Research Of The Mode Ⅱ Interfacial Fracture Property Between HTPB Propellant/Insulation

In case bonded Solid Rocket Motors with composite propellant, the debonding between propellant and insulation will lead to a significant reduction of the stableness and efficiency of SRM, thus, it becomes one of the main reasons for the destruction of the structural integrity. According to NASA, nearly a third of the crashes occurred in a century could be abused to the debonding accident. The shear effect between propellant and insulation enhances while the motor igniting and accelerating, moreover, the high speed rotating while flying also influences the interface strength. In this paper, the interface between HTPB based propellant and insulation is set as research target, the mode Ⅱ interfacial property of propellant/insulation is conducted with experimental and numerical methods.(1)The influence analysis of the damage variable in cohesive zone method. Firstly, the bilinear CZM and exponential CZM were introduced, a new specimen was designed based on the standard Single Lap Joint (SLJ) specimen according to the special mechanical property of propellant and insulation. The experimental preparation, specimen manufacturing and test equipment were all introduced particularly. The improved SLJ rate-independent test was conducted in order to obtain the Mode Ⅱ fracture parameters between HTPB propellant and insulation. Researches were carried out to analysis the influence that the damage variable has on the shape of the CZM, and a customized CZM was built base on the damage variable. The result shows that the improved SLJ test is qualified to determine the Mode Ⅱ parameters of the bonding structure consists of ductile adherends. In the case of adopting the parameters obtained directly from tests, the customized CZM turn out to be more suitable to model the Mode Ⅱ fracture between HTPB propellant/insulation than bilinear or exponential ones.(2) Construction of rate-independent Mode Ⅱ interfacial fracture between HTPB propellant/insulation. Tests with improved SLJs were conducted, mixed mode fracture phenomenon was discovered by observing with microscope and analyzing with 3D finite element method. Thus the Mode Ⅱ parameters obtained from test should only be considered as roughly determined initial values, instead of pure Mode Ⅱ fracture parameters. An inverse optimizing method was introduced and realized by a secondary development base on the Python interface in Abaqus(?). At last, the precise pure Mode Ⅱ interface fracture parameters were obtained with this method and the Mode Ⅱ CZM of HTPB propellant/insulation interface was built.(3) Construction of rate-dependent Mode Ⅱ interfacial fracture between HTPB propellant/insulation. In order to construct rate-dependent Mode Ⅱ CZM of HTPB propellant/insulation, experimental method and inverse analysis method were both adopted. Firstly, the improved SLJs tests were conducted to obtain the interfacial initial parameters under different loading rates, and then the inverse analyzes base on the Hook-Jeeves optimizing method were done, together with the numerical analysis, to obtain the precise pure Mode Ⅱ interfacial parameters. The parameters show a significant rate-dependency, by fitting these parameters, the CZM could by connected to the loading rate. Thus, the rate-dependent Mode Ⅱ CZM was constructed and a verification test under another loading rate is done at last.With this research, the experimental method of testing the bonding property is improved, the mechanism of the damage evolution in CZM is investigated thoroughly, and several kinds of CZMs are reveal in FEM analysis. Experimental, inverse analysis and FEM are adopted in this paper. The rate-independent Mode Ⅱ CZM under lmm/min, and the rate-dependent Mode Ⅱ CZM in range 5mm/min to 100mm/min are obtained. The research offers a theoretical basement for numerical analysis and SRM design in future.