Study On The Adhesion Mechanical Properties Of Hydroxyl-terminated Polybutadiene Propellant/liner Interface

Nowadays,solid rocket motors(SRMs)are widely used in the aerospace and missile industries.During trial productions of the SRMs,it is difficult to avoid the following consequences in flight experiments:deviation from the set exterior ballistics,failure to meet the desired effects,and even an explosion.The main reason for this is the integrity failure of the charge structure.To date,the structural integrity of the charge has become the main technical bottleneck restricting the application and development of SRM technologies.Debonding along the propellant/liner(P/L)interface is one of the major ways in which structural integrity can fail.In this article,investigations on the mechanical characteristics of the P/L interface were carried out,mainly including the following aspects:(1)Studies on the experimental methods of the composite P/L interface fracture.A 3D stress analysis of the rectangular bond specimen was performed.The inadequacies of this standard method currently used to determine the bonding strength of the composite P/L interface were pointed out.Since the composite P/L interface was a flexible bi-material structure,uniaxial tensile tests and double cantilever sandwich beam(DCSB)experiments were designed to measure the mechanical properties of this interface at mode-I fracture.An effective crack length concept was used to determine the fracture energy.Results showed that the adhesive properties of the composite P/L interface were highly relied on the loading rates.(2)Studies on the damage mechanism of the composite P/L interface fracture.Microscopic observation revealed that the liner near the crack tip first appeared significant elastic deformation to form a continuous triangle zone,then the edge of the triangle zone began to produce material fibrosis and holes,finally the crack tip region evolved into a fibrotic damage area.The fracture mechanism of the P/L interface turned out to be the hole formation and consolidation near the crack tip.(3)Studies on the mechanical constitutive model of the composite P/L interface.The applicability of cohesive zone model for the composite P/L interface fracture analysis was discussed.Then the effects of bilinear and exponential cohesive model on the numerical simulation results were compared.A new mechanical constitutive model considering the interface separation rates was established in the framework of cohesive zone model.This model was based on the experimentally observed features,i.e.the elastic deformation and fibrotic damage.This model is clear,easy to extend,and had some physical meaning.(4)Studies on the inverse analysis and identification of the parameters in the mechanical constitutive model.An inverse analysis method combined the standard experiments and direct search algorithm was developed to determine the parameters in the interface constitutive model.An automatic executive program of the inversion analysis was compiled through the script development capabilities of the finite element software ABAQUS.Finally,the accuracy and efficiency of the inversion identification methods and procedures was verified by an example of DCSB specimen with the P/L interface.(5)Studies on the numerical simulation of composite P/L interface fracture.The numerical simulation method of composite P/L interface fracture was established.The finite element discretization of the rate-dependent mechanical constitutive model was derivated.By means of DCSB experiments at different loading rates and the two-step inversion analysis strategy,the detailed expression of parameters in the mechanical constitutive model were obtained.Eventually a group of independent experiments was performed to verify the accuracy and applicability of those theories and methods of interface mechanical model,parameter inversion method,numerical analysis for the P/L interface fracture analysis.In summary,the research objectives of this thesis are the characterization of bonding mechanical properties of the composite P/L interface.The principal contents of this thesis are the fracture experimental tests of the interfacial adhesion properties,the development of the interface mechanical constitutive model and the numerical simulation of interface fracture.The outcome of this thesis has laid a good theoretical foundation for the P/L interface fracture analysis which belongs to the integrity failure of the charge structure,and provides numerical analysis methods for the charge design and security check of SRMs.