Estimation of Thrust Stand Structure Fatigue Life Under Solid Motors Random Vibrations Effects

Successful development, evaluation, and qualification of propulsion systems such as turbojet and turbofan engines and rocket motors require the measurement of the performance and reliability of these systems. Thrust stands or testers are instruments for solid and liquid motors test. In this paper, a method for calculation of solid motors random vibrations effects on a thrust stand structure is developed. At first some Power Spectral Density (PSD) of three kinds of solid motors has been calculated by MATLAB codes. Then a typical thrust stand which has been designed based on special dynamics principles, has been modeled in Solidworks and transferred to ANSYS. In ANSYS, the modal and spectral analysis of the structure has been done. Then each motor's PSD has been applied on structure separately and maximum stress has been determined by ANSYS codes. Followed by structure fatigue life has been estimated by a formula derived from compound of Miner's cumulative fatigue damage ratio equation and Gaussian distribution curve. The results show that the amount of PSD at first frequencies has significant effect on structure fatigue life and it is not possible to reach to a conclusion about the vibrations effect, just based on maximum motor thrust.