| This study deals with predicting the long-term durability of solid rocket motor bondline systems, with emphasis on the bond between the insulator and the case. The former is a filled rubber that is time-dependent and undergoes large deformations and rotations, particularly near the crack tip. The case material was steel, essentially rigid.; The first phase of the study dealt with the development of a nonlinear, time-dependent constitutive model for the insulator. Several pseudo stress models and one pseudo strain model were considered. Measurements from and predictions of uniaxial and biaxial experiments were compared. In addition, the objectivity of the stress measures was considered. As a result, the transformed Cauchy stress and second Piola-Kirchhoff stresses were recommended as suitable pseudo stress models for the crack growth studies that followed.; Interfacial fracture experiments were conducted over a range of mode-mixes and loading rates. They were modeled via finite element analyses that incorporated the nonlinear constitutive behavior above. The analysis also included a cohesive zone model that accounted for the breakdown of material near the crack tip, using a cohesive zone modeling approach. The cohesive zone was also rate-dependent. It captured the rate dependence of the highly strained material near the crack front. Reasonable agreement between experiments and models was obtained, making durability predictions possible. |
