Solid Rocket Grain Analysis

Solid rocket motors with circular port (CP) grain designs typically consist of a system of four cylinders: the propellant grain, the liner, the insulation, and the case. Figure 3 shows a typical CP grain configuration. The propellant, liner, and insulation are relatively soft, rubber-like materials that are nearly incompressible and have a very high coefficient of thermal expansion compared to the case. The case, in contrast, is generally a very stiff metallic or composite material. This situation can result in high tensile stresses between the case and the insulation under thermal cool-down loads. High hoop strains can also be induced on the propellant bore surface. These high stresses and strains are typically what determine the low temperature limit for safe operation.