Авіаційно-космічна техніка та технологія (Aug 2020)
DYNAMIC ANALYSIS OF A COMPOSITE ROCKET DOME DURING SEPARATING TAKING INTO ACCOUNT STRUCTURE DELAMINATING
Abstract
The dynamic processes in the rocket fairing when the pyrotechnic separation system is triggered are considered. The fairing construction is mixed and includes composite and metal elements. The main composite construction element is a fiberglass shell with regular and irregular winding zones. The speed acceleration required to separate the fairing occurs under the action of impulse pressure from the powder gases in the pyrotechnic system. The displacement of the fairing is made up of displacements of the movement as a rigid whole along its axis and vibrations caused by deformations. The calculation of the fairing movement is carried out according to a three-dimensional FEM model using software that uses a topologically regular discretization system. The problem solution in time is performed according to the implicit Wilson finite-difference scheme. When studying the fairing dynamics, it is allowed to break the structure of the shell in the form of lamination, which in the FEM scheme is modeled by a special method. A cut with double nodes is created on the surface of the proposed lamination along topological planes by transforming the finite element mesh. Modification of the stiffness matrix and mass matrix for the transformed mesh is performed based on the created information base of degenerate finite elements and formalized matrix operations. In numerical studies, two types of lamination from irregular zones of fiberglass winding are considered – the internal location from the flange and edge location with access to the fairing free edge. The results of calculating vibrations along the sides of lamination and data on the redistribution of dynamic stresses due to lamination are presented. Radial and axial displacements when passing through the lamination surface discontinue, the magnitude of which for internal lamination is much less, which is explained by the compression of deformation for this case, in contrast to the lamination that goes to the boundary. When estimating the relative axial displacements, the component of the displacement of a rigid whole, determined by a separate calculation, was excluded. The maximum radial displacements during lamination from the edge reach 3 mm, which is one and a half times higher than for an undamaged shell. Axial stresses are maximal from the action of inertial forces during acceleration. Its redistribution over the layers is significantly greater for the edge lamination, for which the maximum values increase almost two times concerning the undamaged shell, which determines this type of lamination as more dangerous.
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