Vibration-Induced Degradation of the Mechanical Properties of Composite Rocket Propellants

Energetic materials such as CRP (composite rocket propellant), are distressed by the vibrational load during real service, when the ammunition is mounted to helicopters, aircraft, fighter, or tactical wheeled vehicles for all terrain. The test methods outlined in the AECTP-400 (Allied Environmental Conditions and Test Publication) together with associated assessments, provide the basis for a reasonable verification of the material's resistance to the effects of the specific mechanical environments. However, very few scientific studies address the vibration-loading effect on energetic materials. In this work, a quasi-static mechanical test was performed to evaluate the mechanical properties of propellant samples subjected to prolonged vibrational load, simulating conditions on the cargo bed of a wheeled common carrier vehicle for all terrain. Properties such as elastic modulus, maximum stress, strain at maximum stress, and strain at break were analyzed. Results are summarized in stress-strain curves and tables. Prolonged vibrated samples exhibited reductions in mechanical performance compared to fresh samples, particularly in strain at maximum stress and strain at break, which declined by up to 18.6% and 29.6%, respectively, after 7–8 hours of vibration, which is equivalent to ca. 8,000 km journey (according to AECTP-400). Normality tests (Shapiro-Wilk) confirmed that most datasets followed a normal distribution, enabling analysis of variance (ANOVA). For non-normal data, the Kruskal-Wallis test was applied. Significant differences for maximum stress, strain at maximum stress, and strain at break across vibration times were identified, while the elastic modulus remained largely unchanged. Tukey's multiple comparison tests revealed no significant changes in mechanical properties during shorter vibration durations, but notable differences were found for longer periods. These findings highlight the sensitivity of mechanical properties like strain at break to vibration duration, emphasizing a threshold effect during prolonged exposure. These results provide first insights into the impact of mechanical stress on composite propellant performance and can be used to develop strategies for design and in-service operation.