EVALUATION OF POST-BUCKLING BEHAVIOR OF UNSYMMETRICAL COMPRESSIVE DELAMINATION IN CYLINDRICAL COMPOSITE PANELS OF AIRCRAFT STRUCTURES

The research of surface defects, such as delaminations in elements of thin-walled aircraft structures made of composite materials, is a topical problem. The paper considers an analytical solution to the problem of the overcritical behaviour of thin delaminations close to one of the surfaces in composite panels with surface curvature. The objects of research in this case can be nose parts of composite mechanization units, as well as semicircular specimens that allow laboratory research of these types of defects. Studies on laboratory cylindrical specimens with defects make it possible to determine the allowable dimensions of the defects, as well as the maximum allowable level of loading at which it is impossible for the defects to propagate. In accordance with modern aviation regulations, it is not allowed for defects to propagate (stagger) even under the calculated level of loading. The presented initial relations of the geometrically nonlinear problem consider the possible asymmetric structure of the delamination along the thickness as well as the small curvature of the studied panels. The type of deflection in this case of the delamination corresponds to a rigid support. When solving the problem by the Bubnov-Galerkin method, the stress function and expressions for the corresponding membrane stresses under possible overcritical behaviour of the stratification are obtained. A nonlinear expression linking the deflection amplitude and the compressive force is also written. When considering a linear problem, an analytical expression for compressive critical stresses is obtained. In the general case, the obtained expressions consider the arrangement of composite layers along the thickness, as well as the asymmetric structure of the delamination. Examples of determination of critical forces for panels with asymmetric structure are given.