Aging effects on the structural integrity of carboxyl terminated polybutadiene propellants.

• Viscoelastic fracture mechanics approach is necessary for fracture analysis of propellants. • Mechanically aged samples show lower fracture resistance due to debonded particles. • Thermally aged samples exhibit better fracture response due to higher crosslinking density. • Ozone aged samples show worse fracture performance due to lower crosslinking density. • Cohesive stress is an appropriate parameter to describe propellant fracture, being related to a dewetting mechanism. Structural integrity of composite solid propellants (CSPs) is one of the main concerns when considering the performance of CSP motors. The development of cracks in the propellant's grain, caused by aging during the service life of the motor, is the main reason for its catastrophic failure. In addition, the fracture characterization of these viscoelastic and highly filled materials is not fully solved yet and hardly addressed for aged CSP. This manuscript presents a broad and comprehensive study on the fracture behavior of aged CSPs, where Schapery's viscoelastic fracture mechanics (VEFM) methodology is used to effectively characterize the fracture behavior of a composite solid propellant with carboxyl-terminated polybutadiene (CTPB) binder. For that, stress relaxation, fracture and tensile tests have been performed on non-aged and aged CSP. Three different accelerated aging methods were employed (mechanical, thermal and ozone) that are related to the phenomena that deteriorate the material during the lifespan of the motor. Two main contributions are derived from this work. The first one is the understanding of the fracture processes developed in aged CSP, under different types of aging. The second most relevant contribution is that the cohesive stress, as the fracture parameter inferred from the VEFM approach, is observed to be correlated to the dewetting stress, a material measurable parameter. The results have potential implications for the design and longevity of future solid rocket propellants. [ABSTRACT FROM AUTHOR]