Fatigue Failure Analysis of Structures under Random Vibration Environment

Even though there are no structural resonance and acute vibration, vibration fatigue failure different from static strength failure will occur, when the aircraft served in vibration environment provided that it has met the static strength design requirements. The assumption in classical fatigue failure analysis is that fatigue loads are independent of time, but actually the alternating dynamic stresses generated by the dynamic loads obviously depend on time. The study of structural fatigue failure due to vibration of the structures subjected to dynamic loads such as random-vibration loads is the objective of the present paper. In this paper fatigue life prediction methods of structures subjected to random-vibration loads in terms of power spectral density (PSD) are reviewed. The methods include the statistic analysis of stress response of the structure in random vibration, the link between dynamic stress loads and general fatigue loads and the method of making dynamic loads equal to static fatigue loads, structural life estimation using nominal stress method by S-N curve, etc. In order to make the results more accurate, MSC/NASTRAN and MATLAB were used respectively for frequency response analysis and fast fourier transform. Finally a procedure was developed using Visual C+ + Language Environment to deal with the NASTRAN and MATLAB results and to manage the whole calculating process. A series of fatigue experiments of cantilever plate under random vibration loads were performed to examine the correctness and practicability of the method studied in this paper. The experimental results match well with the numerical results. The method developed could be used in fatigue failure analysis and life estimation of structures under random vibration environment,hence it could have high value in engineering practice.