HERE are imperfections existing in solid propellants. These imperfections may be produced during the manufacturing and/or fabricating process of the solid rocket motor. In analyzing the strength of a solid propellant, the localized imperfection may be idealized as a crack in the material. Besides the idealized crack, large cracks can also develop in solid motors during storage, handling, firing, etc. Therefore, to determine the ultimate strength of solid rocket motors, studies should be conducted to determine the significance of flaw type, size, and rate of growth. In order to conduct these studies, a detailed knowledge of crack growth behavior in solid rocket motors is indispensable. It is well known, on the microscopic scale, that a highly filled composite solid propellant can be considered a nonhomogeneous material. The nonhomogeneous nature of solid propellants is mainly due to the nonuniform distribution of the filler particles, the different sizes of filler particles used, the variation of bond strength between the particles and the binder, and the different crosslink densities of polymer chains. The presence of the filler particles affects not only the bulk properties of the material but also the crack growth behavior. For instance, depending upon the bond strength between the particle and the binder, the fracture path may preferentially either follow or avoid the filler particles, resulting in different fracture surfaces and crack growth rate. In addition to the nonhomogenity of the material, the material may also contain randomly spaced microvoids, incipient damage sites, and microcracks with statistically distributed sizes and directions. Therefore, when this material is strained, highly nonhomogeneous local stress and strength fields can be produced. Hence, the failure location and the degree of damage induced in the material will vary in a random fashion. Because the crack growth behavior is closely related to the local stress and strength fields as well as to the damage state in the material, the variation of these parameters in the material will undoubtedly be a contributing factor to the variability or scatter of