. Verified finite element model and collected flight data are used to obtain the stress history, which is necessary for the fatigue calculations. Fatigue analysis of brackets is performed in three different ways. First of all, according to the frequency domain fatigue theory, a Matlab code is developed and the life of the structure is obtained. In order to test the reliability of the developed Matlab code, the same analysis is performed by using Ncode Design Life, which is a commercial fatigue analysis software. It is founded that the results of both solvers are very close to each other. Finally, accelerated life testing is performed to obtain the fatigue life in experimental conditions with accelerated flight data. In conclusion, it has been determined that the results obtained from theoretical calculations are close enough to the experimental results. Keywords: Finite Element Model, Vibration Based Fatigue, Accelerated Life Testing