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SynopsisThe effect of finite elongation on superposed infinitesimal torsional oscillations has been determined on two propellants, a carbon black-filled rubber and Solithane 113 (Galcit I), as a function of temperature at various fixed frequencies. Torsional storage modulus-temperature data for carbon black-filled rubber and propellant show that the effect of the imposed tensile elongation cannot be explained by any simple temperatureelongation shift relationship. The shift factors for the torsional moduli of these two polymeric systems have been calculated as a function of temperature at various tensile elongations. The WLF constants C l and C2 have been computed for these systems as a function of the elongation. The values of the constants a t 0% elongation are larger than those commonly found in unfilled materials. The temperature dependence of the shift factor of the torsional storage modulus was found to differ from that of the loss modulus in the cases of carbon blackfilled rubber and propellant. This difference is slight for the rubber and large for the propellant. The effect of increased elongation is to increase the difference in the shift behavior of the moduli for each of these filled polymers. The shape of the loss tangent curve of the propellants examined indicates that these propellants are not thermorheologically simple.The constants decrease with increasing elongation.

SynopsisThis paper describes the results of simultaneous dynamic measurements in tension and torsion made on propellant samples. The complex dynamic moduli E', E", G', and G" a t low frequencies were determined within a temperature range from room temperature to -9OOC. Time temperature shift factors and reduced master curves for both tension and shear properties are discussed. The effect of dewetting on the dynamic properties in tension and shear was also investigated. A preliminary attempt is made to compute the degree of dewetting in a propellant by applying Beer-Lambert's law.

SynopsisA simple test procedure was used to determine the total damage in a propellant that accumulates during a tensile test from 0% strain to failure. Damage energies of two propellants were measured at various temperatures and straining rates, and Williams-Landel-Ferry shift procedures were applied t o the results. The reduced master curves for the total damage energy at failure are used to compare the failure behavior of the two propellants. INTRODUCTIONThe failure behavior and cumulative damage properties of rubbers and solid propellants have been studied from different viewpoints by several investigators. Smith'.' describes the ultimate failure properties of rubbers by a failure envelope of log stress versus strain at break obtained from uniaxial straining experiments at different rates and temperatures. Bills and coworkers:3 developed the cumulative damage theory, which describes the failure behavior of solid propellants by a time-to-failure ( t f ) under given stress conditions. The stress conditions are defined by the difference between the applied true stress ( ut ) and a critical stress (ucr) below which no failures are observed. The time-to-failure is a constant for any given stress difference and obeys the Williams-Landel-Ferry (WLF) time-temperature shift law, ( ut -ucr) = C(logtf/aT), where C is a constant and aT is the WLF shift factor. None of the methods for characterization of failure properties considers mechanical energy dissipations as criteria for microstructural damage. This paper describes a simple test procedure for measuring the part of the total mechanical energy input which is attributable to the uniaxial damage process from 0% strain to failure. It will be shown that the energy dissipation is a fundamental property of a composite propellant and obeys the WLF time-temperature shift relationship.

SynopsisThis paper describes a testing device designed for measuring the isotropic or anisotropic hydrostatic compression properties of filled polymers like solid propellants, including the initial void content and the bulk modulus. The propellant test samples used are either cubical, cylindrical, or rectangular specimens. Three pressure-sealed linear variable differential transformers (LVDTs) are used to monitor the dimensional changes of a cube specimen during hydrostatic pressurization simultaneously in the XYZ directions. The moduli Ell, &, and E33 and the compression strain ratios wzI, w32r and wQ1 can be determined as a function of pressure. The three LVDTs can also be used to measure the length changes of three rectangular or cylindrical test specimens under hydrostatic compression only in the vertical 2 direction. The bulk modulus and void content can be computed when isotropic behavior is assumed. The entire test procedure is controlled by an Apple I1 microcomputer via an A113 1Zbit analog input system. Some typical test results obtained with undamaged and damaged propellant samples are described.