Research on Damage Constitutive Characteristic of HTPB Propellant Under Constant Strain Aging

Accelerated aging tests under constant strain were conducted on HTPB propellant with the goal of investigating its mechanical properties and constitutive behaviors. Considering the random distribution of internal defect in propellant, a statistical damage constitutive model of propellant was established. The initial damage coefficient, making aging process of propellant equivalent to a form of damage, was introduced to construct the damage variable. Based on the uniaxial tension test of propellant samples aged under constant strain, the model was validated. Results show that theoretical model has good agreement with experimental results and can accurately describe the mechanical behavior of propellant during the constant strain aging. Further analysis indicated the damage effects caused by chemical aging and constant strain can be identified from the equation of initial damage coefficient. Chemical aging can not only influence the tensile strength of propellant in damage phase, but also change the shape characteristics of stress-strain curve. There are obvious yield zones in the stress-strain curves when aging time is below 284 days while there are nonsignificant yield zones at aging time above 284 days under the aging temperature of 55℃. The constant strain only decreased the tensile strength in damage phase. The strain threshold value decreased linearly along with the aging time and constant strain level during aging process.