Developing a novel approach for modeling liner interface debonding in solid propellant rocket motors

Solid propellant rocket motors are subsystems widely used in tactical missile systems and provide the required thrust for the missile. In case bonded motor configuration, propallant is casted into the case after being insulated and application of liner. Liner is applied into case/insulation and propellant interface to ensure the bonding of the propellant. Debonding occuring at the liner interface may lead to failure of the motor. Motor is exposed to various challenging environment which may cause debonding of the interface throughout the time between production and fire. It is important to maintain the structural integrity of the motor during this time. Therefore, determining the characteristic properties of the liner gains prominence. Since liner acts as an adhesive, it can be modeled as an adhesive. Commonly, adhesive interface can be modeled via cohesive zone model which is defined with adhesive strength, fracture energy and initial modulus.The aim of this study is to model the liner interface with cohesive zone model in solid rocket propellant motors and to examine the usage of peel test for this model. It is aimed to simplify the creation of cohesive zone model by direct usage of specimen level test data. Initially; propellant, insulation and liner material models are validated with a study from literature for this study. After the validation, bond in tension and peel tests are performed. Liner's fracture energy is calculated with outputs of peel test and energy equations. Cohesive zone model of liner is created with adhesive strength obtained from the bond in tension tests and fracture energy obtained from the peel tests. Finite element analysis of the peel test is performed with the created cohesive zone model. Force-displacement graphics obtained from the analysis and test output are compared. In addition, traction-separation curves obtained from the analysis and defined with cohesive zone model are compared. It is observed that sufficient similarity is accomplished between analyses and tests for the both of the comparisons. Finite element analysis of double cantilever sandwich beam test is performed that includes the cohesive zone model created via peel test to evaluate the usage of peel test instead of commonly used double cantilever sanwich beam. Traction-separation curves obtained from the analysis are compared and sufficient similarity is accomplished. As a conclusion, it is evaluated that peel test can be used for modeling the cohesive zone model of the liner interface and process of creating cohesive zone model is simplified. Due to switch to a more feasible test method, the cost is reduced and efficiency is increased in terms of model development process.