Long Term Aging of Aerospace and Tactical SRM. Experimental Study.

The study of the aging has an important role for the SRM, requiring long times of service and wide range of temperatures . Several hypothesis about the mechanism of the aging of the solid propellants have been formulated, among which the most probable, according to the performed experience, seem to be the oxidation effect of the HTPB double bonds and the deboncling of the A.P. from the matrix. Some models of the time-temperature relationship have been set, in agreement with the Arrhenius law, for extrapolating propellant properties from tests carried out on samples treated by accelerated aging. Also the role of the mechanical stresses of the propellant in the SRM must be taken into account for the thermal cycles and thermal expansions and suitably correlated with the data coming from the free-standing samples. The mechanical properties show the most critical behaviour toward the aging. The calculation of the margin of safety proves that up -15% loss of elongation is acceptable, also because balanced by the increasing of the Young modulus. Some aging phenomena, such as the moisture absorption, have been demonstrated to be reversible and nondestructive methods for analysis have been set up.