Research Of The Mode I Interfacial Debonding Property Between CMDB Propellant/EPDM Inhibitor Film

The burning surface area is controlled by the inhibitor in free filling solid rocket motors(SRM). There are many bonding defacts existing in the interface between the propellant and the inhibitor, due to the differences between the propellant and the inhibitor in the mechanical and chemical properties, and the influence of the bonding condition and environment, which lead to the interface became a weak part in solid rocket motors. The interface is easy to debond when the SRM suffer in the external load, and the interior ballistics will be affected due to the change of burning surface aera. It may lead to the whole motor failure when the debonding is serious. In this thesis, the interface between composite modified double-base(CMDB) propellant and ethylene-propylene-diene monomer(EPDM) film inhibitor was researched, experiments and simulations were combined to investigate the type I debonding of the interface, the relevant interface debonding models were built, and the reliability of these models had been certified. The contents of this thesis are as follows:(1) The tpye I debonding experiment research of CMDB propellant/EPDM inhibitor interface. The double cantilever beam (DCB) specimen and bonding uniaxial tensile specimen were designed based on the ASTM (American Society for Testing Material) standard. The experiments were conducted by using DCB specimens at different tensile rates, and the experiment load-displacement curves were obtained, the debonding processes were observed by electron microscope, the cohesive energy were obtained by dealing with the experiment results. Meanwhile, the cohesive strength was obtained by the adhesive joints uniaxial tensile experiment. Besides, In order to investigate the mechanical behavior of the EPDM inhibitor film, uniaxial tensile experiments at different tensile rates and multi-step relaxation experiment were conducted, and its constitutive model was established.(2) The rate-independent property of CMDB propellant and EPDM inhibitor interface debonding. In order to investigate the rate-independent debonding property between propellant and inhibotor, bilinear cohesive zone model was introduced, and the cohesive parameters were obtained by dealing with the DCB experiment result at lmm/min. The rate-independent CZM model was applied to the finite element analysis of the CMDB propellant/EPDM inhibitor interface debonding, the simulation load-displacement curves and change process of the debonding crack length were obtained. This rate-independent model was vertified to have a good reliablity by comparing the simulation and experiment results. Meanwhile, the virtual crack closure technique(VCCT) was also applied to this interface debonding analysis, and the VCCT simulation resules were compared to the CZM’s, which showed that using the CZM method will get a higher simulation precision, and it is more sultable for describing the CMDB propellant/EPDM inhibitor interface debonding.(3) The rate-dependent property of CMDB propellant and EPDM inhibitor interface debonding. A rate-dependent CZM model was introduced to investigate the interface rate-dependent debonding property. The model consists with a Maxwell element and a rate-independent exponential CZM model, it has a exponential cohesive damage characteristic and exists the rate-dependent property. In order to apply the model to the type I interface debonding finite element analysis, it was discretized, and the user defined material subroutine (UMAT) was established. Four unknown cohesive parameters in this model were obtained by a inversion algorithm, which was proposed based on the Hooke-Jeeves optimization method and combined the experiment results with simulation results. The compute efficiency was improved and the parameters optimization time was shorten. Multistage loading experiment was developed to verify the model’s accuracy. The result showed that the change trend was consistent, which certificated that the interface model can be applied to predicted the interface debonding under complex load conditon, this interface model had some reference values for the structure integrity analysis in the SRM.In this thesis, the debonding experiment methods were described comprehensively, the rate-independent and rate-dependent debonding models of the CMDB propellant/EPDM inhibitor interface were established, and the Hooke-Jeeves inversion algorithm was introduced to optimizi the model parameter values. The research result showed that the interface models had high precision, it can be used in the SRM for the propellant/inhibitor interface debonding analysis, and had some reference values for the design and application.