Influence of Delamination Defects on the Dynamic Stress-Strain State of Composite Elements of Launch Vehicles

The application of the methodology for modeling cracks in the scheme of the finite element method is considered for evaluating the effect of delamination in composite elements of launch vehicles on the dynamic stress-deformed state. Cracks are modeled by modifying the finite element mesh and applying formalized operations to the stiffness and mass matrices of the initially intact body. The problem of calculating oscillations is reduced to a system of differential equations of the finite element method in time for a body with curvilinear anisotropy of properties and stiffness and mass matrices reflecting the presence of cracks. The solution to the initial problem is performed according to Newmark’s and Wilson’s finite-difference schemes. A computational analysis of the dynamic stress-deformed state of the rocket fairing in the process of its separation by the pyrotechnic system is carried out. Delamination in irregular fiberglass-winding zones is simulated in the composite shell, which is part of the assembled structures of launch vehicle fairing. It is shown that external delamination from the shell edge is more dangerous than internal delamination and leads to a significant increase in dynamic stresses. The problem of lateral oscillations of a rod with a near-surface crack, taking into account the local buckling of delamination, is posed and solved. A model of delamination is constructed, the stiffness of which depends on the amount of deformation and the fulfillment of the condition for buckling, which leads to the nonlinearity of oscillations. The effects of nonlinear oscillations associated with the nonisochronism of free oscillations and super- and sub-harmonic resonances are investigated.