Fatigue lifetime estimation of the solid rocket motor charge by road roughness loads on mechanical methods

In the rocket transportation the road roughness load can cause its solid motor charge to vibrate randomly. To get information about the motor charge's dynamic characteristic and damage degree, this paper calculated the charge's vibration responses by road excitations on the numerical method of mechanical modeling. First the rocket launcher's simplified model was built and the transfer function was obtained. Then By the road roughness excitation PSDs (Power spectral density) response PSDs of the rocket's supporting points on the launcher were calculated. Moreover the rocket FEM model was established and its random vibration responses were acquired by the launcher's supporting point excitations (namely response PSDs of the rocket's supporting points). At last by Miner liner cumulative damage law and the danger point's stress results the motor charge's fatigue damage amount was solved. Results show that in the rocket transport process road loads can lead to the motor charge's remarkable structural vibration as well as fatigue damage and with loading time increasing it comes into the structural failure in the end.