Research On Fatigue Damage Of NEPE Propellant

Various cyclic loads, such as cyclic temperature and force, affect the mechanical properties of solid rocket motor (SRM) during the process of manufacture, transportation, storage and usage. As an indispensable part of the SRM, propellant which is turned out to be a viscoelastic material would suffer the most significant impact. The load intensity may not lead to the failure of the structure at once. But on the long run, fatigue damage would occur in the propellant grain in a cumulative way, which would lead to explosion on-stream. So it is necessary to study the fatigue property of the propellant. In this paper, quasi-static and dynamic mechanical properties of NEPE propellant have been systematically studied, the specific contents are as follow:In normal temperature, uniaxial tensile tests under different rate were carried out to investigate the quasi-static mechanical property of NEPE propellant. Relaxation modulus in the form of Prony series was gained from the stress relaxation test data using the Sorvari method. Then the mechanical property of NEPE propellant was analyzed.The dynamic mechanical analysis tests were employed to measure dynamic viscoelastic characters. The glass transition temperature and temperature spectrums of storage modulus, loss modulus and loss tangent were obtained. Using the time-temperature equivalence principle, the master curves of storage modulus, loss modulus and loss tangent were calculated, which were the key performances of the dynamic mechanical properties of NEPE propellant under different excitation frequencies and temperatures.Cyclic loading experiments were conducted in different strain amplitudes and temperatures with the sinusoidal loading frequency of 10 Hz. Based on fatigue experimental data, a strain-fatigue life equation was presented. The relationship between fatigue life influenced by temperature and strain amplitudes was analyzed. A new nonlinear fatigue damage model was proposed in this paper based on damage mechanics and visco-elasticity theory, which took the stiffness degradation into account. Five strain amplitudes experimental data of NEPE propellant were employed to obtain the model parameters and verified the presented model. The effect of strain loading history on the mechanical properties of the propellant was analyzed combined with microscopic examination (CCD). The achievement and the conclusions provide evidence for the solid rocket motor design.