Solid propellant is a mixture of fuel and oxidizer, which burn together to provide hot gases that are passed through a nozzle to provide thrust. It is used in solid rocket motors, which are regularly used in the defense and space applications. Solid propellant grains in rocket motors are exposed to various loads during handling, transportation, storage, and operation. It is important to study the mechanical behaviour of the propellant grains under these conditions. Biaxial tests are more
accurate representations of the in-service loads will be used to study the mechanical behaviour of the propellant grains. The primary reason for the failure of solid rocket motors is related to the structural integrity of the propellant grain. During the service life, propellants are subjected to stresses that can cause cracks in the propellant grain. Cracks lead to the development of additional burning surfaces, thus increasing pressure and leading to combustion instability. Structural analysis of the solid propellant grain is thus essential to avoid such failure. This requires failure criteria which determine the limits on operating conditions. The multi-axial failure criteria for solid propellant grains are not yet defined. Hence, the failure criteria for solid propellants are selected intuitively.
Existing failure theories that correlate the results of uniaxial tests to the failure under multi-axial stress states have been developed for simple linear elastic materials and might be inadequate for these materials. The objective of the present work is to study the mechanical behavior of composite solid propellant under biaxial loading of cruciform specimens under different load ratios at different temperatures and strain rates. A multi-axial failure criteria suitable for solid propellant grain will thus be developed from the experimental observations.