Stress-Strain Assessment for Laminated Aircraft Cockpit Windows at Static and Dynamic Loads

The method of strength calculations for laminated aircraft cockpit windows influenced by different operating factors (bird strike, pressurization) is devised. The method is based on embedding the initial uncanonical shell in the auxiliary one of canonical form in plan with the boundary conditions, which permit of a simple analytical problem solution as a trigonometric series. For satisfying the initial boundary conditions, the auxiliary shell is supplemented with compensating loads, which are continuously distributed over the contour of the initial shell. The compensating loads enter in the equations of motion for the auxiliary shell as integral relations. The system of motion equations is rearranged in the system of ordinary differential equations of second order, which is integrated by the solution expansion in the Taylor series. The windows are treated as a laminated open-ended cylindrical shell consisting of isotropic layers of constant thickness. The laminated window model is based on the modified theory of first order that accounts for transverse shear strains, thickness reduction, rotary inertia, and compression of the normal element in each layer. For the composition, the hypothesis of broken line is valid. The model of pressure pulse that apparently represents the effect of the bird impact on the windows was constructed on the basis of experimental studies. The stress-strain state of the window element in AN aircrafts was evaluated, set on the bird strike and cockpit pressurization. Five window alternatives are examined. Calculation results are in good agreement with experimental data. The results become theoretical and practical backgrounds for engineering calculations and optimum design of laminated aircraft window elements influenced by different operating factors. Thus, the advanced method can be applied to estimation of the lifetime of existing window elements and development of the new ones.