Random Fatigue Life Study Based On Structural Dynamic Characteristics

Fatigue failure is one of the failure modes with high incidence in the structure.The engineering structure will inevitably bear the random load in the service process Therefore,it is of great theoretical and engineering value to study structural fatigue damage and life estimation under random loads.The analysis shows that under the random vibration load,the dynamic characteristics of the structure often have a great impact on the fatigue life.However,most of the existing random fatigue theory studies focus on the life estimation methods of random stress process,and often neglecte the effects of structural dynamic characteristics on fatigue.In view of this,the random fatigue is combined with the structural dynamic characteristics in this paper,and the random fatigue life estimation based on the dynamic characteristics is analyzed.The main research contents include:Through the analysis of the constant amplitude,variable amplitude and random fatigue theory,the calculation methods of three fatigue lifes are summarized and several influencing factors of random fatigue life are analyzed.For the variable amplitude fatigue,the equivalent stress amplitude formula was corrected by introducing the parameters of the mean stress and the fatigue limit,and the correctness was verified by the simulation of the cast steel standard test piece.Based on the analysis of the expression of frequency response function under random load,the influence of structural dynamic characteristics on the frequency response function is quantitatively analyzed.Taking the frequency ratio and the modal damping ratio as independent variables,the central frequency band of the resonance point is determined through the area ratio.Combined with the first three maximum peak points of the response power spectrum density,a load reduction method for wideband stationary gaussian random process is proposed.Considering the effect of spectral width of structural response after load reduction,the applicability range of common frequency domain methods to spectral width parameters is analyzed by different simulation spectral curves and different material parameters.On this basis,a modified frequency domain method is proposed.The modified method is verified by different simulated spectra,which shows that it can be better applied to most spectral width parameters and has good applicability.The random vibration simulation of a practical engineering example shows that the load reduction method and the frequency domain correction method proposed in this paper can obtain better results,thus providing effective theoretical support for engineering applications.