## Service Life Prediction of Solid Rocket Propellants Considering Random Thermal EnviroOkan Yilmaz Bayindir Kuran Gokhan Ozgen Solid propellant rocket motor is the primary propulsion technology used for tactical missiles. Its widespread usage gives rise to diversity of the environments which it is handled and stored. These uncontrolled thermal environments induce random stresses and strains in the propellant of a rocket motor which provoke mechanical damage along with chemical degradation. In this study, a service life prediction technique which is based on response surface method is used and explained. A time dependent random function is used for the temperature model. Solid rocket propellant is modeled using linear viscoelastic material model. Mechanical properties of the propellant corresponding different temperatures and loading rates are found from the mechanical tests performed on test samples. A three dimensional finite element model is used to predict stresses and strains induced on the propellant. A cumulative damage model is used since during the storage and the deployment stresses in the propellant accumulate with time. Aging behavior of the propellant is taken into consideration as well and Layton model is used for this purpose. Response surface method is used to construct surrogate models in terms of parameters associated with the material properties and the propellant temperature. Latin Hypercube Sampling (LHS) is used for the generation of multivariate samples. Limit state functions are used for failure modes of the propellant. The instantaneous reliability indexes and the probability of failure for thermal loading are predicted by means of the First Order Second Moment (FOSM) Method. The progressive reliability of the propellant is illustrated on a rocket motor. |