Reliability Assessment of Solid-Propellant Rocket Motors Under Storage and Transportation Loads

A methodology for the assessment of the service life of solid-propellant rocket motors under random storage and transportation loads is presented. In storage conditions, the propellant grain is subject to random thermal environments while during transportation to vibration loads, both of which induce strain and stress. Over long periods of time, storage and transportation cause damage accumulation in the propellant. Aging mechanisms also contribute to the accumulated damage. Thermal loading is modeled as a harmonic function of time and vibratory loads of different transportation scenarios, such as ground, air, and sea transportation are used with the corresponding acceleration spectral density functions. The loading and material parameters are taken into consideration with their uncertainties. A linear viscoelastic material model is used for the propellant. Degradation of the structural capability is represented using Laheru’s cumulative damage model and the aging effect is simulated with Layton’s model. To find the stress and strain accumulated in the grain, the finite element method is used. The response surface method is used to use the surrogate mathematical models for the induced stress and strain. The limit-state functions are formed to predict failure. The instantaneous reliability is calculated within a confidence interval using a first-order reliability method.