A tensile module system placed within a Scanning Electron Microscope (SEM) was utilized to conduct in-situ tensile testing of propellant samples. The tensile module system allows for real-time in-situ SEM analysis of the samples to determine the failure mechanism of the propellant material under tensile force. The focus of this study was to vary the experimental parameters of the tensile module system and analyze how they affect the failure mechanism of the samples. The experimental parameters varied included strain rate and sample temperature (-54, +25 and +40°C). Stress-strain diagrams were recorded during the in-situ tensile tests, and these results were coupled with the in-situ images and videos of the samples captured with SEM analysis. The experiments conducted at -54°C showed a different failure behavior of the propellant sample due to its rigidity at this low temperature, while experiments conducted at +25 and +40°C displayed a similar failure mechanism. For future testing using this tensile tester, special attention should be given to improved temperature control of the specimen, especially at low temperatures.

The failure mechanism of a propellant consisting of hydroxyl terminated poly-butadiene filled with ammonium perchlorate and aluminum (HTPB/AP/Al) was determined by performing in-situ uniaxial tensile tests in a scanning electron microscope (SEM). The experimental test plan contained uniaxial tensile test experiments performed at room temperature (25 °C) at three different strain rates (30, 150 and 750 μm min⁻¹). The in-situ images and in-situ videos collected by the SEM were correlated with the stress-strain diagrams created with the tensile experiments, in order to relate the failure mechanism to the features found in the stress-strain diagram. No significant strain rate dependency of the failure mechanism was observed when working with strain rates up to 750 μm min⁻¹ and working at room temperature. The stress-strain diagram showed indications of existing cracks and voids opening up prior to the creation of new cracks and/or voids in the sample, debonding of binder with AP particles as well as nucleation and coalescence of voids. On the fracture surfaces of the samples, it was apparent that the binder cleanly separated from the large AP particles but had a better bond with the aluminum particles. However, a difference in the appearance of a short drawing phase in the stress-strain diagram of the propellant is observed at different strain rates. The presented results clearly demonstrate the major advantage of the combination of microscopic tensile tests with microscopic observations, linking the stress-strain behavior to the mechanical deformation processes taking place in these propellant samples at the microscopic level.