RESEARCH OF DISTORTIONAL BUCKLING OF STRINGER

Local buckling of elements supporting the compressed power panels of aircraft structures, stringer, is considered. It has been shown that the identification of critical stresses of the local stability of the stringer and the critical stresses of its weakest wall can lead to significantly overestimated results. The use of this approach omits the form of extrusion of the stringer, in which one of the reinforcing elements is not edged as an infinitely long plate, but as a beam. Such an element not only reduces the supporting effect on other elements, but can itself provoke a loss of stability of the entire stringer. The case of a uniformly compressed stringer in the form of a wall reinforced by a belt was considered. The problem of determining the critical stresses of the stringer under the assumption of free support of the plate along three sides and elastic coupling with the compressed hinged beam on the fourth was solved analytically. In this setting, the deflection function of the plate wall in one direction was written in the form of a series in terms of the sine function. After integrating the obtained ordinary differential equation and satisfying the boundary conditions, the critical stresses were determined from the condition for a non-trivial solution. The solution was reduced to a transcendental equation for dimensionless critical stresses, written through the dimensionless values of the flexural, torsional rigidity of the beam, its cross-sectional area, the elongation of the plate, and the Poisson's ratio. The resulting stresses up to the square of the elongation are the coefficient of plate support in the well-known formula for determining the critical stresses of the plates. Parametric studies were carried out: the influence of the elongation of the stringer, the relative area and dimensions of the beam cross-section supporting the plate on the value of the support coefficient. It was shown that for stringers having a relatively weak belt, the support ratio may be less than the value adopted for a compressed plate with three freely supported sides and one free edge (0.46), i.e. in this case, buckling provokes a compressed beam. For the convenience of practical use of the results obtained, plots of the dependence of the support coefficient on elongation and the ratio of the wall and shelf dimensions were given. Recommendations were given to increase the critical stresses of local buckling of the stringe