Mechanical analysis on rocket propellants

Abstract

The mechanical properties of solid rocket propellants are very important for good functioning of rocket motors. During use and storage the mechanical properties of rocket propellants are changing, due to chemical and mechanical influences such as thermal reactions, oxidation reactions or vibrations. These influences can result in malfunctioning, leading to an unwanted explosion of the rocket motor. Most of modern rocket propellants consist of a polymer matrix (i.e. HTPB) filled with a crystalline material (i.e. AP, AN). However, the more conventional double base propellants consist of a solid gel matrix with additives, such as stabilizers. Both materials show a mechanical behaviour, quite similar to that of general polymers. To describe the material behaviour of both propellants a linear visco-elastic theory is often used to describe the mechanical behaviour for small deformations. Because the time-temperature dependency is also valid for these materials a mastercurve can be constituted. With this mastercurve the response properties (stiffness) under extreme conditions can be determined. At TNO-PML a mastercurve of a double base propellant was constituted using dynamical mechanical analysis (DMA) and compared with a mastercurve reduced from conventional (static) stress relaxation tests. The mechanical properties of this double base propellant determined by DMA were compared with conventional (quasi-static) tensile test results.