Research on the low-frequency fatigue behavior of NEPE solid composite propellant based on fractional derivative constitutive model

Abstract

The long-term fatigue loading history from offshore vibration environment will cause microdamage and affect the mechanical properties of NEPE solid propellant grains. The paper investigates the evolution law of microdamage through constant-strain-amplitude fatigue tests, and proposes an improved fractional derivative constitutive model for effectively predicting the low-frequency fatigue behavior of NEPE solid propellant based on the experimental phenomena. The evolution law of microdamage is negative power functional with the loading time and exponential with the maximum loading strain during the fatigue loading process. The stress-softening behavior, the Mullins effect, and the accumulation of residual strain are observed, as characteristics of low-frequency fatigue behavior. The theoretical modeling of the stress-softening behavior and the Mullins effect is proven to be significant for effectively predicting the low-frequency fatigue behavior by the improved fractional derivative constitutive model, while strain-modfication is also necessary for eliminating the influence of residual strain. The fatigue damage in solid propellant grains cannot be neglected when assessing the structural integrity of a solid propellant grain which has experienced long-term transportation or offshore storage.