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Mechanical properties of viscoelastic filled polymers strongly depend on temperature and strain rate and vary for several orders of magnitude. During service life, a viscoelastic body, especially carboxy-terminated polybutadiene (CTPB) composite solid rocket propellant grain, is subjected to many stress-inducing loads. Its structural integrity analysis (hereafter: “structural analysis”), unlike elastic bodies, is quite complex and sometimes impossible under the action of just a single load. An even greater problem occurs when multiple different types of loads act simultaneously. This study is based on a complete uniaxial mechanical characterization of a viscoelastic CTPB composite rocket propellant, made in MTI- -Belgrade, whose results were used for the analysis of the propellant grain reliability. Through an example, this paper shows a behavior of the viscoelastic propellant grain when it is subjected to extremely different environmental loads at the same time. Similar explicit examples are difficult to found in the literature, except in the form of recommended principles for analysis. It is shown that the tensile strength under the action of fast load due to the pressure may be almost 20 times greater than the tensile strength under the slow temperature load. A probabilistic approach is presented in evaluation the reliability and service life. An example is shown for a rocket propellant grain as a viscoelastic body. The presented principles of the analysis can be applied to any arbitrary viscoelastic body in other areas.

This paper presents the procedure of uniaxial mechanical characterization of composite solid rocket propellant based on hydroxy-terminated polybutadiene (HTPB), whose mechanical properties strongly depend on temperature, strain rate, natural aging and accumulated damage. A method of processing data is presented in order to determine time-temperature shift factor and master curves for tensile strength, ultimate strain and relaxation modulus, depending on reduced time. Functional dependences of these features represent an input for structural analysis of a rocket motor propellant grain. The effects of natural aging on the mechanical properties are also considered. [Projekat Ministarstva nauke Republike Srbije, br. TR 36050: Research and development of unmanned aircraft in support of traffic infrastructure monitoring]