Nonlinear response and fatigue of stiffened panels

The surface protection systems of aerospace and aircraft structures are often constructed from discretely stiffened panels. The information that is available indicates that response of surface panels exposed to high intensity surface flow and/or acoustic pressure is nonlinear. A theoretical study on nonlinear response of discretely stiffened panels to random pressures and thermal loads is presented in this paper. The random pressures are simulated in time-space domain and the nonlinear equations of motion are solved numerically by a Monte Carlo type approach. In addition, preliminary estimates of sonic fatigue based on the nonlinear stress distribution of response peaks and fatigue data from constant amplitude tests are given. The numerical results include deflection and stress response time histories, spectral densities, root mean square values, crossing rates, probability distribution, peak distribution and fatigue damage.