Studies Into Modeling And Mechanic Properties Of Marman Clampband Joint

The Marman Clampband (MC) joint is widely used in space industries to provide connection and separation mechanism between a pair of launch vehicle and satellite. The MC works during the launch stage, in which the dynamic loads that a satellite suffers are most severe among the whole mission life. As a connector between the launch vehicle and the satellite, the MC has significant effects on the overall dynamics of the launch vehicle and the satellite structures. Thus, the effect of MC has to be taken into account during the modeling of aircraft structures. However, the mechanical behavior of MC is not well understood until now. This paper presents an overall investigation of MC by both direct modeling method and experiments.The theory of contact mechanics is firstly investigated. A three-dimensional finite element (FE) model is developed, and the pretension loading progress and axial loading case are simulated. The deformation and stress distribution of the components and contact force between components are analyzed. The results of simulation provide basis for improving the design of MC and pretension loading plan.There are three kinds of contact surfaces involved in MC, that is, contact surfaces between strap and V-segments (S-V), contact surfaces between V-segments and interface rings (V-R), and contact surface between interface rings (R-R). This paper investigates the contact forces on these surfaces and relationships between them. With this relationship, an analytical model of MC is developed, with consideration of such factors as pretension and stiffness of strap, V-segment, and interface rings.In order to incorporate the MC model into conventional FE model, the MC model is introduced into the virtual work equation of system. The FE formulation of MC model is derived based on beam element. The contact forces on V-R and R-R surfaces are expressed in term of nodal displacements of interface rings. Further, the equivalent nodal force vectors are derived. As a structure with the MC as a part is nonlinear, the dynamic equations of the structure are solved with the Newmark's direct integration method, and thus resulted nonlinear algebraic equations are solved with the Newton-Raphson iterative method. To take the pretension effect into MC model, the static displacements under a certain pretension is firstly obtained, and then a coordination transformation is conducted to set the configuration as initial configuration for dynamic analysis.Based on the nonlinear mode theory, eigenvalue perturbation theory and describing function method, this paper proposed a parameter identification method which is applicable to large scale structures. The describing function method is used to evaluate the generalized quasilinear matrix which is treated as a perturbation of the underlying linear system. Then the eigenvalue perturbation theory is introduced to derive the identification equation. The proposed method consists of two steps. In the first step, the underlying linear parameters are obtained base on the response to excitations of low level; in the second step the nonlinear parameters are identified base on the response to excitations of high levels. In addition, the response of nonlinear degrees of freedom (DOFs) is sometimes immeasurable. To overcome this difficulty a method is developed to estimate the response of nonlinear DOFs by the response of measured DOFs.Finally, in order to validate the proposed modeling method and show the dynamic characteristics of MC, a prototype is designed. To minimize the FE model inaccuracy of components and identify the dynamic characteristics of MC, the FE models of components are updated separately with the first several natural frequencies using the inverse eigensensitivity method. For the assembly, a series of step sweep experiments of different excitation levels under different strap pretension conditions are conducted. Both the computational and experimental results show the same trends that the resonance frequency decreases evidently with increases in the amplitude of the applied harmonic excitation, and the resonance frequency shifts down and the degree of nonlinearity increases as the strap pretension decreases.