M. S.

Defects formed in solid rocket propellant during manufacturing, transportation, storage, and assembly can lead to alterations in the thrust time profiles and possibly catastrophic failure of the entire rocket. In order to determine the effects of temperature, loading rate, and thickness on this particulate composite, tests were conducted at three temperatures and two loading rates. Both uncracked and edge cracked "biaxial" specimens were produced from solid rocket propellant. The stress relaxation modulus and stress-strain data were obtained from load curves formed during "biaxial" tension tests. Near crack tip displacements and strains were calculated from photographs taken of a surface grating on the pre-cracked specimens during crack propagation. The effect of thickness, temperature, and loading rate on the stress intensity factor was also studied. Finally, by applying continuum theory the displacement singularity was determined at different stages of crack growth. From the stress strain data, it was found that temperature had a greater influence on behavior than loading rate over the ranges studied. The crack growth in the composite material consists of a series of crack opening, crack blunting, and crack growth/resharpening stages which are highly nonlinear. However, the thick specimen at low temperature did not follow this crack growth mechanism. At -65°F the thick specimen developed transverse constraints which caused a brittle fracture to occur when the specimen was loaded. Determination of the displacement singularity order for the sharp cracks was found to be consistent with the theoretical results predicted by Benthem. / Master of Science