Viscoelastic Interface Fracture And Interface Debond Of Solid Rocket Motor

Interface debond between propellant and liner is a key form of failure of the structure integrity in the analysis of solid rocket motor. Causation about interface debond are composed of two aspect of physics and chemistry, the main physical reasons are stress intensity and material damage near motor interface created under various work loads. After igniting the motor, the combustion gas coming into the debond cavity may expand the debond cavity, and make an additional combustion area and lead to larger load. This kind of positive feedback may extend the debonded area and result in out of control of pressure on the firebox, or even the explosion of the motor. Hence, it is very significant to analyze the mechanism and extend law of interface debond of solid rocket motor. Because the propellant grain is viscoelastic material, the liner and adiabatic layer are also viscoelastic one, the interface debond problem is actually interface crack about elastic-viscoelastic or bi-viscoelastic materials. Research about this problem relates to the knowledge of viscoelastic mechanics and interface fracture and combustion.Numerical analysis method about interface debond on solid rocket motor is researched in this paper. Based on viscoelastic integral constitutive relationship, viscoelastic increment FEM and Interface Element Method (IEM) formula are deduced respectively. In order to make full use of advantages of high stress precision in IEM and wide use of FEM, Zonal FEM-IEM is constructed to establish a foundation of method in viscoelastic interface mechanics. Calculating examples are given to illustrate the application of the method on structure integral analysis of solid rocker motor.The property of viscoelastic interface fracture and the calculating method of fracture parameter are investigated. Constants of viscoelastic material described by prony series constitutive relation are deduced. For the case of interface crack in viscoelastic material infinite board under the load of mixed type 1, 2 and type 3 respectively, Laplace transform is used to change the basic equations from time domain to frequency domain. According to the corresponding principle, viscoelastic solution can be obtained by substituting the viscoelastic constant into elastic one. Modified Dubin numerical anti-transform method is used to obtain the discrete time domain solution. Calculating example shows that the fracture parameters of viscoelastic interface crack have a time correlation behave, its extend is a kind of delay instability.For the purpose of improving calculation precision and reduce workload, viscoelastic similar shape element is generated in the numerical research about crack problem, using the characteristic of similar stiffness matrix between element near crack tip. The condensation method is used to form a super interface element. Examples indicate that the...