Dynamic stress analysis and fatigue life prediction for structures subjected to random excitations

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Dynamic stress analysis and fatigue life prediction for structures subjected to random excitations

Fei, Guan / Ping, Chen

A general method, which is based on the methods of component mode synthesis, is presented for calculating the dynamic stress of complex structures subjected to random excitations. From the relationship between the responses and excitations in frequency domain, the spectral density function of response stress can be developed. As an example of the application of this method, the dynamic stress is calculated for the frame of a vehicle moving on a given rough road. It shows that, if the model is suitable and the number of modes taken into account is large enough, the computed rms stress approaches to the exact and agree with the experimental. Acconding to the spectral density function of response stress, the stresstime history can be developed by means of Monte-Carlo's method. Then using the rain-flow method and Miner's rule, we can predicte the fatigue life of the structure. A computer program for this method has been proposed in this paper. As an practical example, the fatigue life prediction of a vehicle frame is completed by this computer program.